Infectious Diseases

· Infectious diseases are diseases caused by pathogens.
· They are transmissible, meaning they can be passed from one host to another.
· A pathogen is a disease-causing organism or agent, such as a bacterium, virus or protoctist.
· High-scoring answers should link each disease to: pathogen type, method of transmission, and prevention/control measures.
· Disease control depends on understanding both the biology of the pathogen and its mode of transmission.

Cholera

· Disease: cholera.
· Pathogen: Vibrio cholerae.
· Type of pathogen: bacterium.
· Transmission: mainly through contaminated water or contaminated food containing faecal material from infected people.
· Spread is increased by poor sanitation, unsafe drinking water, overcrowding, and limited access to sewage treatment.
· Prevention/control: provide clean water, improve sanitation, ensure safe food preparation, promote handwashing, and isolate/treat infected individuals where appropriate.
· Biological factor: bacteria survive and spread through faecal contamination of water/food.
· Social factor: lack of sanitation infrastructure increases exposure.
· Economic factor: poverty can limit access to clean water, healthcare and public health systems.

Vibrio cholerae is the bacterium that causes cholera. The curved rod-shaped bacteria are transmitted mainly through water or food contaminated with faeces. Preventing cholera depends strongly on clean water and sanitation.

Malaria

· Disease: malaria.
· Pathogens: Plasmodium falciparum, Plasmodium malariae, Plasmodium ovale, and Plasmodium vivax.
· Type of pathogen: protoctists.
· Transmission: by a vector, the female Anopheles mosquito, which transfers Plasmodium from one human host to another during feeding.
· Details of the malarial parasite life cycle are not expected, but candidates must know transmission involves a mosquito vector.
· Prevention/control: reduce mosquito bites using insecticide-treated bed nets, window screens, repellents, and protective clothing.
· Prevention/control: reduce mosquito populations by draining stagnant water, using insecticides, and improving environmental management.
· Biological factor: transmission depends on both the Plasmodium parasite and the Anopheles mosquito vector.
· Social factor: housing quality, education, and use of bed nets affect exposure.
· Economic factor: malaria is harder to control where healthcare access, mosquito control programmes and prevention resources are limited.

This diagram shows how malaria transmission depends on both humans and mosquitoes. For CIE 10.1, focus on the key idea that Plasmodium is transmitted by the female Anopheles mosquito. Full life-cycle details are not required. Source

Tuberculosis / TB

· Disease: tuberculosis / TB.
· Pathogens: Mycobacterium tuberculosis and Mycobacterium bovis.
· Type of pathogen: bacteria.
· Transmission: mainly through airborne droplets released when an infected person coughs, sneezes or speaks.
· TB spreads more easily in crowded, poorly ventilated conditions.
· Prevention/control: identify infected individuals, provide effective treatment, improve ventilation, reduce overcrowding, and use public health screening where appropriate.
· Biological factor: bacteria can infect the lungs and be released in droplets from the respiratory tract.
· Social factor: overcrowded housing, poor ventilation and delayed diagnosis increase transmission.
· Economic factor: lack of access to healthcare can delay diagnosis and treatment, allowing further spread.

Mycobacterium tuberculosis is one of the bacteria that causes TB. TB is transmitted mainly by airborne droplets from infected people. Control depends on diagnosis, treatment, ventilation and reducing overcrowding. Source

HIV / AIDS

· Disease: HIV/AIDS.
· Pathogen: human immunodeficiency virus (HIV).
· Type of pathogen: virus.
· Transmission: through exchange of infected body fluids, especially during sexual activity, sharing contaminated needles, blood-to-blood contact, and from mother to child.
· HIV infects cells of the immune system and can lead to AIDS if untreated.
· Prevention/control: use condoms, avoid sharing needles, screen blood products, provide education, and support testing and treatment programmes.
· Biological factor: HIV is transmitted in specific body fluids, not by casual contact.
· Social factor: stigma, lack of education, and limited testing can increase spread.
· Economic factor: access to testing, prevention, and treatment affects control of HIV transmission.

HIV is a virus, not a cellular organism. Its structure includes genetic material inside a protein-containing particle with an outer envelope. In CIE 10.1, the key focus is that HIV causes HIV/AIDS and is transmitted through infected body fluids. Source

Comparing the Four Required Diseases

· Cholera → Vibrio cholerae → bacterium → transmitted by contaminated water/food.
· Malaria → Plasmodium species → protoctists → transmitted by female Anopheles mosquito vector.
· TB → Mycobacterium tuberculosis / Mycobacterium bovis → bacteria → transmitted by airborne droplets.
· HIV/AIDS → HIV → virus → transmitted by infected body fluids.
· Exam answers should avoid vague phrases such as “spread by germs”; always name the specific pathogen, pathogen type, and transmission route.

Prevention and Control: Biological, Social and Economic Factors

· Biological factors = features of the pathogen, host or vector that affect spread, e.g. mosquito transmission, airborne droplets, or faecal contamination.
· Social factors = human behaviours and living conditions, e.g. sanitation, overcrowding, education, sexual behaviour, and use of bed nets or condoms.
· Economic factors = availability of money, infrastructure and healthcare, e.g. clean water systems, vaccination or treatment programmes where relevant, screening, and public health campaigns.
· Strong discussion answers should explain that disease control usually needs more than one strategy.
· Best exam phrasing: “Control depends on interrupting the transmission route.”
· For cholera, interrupt transmission by improving water quality and sanitation.
· For malaria, interrupt transmission by reducing mosquito bites and mosquito breeding sites.
· For TB, interrupt transmission by reducing exposure to airborne droplets and treating infected people.
· For HIV, interrupt transmission by preventing exchange of infected body fluids and increasing testing/treatment access.