Infectious Diseases, Immunity and Vaccination
Senior 2 · Biology
Infectious Diseases, Immunity and Vaccination
Lesson 2 of 5
22 min
In Rwanda, community health workers (abajyanama b'ubuzima) in every village can test a child with fever for malaria and start treatment the same day. That system works only if people recognise the warning signs early and go for help. Knowing the signs of common infections, and what does and does not treat them, is one of the most useful things a biology course can give you.
A symptom is what the sick person feels, such as a headache, pain or tiredness. A sign is something another person can see or measure, such as a temperature of 39 °C on a thermometer, a rash or a fast pulse. Health workers use both to make a diagnosis, usually confirmed with a test.
| Disease and pathogen | How it spreads | Main signs and symptoms | Prevention and control | Treatment |
|---|---|---|---|---|
| Malaria: Plasmodium (protist) | Bite of an infected female Anopheles mosquito | Fever that comes and goes, chills, heavy sweating, headache, body pains, vomiting. Severe malaria causes anaemia, confusion and can kill. | Sleep under an insecticide-treated net every night; spray inside houses; drain standing water; long sleeves in the evening | Test first (a rapid diagnostic test), then take the full course of an artemisinin-based combination therapy (ACT) as prescribed |
| Cholera: Vibrio cholerae (bacterium) | Water or food contaminated with faeces | Sudden, very watery diarrhoea (pale "rice-water" stools), vomiting, rapid dehydration | Safe water, latrines, handwashing, well-cooked food; oral cholera vaccine | Replace lost water and salts at once with oral rehydration solution (ORS); a drip in severe cases; sometimes antibiotics |
| Typhoid: Salmonella Typhi (bacterium) | Water or food contaminated with faeces | High fever lasting many days, headache, stomach pain, weakness, constipation or diarrhoea | As for cholera; typhoid vaccine | Antibiotics prescribed after testing |
| Tuberculosis (TB): Mycobacterium tuberculosis (bacterium) | Airborne, from the coughs of a person with TB of the lungs | Cough lasting more than two weeks, sometimes with blood; night sweats; weight loss; fever | BCG vaccine at birth; good ventilation; finding and treating cases early | Several antibiotics taken together every day for at least six months |
| Influenza and colds: viruses | Droplets, hands and objects | Runny nose, sore throat, cough, fever, aching body | Cover coughs, wash hands, ventilate rooms; influenza vaccine | Rest and fluids. Antibiotics do not help. |
| Intestinal worms: roundworm, hookworm | Eggs swallowed with dirty food or water; hookworm larvae burrow through bare feet | Stomach pain, poor growth, tiredness; hookworm causes anaemia | Latrines, handwashing, wearing shoes, washing fruit and vegetables | Deworming tablets |
| Ringworm: fungus | Contact with an infected person or animal, or a shared comb, cap or towel | Round, itchy, scaly patches on the skin or scalp | Do not share combs, caps or towels; keep skin clean and dry | Antifungal cream or tablets |
Antibiotics are medicines that kill bacteria or stop them from growing. They attack structures that bacteria have and your cells do not, such as the bacterial cell wall. Viruses have no cell wall and reproduce inside your own cells, so antibiotics cannot touch them. An antibiotic taken for a cold does nothing for the cold.
Misusing antibiotics causes antibiotic resistance. When a course is stopped early or doses are skipped, the few bacteria that happen to be most resistant survive and multiply, and their offspring are resistant too. Soon the medicine no longer works for anyone. So take antibiotics only when a health worker prescribes them, and finish the whole course even when you feel better.
Habimana, aged 15, lives near rice fields in Bugesera. For two days he has had fever and chills; the fever rises every evening and he sweats heavily at night. He does not sleep under a net. Which disease is most likely, and what should happen next?
Tip
Two rules examiners love
For diarrhoea, remember that dehydration is what kills, so the first treatment is always to replace water and salts with ORS.
State whether each of these is prevention, control or treatment: (a) giving BCG vaccine to newborn babies; (b) isolating cholera patients in a treatment centre; (c) giving ORS to a child with diarrhoea.
Answer: (a) prevention: it stops TB infection before it happens; (b) control: it reduces spread once cases exist; (c) treatment: it helps the sick child recover.
Mutesi has had a cough for three weeks, has lost weight and sweats at night. Which disease should be tested for first, and why must her treatment continue for months?
Answer: Tuberculosis, because a cough of more than two weeks, weight loss and night sweats are its classic signs. TB bacteria grow very slowly and some hide inside cells, so several antibiotics must be taken together for at least six months to kill them all. Stopping early lets resistant TB develop.
A boy with a cold asks his father to buy antibiotics. Explain, using biology, why this is a poor idea.
Answer: A cold is caused by a virus. Antibiotics act on bacterial structures such as the cell wall, which viruses do not have, so they will not cure the cold. Using them unnecessarily also exposes bacteria in his body to the drug, which selects for resistant bacteria.
Explain why cholera can kill within a day, even though the bacteria stay in the intestine.
Answer: A toxin made by the bacteria makes the intestine pour out large amounts of water and salts, causing very watery diarrhoea. The body loses water and salts faster than it can replace them, and severe dehydration leads to shock and death. Replacing fluids quickly with ORS or a drip saves the patient.
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