Integrated Science ECLPE

Key unit competence

Implement ways of preventing and controlling common diseases and hygiene related issues.

Introductory Activity

The figure 1-11 indicates different situations.

a) According to what you always observe in community you live in, suggest what happened.

b) What do you think is a cause of each case in figure?

c) What can you do in community for limiting those situations?

2.1. Common diseases

Activity 2.1.a

1) The government of Rwanda encourages people to visit hospitals and test their blood. A person has done that test and he found having HIV positive.

a. Which opportunistic information can be associated with HIV?

b. What is its causative agent?

c. How is it transmitted from one people to another?

2) Basing on the ways of transmission, suggest other diseases that can be transmitted as the disease stated in a.1

3) How can you prevent those diseases?

Infectious diseases are caused by microorganisms known as pathogens which may include viruses, bacteria, fungi and protozoa. Those diseases are called communicable diseases as they can be transmitted from one person to another. They include cholera, malaria, typhoid, HIV and AIDS...Malaria is one of the most dangerous infectious diseases, endemic in Latin America, Africa and South-East Asia.

Some infectious diseases can also be from animals to humans.

Some technical terms used when discussing about infectious diseases are:

– Aetiology: The study of the cause of disease.

– Epidemiology: The study of all the factors that contribute to the appearance of a particular disease

– Causative agent: The organism which causes the disease

– Vector: An organism which carries the causative agent of the disease from one person to another or from infected animal to human.

– Incubation period: The period of time between the original infection and the appearance of signs and symptoms.

– Infective period: The time during which a person is capable of passing the disease on to another person.

– Carrier: The person who has been infected but develop no signs and symptom, the carrier can pass the disease on to another person.

– Prevention: Measures taken to prevent diseases.

– Treatment: Measures taken to cure diseases.

– Antibody: Is a protein produced by the body’s immune system when it detects harmful substances called antigen.

– Antigen: Is any substance that causes your immune system to produce antibodies against it.

– Host: A host can be anything living organism ion which pathogens can survive

– Hygiene: Practices that help to maintain health and prevent the spread of diseases

– Immunity: Is the ability of the body to resist to infections.

Some groups of communicable diseases

• Bacterial diseases: these are diseases caused by bacteria. They include cholera, typhoid, tetanus, tuberculosis, etc.

• Viral diseases: these are diseases caused by viruses. They include AIDS, polio, measles, Ebola, etc.

• Protozoan diseases: these are diseases caused by protozoa. They include malaria, sleeping sickness, trichomoniasis, etc.

• Fungal diseases: these are diseases caused by fungi. They include candidiasis, athlete’s foot, ring worms, etc.

• Worm diseases: these are diseases caused by worms. They include elephantiasis, bilharzias, etc.

• Sexually transmitted diseases: these are diseases transmitted through sexual contact. They include HIV-AIDS, syphilis, gonorrhea, etc. c.

Transmission of infectious diseases

Pathogens can spread when you have direct contact with an infected person.

For example, if you have contact with the person’s blood, body fluids or open wounds. Pathogens can also be spread through contaminated food, water or air. Infected animals can spread pathogens to people.

The following conditions lead to the spread of an infectious disease:

• A pathogen which causes the disease.

• A source which is an infected organism.

Mode of transmission: A pathogen must be able to enter the body of the new host to cause an infection. Infectious diseases follow a pattern of development from the time of infection.

2.1.1. Cholera

Cholera is a good example of a waterborne disease. It is endemic in parts of Asia, particularly India. The organism which causes cholera is a comma shaped motile bacterium called Vibrio cholerae.

a) Transmission and symptoms of cholera

The main source of infection is water contaminated by feces with Vibrios.

It is estimated that only about one infected person in 50 develops the disease, the rest being carriers. Drinking contaminated water, or washing food or utensils in it, is the most common means of transmission. Direct contamination of food with feces as a result of poor hygiene is also possible, house flies being the main vector in this last case.

b) Signs and symptoms of cholera

Vibrio cholerae multiply in the intestine, releasing a powerful toxin which results in violent inflammation of the intestine and production of the watery diarrhea.

The main sign of the disease is severe diarrhea due to irritation of the bowel by toxins from the vibrios. The liquid of the feces is so profuse and cloudy like “rice water”.

Abdominal pain and vomiting are also common. Dehydration is rapid and quickly results in death unless rehydration treatment is given.

Fever is absent; in fact, the skin feels deathly cold and often damp.

Table 2.1: The features of cholera.

c) Treatment of cholera

The prime cause of death from cholera is dehydration i.e. loss of water with its minerals salts. For that it is obligatory to rehydrate with oral serum which contain mineral salts and sugar, The fluid lost may be replaced by administration of a drip food into a vein.

Various antibiotics, such as tetracyclines and chloramphenicol, are used to treat cholera. Chloramphenicol is effective against tetracycline-resistant vibrias.

d) Prevention of cholera

– Use clean drinking water,

– Proper treatment of sewage and sanitation

– High standards of public and personal hygiene, particularly in relation to food ( such as washing hands after defecation)

– Health education

– Vaccination is recommended for people visiting areas where cholera is endemic and for those living in such areas. But this vaccine lasts few months.

– Isolation of patients and hygienic disposal of feces and vomit from patients.

e) Failure to eradicate cholera

– Vaccination is not very effective

– It is a waterborne disease i.e. transmitted through contaminated water

– Poor sanitation condition in camps.

2.1.2. Tuberculosis

a) Causal agent of tuberculosis

Tuberculosis is caused by bacterium called Mycobacterium tuberculosis, first discovered by Robert Koch in 1882. It is sometimes referred to as the tubercle bacillus, bacilli being rod-shaped bacteria. The common form is pulmonary TB which infects the lungs, although other organs may be affected.

Two strains of the bacterium may cause the disease, the human and the bovine forms. The latter can be present in cattle and can enter the milk of cows. It is very resistant and can remain alive for long time in milk products as well as in durst.

