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Feline infectious respiratory disease (Proceedings)

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Nov 01, 2010

Feline upper respiratory infection (URI) is perhaps the most frustrating illness facing shelter veterinarians, managers and staff. Many cats enter shelters already silently carrying the viruses that lead to illness; vaccines are partially effective at best; and specific treatments are limited. Factors such as overcrowding, poor air quality, poor sanitation, stress, concurrent illness, parasitism, poor nutrition, and other causes of immunosuppression predispose to disease.

In spite of these challenges, recent research has shown that some shelters have dramatically greater success than others in controlling this seemingly ubiquitous disease. We now know that having fewer than 5% of cats develop URI in shelter care is an achievable goal. Because of its close association with herpesviral activation and stress, URI is also a bellwether for overall shelter cat health and wellbeing. We can not sincerely expect to provide a humane, safe sheltering experience for cats if a substantial fraction develop illness in our care. Conversely, the measures necessary to control URI can have a widespread impact on overall cat comfort, well being and even likelihood for adoption.

Etiologic agents

Any of the agents listed below can be a primary cause of URI. In general, approximately 80-90% of cases are thought to be caused by one of the two viruses listed. In shelter cats, herpesvirus appears to be more closely linked to endemic shelter URI. Calicivirus, while undoubtedly the cause of periodic outbreaks, has not been consistently associated with an increased risk of URI in shelter populations nor does it appear to spread as readily as herpesvirus or even coronavirus. Contrary to popular belief, aerosol transmission is not a significant means of spreading URI. FADDIN EN.CITE. Feline URI is much more readily spread via fomites and droplet transmission (over distances of 5 feet or less), or, importantly, via reactivation of latent herpesvirus due to stress.
      1. Feline Herpesvirus-1 (FHV-1 - probably the most common)
      2. Feline Calicivirus (FCV - perhaps not as common as herpes, but potentially more severe)
      3. Chlamydophila felis
      4. Mycoplasma spp.
      5. Bordetella bronchiseptica

Diagnosis

Most often, a causative agent is not identified in individual cases of URI. Sometimes a best guess can be made based on clinical signs: FCV is relatively likely to be associated with oral ulceration or limping, FHV-1 is more likely to cause keratitis or corneal ulceration, Chlamydophila and Mycoplasma more often seen with conjunctivitis without other signs. However, all can cause overlapping clinical signs. In some cases additional testing to identify specific pathogen(s) is indicated, e.g.:
     • Unusual signs, severity or frequency of disease in a population of cats
     • Planned husbandry changes (e.g. before investing in vaccination for a particular pathogen such as Bordetella.)
     • Legal issues (e.g. hoarding investigation, liability concerns)
     • Detect carriers (e.g. low turnover shelter that has recurrent severe disease)

Diagnostic testing has become more widely available in recent years with the advent of RT-PCR testing and panels specific for feline URI. A negative test result in a correctly handled specimen is a reasonably sure way of ruling out acute infection, though intermittent shedding can occur with several of the URI pathogens. Interpretation of positive test results in an individual cat, however, is complicated by the fact that any of these pathogens can be isolated from clinically normal cats. A positive PCR test result on an oro-nasal sample from an individual cat has little meaning. Ideally at least 5-10 typically-affected cats should be sampled and evaluated in light of the expected frequency of carriage in shelter populations. Samples should be obtained from the most prominently affected location (e.g. eyes, oral cavity, nasal swabs), or as per laboratory guidelines. In a serious outbreak when cats are dying or being euthanized as a result of severe URI, necropsy and histopathology should be performed. This can often rapidly identify a cause and permit effective intervention.