AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES Basic Field Epidemiology Session 6 – How disease progresses Recorded PowerPoint file

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

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

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

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.

AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES 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 SusceptibleInfectedOutcomes of infection Start of infection Exposure

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

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 infect Animal. Animal dies.

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)

AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES Recovered animals Immune Susceptible

AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES Progression of disease in a population Introduce one animal infected with a contagious disease Into a susceptible population Over time – the whole population may get sick.

AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES Progression of disease in a population Immune animal Susceptible animal Infected animal that is infectious to others

AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES Progression of disease in a population Herd immunity

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

AUSTRALIA INDONESIA PARTNERSHIP FOR EMERGING INFECTIOUS DISEASES Close of video