Table 2.2: Features of TB.

b) Transmission of tuberculosis

Tuberculosis is mainly airborne disease. The infection is done through the droplets from the patient.

It is much less infectious than the common cold and requires prolonged contact between people, poor ventilation and overcrowded living conditions.

Other factors include poverty, bad housing, malnutrition, age, smoking and AIDS. In addition, TB is an opportunistic infection, striking many people with a depressed immunity.

c) Signs and symptoms of tuberculosis

The disease frequently shows itself by vague symptoms such as: loss of appetite; loss of weight; excessive sweating; coughing, appearance of blood in the sputum, pains on the chest, shortness of breath (case of lung tuberculosis).

d) Treatment and prevention of tuberculosis

The development of an effective vaccine against the disease result of the work of Abert Calmette and Camile guérin (BCG). A cure for people already affected by T.B did not come until 1843 when the antibiotic streptomycin was discovered. The number of cases started to fall more rapidly after this and continued to decline aided by introduction of further antibiotics such as rifampicin, isoniazid and others.

e) Failure to eradicate tuberculosis

– Patients can carry pathogen and infection without showing symptoms.

Therefore they are difficult to identify and isolate / long period of incubation

– Germs of tuberculosis can survive longer in the house dust

– The disease is related to poverty where many people share the same room and have malnutrition.

– The disease is associated with AIDS that reduced the body immunity

– Long period of medication (6-8 moths), hence patients give up when not yet fully healed. The pathogens then form endospores that resists to medicines.

– The disease is also spread through milk from infected animals. Hence it is difficult to vaccinate.

– Tuberculosis is an airborne disease i.e. spread in air.

2.1.3. Malaria

a) Causal agent of Malaria

Human malaria is caused by infections from four species of plasmodium:

Plasmodium falciparum, P. vivax, P. ovale, and P. malariae, each responsible for a different form of the disease.

Malaria is characterized by chills, fever, and, in the most severe cases, coma leading to death.

The parasite, Plasmodium is transmitted by the bite of female mosquitoes (the vector) belonging to the genus Anopheles.

The life cycle of Plasmodium involves both sexual reproduction within the host mosquito, and asexual reproduction within the human being.

It is the reproductive activity of the parasite within the human bloodstream that produces the characteristic recurrent attacks of the disease.

The infection begins when a mosquito vector injects parasite particles (infectious stages) called sporozoites, present in the mosquito’s saliva, into the bloodstream when it feeds on a human blood.

b) Symptoms

Malaria is a very serious disease characterized by severe chills, fever, sweating, fatigue and great thirst. Malaria is caused by a protozoan of the genus Plasmodium.

Victims die of anemia, kidney failure or brain damage. The genus Plasmodium infects humans, and all have life cycles that involve the female anopheles mosquito.

c) Life cycle of Plasmodium

It is the reproductive activity of the parasite within the human bloodstream that produces the characteristic recurrent attacks of the disease.

The infection begins when a mosquito vector injects parasite particles (infectious stages) called sporozoites, present in the mosquito’s saliva, into the bloodstream when it feeds on a human blood.

These enter liver cells where they multiply by asexual reproduction for about 7 to 14 days (the incubation period of the disease) before producing daughter cells called merozoite, which invade red blood cells. The parasites multiply in the red cells, again by asexual reproduction, to produce between 8 and 16 merozoites every 48 or 72 hours, depending on the species of Plasmodium. These merozoites are released by the bursting of the infected red blood cells and the cycle is repeated.

The bursting of the red blood cells and the release of toxic substances cause the characteristic fever of malaria. After a number of such cycles, sexual stages, male and female gametocytes, are produced, and these are taken up by a feeding mosquito, in which the Plasmodium life cycle is completed by sexual reproduction, resulting in new sporozoites.

d) Prevention of malaria

- Drainage of stagnant water: The larval stages of the mosquito live in stagnant water, so drainage removes breeding sites. This has had some success.

- Destruction of the breeding sites of the mosquito: The larvae and pupae of mosquitoes obtain their oxygen by means of small tubes which are pushed through the water surface film. Thus any method of blocking these tubes will result in the death of the intermediate life stages of the mosquito (petrol, oil….)

- Destruction of the adult mosquitoes: This is aimed at killing the mosquitoes that enter houses. Thus, the indoor surfaces are sprayed with a persistent insecticide.

Use of mosquito nets.

e) Occurrence of malaria

The disease now occurs in tropical and subtropical regions of the world, and its distribution is limited by conditions that are inimical to the development of the mosquito vector, such as temperature and altitude.

Malaria is endemic in tropics because:

– Tropical climate provides the best breeding and living conditions for the Anopheles mosquito which transmits malaria

– The Anopheles cycle requires areas of stagnant water and these are common within tropics

– In the tropical areas there is presence of bushes or abundant vegetation which makes suitable habitat for mosquitoes

Plasmodium needs temperature in excess of 20ᵒC for it to complete its cycle within the mosquito.

Table 2.3: The features of malaria

Treatment of malaria

The common drugs used in treatment of malaria include the following:

Chloroquine, Atovaquone-proguanil (Malarone), Artemether-lumefantrine (Coartem), Mefloquine, Quinine, Doxycycline (used in combination with quinine)

f) Failure to eradicate malaria

– There is no effective vaccine against malaria

– The pathogens are transmitted by mosquitoes which are not eradicated.

– The plasmodium have become resistant to different anti-malarial drugs

– Ignorance of some people toward the disease and how it is spread.

2.1.4. HIV/AIDS and other Sexual Transmission Diseases (STD)

AIDS (Acquired Immune Deficiency Syndrome) is a disorder which damages the human body’s immune system. It is caused by the HIV virus (Human Immunodeficiency Virus).

semen. In 90% of cases the transmission is achieved by sexual contact.

People can contract the disease as follows:

– Intimate sexual contact. The most frequent mode of transmission of HIV is through sexual contact with an infected person.

– Infected blood entering bloodstream: by means of unsterilized needles and syringes. Unfortunately the disease can be contracted after being given blood or blood products already infected with HIV.

