Module 08 - Basic Diseases and the Animal Facility

Introduction

The spectre of disease in the animal facility sends shivers down the backs of facility managers, veterinarians and investigators who have experienced outbreaks previously. This is partly because they understand the devastating effects some diseases have on the research program, and the huge amount of work and cost involved in cleaning up after a disease outbreak.

Facility managers and veterinarians are not alone in their efforts to prevent infectious organisms from gaining entry to the animal facility. All people who regularly work in the animal facility (e.g., technicians, researchers, research staff, graduate students) must understand how diseases may be introduced and spread. Facility guidelines and standard operating procedures (SOPs) designed to limit the risk of introducing or spreading disease must be followed by everyone. Mechanical systems must work as expected (e.g., to sterilize cages, to maintain air pressure gradients) so even the facility maintenance staff is involved.

Diseases may be broadly classified as infectious or non-infectious. This module concentrates on infectious disease. Infectious diseases are caused by a variety of organisms, such as viruses, bacteria, yeast, fungi, and parasites.

Laboratory animals, like people, are regularly exposed to potentially infectious microorganisms; however, not all such exposures result in infection. Whether a laboratory animal becomes infected depends on a number of factors related to the infectious organism, and the animal host. For example, microorganisms vary in virulence, or the animal may be exposed to only a small number of infective particles. The animal, species, or strain may be partially or entirely resistant to infection, or more susceptible because it has a deficient immune system, is stressed, or poorly nourished.

If an organism does infect an animal, there are several possible outcomes. The infection may be silent or latent, in which case the animal displays no outward evidence of infection; or the infection may cause overt disease with the animal showing a variety of clinical signs depending upon the organs or systems affected. The disease may run its course with complete recovery with or without treatment, leave some damage (residual pathology from the disease), or even lead to the death of the animal. Any animal that recovers from the disease and those animals that have had a latent infection may become carriers of the infectious organism.

Infectious diseases pose a threat to animal colonies through a wide variety of mechanisms. Clinically ill animals are poor research animals because of the disruption to their normal physiology and biochemistry. Recovery may be prolonged and recovered animals often continue to carry and shed the organisms that caused the disease, acting as potential sources of infection for healthy animals. Latent or silent infections may also adversely affect the results of an experiment due to changes in the animals' biochemistry or immune system.

In thinking of means of controlling infectious diseases, it is important to know how diseases spread, the routes of infection and the routes of excretion of the organism from an infected animal.