1. Infectious Diseases

2. Definitions Disease ≡ a disordered or incorrectly functioning organ, part, structure, or system of the body resulting from the effect of genetic or developmental errors, infection, poisons, nutritional deficiency or imbalance, toxicity, or unfavourable environmental factors.

3. Infectious Disease ≡ Any disease caused by the entrance, growth, and multiplication of microorganisms in the body. It may not be contagious. Non – infectious Disease ≡ Diseases that are not caused by a pathogen and cannot be shared from one person to another. May be caused by either the environment, nutritional deficiencies or genetic inheritances. –Eg. Environmental causes such as skin cancer from radiation, or lack of food e.g. Scurvy

4. Cholera Infectious agent: Vibrio cholerae Transmission: Through ingestion of vibrio-contaminated water, food Incubation : 1 – 5 days Site of action of pathogen: wall of small intestine The bacteria releases a toxin that causes increased release of water in the intestines, which produces severe diarrhea.

6. Cholera occurs in places with poor sanitation, crowding, war, and famine. There are an estimated 3–5 million cholera cases and 100 000–120 000 deaths due to cholera every year.

7. Occurrence (1997) Occurrence key: yellow = low, orange = medium, and red = high

9. Up to 80% of cases can be successfully treated with oral rehydration salts. Provision of safe water and sanitation is critical in reducing the impact of cholera Oral cholera vaccines are considered an additional means to control cholera, but should not replace conventional control measures.

10. poor surveillance and fear of international stigmatisation and sanctions lead to underreporting of official numbers by affected countries. increasing spread of cholera in recent years may reflect –a lack of international quarantine enforcement by some countries which also have primitive public water supplies and inadequate sanitary regulations, –the international mobility of carriers in the world's population, –and the quick transport of contaminated food and water by ships and aircraft.

11. Cholera can cost governments billions of dollars to eradicate. Absenteeism by the workforce caused by cholera adversely affects industrial output. Cholera outbreaks can adversely affect tourism Cholera outbreaks may lead to loss of trade.

12. Measles Causative agent: Morbillivirus Transmission: air-borne Incubation period: 3-7 days for rash to appear Site of action: highly contagious infection of the respiratory system.

15. Prevention and control Treatment - bed rest, fluids and medicine for fever and headache. Prevented with measles vaccine. Recommended for children at 12 months of age. This shot is given as measles, mumps, rubella (MMR) vaccine.

16. Vaccination Between 2000 and 2007, 576 million children were vaccinated against measles, resulting in a 74 percent decrease in measles-related deaths worldwide. Education and availability of vaccine will decrease deaths further

18. Problems with eradicating measles: (1) the role of humans in maintaining transmission, (2) the availability of accurate diagnostic tests, (3) the existence of effective vaccines, (4) lack of political will in some industrialized countries, (5) increasing urbanization and population density, (6) the HIV epidemic,

19. World occurrence Mortality in developed countries is ~1/1000. In sub-Saharan Africa, mortality is ~10%. On average, ~450 children die every day from measles. factors contributing to continued transmission: –Lack of infrastructure, –inadequate health care systems, –lack of funds

22. Malaria Causative agent: Plasmodium falciparum, P. vivax, P. ovale, P. malariae Transmission: female anopheles mosquito Incubation period: 1 week to a year Site of action of pathogen: liver, red blood cells, brain

25. Prevention and control Protective clothing over the arms and legs, screens on windows, insect repellent. Education to cover over areas of stagnant, still water Chloroquine is the drug of choice for protecting against malaria. But Falciparum malaria is becoming increasingly resistant to anti-malarial medications. People who are taking anti-malarial medications may still become infected.

27. Prevention cheaper than cure but the capital costs required are out of reach of many of the world's poorest people. estimates that malaria can be controlled for US$3 billion in aid per year.