Close contact between infected and non infected people through cuts and open wounds has also been known to pass on the virus.

– From mother to baby: An infected pregnant woman can pass on the virus to her baby through the placenta, at birth or through breast milk during suckling. The chances of infection being transmitted from the mother to her baby are currently estimated to be 25-50%.

TEST FOR THE DISEASE

A blood test is used to tell whether or not a person has been infected by the HIV virus. Under normal circumstances the immune system reacts to infection by producing antibodies and when the HIV virus enters the body, anti-HIV antibodies are produced. The blood of the person being tested is added to HIV proteins which have been commercially prepared. If there are anti-HIV antibodies in the blood sample they will bind to the viral proteins and the person is described as HIV positive. However, if the test proves negative that person may still be infected. This is because it takes up to three months or longer for HIV antibodies to be produced after infection.

PREVENTION OF THE DISEASE

There are many precautions which can be followed in trying to prevent the disease:

The use of a barrier during intercourse can prevent the virus from infecting through blood or semen. Thus the use of a sheath or condom is recommended.

This practice has been encouraged through many advertising campaigns throughout the world.

• Restriction to one sex partner and the absence of promiscuity will also clearly reduce the risk of infection.

• A reduction in the spread of HIV can be brought about by the use of clean needles and syringes by drugs addicts.

• The blood donated should be tested for the presence of antibodies to HIV which indicates whether or not the donor is infected. Blood containing these antibodies is not used.

• Educating the people about the disease.

• Taking antiretroviral during pregnancy and delivery.

• To avoid breastfeeding and to administer antiretroviral drugs to the newborn.

Table 2.4: The features of HIV/AIDS

Other sexual transmission diseases (STD)

Sexually transmitted diseases (STDs) are transmitted by infected persons to healthy persons during sexual intercourse.

Sexually transmitted diseases (STD), also referred to as sexually transmitted infections (STI) and venereal diseases (VD), are illnesses that have a significant probability of transmission between humans by means of sexual behavior, including vaginal intercourse, anal sex and oral sex. Some STIs can also be contracted by using drug needles after their use by an infected person, as well as through any incident involving the contact of a wound with contaminated blood or through childbirth or breastfeeding.

Sexually transmitted infections have been well known for hundreds of years, and venereology is the branch of medicine that studies these diseases.

While in the past, these illnesses have mostly been referred to as STDs or VD, the term sexually transmitted infections (STIs) has been preferred by many up-to-date medical sources, as it has a broader range of meaning; a person may be infected, and may potentially infect others, without having a disease.

There are 19 million new cases of sexually transmitted infections every year in the United States, and, in 2005, the World Health Organization estimated that 448 million people aged 15–49 were being infected a year with curable STIs (such as syphilis, gonorrhea and chlamydia).

Until the 1990s, STIs were commonly known as venereal diseases, the word venereal being derived from the Latin word venereus, and meaning relating to sexual intercourse or desire, ultimately derived from Venus, the Roman goddess of love. Social disease was a phrase used as a euphemism.

While many people with STDs show no signs or symptoms of their infection, when there are signs of STDs they are most likely to be in the genital area.

The genital area in women includes the vulva (the area around the vagina including the lips), vagina (the opening where menstrual blood comes out),buttocks, urethra (the opening above the vagina where urine comes out) and anus (the opening where a bowel movement comes out). The genital area in men includes the penis, scrotum (“balls”), urethra, and anus.

What Are the Symptoms of STDs?

Sometimes, there are no symptoms of STDs. If symptoms are present, they may include one or more of the following:

• Bumps, sores, or warts near the mouth, anus, penis, or vagina.

• Swelling or redness near the penis or vagina.

• Skin rash.

• Painful urination.

• Weight loss, loose stools, night sweats.

• Aches, pains, fever, and chills.

• Yellowing of the skin (jaundice).

• Discharge from the penis or vagina. (Vaginal discharge may have an odor.)

• Bleeding from the vagina other than during a monthly period.

• Painful sex.

• Severe itching near the penis or vagina.

Examples of these diseases are chlamdia, gonorrhoea, syphillis and, HIV and AIDS.

1. Chlamydia

Chlamydia is caused by the bacterium Chlamydia trachomatis.

 Neisseria gonorrhoeae.

The bacteria attaches on the epithelial cells of the vagina or male urethra.

This results in inflammation and discharge of pus. If left untreated, the infection spreads to the other reproductive parts and may eventually block the passages resulting to infertility. Signs and symptoms of gonorrhea.

Some men with gonorrhea may have no symptoms at all. However, men who do have symptoms may have:

• A burning sensation when urinating.

• A white, yellow, or green discharge from the penis.

• Painful or swollen testicles (although this is less common).

Most women with gonorrhea do not have any symptoms. Even when a woman has symptoms, they are often mild and can be mistaken for a bladder or vaginal infection.

Women with gonorrhea are at risk of developing serious complications from the infection, even if they do not have any symptoms.

Symptoms in women can include:

• Painful or burning sensation when urinating.

• Increased vaginal discharge.

• Vaginal bleeding between periods.

Treatment

Gonorrhea can be treated using antibiotics like penicillin.

3. Syphilis

Syphilis is transmitted from person to person by direct contact with a syphilitic sore, known as a chancre. Chancres occur mainly on the external genitals, vagina, anus or in the rectum. Chancres also can occur on the lips and in the mouth.

eating a food of energy giving food without adequate proteins.

Application activity 2.1

1. List the ways in which cholera is transmitted from person to person.

2. Explain why there is such a high risk of cholera following natural

disasters such as earthquakes, hurricanes, typhoons and floods.

3. Explain why there is a high death rate from TB in countries with a

high proportion of the population who are HIV-positive.

4. TB is an opportunistic infection. Why?

5. Describe how malaria is transmitted.

6. Describe the biological factors that make malaria a difficult disease

to control.

7. Describe the precautions that people can take to avoid catching

malaria.

