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

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

Feline Calicivirus (FCV)

     • Highly variable: some strains are more likely to cause limping, some more likely to cause oral ulcers, some cause very severe disease, some are mild, etc. More likely to be associated with oral ulcers or inflammation than other URI. Some strains associated with pain and swelling in multiple joints

     • Vaccine resistant strains are common

     • Hard to kill

     • Inactivated by bleach, potassium peroxymonosulfate

     • Persists for weeks if not inactivated by disinfection

     • Incubation 1-5 days (can be shorter than herpesvirus)

     • 50% of infected cats will shed at least 75 days post-recovery regardless of stress

     • Long term healthy appearing carriers can perpetuate severe disease

Virulent Systemic Feline Calicivirus

     • Rapid onset (1-3 days) with swelling of the face and/or limbs, areas of hairloss and skin ulceration and oozing in adult, vaccinated cats.

     • ~ 50% mortality

     • Jaundice that appears infectious

     • "Peracute hepatic necrosis with hepatocellular individualization" commonlyreported on necropsy

     • BUT...Dying cats in a shelter with or without FURDC think panleukopenia until proven otherwise!

Bacterial Infections

Primary

     • Chlamydophila felis: Conjunctivitis (may be unilateral)+/- mild to severe URI, fever early in disease. LONG treatment (3-6 weeks) required to clear infection, generally to responsive to doxycycline; doxycycline is likely going to be more effective than azithromycin

     • Bordetella bronchiseptic: Cats may act as reservoir for dogs. URI, usually mild, ocular and nasal discharge, conjunctivitis, tracheobronchitis. Bordetella pneumonia in young kittens primary) or secondary to viral infection or immunosuppression. ?? Most infected cats do not show clinical signs. Extensive B. bronchiseptica associated disease may be a marker for husbandry problems . Always resistant to Cephalexin.

     • Mycoplasma spp. Conjunctivitis. Role in URI uncertain – generally thought to be minor player, but significantly associated in recent survey of shelter cats, recovered from 25% of cats with URI in that study. Isolated from 10/10 cats in two outbreaks of unusually severe URI in shelters.

Secondary Bacterial Infections

     • Wide variety, including gram positive, gram negative and anaerobic

     • Almost all can be found in normal cats as well

Diagnosis

Often will not affect your treatment plan and can be cost prohibitive. You may consider doing diagnostics such as culture and sensitivity or respiratory PCR panels if:

     • Signs persist longer than expected

     • Unusually severe clinical signs

     • More frequent disease in population

Prevention

Crowd Control = The single most important tool for feline URI control in shelters

Increased population density leads to a greater risk of disease introduction, higher contact rate, reduced air quality, and often, compromises in housing and husbandry. Unfortunately, crowding in shelters is not uncommon, either due to insufficient facilities, or (as is increasingly common) a well-intended attempt to decrease euthanasia by housing more animals. Tragically, such efforts may not only fail to improve the number of animals adopted, they may actually lead to increased disease and death. Always keep in mind that:

     • Lives saved is determined by adoptions and prevention

     • Adoptions are determined by adopters, not number of cats in the shelter

     • Prevention is determined by stress reduction, vaccinations, sanitation, segregation, length of stay, and crowd control.

Stress Reduction

Because FHV is often activated by stress, enrichment and stress reduction are crucial to feline URI control. Even moving cats from cage to cage is enough to induce reactivation in some cats. "Spot cleaning" where possible, and prioritizing housing for cats that does not require extensive movement or handling for care is likely key to control of URI. Providing hiding places, decreasing noise exposure, maintaining light/dark cycles and comfortable temperatures, and providing toys and scratching surfaces are also important to relieving feline stress.

Vaccination: Fvrc-P

Although URI is not a vaccine preventable disease having a good vaccination protocol in place is a central piece of disease control. Cats vaccinated for herpesvirus are significantly less likely to be shedding herpes than non-vaccinated cats. However, there was no significant difference in likelihood of shedding calicivirus between vaccinated and non-vaccinated cats.

Feline calicivirus is extremely variable, and mutates from year to year. Currently available vaccines are based on strains of feline calicivirus isolated many years ago and do not protect against all the strains of calicivirus now seen. The bottom line is that vaccination against calicivirus provides, at best, limited protection against only some strains.

Disinfection

Most URI pathogens survive in the environment no more than a few hours to a few weeks and are inactivated by routinely used disinfectants. Feline calicivirus is the notable exception, and may survive for up to a month or even longer in dried discharge. FCV is inactivated by household bleach (5% sodium hypochlorite) diluted at 1:32, or by potassium peroxymonosulfate (Virkon® or Trifectant®).

Isolation

Many cats shed URI pathogens without showing clinical signs, hence the need for careful hygienic precautions even when handling apparently healthy cats. Cats with active signs of infection are likely to be shedding much greater amounts of the pathogen involved, and isolation of these cats from the general population is a requirement for even a minimal disease control program.

Monitoring

Countless dollars, hours and endless heartache are spent in efforts to control URI in shelters, yet we often rely solely on vague clinical impressions to determine whether our efforts are justified by the result. Just as we do for the individual patient, we need measures to monitor the success of our "population treatment plan".