ANSWERS

1. What is the name given to the study of the occurrence and spread of disease?
   Epidemiology.
2. What is an obligate pathogen?
   A micro-organism that will always cause disease.
3. What is the term that describes the interval of time between an animal coming into contact with a pathogen and the development of clinical signs of disease?
   The incubation period.
4. What is the difference between morbidity rate and mortality rate?
   Morbidity rate describes the time in which the disease takes to produce a diseased state that causes an animal to be close to death, whilst mortality rate is the time taken for the disease to prove fatal.
5. List the 4 major groups of infectious agent and give an example of each.
   • Bacteria - Salmonella sp.
   • Viruses - Parvovirus.
   • Fungi - Aspergillus spp.
   • Protozoa - Giardia lamblia.
6. List the 4 main factors that affect the incubation period of a disease.
   • Quantity of micro-organisms.
   • Immune status of the animal.
   • The general health of the animal.
   • The age of the animal.
   • The route of entry (see Module 4).
7. Define the following terms: endemic, epidemic and pandemic.
   • Endemic = an infection that is constantly present within a locality (also known as enzootic).
   • Epidemic = an infectious disease with a sharp increase of incidence and a large number of individuals affected (also known as epizootic).
   • Pandemic = An epidemic spreading over a wide area, sometimes all over the world.
8. What is a zoonotic disease?
   A disease of animals that is transmissible to man. (Also known as a zoonosis - see Module 3).
9. What is a carrier?
   An animal that has come into contact with disease-causing micro-organisms but does not show any clinical signs or evidence of ill-health.
10. What is the difference between a closed carrier and an open carrier?
    A closed carrier carries disease-causing micro-organisms without shedding them into the environment, whilst an open carrier continuously sheds pathogens into the environment.
11. What is the name given to an animal which has recovered from an infectious clinical disease that sheds large numbers of pathogens into the environment for variable periods following recovery?
    A convalescent carrier.
12. What is meant by a healthy carrier?
    An animal which has never shown clinical signs of an infectious disease, yet carries the micro-organisms and sheds them into the environment. These animals are usually immune to the pathogens involved.
13. What is the name of the enzyme present in tears, nasal mucus and saliva that can kill most bacteria coming into contact with it?
    Lysosome.
14. What is the name of the iron-binding protein found in neutrophils and bodily secretions that has bactericidal properties?
    Lactoferrin.
15. What is the name of the protein that is produced by cells infected by a virus that has an inhibitory effect upon viral replication?
    Interferon.
16. What is the name given to a substance that has a damaging effect on the cells of the host?
    A toxin. Toxins disrupt specific physiological processes in the host.
17. What is the name given to antibodies that neutralise toxins thus rendering them harmless?
    Antitoxins.
18. A neurotoxin is so-called due to its activity within the nervous system. Can you name an example?
    The tetanus toxin.
19. Give an example of an enterotoxin (a toxin which functions within the gastrointestinal tract).
    Staphylococcus aureus.
20. Give an example of an exotoxin (a toxin manufactured by living micro-organisms and then released into the surrounding medium).
    Clostridium tetani.
21. Which are more toxic, endotoxins or exotoxins?
    Exotoxins.
22. From what are endotoxins made?
    Part of the cell wall of certain Gram -ve bacteria (endotoxins are released only when the cells die and disintegrate).
23. What is the name of the toxin made by the saprophytic fungus Aspergillus flavus?
    Aflatoxin.