8. Which of the following diseases is transmitted by an insect vector?

a) Cholera

b) HIV/AIDS

c) Malaria

d) TB

9. Tuberculosis is a serious infectious disease.

a) Name the causative agent of tuberculosis.

b) Explain how tuberculosis is transmitted.

c) State the regions of the world with the highest number of cases of

tuberculosis.

d) Suggest reasons for the high number of tuberculosis in some parts

of the world.

10. The table shows the number of cases of cholera and deaths from

the disease for the five countries with the greatest outbreaks as

reported to the WHO in 2010.

a) Describe how cholera is transmitted.

b) With reference to the table:

i. Calculate the case fatality rate for Haiti in 2010.

ii. Suggest why the case of fatality rate varies between countries.

iii. Explain why it is important that the WHO collects data on

outbreaks of cholera.

c) Explain why there no epidemics of cholera in highly economically

developed countries such as Australia, Malaysia and USA.

2.2. Hygiene practices

Activity 2.2

Discuss the possible hygiene practices you always have every

morning at your school.

It is important to understand family health issues, because poor personal

and environmental hygiene may cause hygiene related diseases. It

is therefore important to acquire knowledge and skills on personal and

environmental hygiene in order to avoid such diseases.

2.2.1. Personal hygiene

Personal hygiene and sanitation is very important because:

– It insures proper growth and development of children.

– It helps to prevent diseases especially hygiene related diseases.

– It prevents bad smell it helps to keep the environment clean, tidy and

beautiful.

– It makes the environment appealing and attractive.

The personal hygiene may be maintained through the hygiene practices

below:

– Washing the body regularly with clean water and soap.

– Wearing clean clothes.

– Living in clean environment with adequate fresh air.

– Eating adequate balanced diet. Young children should be fed between

5 to 6 times per day. Their diet should be rich in proteins.

– Having regular exercises.

To insure personal hygiene, the important aspects below are considered:

Care of body

To prevent skin diseases and bad smell one needs:

– Washing the body regularly with clean water and soap.

– Avoid sharing clothes, socks and towels.

– Wearing clean under wears.

– Stay in clean environment.

– Wear clean clothes.

Care of the feet

– Washing the feet regularly with water and soap.

– Keeping the feet dry to avoid fungi or foot rot and bad smell.

– Wearing clean socks.

– Avoid sharing socks.

– Keep nails short and clean.

– Airing your feet daily.

– Apply some oil like Vaseline to keep the feet smooth.

Care of hands

– Wash hands regularly with clean water and soap.

– Keep nails short and clean.

– Wash hand before touching and preparing the food

– Wash hand before eating.

– Wash hand after visiting the toilet.

– Apply some oil like Vaseline to keep the hands smooth.

Care of hair

– Wash your head regularly with clean water and soap.

– Keep your hair well combed.

– Oil your hair to prevent dandruff.

Care of teeth

– Brush your teeth daily with a tooth brush, clean water and tooth paste.

– Avoid eating too much sweet, biscuits and sugary foods, as they can

cause tooth decay and dental cavities.

– Eating foods that help build strong teeth like milk, eggs, vegetables,

fruits and fish.

– To visit dentist regularly for checkups.

– To avoid putting sharp dirty objects in the mouth.

– Pregnant mothers should feed on dies rich in Calcium which is used to

make teeth.

Care for eyes, ears and nose

These sensory organs are very important. We must care for them well. Injury

may result in permanent disability such as: blindness, deafness and lack

ability to detect smells.

Care of the eyes

– Wash eyes with clean water.

– Protect your eyes from foreign objects and dusts.

– Protect your eyes from too much or too low light. You always read

under adequate light.

Care for ears

– Wash ears with clean water and soap.

– Never insert hard objects in the ear, this may damage your ear and

cause deafness.

– Avoid very loud noise.

– Clean ears with cotton around a matchstick or use ear buds and use it

gently.

Care for the nose

– Never insert hard objects in the nose.

– Keep the nose clean by blowing it regularly.

– Avoid being hit in the nose.

2.2.2. Environmental hygiene

Our surrounding environment including water, air and soil should be protected

and kept clean. There should be different hygiene practices to prevent soil

pollution, water pollution and air pollution.

Application activity 2.2

1) What are possible hygiene activities are required to care for;

a) Eyes

b) Nose

c) Feet

2) Explain the general human body hygiene practices.

2.3 Human immune system: immunity, structure and role of

antibodies, immunization and vaccine

Activity 2.3

The human body is always exposed to environment full of pathogens and

it remains healthy. How is this possible?

IMMUNITY is a process by which the body of a living organism defends itself

against pathogens. The immune system is a protective system that is made

of a series of defenses that fight against diseases by: recognizing, attacking,

destroying and remembering each type of pathogen that enters the body. It

does this by producing specialized cells which inactivate pathogens.

Defense mechanisms against infections

The immune system includes two general categories of defense mechanisms

against infections: nonspecific defense and specific defense.

2.3.1 Nonspecific defenses

They include physical barriers (skin) and chemical barriers (mucus, tears and

sweat) which prevent foreign pathogens from entering the body. Nonspecific

defenses occur into two lines of defense:

a) First line of defense: its function is to keep pathogen out of the body. This

role is carried out by: the skin, sweat, tears and mucus. The most important

nonspecific defense is the skin. The skin epidermis consists of layers of dead

cells called keratinocytes (which have been keratinized: their cytoplasm is

replaced by a protein called keratin). The keratinized layers of dead cells

act as an effective barrier to pathogens and cannot normally be penetrated

by bacteria or viruses.

Likewise, the mucous that line the digestive,respiratory, nose and genitals

block the entry of harmful microbes. Beyond theirrole as a physical barrier,

the skin and mucous membranes counter pathogens with chemicaldefenses.

