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Why do we have respiratory disease in our shelter cats and what can we do to control it? (Proceedings)

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Aug 01, 2010

Feline upper respiratory infection (URI) is a disease complex born in large parts from stress and crowding. I would dare say that URI is perhaps the most frustrating illness facing shelter veterinarians, managers and staff in that many cats are chronically infected, vaccines are partially effective at best, and specific treatments are limited. It is also a challenging problem to overcome since it so easily spread by fomites or droplet transmission, and some URI agents are resistant to disinfection. Other factors such as overcrowding, poor air quality, poor sanitation, stress, concurrent illness, parasitism, poor nutrition, and other causes of immunosuppression predispose to the disease, and many of these are difficult or impossible to completely eliminate in a typical shelter, cattery or rescue home.

In spite of these challenges, some shelters and catteries clearly suffer less from URI than others, and although URI can never be totally eradicated, the frequency and severity of cases can be greatly reduced through a systematic management strategy.

While URI in most pet cats resolves relatively easily and often without treatment, URI is the one of the most common reasons for euthanasia of shelter cats. Understanding the "herd health" pathogenesis of URI will help us to understand how to best prevent it.

Who are the culprits?
     • Viruses, especially feline herpesvirus (FHV) and feline calicivirus (FCV) (80-90%)
     • Bacteria
     • Modified live vaccines (mild signs in most cases)
     • FIV, fungal infection, polyp, foreign bodies...etc
     • Just because it's one of the viruses the great majority of the time, don't forget to rule out less likely causes in a cat that is not getting better!

How is it spread?
     • Fomites
     • Direct contact
     • Droplet (4-5 feet)

Cat to cat transmission plays a clear role in group housing situations, while in single cat housing transmission occurs via fomites rather than aerosol spread, as is commonly thought. This has been demonstrated for herpesvirus and calicivirus: When cats were kept in open sided wire cages in a common air space separated by 6 feet, there was no transmission, when healthy cat cages were cleaned first and fomite transmission was strictly controlled. However, when cleaning was random, with sick cats being cleaned first some of the time, transmission occurred frequently.

Virus can be easily transmitted on clothing, particularly if it is present on hair picked up by caretaker's clothing. Because cats groom themselves, virus present in saliva or respiratory secretions is likely present on hair. In outbreaks of virulent systemic feline calicivirus, pet cats belonging to veterinary technicians have been fatally infected, presumably via virus transported on clothing or shoes.

The Environment

Reduction of overcrowding, effective cleaning, adequate ventilation, stress control, and good preventive medicine are the cornerstones of URI control in feline populations.

Common Pathogens

Feline Herpesvirus
     • Relatively stable, some variation in predominant clinical signs may occur. Some strains may cause more conjunctivitis, versus some strains that cause more sneezing. Keep in mind though that variation in clinical signs can also be due to a cat's individual immune system. For example, a cat with herpetic ulcers is not particularly likely to give another cat herpetic ulcers. Development of ulcers in the eyes has more to do with that cat's immune system than variation in the herpesvirus.
     • Vaccine resistant strains have not been reported.
     • Not hard to kill; inactivated by all commonly used disinfectants
     • Incubation period of about a week
     • Persists in nerve roots in 80-90% (all?) of recovered cats and is reactivated by stress in 50% of chronically infected cats, with or without signs