28. Malaria stays in an area due to –high human population density, –high mosquito population density –high rates of transmission from humans to mosquitoes and from mosquitoes to humans. Many countries are seeing an increasing number of imported malaria cases owing to extensive travel and migration.

29. Occurrence Endemic in a broad band around the equator, in areas of the Americas, many parts of Asia, and much of Africa; however, it is in sub-Saharan Africa where 85– 90% of malaria fatalities occur. 300-500 million cases of malaria each year, and more than 1 million people die from it.

33. Tuberculosis Causitive agent: Mycobacterium tuberculosis, M. Bovis Transmission: airborne droplets, unpasteurised milk and meat Incubation period: few weeks or months Site of action of pathogen: primary infection in lungs, secondary infection in lymph nodes, bones and gut.

34. The immune system "walls off" the TB bacilli, which is protected by a thick waxy coat, can lie dormant for years. When someone's immune system is weakened, the chances of becoming sick are greater.

36. Prevention and control Detection of infected individuals and treatment of them. Mass vaccination of children Treatment long term – 6 to 24 months Stopping treatment early causes resistant strains Poor people can’t afford it Leading cause of death of people with HIV

38. Occurrence An estimated 1.7 million people died from TB in 2009. The highest number of deaths was in the Africa Region. 2000 – 2004 20% increase in resistance Overall, one-third of the world's population is currently infected with the TB bacillus.

40. AIDS Causative agent: HIV virus Transmission: during sexual intercourse, blood transfusions, across the placenta, in breast milk, in blood in infected needles Incubation period: few weeks to 10 years Site of action of pathogen: T helper lymphocytes, macrophages and brain cells

42. Unprotected sex is HIV's main route into humans, where it targets the white blood cell known as CD4. The virus replicates inside, eventually bursting out and flooding the body in the billions. The immune system then kicks in, and the body and the virus wage all-out war. During the height of battle billions of CD4 cells can be destroyed in a single day. During the height of battle billions of CD4 cells can be destroyed in a single day. As the cell count drops, the immune system begins to fail and opportunistic infections such as tuberculosis take hold.

44. Prevention and control Treatments But No Cure prevention focuses on sex education and the use of condoms. treatments combat its onset. –Antiviral drugs work by slowing the replication of HIV in the body. These drugs need to be used in combination because the virus readily mutates, creating new and often drug-resistant strains. –Such treatments are expensive, however, and are still denied to millions of people in the developing world. Researchers are currently working on an AIDS vaccine.

45. Poverty; inadequate health care and education, and promiscuity have all been highlighted to explain Africa's AIDS nightmare.

46. Occurence AIDS today is a global pandemic affecting every country. In 2006, an estimated 39.5 million people had HIV/AIDS. Almost three million of them died. In 2006, an estimated 39.5 million people had HIV/AIDS. Almost three million of them died. Sub-Saharan Africa accounts for two-thirds of the world's HIV cases and nearly 75 percent of deaths due to AIDS. Infection rates in Zimbabwe's adult population exceed 20 percent, while in Swaziland a third of adults are HIV-positive.

48. Smallpox Causative agent: Variola major and Variola minor Transmission: inhalation of infected air droplets, direct contact with infected bodily fluids or contaminated objects such as bedding or clothing. Incubation period: 12 – 14 days Site of action of pathogen: in small blood vessels of the skin and in the mouth and throat.

51. Antibiotics Two types: –Broad spectrum –Narrow spectrum They show selective toxicity – killing the pathogen but not damaging the host cell.

52. How they work The Greek word anti means "against", and the Greek word bios means "life" 1.Prevent the bacteria from forming cell walls during reproduction. This leads to osmotic lysis. Only work on growing bacteria not dormant ones.

53. 2. 2. Inhibit protein synthesis by binding to bacterial ribosomes 3. 3. Disrupt synthesis of nucleic acids. 4. 4. Disrupt cell membranes.

55. Essay Discuss the role of epidemiology in determining patterns of disease. Illustrate your answer with specific examples of named diseases. 20 marks