For example, secretions from sebaceous and sweat glands give the skin an

acidic PH ranging from3 to 5, which kills bacteria. Many secretions of the

body including: tears, mucus and saliva contain lysozyme, ananti-microbial

enzyme that breaks the walls of bacteria. Also, stomach acid and digestive

enzymes destroy many pathogens which are swallowed with the food.

b) The second line of defense: Microbes which have managed to penetrate

the first line of defense face the second line of defense which depends mainly

on phagocytosis,inflammatory response and on certain antimicrobial

proteins.

i. Phagocytosis:

When pathogens are detected in the body, the immune system produces

millions of white blood cells which fight the infection. Many of this white

blood cells are phagocytes, which engulf and destroy bacteria.

The word Phagocyte comes from Greek where: phag means: to eat and

kutos means cell. Thus phagocytes are cells that engulf and destroy

pathogens. There are two types of phagocytes:

• Neutrophils are the common phagocytes produced in bone marrow

and carried in blood to be released in tissue fluid. They will be released

in large number as a result of infection.

The phagocytic cells called neutrophils constitute about 60 % to 70%

of all white blood cells (leucocytes). The neutrophils enter the infected

tissue, engulfing and destroying microbes there.

• Macrophages are large cells manufactured in bone morrow and travel

in blood as monocytes. They tend to be settle in lymph nodes, liver

and in spleen.

How phagocytes work: when pathogens enter the body, phagocytes move

towards them, they engulf and destroy them. Once the phagocyte is bound

to the pathogen, it will envelop it by folding its membrane inwards. The

pathogen is trapped inside the vacuole called phagosome. Lysosomes

fuse with the phagosome and release enzymes called lysins into it. These

enzymes digest pathogens and the end products are harmless nutrients that

can be absorbed into the cytoplasm.

ii. Inflammatory response

One result of phagocytosis is inflammation or inflammatory response

that is characterized by: redness, hotness, swollen and painful at the site

of local infection. An inflammatory response is a nonspecific defense

reaction to tissue damage caused by injury or infection.

The tissues injured by bacteria or physical damage (like a cut) release

chemicals such as histamine and prostaglandins. These chemicals work

as signals which induce an increased heart rate and increased blood

capillary permeability (so that white blood cells get to the site of infection

faster).

Infected cells also release chemicals which attract phagocytes. When

phagocytes and macrophages arrive at the site of injury, they engulf and

destroy pathogens and the tissues heal.

The inflamed tissues contains many bacteria and phagocytes, many of which

die and form the pus. The increased body temperature slows or stops the

growth of pathogens. The fever and increased number of leucocytes are two

indications that the body is working hard at fighting infections

iii. Anti-microbial proteins

Two groups of proteins: interferons and the complement system provide

short-term, nonspecific defense to viral and bacterial infections. Interferons

are proteins secreted by virus-infected cells which inhibit the synthesis of

viral proteins in affected cells and help to block viral replication. They

diffuse to neighboring cells and stimulate them to produce antiviral proteins,

which prevent viruses from multiplying within them.

Interferons also activate natural killer cells and macrophages, which

destroy infected host cells before they release more viruses. Interferons can also promote destruction of cancer cells. The complement system consists of about 30 proteins in blood plasma that function together to fight

infections. These proteins circulate in an inactive state and are activated by substances on the surface of many microbes. Activation results in a cascade of biochemical reactions leading to lysis (bursting) of invading cells. The complement system also functions in inflammation.

2.3.2 Specific defense/immunity: third line of defense

If pathogens are able to get past the body’s non-specific defenses, the immune system reacts with a series of specific defenses that attack the particular disease-causing agent. These defenses are called immune response. A substance that triggers (causes) this response is known as an antigen. Viruses, bacteria and other pathogens may serve as antigens.

The cells of the immune system that recognize specific antigens are two types of lymphocytes:

a) B lymphocytes (B cells): which originate in the bone marrow and migrate to the lymph nodes where they proliferate into plasma cells which produce antibodies.

B cells provide immunity against antigens and pathogens in the body fluid.

B lymphocytes give rise to the humoral immunity or antibody-mediated immunity.

b) T lymphocytes (T cells): originate in bone marrow and migrate into the

thymus. They don’t produce antibodies, but they themselves provide

defense against antigens and pathogens inside living cells. T lymphocytes

give rise to the cell-mediated immunity.

Humoral immunity

When pathogens invade the body, their antigens are recognized by few B

cells of the body. These B cells grow and divide rapidly, producing large

number of plasma cells and memory cells. Plasma cells produce and

release antibodies. Antibodies are proteins that recognize and bind to

antigens. They are carried in the bloodstream to attack the pathogen at the

site of infection. As antibodies overcome pathogens, the plasma cells die out

and stop producing antibodies.

Once the body has been exposed to a pathogen, millions of memory B cells

remain capable of producing antibodies specific to that pathogen. These

memory B cells, greatly reduce the chance that the disease could develop a

second time. If the same antigen enters the body a second time, a second

response occurs. The memory B cells divide rapidly, forming new plasma

cells. Plasma cells produce the specific antibodies to destroy the pathogen

as faster as possible.

An antibody is shaped like the letter Y, and has two identical antigenbinding

sites. The shape of the binding site allows the antibody to recognize

a specific antigen with a complementary shape. The different shapes give

antibodies the ability to recognize a large variety of antigens. A healthy adult

cane produce about 100 million different types of antibodies.

Cell-mediated immunity

It is the body’s primary defense against its own cells when they have become

cancerous or infected by viruses. The cell-mediated immunity is also

important in fighting infection caused by fungi and protists. When viruses

and other pathogens get inside living cells, antibodies alone cannot destroy

them. During cell-mediated immunity, T cells divided and differentiated into:

killer T cells (cytotoxic T cells), helper T cells, suppressor T cells and

memory T cells.

Killer T cells track down and destroy bacteria, fungi, protozoa and foreign

tissues containing antigens. Helper T cells produce memory T cells. The

memory T cells, like memory B cells, will cause a secondary response, if

the same antigen enters the body again. As pathogens are brought under

control, suppressor T cells release substances that shut down the killer T

cells.

