10.1 Infectious Diseases
- Syllabus
- 9700–2028–2029
- Topic
- 10.1
- Level
- AS
Learning objectives
10.1.1Pathogens and infectious disease• Pathogens cause transmissible infectious diseases10.1.2Examples of infectious diseases• Examples:- Cholera: bacterium Vibrio cholerae- Malaria: protoctists Plasmodium species- TB: bacteria Mycobacterium tuberculosis and M. bovis- HIV/AIDS: human immunodeficiency virus10.1.3Transmission of cholera, malaria, TB, HIV• Transmission of cholera, malaria, TB, HIV10.1.4Prevention and control• Prevention and control: biological, social, economic factors
Infectious diseases are caused by transmissible pathogens
An infectious disease is caused by a pathogen and can be transmitted from one host to another. A pathogen is the disease-causing infectious agent; the disease is the harmful condition that results in the host.
Transmissible means that the pathogen can reach a new host by a suitable route, either directly or indirectly. The route may involve contaminated material, droplets, body fluids or a vector, but the vector or medium is not itself automatically the pathogen.
Not every disease is infectious: inherited and deficiency diseases are not caused by transmissible pathogens. A mosquito that carries a pathogen is a vector, not the disease-causing organism.
Four diseases are identified by exact pathogen names and types
| Disease | Pathogen name | Pathogen type |
|---|---|---|
| Cholera | Vibrio cholerae | bacterium |
| Malaria | Plasmodium falciparum, P. malariae, P. ovale, P. vivax | protoctists |
| Tuberculosis (TB) | Mycobacterium tuberculosis, M. bovis | bacteria |
| HIV/AIDS | human immunodeficiency virus (HIV) | virus |
Malaria is the disease; its pathogen is one of the named Plasmodium species, while a female Anopheles mosquito is only the vector. HIV is the virus; AIDS is the disease state that may develop after HIV damages immune function.
Scientific names identify the pathogen and must not be replaced by the disease name. Mycobacterium and Vibrio are bacteria; Plasmodium is eukaryotic and is classified here as a protoctist; HIV is not a cell.
Each infectious disease follows a specific transmission chain
| Disease | Transmission chain |
|---|---|
| Cholera | V. cholerae leaves an infected person in faeces → contaminates water or food → is ingested by a new host |
| Malaria | A female Anopheles mosquito feeds on an infected person and acquires Plasmodium → later injects the pathogen while feeding on another person |
| TB | M. tuberculosis in droplets/aerosols released by an infectious person is inhaled; M. bovis may be acquired from infected cattle through unpasteurised milk or contaminated animal products |
| HIV | Infected blood, semen, vaginal fluids or breast milk reaches another person through sexual contact, contaminated needles/blood, or mother-to-child transfer during pregnancy, birth or breastfeeding |
A complete explanation names the source, the compatible route or vector, and entry to the new host. The pathogen must survive that route; merely being near an infected person does not establish every form of transmission.
The female Anopheles mosquito is a vector, not the malaria pathogen. HIV is not spread by ordinary casual contact. Detailed stages of the malarial parasite life cycle are outside this syllabus outcome.
Disease control must be biologically effective and socially feasible
Prevention and control must match the pathogen and transmission route, but success also depends on social acceptance, infrastructure, access and cost. A discussion therefore links each measure to both its biological effect and its practical limitation.
| Disease | Biological factors and route-matched measures | Social and economic factors that affect success |
|---|---|---|
| Cholera | Safe water, sewage treatment, hygiene and vaccination interrupt faecal–oral transmission; rapid detection and rehydration reduce harm during outbreaks | Water and sanitation infrastructure are expensive; disasters, overcrowding, education, reporting and vaccine access affect coverage |
| Malaria | Insecticide-treated nets, indoor spraying and breeding-site reduction target the Anopheles vector; preventive drugs, diagnosis, treatment and vaccination can reduce infection or transmission | Mosquito/drug resistance and many breeding sites limit biology; climate, housing, correct net use, healthcare access and continuing programme cost affect control |
| TB | Ventilation, reduced crowding, case detection, contact tracing, effective multidrug treatment and BCG vaccination reduce transmission or susceptibility; cattle testing and milk pasteurisation limit M. bovis | Long treatment encourages incomplete courses and resistance; stigma, delayed diagnosis, crowded housing, clinics, drug supply and programme funding affect control |
| HIV | Condoms, sterile needles, screened blood, testing and antiretroviral therapy reduce body-fluid transmission or viral load; treatment in pregnancy reduces mother-to-child transmission | Long asymptomatic infection delays diagnosis; stigma, consent, education, sexual behaviour, unequal access and lifelong treatment cost affect uptake and continuity |
Evaluation rule: identify where a measure breaks the transmission chain; state the biological limitation; then explain one social or economic condition that changes coverage, adherence or sustainability. Layered control is usually stronger because no single measure removes every route or constraint.
Treatment and prevention are not interchangeable, and the same measure does not fit every disease. Do not list controls without explaining why they work and why implementation may still fail. Detailed malaria parasite life-cycle stages are not required.