Canine infectious respiratory disease complex: management and prevention in canine populations (Proceedings)

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Canine infectious respiratory disease complex: management and prevention in canine populations (Proceedings)

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Nov 01, 2010

Diagnostic options for CIRDC outbreaks

Virtually all pathogens listed above cause a similar overall clinical presentation of coughing and/or nasal discharge. While Bordetella-induced kennel cough is classically thought of as causing only relatively mild disease, more severe disease may be seen, especially in a crowded shelter or boarding facility where stress and a high load of secondary pathogens provide a synergistic effect. Therefore, the cause of CIRDC cannot be diagnosed based on clinical signs in a single dog. However, the pattern of affected animals can at least provide some clue as to the likely pathogens. For example, canine distemper is unlikely to affect vaccinated dogs over four months of age. Canine influenza, on the other hand, is likely to affect a high percentage of exposed dogs, regardless of age or vaccine status. Therefore this rule-out would be unlikely in an outbreak limited to puppies or unvaccinated animals. If some animals show distinctive clinical signs, such as neurological signs characteristic of distemper, it is possible that other dogs showing milder disease are also infected with the same pathogen. Conversely a distemper outbreak is unlikely if many dogs are affected and none show characteristic neurological signs.

Additional diagnostics are warranted if CIRDC is occurring in a population with unusual frequency or severity, or if there is the slightest suspicion of zoonotic infection. Acutely affected animals should be sampled – ideally 10-30% of the affected population, with a minimum of 5-10 dogs. The cause of an outbreak can not be identified based on a specimen from a single dog. The ideal sample depends on the localization of clinical signs: if signs are predominantly upper respiratory, deep nasal swabs should be obtained. If lower respiratory disease is suspected, tracheal wash is the preferred specimen. Samples should be submitted for bacterial culture and sensitivity for Bordetella, Mycoplasma, Streptococcus and others such as e.coli, Klebsiella, Pasteurella, enterobacter etc. PCR is the most practical option for viral detection; panels are available which include most common viral pathogens. PCR testing is available at a discounted rate for shelters through Idexx laboratories. See http://www.sheltermedicine.com/services/pcr.shtml for more information about this program. Keep in mind that false negatives may be caused by problems with sample handling or timing. For instance, canine influenza is shed only very early in the course of disease, and may be missed by the time clinical signs are recognized. False positives can occur following vaccination, especially with a very sensitive method such as PCR; this has been documented as long as three weeks after vaccination for canine distemper, for example.

Merely documenting the presence of a pathogen does not necessarily indicate causation, of course. Most of the pathogens associated with CIRDC can be isolated with some frequency even from clinically normal dogs, especially in a densely housed canine population. If the same pathogen is found in several dogs, this raises the index of suspicion that a causative relationship exists, but still does not rule out other contributing, or even primary, agents. For definitive diagnosis, necropsy is the most powerful tool available, and should be utilized if possible whenever dogs die or are euthanized with suspected severe infectious respiratory disease. If you are uncertain whether a single death represents an isolated incident or the beginning of an outbreak, it is prudent (and virtually free) to obtain lung specimens and oropharyngeal swabs and hold for future analysis if indicated. Formalin fixed, frozen and refrigerated specimens should be obtained, for histopathology, viral isolation, and bacterial culture respectively.

Prevention of CIRDC

Strategies for prevention of CIRDC rely on supporting the animal's ability to ward off disease and reducing the level of environmental contamination. Important strategies to accomplish the first goal include vaccination, stress reduction, and prevention of airway irritation (e.g. by minimizing barking). The latter goal is accomplished through reduction of crowding, effective sanitation, and maintenance of good air quality.

Reduction of crowding and stress

Crowding and the attendant stress is undoubtedly the single greatest risk factor for severe respiratory (and other) disease outbreaks in populations. Increased population density leads to a greater risk of disease introduction, higher contact rate, reduced air quality, and often, compromises in housing and husbandry. Housing dogs in each side of a double-sided cage intended for a single dog; housing multiple unrelated dogs per cage (particularly if not done in "all in/all out" fashion"); failure to isolate symptomatic animals; and delays in moving animals through the facility are frequent precursors of serious outbreaks in over-crowded shelters. Even in a boarding facility or vet clinic, it is important to anticipate times of peak population, recognize that these will be periods of increased risk for respiratory disease outbreaks, and plan sufficient additional staff that husbandry is not compromised.

An underappreciated strategy for CIRDC prevention is to simply reduce the amount of time dogs spend in densely housed environments. One study showed that each day in a shelter increased the risk if CIRDC by 3%[2]. Reducing length of stay may not be possible (or desirable) in a boarding facility or vet hospital, but management practices that increase length of stay for shelter dogs should be carefully assessed to ensure the benefit of these practices outweighs the risk of disease they may create. This could include routine quarantine of apparently healthy animals, delays while dogs await behavior assessment or surgery, or failure to move dogs to public-viewing areas of the shelter as soon as they are available for adoption. Increased time for each dog in the shelter also contributes to increased crowding with all the associated risks.