Outbreak! How can your pathologist help you? (Proceedings)

Nov 01, 2009

Animal shelters create a unique environment for the emergence and propagation of infectious diseases. Some of them cause significant physical illness and fatality while others manifest in more moderate chronic disease that can become just as problematic. Infectious agents such as viruses and bacteria require hosts in which they can reproduce. The amplification of hundreds to millions of infectious particles is even higher when there are many bodies available. Shelters provide the perfect environment for many infectious disease risk factors to occur and spread. These factors include transportation, stress (immunosuppression), increased contact (crowding), poor nutrition, other concurrent diseases, high animal turnover, and indiscriminate use of antibiotics.

Although it is not always necessary to get an exact diagnosis for every sick animal in a shelter it becomes more important when more animals than usual are ill. The diagnostic information is also crucial when there is odd or unusual manifestation of what was considered to be the "same old" disease. The life of microbes is not static and many of these pathogens are very capable of evolving and changing quickly. The chances of this happening increase when there are more hosts in which to mutate. For this reason it is important not only to figure out what is causing high mortality in the shelter but also to catch new and emerging pathogens early in the course of their evolution. An emerging infection is one that has newly appeared in the population, or one that has existed but is altered in incidence, geographic range, or character (virulence, unique species).

Recognizing that there is a problem

Obviously most shelters do experience some infectious disease amongst their animals some of the time. It is difficult for a large transient population that is housed closely together not to. However, many sick animals, chronic disease or outbreaks should be the exception not the rule. This lecture will not focus on treatment as almost all outbreaks or severe illness in shelters is caused by having too many animals under one roof. Therefore, the first line of treatment and defense strategy when confronted by exceptional disease problems is to work toward decreasing the population.

Ideally all shelters would have unlimited resources to investigate every illness with full diagnostics. Unfortunately this is rarely the case and shelters must weigh the cost of contacting labs, submitting samples, running tests and performing necropsies with the risk of not doing so. The question is often when to start running these diagnostics and when to save the money and focus instead on treatment i.e. getting the population moving and adopted in order to decrease crowding.

Step one: Is there an outbreak?

It is vital that the shelter be able to recognize early that "something is not right". The shelter needs concrete data to confirm this initial observation. Statistics are needed not only on the shelter's typical disease prevalence but also data on disease manifestations. An initial question to consider when faced with what seems like an outbreak or "new" disease is to ask "is this situation/disease different from one month ago, or more importantly "is it different from the same time last year". This sort of inquiry allows shelters to step back from the urgency of the current problem and focus on the reality of the situation. Having good shelter statistics is very helpful. Some questions to ask when faced with the possibility of an outbreak or new disease are:
     • Is there a higher proportion of animals getting sick?
     • Is the severity of illness worse than usual or are the animals no longer responding to treatment?
     • Are animals dying from what is normally mild disease?
     • Are different types of animals getting sick (e.g. adults)?
     • Has staff or members of the public complained of similar illness in their own pets?

Step two: Begin to record the outbreak

This requires comprehensive and accurate record keeping. It may be best to designate one shelter staff member to write down all details and to coordinate a diagnostic plan and course of action. The records should include not only how many animals are affected but also information on the type of symptoms, when they began, which animals are affected (age, location, source), treatments tried etc.