An Update on
Presentation 3.1:
The researchers looked at 292 cats that were seen at various clinics across the Czech Republic. They then compared their results to 292 cats that were tested in Austria during an equivalent period of time. Most of the Czech cats were less than one year old when tested, but the cats from Austria were generally older. The researchers looked at coronavirus antibody test results based on indirect immunofluoresence assays. They compared the signalment of both groups and while they differed in age, sex, percentages pedigreed, and health status, the percentages testing positive for coronavirus were relatively similar in cats from the two countries. Overall, 58% to 64% were coronavirus antibody-positive, with the highest proportion being in those cats under one year of age. The researchers concluded that coronavirus exposure is fairly widespread and does not differ significantly between the Czech Republic and Austria.
Presentation 3.2:
This study looked at samples taken from feral cats in the county around Gainesville, Florida. These cats were acquired as part of a local Trap/Test/Vaccinate/Neuter and Release program. Samples were collected during the period July 1999 to February 2000 from trapped cats that were considered to be adults. The blood samples were tested for the presence of various disease-causing agents, including: FeLV, FIV, heartworm, coronavirus, Haemobartonella, and Ehrlichia. Of the 557 cats tested using an indirect immunofluorescent assay for coronavirus antibodies, the majority was seronegative (a titer less than 1:40). Of the free roaming cats, 81.9% had no significant antibody titers. They compared the males to the females and while the males had a slight lower percentage of seropositive tests, it was statistically insignificant. The researchers concluded that this was consistent with a fecal-oral transmission route for feline coronavirus and supports the proposition that this is a disease of multi-cat environments.
Presentation 3.3:
The purpose of this study was to look at the early weaning and isolation approach in at-risk catteries in Switzerland. Eighteen breeders with a history of feline infectious peritonitis agreed to participate in the study to evaluate the effectiveness of early weaning and vaccination versus conventional rearing. The mean number of adult cats per breeder was 11.1 with the mean number of queens being 6.6. The researchers looked at 63 litters (31 early weaned and 32 conventionally weaned). For the early weaning protocol, the breeders were asked to separate the queens from the other cats in their household at least two weeks prior to birthing. There was no contact between kittens and other cats in the catteries and strict hygiene was required. Conventionally reared kittens were not kept separate. Fecal samples from all the kittens were analyzed at two, four, six, nine, and 12 weeks using RT-PCR (Taqman technique). Blood samples were tested for coronavirus antibodies using an immunofluorescence assay.
All the queens in the study were seropositive for coronavirus antibodies before kittening. The researchers then looked at the shedding frequency and found approximately 45%-50% of the queens were also shedding virus before kittening. This was followed by a decrease to 20% shedding at the time of birth and then an increase later.
Coronavirus shedding was found in kittens as early as two weeks of age, whether conventionally reared or early weaned. Thus, it raises questions about the earlier assumption that maternal antibodies are protective against FCoV infection. By two weeks of age, up to 12% of the early weaned kittens were shedding virus. By six weeks, 50% of all the kittens in both groups were shedding virus. By nine weeks of age, over 50% of all the kittens from both groups were seropositive for coronavirus antibodies.
The researchers also looked at the relationship between the viral load and coronavirus antibody titers when the kittens were nine weeks old. Because the kittens with higher titers at nine weeks of age had significantly higher shedding intensity in their fecal tests, the researchers concluded that a kitten's antibody titer reflects its degree of viral shedding. Higher antibody titers were also associated with earlier age of infection. They also discovered there was a high correlation between antibody titer level and viral shedding frequency in the queens.
They were unable to raise FCoV-free litters in these cattery situations. However, the early-weaned kittens had significantly fewer cases of diarrhea than the conventionally reared kittens. By the end of the study (21 months), almost the same number of kittens from each group had died of FIP (four of the early weaned kittens and five of the conventionally reared kittens).