Types of immunity

Immunity can be active or passive. In active immunity, the body makes its

own antibodies after exposure to an antigen, whereas in passive immunity,

the body acquires antibodies produced by other person or other animals.

Either active immunity or passive immunity can be naturally or artificially.

Thus, there are four types of immunity:

a) Natural active immunity

In natural active immunity, the body makes its own antibodies, in response

to an antigen.

b) Artificial active immunity

In artificial active immunity, the body makes its own antibodies, as a result

of vaccination against diseases. Vaccination (immunization) is the

production of immunity as a result of injection of weakened pathogens

which cannot cause diseases to the body, but which can induce production

of specific antibodies to those pathogens.

c) Natural passive immunity

Natural passive immunity is a temporary immunity resulting from acquiring

antibodies produced by another individual. The only natural passive immunity

is when a foetus acquires antibodies from the mother, either through the

placenta before birth, or through the breast feeding after birth. This immunity

protects the child against most infectious diseases for the first few months of

its life, or longer, if the infant is breast-fed.

d) Artificial passive immunity

It is a temporary immunity that results from the injection of the serum

containing antibodies from another organism. In this passive form of

immunity, a recipient is not induced to produce his or her own antibodies,

but is supplied with them, from an outside source. For example: the horse

serum well prepared, can then be used to protect humans against diseases.

The trouble with the protection induced by this immunity is that it is shortlived.

Nowadays, the passive immunity is normally used only in emergencies,

when is too rate for active immunization to work quickly enough.

Application activity 2.3

I. Multiple Choice Questions

1. Humoral immunity is carried out by the

a) B lymphocytes

b) T lymphocytes

c) Phagocytes

d) T lymphocytes, phagocytes and NK cells

2. Plasma cells represent

a) B lymphocytes which are actively secreting antibodies.

b) T lymphocytes which are actively secreting cytokines

c) Monocytes which have entered tissues

d) CTL which are secreting perforins.

3. Live attenuated vaccine types have the disadvantage over the inactivated

vaccine types as

a) They require booster shots

b) They do not confer life-long immunity

c) They may mutate to virulent form

d) They do not stimulate the immune system strongly.

4. Immune response is

a) The defense mechanism of our body.

b) Reaction of the cells and fluids of the body.

c) A substance that destroys or inhibits the growth of other

microorganisms

d) None of the above

II. Long Answer Type Questions

1. With an illustrative diagram, state the origin and describe the mode of

action of phagocytes.

2.4. Common addictive substances and their effects

Application activity 2.4

Carefully, Analyze the substances 1-7 in figure above and answer to the

following questions

1. Among those substances which one you use in daily life?

2. Which do you think are dangerous to life?

3. Suggest one effect of each of the dangerous substances

Tobacco, Alcohol and drugs addiction is the physical and psychological

need to continue using these substance, despite its harmful or dangerous

effects.The signs and symptoms of drug addiction drug vary according to the

individual and the substances he or she uses.

2.4.1. Tobacco smoking and its effects

Smoking harms nearly every organ in your body. Among heavy smokers,

two in three will die from a disease caused by smoking. Tobacco smoke

is made up of thousands of chemicals and many of them are very harmful.

Around 70 of them cause cancer. Cigarette smoke contains over 4000

different chemicals. Many of them are harmful. The most harmful substances

in cigarette smoke include: nicotine, carbon monoxide and tar.

Cigarette smoke contains over 4,000 chemicals, including 43 known

cancer-causing (carcinogenic) compounds and 400 other toxins. These

cigarette ingredients include nicotine, tar, and carbon monoxide, as well as

formaldehyde, ammonia, hydrogen cyanide, arsenic, and DDT. Nicotine is

highly addictive.

a) Effects of Tar and carcinogens in tobacco smoke on the gas

exchange system

Tar is a combination of severe chemicals lying on the lining of the airways

and alveoli. This increases the diffusion distance for Oxygen entering the

blood and CO₂ leaving the blood. The lumen of airways gets smaller and this

restricts the flow of air to the alveoli. The tar paralyses or destroys the cilia

on the surface the airways, so they are unable to move the mucus away.

Bacteria and viruses trapped in mucus are not removed. They can multiply

in the mucus and may block the bronchioles and affect breathing process. A

combination of bacteria, viruses and mucus in airways and alveoli causes

the lungs to be more susceptible to infections. Smokers are more likely to be

attacked by influenza and pneumonia.

Tar contains also the carcinogen compounds which cause cancer. When

the tar lies on the surfaces of airways, carcinogens enter the cells of lung

tissues. They enter the nucleus of these cells and have a direct effects on

their genetic material. Any change on genetic material is called mutation,

if mutations affect the genes that control cell division, then uncontrolled cell

division take place. This is cancer. Lung cancer often takes 20-30 years to

develop, and a cancer may grow for many years before it is discovered.

b) Effects of Nicotine and carbon monoxide on the cardiovascular

system

i. Carbon monoxide (CO): is fatal in large amount. This poisonous

gas is also found in car exhaust fumes. CO enters the red blood cells

and combines with haemoglobin more rapidly than Oxygen, and form

the carboxyhaemoglobin. This reduces the oxygen-carrying capacity

of blood, preventing your lungs, heart, and other organs from getting

oxygen they need to function properly. CO can also damage the lining

of arteries, and may rise the heart beat rate.

ii. Nicotine: is a poisonous alkaloid drug that is additive. 60 mg of

nicotine placed on the tongue would kill an individual within minutes.

It is absorbed by the body very rapidly, reaching the brain in less than

30 seconds.

