Infectious Infectious DiseasesDiseases

DefinitionsDefinitions

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

Infectious Disease ≡ Any disease caused by the Infectious Disease ≡ Any disease caused by the entrance, growth, and multiplication of entrance, growth, and multiplication of microorganisms in the body. It may not be microorganisms in the body. It may not be contagious. contagious.

Non – infectious Disease ≡ Diseases that are Non – infectious Disease ≡ Diseases that are not caused by a pathogen and cannot be shared not caused by a pathogen and cannot be shared from one person to another.  May be caused by from one person to another.  May be caused by either the environment, nutritional deficiencies or either the environment, nutritional deficiencies or genetic inheritances. genetic inheritances. – Eg. Environmental causes such as skin cancer from Eg. Environmental causes such as skin cancer from

radiation, or lack of food e.g.  Scurvy radiation, or lack of food e.g.  Scurvy

CholeraCholera

Infectious agentInfectious agent: : Vibrio choleraeVibrio cholerae TransmissionTransmission: Through ingestion of : Through ingestion of vibrio-contaminated water, food vibrio-contaminated water, food Incubation Incubation : 1 – 5 days: 1 – 5 daysSite of action of pathogenSite of action of pathogen: wall of small : wall of small intestineintestineThe bacteria releases a toxin that causes The bacteria releases a toxin that causes increased release of water in the increased release of water in the intestines, which produces severe intestines, which produces severe diarrhea.diarrhea.

Cholera occurs in places with poor Cholera occurs in places with poor sanitation, crowding, war, and famine.sanitation, crowding, war, and famine.

There are an estimated 3–5 million cholera There are an estimated 3–5 million cholera cases and 100 000–120 000 deaths due to cases and 100 000–120 000 deaths due to cholera every year.cholera every year.

Occurrence (1997) Occurrence (1997)

Occurrence key: yellow = low, orange = medium, and red = highOccurrence key: yellow = low, orange = medium, and red = high

Up to 80% of cases can be successfully Up to 80% of cases can be successfully treated with oral rehydration salts.treated with oral rehydration salts.

Provision of safe water and sanitation is Provision of safe water and sanitation is critical in reducing the impact of cholera critical in reducing the impact of cholera

Oral cholera vaccines are considered an Oral cholera vaccines are considered an additional means to control cholera, but additional means to control cholera, but should not replace conventional control should not replace conventional control measures.measures.

poor surveillance and fear of international poor surveillance and fear of international stigmatisation and sanctions lead to stigmatisation and sanctions lead to underreporting of official numbers by underreporting of official numbers by affected countries. affected countries. increasing spread of cholera in recent increasing spread of cholera in recent years may reflect years may reflect – a lack of international quarantine enforcement a lack of international quarantine enforcement

by some countries which also have primitive by some countries which also have primitive public water supplies and inadequate sanitary public water supplies and inadequate sanitary regulations, regulations,

– the international mobility of carriers in the the international mobility of carriers in the world's population, world's population,

– and the quick transport of contaminated food and the quick transport of contaminated food and water by ships and aircraft. and water by ships and aircraft.

Cholera can cost governments billions of Cholera can cost governments billions of dollars to eradicate. dollars to eradicate.

Absenteeism by the workforce caused by Absenteeism by the workforce caused by cholera adversely affects industrial output.cholera adversely affects industrial output.

Cholera outbreaks can adversely affect Cholera outbreaks can adversely affect tourism tourism

Cholera outbreaks may lead to loss of Cholera outbreaks may lead to loss of trade. trade.

MeaslesMeasles

Causative agent: MorbillivirusCausative agent: Morbillivirus

Transmission: air-borneTransmission: air-borne

Incubation period: 3-7 days for rash to Incubation period: 3-7 days for rash to appearappear

Site of action: highly contagious infection Site of action: highly contagious infection of the respiratory system. of the respiratory system.

Prevention and controlPrevention and control

Treatment - bed rest, fluids and medicine Treatment - bed rest, fluids and medicine for fever and headache. for fever and headache.

Prevented with measles vaccine. Prevented with measles vaccine. Recommended for children at 12 months Recommended for children at 12 months of age. This shot is given as measles, of age. This shot is given as measles, mumps, rubella (MMR) vaccine. mumps, rubella (MMR) vaccine.