Presentation 3.4:
A team of veterinarians at the University of California, Davis, undertook a major study of shelters in California to determine the infection status of entering cats. The team tested the cats at the time of entry and at one, two, and three weeks later. Almost all the cats were adopted before week three. They assessed the cats for feline coronavirus infection using fecal swabs and RT-PCR (Taqman technique). They also looked for feline calicivirus (from oral swabs) and feline herpesvirus (from conjunctival swabs) using tissue culture techniques. The results of the various studies they undertook provide some important insights for both shelter managers and others who manage multi-cat situations, including breeders.
Infection status of cats entering the shelters in Northern California (162 cats tested):
At the end of the 1st week, they re-tested 60 cats and found significant differences in the infection rate:
In reviewing the ages of the animals tested, they concluded that the younger animals had the highest rates of shedding for both FCV and FHV, so introduction of young animals into a multi-cat situation should be kept to a minimum to avoid outbreaks of either disease. Further, within one week of entering the shelter, 50% of the cats that were negative had become positive for FECV.
When they looked at the infection rates for FECV, they discovered that the lowest rates of infection were in those animals under eight weeks of age. The highest were in cats between eight and 56 weeks of age. The percentage of infected cats declined after 56 weeks of age.
The study also looked at the degree of FECV shedding in the cats. They saw shedding as early as one week post exposure (i.e., one week after entering the shelter). Kittens had a significantly higher shedding rate during primary infection than did adults. At the end of the first week in a shelter, the shedding rates had increased by 10 to 100 times. Dr. Pedersen thinks the stress of putting the cat into a shelter may cause this dramatic increase in shedding, similar to the effect of stress on herpesvirus infections. The degree of coronavirus shedding varied widely among the cats, with cats shedding at both low and high levels.
Conclusions: A significant proportion of the kittens and adult cats were infected with FECV prior to entering the shelters. However, no kitten under eight weeks of age was infected at the time of entry. Virtually all of the cats between the ages of eight weeks and 56 weeks were infected. Thus, FCoV infection is widespread in all cat populations. They also noted that naïve cats (those with no prior exposure to coronavirus) became infected almost immediately upon arrival in the shelter. They concluded that the increased incidence of FIP in young shelter cats could be explained by:
Presentation 3.5:
Dr. Diane Addie and her team also looked at cats relinquished to shelters in the United Kingdom. Their studies showed that 16.8% were seropositive for FCoV by immunofluorescence antibody testing when entering the shelter and that the percentage increased slightly in relation to the number of days the animal remained in the shelter. The results included the following findings:
Presentation 3.6:
Researchers now know that there are at least two serotypes of FCoV, commonly referred to as Type I and Type II. Type I viruses are species-specific and are difficult to grow in cell culture. Type II viruses, however, are easily grown in cell culture and are often used for the various FIP/FCoV studies. Type II viruses arise by recombination between Type I feline coronavirus and canine coronavirus.
These researchers looked at a group of 314 Austrian cats including 154 cats that had died of confirmed FIP. Of the 160 cats that did not have FIP, 71.1% tested seropositive for FCoV using an immunofluorescence antibody assay. Using RT-PCR, the researchers found 26% of these 160 cats positive for coronavirus. Dividing these RT-PCR positive cats by serotype, 55% were found to be Type I, 29% were found to be Type II, and 17% had mixed infections. No significant correlation was found between the results of RT-PCR analysis and antibody titers.
Of the 154 cats confirmed with FIP, tissue samples were available for RT-PCR testing from 94 cases. When these samples were tested, the researchers were able to confirm the serotype using specialized RT-PCR tests in 74 of the cats. Interestingly, 86% of these cats tested positive for Type I coronavirus. However, there were no pathological changes present on examination of the tissues that correlated particularly with either Type I or Type II virus infections.
In general, Type I viruses were more common in both the FIP and non-FIP group. Since Type II coronaviruses are produced by recombination of feline coronavirus Type I and canine coronavirus, it is possible that canine coronavirus plays a role in the 14% of FIP cases in this study confirmed to have Type II viruses. Finally, those cats at highest risk of FIP in this study were pedigreed cats under the age of one year.