It is a highly toxic chemical and its manufacture, use and sale is

controlled under the State Poisons Acts, except where it occurs in

tobacco.This exception of tobacco is for political reasons, not because

nicotine is deemed ‘safe’ in cigarettes. Nicotine, once inhaled, affects

the body very quickly. It causes changes to the structure and the

working of the brain, which lead to nicotine addiction. Nicotine also

raises heart rate, blood pressure, releases hormones (adrenaline)

affecting the central nervous system, and constricts small blood

vessels (arterioles) under the skin. In the long term, nicotine may be a factor in causing coronary disease. It is believed to be involved

in the development of gastrointestinal disorders and problems during

pregnancy, and is linked with the development of cancers.

c) Contribution of tobacco smoking to atherosclerosis and

coronary heart disease

i. Atherosclerosis is the deposition of fatty substances in the walls of

the arteries. The CO in the cigarette smoke can damage the inner

lining of arteries. This encourages the deposit of fatty substances like

cholesterol on the walls of arteries. This reduces the lumen of arteries,

which reduces blood flow, and causes high blood pressure.

ii. Coronary heart disease (CHD) is a disease of the heart caused by

malfunction of the coronary artery. Coronary arteries are the arteries

which carry blood to the heart.

The nicotine and carbon monoxide found in cigarette enter the lungs

and diffuse into blood in blood capillaries, that conducting them into

coronary arteries. This causes the atherosclerosis in coronary arteries,

which reduces the blood flow in the heart muscles which receive less

oxygen for respiration. This can lead to coronary heart diseases, which

take three forms: In circulatory system, they cause changes which lead

to cardiovascular diseases like:

iii. Angina: a severe pain in the chest, which may extend down the left

arm or up into the neck.

iv. Heart attack or myocardial infections: caused by a clot in the

coronary arteries, blocking the flow of blood to the heart muscles.

v. Heart failure: when the heart cannot sustain its pumping action. This

can be caused by the blockage of the major coronary arteries.

d) Symptoms of lung cancer and chronic obstructive pulmonary

diseases (COPD)

– Chronic obstructive pulmonary disease: is a combination of

diseases that include chronic bronchitis, emphysema and asthma.

The symptoms of COPD are a combination of symptoms of chronic

bronchitis, and of emphysema.

– Chronic bronchitis: is the inflammation of the airways. This is

accompanied by damage to the cilia and the over production of mucus.

The symptoms are: irritation in lungs, continual coughing, and coughing

up mucus that is often filled with bacteria and white blood cells.

– Emphysema: is the loss of elasticity in alveoli, which causes the alveoli

to bust. The symptoms are: short breath, hard exhalation, the blood is

less well oxygenated and fatigue occurs.

– Lung cancer: the symptoms of lung cancer can be recognized by:

continual coughing, shortness of breath, pain in the chest and the blood

coughed up in the sputum is often the first sign of the lung cancer.

e) Evidences linking cigarette smoking to diseases and early

death.

i. Links of cigarette smoking to early death

– Regular smokers are three times more likely to die prematurely than a

non-smoker.

– 50% of regular smokers are likely to die of a smoking-related disease

– The more cigarettes a person smokes per day, the more he is likely to

die prematurely.

ii. Links of cigarette smoking to lung cancer

– A smoker is 18 times more likely than a non-smoker to develop lung

cancer.

– 25% of smokers die of lung cancer.

– A heavy smoker (more than 25 cigarettes a day) is 25 times more likely

than a non-smoker to die of lung cancer

– The chances of developing lung cancer reduce as soon as a person

stops smoking.

iii. Links to other lung diseases

– COPD is rare in non-smokers

– 98% of people with emphysema are smokers.

– 20% of smokers have emphysema

2.4.2. Alcohol

Alcohol is any organic compound in which the hydroxyl functional group (–

OH) is bound to a carbon. The term alcohol originally referred to the primary

alcohol ethanol (ethyl alcohol) which is used as a drug and is the mainalcohol

present in alcoholic beverages.

Alcohol is produced by adding yeast on a liquid that contains sugar in absence

of oxygen. This yeast ferment sugar to produce energy, alcohol and alcohol.

Most popular alcohol containing drinks include fermented drinks such as

beer and wine, other drinks such as vodka, whiskey, scotch, and gin are

made by distillation

accident that may kill people.

2.5.3. Drugs

Drug is any substance that cause a change in the body. Drugs affect the

body in different ways, because some are very powerful and dangerous and

their possession is not allowed. Other drugs like penicillin and codeine are

drugs that can be used under the supervision of doctor.

All drugs (legal and illegal ones) have the capacity of harming life if they are

abused. In this section, some of the most commonly abused drugs and the

way they affect the body will be considered.

Drugs affect the particular system of the body like digestive and circulatory

systems.

The following are the most powerful drugs that can also affect the nervous

system and their negative side effects.

a) MARIJUANA ( Also called Hashish or Hash)

i. Negative effects of using marijuana

– Addiction: Marijuana is physically addictive and psychologically

addictive, especially as it concerns younger.

– Memory Loss: People who always use marijuana developed a poorer

verbal memory in middle age than people who didn’t smoke.

– Social Anxiety Disorders: Regular use of marijuana can lead to mental

health issues such depression, anxiety and even schizophrenia.

– Paranoia: researches indicated that the use of marijuana can lead

users to feel a sense of paranoia as a result of the changes in their

sensory perception

– Heart Damage: Marijuana can also significantly raise a person’s heart

rate for up to three hours. Even, people who use marijuana are more

likely to have a stroke https://www.livescience.com/58210-stroke-heartfailure-

linked-to-marijuana.html at some point in their lives than people

who didn’t use it.

– Other effect are: Lung problems, low testosterone, appetite

irregularities, risk of greater potency, decrease in motor

Responses, poor decisions.

b) HALLUCINOGENS

Hallucinogens are drugs that cause hallucinations. Users see images,

hear sounds and feel sensations that seem very real but do not exist. Some

hallucinogens also produce sudden and unpredictable changes in the

mood of those who use them.

There are many types of hallucinogens but the two common types such

as LSD(Lysergic acid diethylamide ) and PCD(Phencyclidine) are the ones

which are used.

LSD is a powerful hallucinogen that interferes with the normal transmission

of nerve impulses in the brain. Its effects vary from person to person and all

people who use LSD regularly have abad trip. Some of LSD users have lost

touch with reality after only one single dose.