VaccinationVaccination

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

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

World occurrenceWorld occurrence

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

MalariaMalaria

Causative agent: Plasmodium falciparum, Causative agent: Plasmodium falciparum, P. vivax, P. ovale, P. malariaeP. vivax, P. ovale, P. malariae

Transmission: female anopheles mosquitoTransmission: female anopheles mosquito

Incubation period: 1 week to a yearIncubation period: 1 week to a year

Site of action of pathogen: liver, red blood Site of action of pathogen: liver, red blood cells, braincells, brain

Prevention and controlPrevention and control

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

Prevention cheaper than cure but the Prevention cheaper than cure but the capital costs required are out of reach of capital costs required are out of reach of many of the world's poorest people. many of the world's poorest people.

estimates that malaria can be controlled estimates that malaria can be controlled for US$3 billion in aid per year. for US$3 billion in aid per year.

Malaria stays in an area due toMalaria stays in an area due to– high human population density, high human population density, – high mosquito population densityhigh mosquito population density– high rates of transmission from humans to high rates of transmission from humans to

mosquitoes and from mosquitoes to humans. mosquitoes and from mosquitoes to humans.

Many countries are seeing an increasing Many countries are seeing an increasing number of imported malaria cases owing number of imported malaria cases owing to extensive travel and migration. to extensive travel and migration.

OccurrenceOccurrence

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

TuberculosisTuberculosis

Causitive agent: Mycobacterium Causitive agent: Mycobacterium tuberculosis, M. Bovistuberculosis, M. Bovis

Transmission: airborne droplets, Transmission: airborne droplets, unpasteurised milk and meatunpasteurised milk and meat

Incubation period: few weeks or monthsIncubation period: few weeks or months

Site of action of pathogen: primary Site of action of pathogen: primary infection in lungs, secondary infection in infection in lungs, secondary infection in lymph nodes, bones and gut.lymph nodes, bones and gut.

The immune system "walls off" the TB bacilli, which is The immune system "walls off" the TB bacilli, which is protected by a thick waxy coat, can lie dormant for years. protected by a thick waxy coat, can lie dormant for years.

When someone's immune system is weakened, the When someone's immune system is weakened, the chances of becoming sick are greater.chances of becoming sick are greater.

Prevention and controlPrevention and control

Detection of infected individuals and Detection of infected individuals and treatment of them.treatment of them.

Mass vaccination of childrenMass vaccination of children

Treatment long term – 6 to 24 monthsTreatment long term – 6 to 24 months

Stopping treatment early causes resistant Stopping treatment early causes resistant strainsstrains

Poor people can’t afford it Poor people can’t afford it

Leading cause of death of people with HIVLeading cause of death of people with HIV

OccurrenceOccurrence

An estimated 1.7 million people died from An estimated 1.7 million people died from TB in 2009. The highest number of deaths TB in 2009. The highest number of deaths was in the Africa Region. was in the Africa Region.

2000 – 2004 20% increase in resistance2000 – 2004 20% increase in resistance

Overall, one-third of the world's population Overall, one-third of the world's population is currently infected with the TB bacillus.is currently infected with the TB bacillus.

AIDSAIDS

Causative agent: HIV virusCausative agent: HIV virus

Transmission: during sexual intercourse, Transmission: during sexual intercourse, blood transfusions, across the placenta, in blood transfusions, across the placenta, in breast milk, in blood in infected needlesbreast milk, in blood in infected needles

Incubation period: few weeks to 10 yearsIncubation period: few weeks to 10 years

Site of action of pathogen: T helper Site of action of pathogen: T helper lymphocytes, macrophages and brain cellslymphocytes, macrophages and brain cells

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

Prevention and controlPrevention and control

Treatments But No CureTreatments But No Cureprevention focuses on sex education and the prevention focuses on sex education and the use of condoms. use of condoms. treatments combat its onset. treatments combat its onset. – Antiviral drugs work by slowing the replication of HIV Antiviral drugs work by slowing the replication of HIV

in the body. These drugs need to be used in in the body. These drugs need to be used in combination because the virus readily mutates, combination because the virus readily mutates, creating new and often drug-resistant strains. creating new and often drug-resistant strains.

– Such treatments are expensive, however, and are still Such treatments are expensive, however, and are still denied to millions of people in the developing world.denied to millions of people in the developing world.

Researchers are currently working on an AIDS Researchers are currently working on an AIDS vaccine. vaccine.

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

OccurenceOccurence

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

SmallpoxSmallpox

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

AntibioticsAntibiotics

Two types:Two types:– Broad spectrumBroad spectrum– Narrow spectrumNarrow spectrum

They show selective toxicity – killing the They show selective toxicity – killing the pathogen but not damaging the host cell.pathogen but not damaging the host cell.

How they workHow 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.

2. Inhibit protein synthesis by binding to bacterial ribosomes

3. Disrupt synthesis of nucleic acids.

4. Disrupt cell membranes.

EssayEssay

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

20 marks20 marks