5.3 Pathogens and Disease

5.3.1 Define Pathogen.
Pathogen - an organism or virus that causes a disease.

5.3.2 State one example of a disease caused by members of each of the following groups: viruses, bacteria, fungi, protozoa, flatworms, and roundworms.
Students should know to which group the pathogen that causes each disease belongs

Type of pathogen
Name of pathogen
Adeno virus
Common cold
Food poisoning
Epidermophyta flaccosum
Tinea faciei (ringworm)
Plasmodium falciparum
Fasciola hepatica
Toxocara canis

5.3.3 List six methods by which pathogens are transmitted and gain entry to the body.

1. Food
2. Water
3. Airbourne
4. Touch
5. Sexual Transmission
6. Vectors

5.3.4 Describe the cause, transmission and effects of one human bacterial disease.


The disease causing agent of Tuberculosis is Mycobacterium tuberculosis, a rod-shaped bacterium. The chance of infection increases with the advent of malnutrition, overcrowding and stress.

Tuberculosis is transmitted through airbourne particles. For example, people suffering from tuberculosis will cough frequently and will therefore spread miniscule droplets that harbor the bacterium. Another person may become infected if they inhale these droplets. If inhalation of the contaminated droplets occurs, the bacteria will enter the lungs and begin to grow and divide there.

A rare form of tuberculosis is transmitted from cattle to humans via infected milk. This is why milk is now pasteurized/sterilized to kill the bacteria and prevent the transmission of tuberculosis.

Phagocytes move to the areas of infection in the lungs and ingest the bacteria. The bacteria usually are able to survive and multiply inside the phagocyte. The infected phagocytes form part of small rounded swellings called tubercles in the lungs. The infection does not usually spread from the lungs and gradually becomes less severe, unless re-infection occurs, in which case chronic tuberculosis develops. Re-infection compounds the disease, causing for the gradual destruction of lung tissue, the development of fever, loss of appetite, and a persistent cough. in serious cases the infection can spread from the lungs to the lymph nodes, bones and gut.


Genus: Salmonella

The cause of this disease is the Salmonella bacteria colonizes the small intestine and releases exotoxins that disrupt cellular metabolism.

Salmonella is transmitted by contact with animal or human feces. It is also transmitted by the ingestion of poultry (most frequently) or products with eggs in them, such as mayonnaise or ice cream, that are undercooked or are raw.It is difficult to identify whether or not chickens are infected, due to the fact that they do not show any symptoms. Even though these products are the predominant sources of this illness, any food can become contaminated if cooked with kitchen tools which are uncleaned and unsanitary.

The effects of Salmonella are severe headaches, vomiting, diarrhea, and abdominal pain for around 48 hours. Recovery time is about 2-3 days. It can lead to adverse illnesses such as Typhoid fever, and Paratyphoid Fever.

5.3.5 Explain why antibiotics are effective against bacteria but not viruses.
Antibiotics block protein synthesis in bacteria but not in eukaryotic cells. Bacteria are independent; they carry out most processes on their own. Viruses on the other hand carry out very few processes without help from host cells. In most cases the host cells are human cells. Therefore if these processes are blocked by antibiotics, the host cells would be affected. Viruses also contain genetic material but are not complete cells and for this reason their reproduction cannot be stopped by antibiotics.

5.3.6 Explain the cause, transmission, and social implications of AIDS.
Cause- HIV virus, but the origin of the virus is not confirmed
Common methods of transmission- via the blood (mother/child placenta, blood transfusions, contaminated needles)
- via sexual intercourse
Social implications- ostracising of HIV positive people
- unease created over blood transfusions
- changes in sexual behavior, such as reduced promiscuity and increased use of condoms