PCP produces fillings of strength and great power. High dose of PCP heart

attacks. The users of PCP often become extremely violent and are danger

to themselves and others.

c) STIMULANTS

These are drugs that speed up the actions of nervous system. The most

powerful stimulants are Amphetamines, these chemically resemble natural

neurotransmitters found in the body ( Compounds that pass nerve impulse

from one neuron to another). Once amphetamine enters the blood stream, it

floods the body and behaves like neurotransmitters. This causes the nervous

system to increase its activity producing a feeling of strength and energy in

the user body. Later the user suffers from fatigue and depression as the

nervous system becomes unable to handle the overstimulation produced by

amphetamines after their dose wears off.

Long-term use of amphetamines causes hallucinations, circulatory problems.

Psychological difficulties.

d) DEPRESSANTS

These are drugs that reduce the rate of nervous system activity. These drugs

are also known as downers. People become dependent on them as long as

they use them. Example of downers is barbiturates. Use of the barbiturates

with alcohol is fatal, because the nervous system becomes so depressed

and breath stops.

The barbiturates abuse is danger because it brings about serious medical

problems that must be immediately treated once the user stops supplying

the drugs to the body.

e) COCAINE

This drug is compound extracted from leaves of coca plant. Users supply it

to the body by smoking it, sniffing it or inject it into the bloodstream.

Cocaine stimulate the release of neurotransmitter called dopamine which is

normally released by the brain if person is satisfied during lunch or dinner.

So, cocaine creates feeling of pleasure and satisfaction

i. Effects of using cocaine

– Heavy use of cocaine leads to lung damage similar to emphysema.

Overdose stops breathing.

– Use of cocaine increases the heart rate and blood pressure leading to

risk of irregular heartbeat or even heart attack.

– Cocaine causes extreme mood changes, irritability. Long-term use can

lead to psychological problems.

– Cocaine causes the users to experience the sensation of bugs crawling

over the skin.

– Cocaine usage reduces a desire for food, leading to body weight loss.

f) OPIATES

This is a group of drugs produced from the opium poppy. The most common

opiates are opium produced directly from the opium poppy. Other examples

of opiates are morphine and heroin which are forms of opium. Apart from

heroin, other opiates can be used under supervision of doctor to reduce

severe pain as they are used as pain killers. If opiates are taken in large

dose, they can result to death.

In addition, opiates such as heroin, are example of drugs that cause a strong

physical dependence. The regular user becomes addicted and the nervous

system becomes also dependent on the supply of drugs. Any attempt of

withdrawal or stopping the use of drug will cause severe pain, nausea, chills and fever.

Application activity 2.4

I. Choose whether the following statements are True (T) or False (F)

1. Smoke from cigarettes can make non-smokers sick.

2. Smoking can affect a person’s ability to smell and taste food.

3. Secondhand smoke kills about 3,000 non-smokers each year from lung disease.

4. It takes about ten seconds for nicotine absorbed into the

bloodstream to reach the brain.

5. Smoking is a difficult habit to quit.

6. Nicotine, the chemical found in cigarettes, is an addictive drug.

7. A smoker is twice as likely to have a heart attack as a non-smoker is.

8. Cigarette brands that are heavily advertised on TV, in magazines,

on billboards, and on T-shirts are the brands more teens buy.

9. One out of every ten smokers will die of a smoking-related sickness.

10. More germs get into your lungs when you smoke.

II. Suggest the components of a tobacco smoke

III. Give the effects of alcohol on human body health

SKILLS LAB 2:

After studying this unit” Common diseases and hygiene”, and after finishing

their studies as well as working as cooperative, Student-teachers will help

society by creating a center for people workshop about nutrition, hygiene

and sanitation, so that different diseases can be eradicated from Rwanda society.

They will be helping people to fight against malnutrition by talking about

deficiency diseases and how they can prevent them. Here every house

should have its own vegetable plantation around kitchen.

Sensitization about general body hygiene, food hygiene, clothes hygiene,

home hygiene, water sanitation will be the first priority. And again, according

to what they have acquired from the school student-teacher will help people

to know all method of cooking like:

a) Boiling: this is a method involving cooking food completely covered

with water and boiling it until fully cooked

b) Steaming: this is cooking food using steam from boiling water.

c) Frying: this method involves cooking food with hot fat or oil.

d) Stewing: this involves cooking food with low quantities of water.

e) Roasting: this involves cooking food with very hot radiant heat

f) Baking: this involves cooking food using a direct heat

g) Grilling: this involves cooking food with direct heat using a grill.

These methods will be very important in preventing from being infected by

disease germs from uncooked food. Again good storage and preservation

are very significant in preventing many infectious diseases.

Conclusion: This unit will lead student-Teachers when they are still at

school or at home to protect their own life, and even the society life.

End unit assessment 2

I. Choose whether the given statements are True (T) or False (F)

1. Innate immunity is present at birth.

2. Breast milk confers protection to newborn by providing IgE type of antibodies.

3. Antibodies can work by promoting phagocytosis of microbial agents.

4. Antibiotics help a patient in mounting an effective immune response.

5. Treating tuberculosis is becoming difficult because Mycobacterium tuberculosis has become resistant to a number of antibiotics.

6. High fever is a generalized allergic reaction caused by release of active mediators from mast cells.

7. Secondary immune response appears much faster because of the presence of memory cells persisting from previous infection.

8. Vaccination against snakebite is an example of passive immunization.

9. Allergies are of two types—innate and adaptive.

10. Beta-lactam antibiotics kill bacteria by blocking synthesis of their cell walls.

II. Long answers type questions

1. Answer the following questions

a) Name the causative agent of tuberculosis.

b) Explain how tuberculosis is transmitted.

c) State the regions of the world with the highest number of cases of tuberculosis.

d) Suggest reasons for the high number of tuberculosis in some parts of the world.

2. State why vaccination programs are able to eradicate smallpox but not measles, TB, malaria or cholera.

3. Compare roles of B cells and T cells in the immune response.

4. Name organism which have the following effects on health