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Infectious agent (IA)
(micro )organism that can cause illness in humans under favorable conditions (animals too).
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Communicable disease
an illness which has been caused by an infectious agent (or toxic product of an IA) that has been transmitted by any means from person-to-person or animal-to-person.
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Epidemic disease
an outbreak of disease with the number of cases beyond that normally expected. (e.g., 3 cases of typhoid fever in L.A.). In animals, epidemic disease is termed epizootic disease.
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Endemic disease
one constantly present, or at least the IA is present within a given area. (e.g., plague)
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Zoonosis (zoonotic disease)
disease of animals that can be spread to humans, e.g. plague
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Routes of exposure
- ways that infectious agents gain entry into the body.
- 1. Respiratory tract e.g. Valley Fever, IA is a fungus that lives in soil, becomes airborne in dust.
- 2. Gastro-intestinal tract e.g. typhoid fever, transmitted through water by salmonella typhi
- 3. skin e.g. tetanus, IA is a bacterium, Clostridium tetani, that forms spores, lives in soil. Spores enters through puncture wound, germinates and produces toxin that affects nervous system.
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Incubation period (IP)
time period that elapses between contact with a disease agent to onset of disease symptoms. e.g., 2-4 hours for Staph food poisoning.
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Carriers
persons who harbor an IA and serve as sources of that agent, but who show no clinical signs of the illness. e.g. typhoid fever, usually waterborne, but today is also foodborne through "typhoid Marys."
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Reservoir
the organism(s) or inanimate material in which an IA normally survives and reproduces in nature. e.g., the reservoir for plague is infected ground rodents, the reservoir for Salmonella is infected chickens and their eggs.
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Vehicle
the means by which an IA gets from a reservoir or host to a susceptible person or animal. e.g. food, water, milk. Also vectors and inanimate articles (fomites) such as teddy bears, combs, eating utensils, etc.
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Direct transmission
- Direct contact with IA
- Droplets through air (sneeze), within 3 feet of the source.
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Indirect transmission
- Via a Vehicle (food, water, milk, inanimate object, etc. )
- Via a Vector = insect or arachnid (tick, mite) capable of transmitting IA
- a, Mechanical vector = physically transports the IA (e.g. fly) on it's body
- b. biological vector = must be some additional development or increase in the number of IA inside the vector before infective to others (e.g., mosquito carrying malaria)
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Disease control
Source Controls --> transmission Controls --> susceptible person or animal (reservoir, host, or chemical)
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Source control
Eliminating or reducing the chance of transmission of, or contact with an IA. Controls at the source are most desirable.( e.g., eliminate vectors, cook food, water purification, proper sewage and waste handling, etc. )
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transmission controls
Protecting the susceptible person or animal from becoming infected with the IA. More risk of leaving portions of population unprotected. e.g., vaccination (HVB vaccine series), prophylactic procedures (quinine for people in malaria areas, isoniazid for TB infected people).
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Physical and chemical controls
- Water purification
- Sewage control and treatment
- Proper storage facilities for food
- Pasteurization of milk
- Proper ventilation equipment
- Exclusion of vectors
- Disinfection and pesticidal treatments
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Procedural controls
- Washing of hands and other personal hygiene
- Isolation of infected persons
- Cooking/refrigeration of food
- Proper waste handling and disposal
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Personal protective equipment
- Gloves
- Respiratory protection
- Protective clothing
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Legislative or legal controls
- Border checks
- Quarantine of animals and areas (park closures)
- Food protection law enforcement
- Drinking water standards enforcement Meat/poultry/fish inspection
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vaccination and prophylactic measures
- Rabies vaccine for pets
- Hepatitis B vaccine
- Immunization requirements for school children
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Typhoid Fever (Salmonella typhi)
- 1. Symptoms: G.I. aspect and fever, body rash, enlargement of lymphoid tissue. 10% of untreated cases die. Incubation period = 3-4 weeks.
- 2. Transmission: Food or water contaminated by feces/urine of infected person.
- 3. Control: Proper sewage control, water purification, fly control, education of food handlers and the general public on personal hygiene, pasteurization of milk, and cooking shellfish.
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Salmonellosis (Salmonella sp.)
- 1. Symptoms: G.I. aspect and fever. IP = 12-24 hrs.
- 2. Trans.: Food, esp. eggs and poultry, raw milk, meat, pet turtles & chicks.
- 3. Control: Cooking food, educ. foodhandlers, meat/poultry inspection, control in pets and poultry flocks, proper storage of food.
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Dysentery (2 common types)
- 1. Amoebic dysentery (Entamoeba hystolytica) Symptoms: fever, chills, bloody diarrhea from destruction of large intestine. IP = 5 days - 3 weeks.
- Trans.: contaminated water with cysts (leads to epidemic), raw vegetables, flies, foodhandlers. Control: same as for Typhoid fever plus disinfectant dips for fruits & vegetables
- 2. Shigellosis or Bacillary dysentery (Shigella sp., e.g. Shigella sonnei)
- Symptoms: fever, diarrhea with blood, G.I. upset, convulsions in young children. IP = 1-7 days. Trans.: fecal-oral direct contact or indirectly by foodhandlers through contaminated food, water, milk plus cockroaches and flies. Control: same as typhoid fever.
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