Basic Field Epidemiology
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Transcript of Basic Field Epidemiology
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AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES
Basic Field Epidemiology
Session 6 – How disease progressesRecorded PowerPoint file
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AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES
In Session 6 we will explore:
• How disease occurs and the progression of disease states in an individual animal
• The progression of disease in a population of animals
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AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES
Soleh’s place
• All Soleh’s chickens have been sick with influenza in the past
• He brought a sick chicken home and 3 days later most of his other chickens were sick
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AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES
Definitions• Infectious agents include:
– Bacteria– Viruses– Parasites– Protozoa– Fungi– …
• Contagious diseases include: – Foot and Mouth disease – Highly Pathogenic Avian Influenza– …
• Non-contagious infectious diseases include:– Tetanus– Anthrax– Liver fluke– …
Living agents that are capable of causing disease
Infectious agents that can be spread directly from one animal to another
Diseases causes by infectious agents that are not spread directly from one animal to another
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AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES
Definitions• Susceptibility
– An animal must be susceptible to the infectious agent for infection to occur
• Exposure– Contact or interaction between infectious agent and
animal
Some agents only infect one species, others infect multiple species.
Some agents only infect the young or pregnant females or very old or sick.
Not every exposure will result in infection.
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Disease progression in an individual animal
Time
Animal with no infection
Incubation period (no signs of infection)
Clinical disease (showing signs of infection)
Chronic disease(ongoing)
Carrier state
Death
Recovered - signs go away & infectious agent eliminated
Susceptible Infected Outcomes of infection
Start of infection
Exposure
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AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES
Soleh’s place
• Some cows had diarrhoea• All Soleh’s cow were infected with worms
– Not every infected cow was showing clinical signs of disease
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AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES
Soleh’s place
• 2 years ago Soleh had some cows die from Anthrax– All the cows that were infected died
Anthrax spores in soil
Animal eats spores
Spores activate, bacteria grow and infectAnimal. Animal dies.
http://www.cdc.gov/anthrax/basics/index.html
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AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES
• Carrier animals– Bacteria lives in:
• Eyes• Nose• Vagina
– Can spread the bacteria to other susceptible animals and cause disease in other animals
Pinkeye
Animal with pinkeye recovers from infection but can still carry the bacteria (one of the causes of pink eye)
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AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES
Recovered animals
• Immune
• Susceptible
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AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES
Progression of disease in a population
Introduce one animal infected with a contagious diseaseInto a susceptible population
Over time – the whole populationmay get sick.
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Progression of disease in a population
Immune animal
Susceptible animal
Infected animal that is infectious to others
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 150
100
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Susceptible Recovered Clinical
Time (days)
Num
ber o
f ani
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sProgression of disease in a populationHerd immunity
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AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES
Session 6 - Summary• Within an animal there are a number of steps that determine if the
animal develops disease after being exposed to an infectious agent
• Infected animals may develop chronic disease, die from the disease or may recover
• Animals that recover often develop immunity to the infectious agent. Immunity may last a lifetime or it may be shorter. If the immunity declines the animal may become susceptible to infection again
• Herd immunity describes a form of immunity that occurs when a significant portion of a population of animals is immune and this provides protection for the susceptible animals
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Close of video