Presentation 3.7:
Dr. Addie's research group has looked at the shedding and transmission of feline coronavirus in naturally occurring infections for several years. Their studies show that there are no hard and fast rules for the length of time or when a cat might shed. They did learn that:
In a new project, the researchers developed RT-PCR tests that could distinguish between Type I and Type II coronaviruses. Using these new tests, they found that 94% of the coronavirus isolates in the United Kingdom were Type I.
One theory about how persistent coronavirus infections occur is that the virus is able to develop quasispecies within an infected cat - a group of viruses slightly different antigenically so that the immune system's defense mechanisms are evaded. Using tools to study coronavirus strains in infected cats over time, the study found:
Presentation 3.8:
This study looked at 132 cats owned by eight breeders. Using a real-time RT-PCR assay for coronavirus in feces, cats were tested once weekly for a period ranging from 24 to 37 weeks. In addition, two blood samples were collected from each cat (one at the beginning of the study and one at the end) for coronavirus antibody titers using an immunofluorescence antibody assay. Shedding of virus in saliva was also evaluated.
In looking at the shedding of virus in the saliva of these cats, they found this was a less reliable test than when they looked at viral shedding in fecal samples. They also determined that coronavirus in fecal samples is relatively stable at room temperature for at least 10 days, making this a reliable sample to test.
In looking at a profile of shedders, the researchers broke them down into low-frequency shedders (78% of the cats), medium-frequency shedders (21% of the cats), and high-frequency shedders (1% of the cats). Low-frequency shedders shed virus on less than 30% of their fecal samples tested, medium-frequency shedders on 30%-90% of their samples tested, and high-frequency shedders on over 90% of their samples tested. The researchers also demonstrated a high correlation between fecal shedding frequency and the amount of virus shed, with higher shedding frequencies associated with higher viral loads.
Based on the results of their study, the researchers believe that breeders can reduce the infectious pressure if they separate high-frequency shedders from the rest of a cattery population. They believe catteries should consider:
FELINE INFECTIOUS PERITONITIS
Second International FCoV/FIP Symposium
Session 3
Epidemiology of FCoV Infection
Session 3:
Epidemiology of FCoV Infection,
Chair, Dr. Jim Richards, Cornell University
Seroprevalence of Feline Coronavirus in Two Central European countries: Czech Republic & Austria
(K. Moestl et al., University of Veterinary Medicine, Vienna, Austria)
Prevalence of Coronavirus in Feral Cats in Gainesville, Florida
(A. Legendre, B.J. Luria, S.P. Gorman, I.T. Lee, J.K. Levy)
Kinetics of FCoV Infection in Kittens Born in Catteries of High Risk for FIP under Different Rearing Conditions
(H. Lutz et al., University of Zurich, Switzerland)
Feline Enteric Coronavirus Infection in Shelter Cats
(N. Pedersen et al., University of California, Davis, USA)
Prevalence of Feline Coronavirus Antibodies in UK Cats relinquished to a Rescue Charity
(D. Addie et al., University of Glasgow, UK)
Differentiation of Feline Coronavirus (FCoV) Types I and II in Austrian Cat Population
(V. Benetka et al., University of Veterinary Medicine, Vienna, Austria)
The Persistence and Transmission of Type I Feline Coronavirus in Natural Infections
(D. Addie et al., University of Glasgow, Scotland)
FCoV Shedding Pattern of Privately Owned Cats Under Field Conditions
(H. Lutz et al., University of Zurich, Switzerland)
Of the 3,053 fecal samples tested, 26.5% were positive and contained significant quantities of the coronavirus. No catteries were negative for coronavirus. In this study, occasional viral shedders seemed to have lower viral loads. The shedding frequency in kittens under six months of age was much higher as was their viral load. Interestingly, they found 1%-2% cats that tested seronegative also shed virus, but at very low levels. When they looked at cats with confirmed FIP, they discovered that not all of these cats shed virus. Based on their study on conditions within catteries, testing four fecal samples with RT-PCR for coronavirus at one-week intervals should be sufficient to determine if an individual cat is or is not a strong viral shedder. It is thought that identification of strong viral shedders and separating them from other cats may help control FIP.
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Glossary | Selected Bibliography for Feline Coronavirus and FIP
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