Persistent viral infection. The carrier state

Calicivirus Infection in Cats

Feline calicivirus (FCV) is a common pathogen in domestic cats that is highly contagious, resistant to many disinfectants and demonstrates a high genetic variability. FCV infection can lead to serious or even fatal diseases. In this review, the European Advisory Board on Cat Diseases (ABCD), a scientifically independent board of experts in feline medicine from 11 European countries, presents the current knowledge of FCV infection and fills gaps with expert opinions. FCV infections are particularly problematic in multicat environments. FCV-infected cats often show painful erosions in the mouth and mild upper respiratory disease and, particularly in kittens, even fatal pneumonia. However, infection can be associated with chronic gingivostomatitis. Rarely, highly virulent FCV variants can induce severe systemic disease with epizootic spread and high mortality. FCV can best be detected by reverse-transcriptase PCR. However, a negative result does not rule out FCV infection and healthy cats can test positive. All cats should be vaccinated against FCV (core vaccine); however, vaccination protects cats from disease but not from infection. Considering the high variability of FCV, changing to different vaccine strain(s) may be of benefit if disease occurs in fully vaccinated cats. Infection-induced immunity is not life-long and does not protect against all strains; therefore, vaccination of cats that have recovered from caliciviral disease is recommended.

Canine reproductive, respiratory, and ocular diseases due to canine herpesvirus

This review documents how clinical inquiry expands as our knowledge base about canine herpesvirus (CHV) increases. We must understand the various forms of CHV infection that may occur in the dog population. This has prompted the veterinary community to develop more sensitive diagnostic assays. CHV is more common than we considered a decade ago. Up to 70% of some high-risk dog populations have been infected with and are latent carriers of CHV. Recognition of the various forms of CHV-induced disease, availability of diagnostic assays with increased sensitivity, and the formation of reliable biosecurity measures will allow for better control steps.

Pathology of immunodeficient mice with naturally occurring murine norovirus infection

Murine norovirus (MNV) was recently discovered in Rag2-/-/Stat1-/- mice in a U.S. medical research facility. Presently, little is known concerning the epidemiology and natural history of this virus. We studied the pathology of naturally occurring MNV infection in 28 immunodeficient mice of several different genotypes (Rag1-/-/IFNgamma R-/-, OT1 Rag1-/-/IFNgamma R-/-, OT2 Rag1-/-/IFNgamma R-/-, Rag1-/-/Stat1-/-, and Rag2-/-) that were maintained in two U.S. research facilities. The mice were selected for study because sentinel mice housed in their holding rooms had been identified as positive for MNV-specific antibodies during routine screening for infectious agents. Our data indicate that in certain lines of immunodeficient mice, MNV can establish a disseminated infection that is characteristically associated with inflammation in multiple tissues, including liver (hepatitis), lung (focal interstitial pneumonia) and the peritoneal and pleural cavities. In addition, MNV can establish an asymptomatic infection in the mesenteric lymph nodes of Rag2-/- mice. Further studies are needed to determine whether MNV presents a confounding variable in immunological, toxicological and pathological studies in mice naturally infected with MNV.

NEUTRALIZING ANTIBODIES AGAINST FELINE HERPESVIRUS TYPE 1 IN CAPTIVE WILD FELIDS OF BRAZIL

Feline herpesvirus type 1 infection affects domestic cats, causing mainly upper respiratory tract diseases. Although this infection has been described in captive and free-ranging wild felids from Europe, Asia, North America, and Africa, no information is available on its occurrence among wild felids of Brazil. In this study, 250 serum samples of six species of Brazilian captive wild felids (Leopardus tigrinus, Leopardus wiedii, Herpailurus yaguarondi, Puma concolor, Leopardus pardalis, and Panthera onca) were examined for neutralizing antibodies to feline herpesvirus type 1. Positive sera were found in 72% of L. tigrinus samples, 15% of L. wiedii, 6% of L. pardalis, 8% of H. yaguarondi, 18% of P. concolor, and 14% of P. onca. The relatively low percentages of seropositivity and low antibody titers found among the last five species suggest that feline herpesvirus type 1 does not circulate extensively among these animals. Nevertheless, quarantine, serologic screening, and vaccination of newly introduced felids is recommended in zoos in order to prevent virus transmission and outbreaks of the disease among wild felids kept in captivity.

Involvement of apoptosis in syncytial cell death induced by canine distemper virus

The Yanaka strain, a field isolate of Canine distemper virus (CDV), caused extensive syncytial cytopathic effects (CPEs) followed by cell death in vitro. Syncytium formation is an important aspect of CDV pathogenicity, but the mechanism of the fusion-induced cell death is still not understood. In this study, the involvement of apoptosis in the CDV-induced CPE was investigated. We also examined apoptosis in cells infected with a persistent strain of CDV, the Yanaka-BP strain derived from the Yanaka strain, because this strain does not cause obvious CPE. DNA laddering together with Terminal transferase dUTP nick endlabeling (TUNEL) assay indicated that the Yanaka strain infection, but not the Yanaka-BP infection induced apoptosis. In addition, flow cytometric analysis similarly indicated that the Yanaka-BP strain induced apoptosis significantly less frequently than the Yanaka strain did. Thus, absence of apoptosis may be implicated in the CPE and establishment of persistent CDV infection.

An outbreak of virulent systemic feline calicivirus disease

OBJECTIVE

To describe clinical and epidemiologic features of an outbreak of feline calicivirus (FCV) infection caused by a unique strain of FCV and associated with a high mortality rate and systemic signs of disease, including edema of the face or limbs.

DESIGN

Observational study. Animals-54 cats naturally infected with a highly virulent strain of FCV.

PROCEDURE

Information was collected on outbreak history, clinical signs, and characteristics of infected and exposed cats.

RESULTS

A novel strain of FCV (FCV-Kaos) was identified. Transmission occurred readily via fomites. Signs included edema and sores of the face and feet. Mortality rate was 40%, and adults were more likely than kittens to have severe disease (odds ratio, 9.56). Eleven (20%) cats had only mild or no clinical signs. Many affected cats had been vaccinated against FCV. Viral shedding was documented at least 16 weeks after clinical recovery.

CONCLUSIONS AND CLINICAL RELEVANCE

Outbreaks of highly virulent FCV disease are increasingly common. Strains causing such outbreaks have been genetically distinct from one another but caused similar disease signs and were resistant to vaccination. All cats with suspicious signs (including upper respiratory tract infection) should be handled with strict hygienic precautions. Sodium hypochlorite solution should be used for disinfection following suspected contamination. All exposed cats should be isolated until negative viral status is confirmed. Chronic viral shedding is possible but may not be clinically important. This and similar outbreaks have been described as being caused by hemorrhagic fever-like caliciviruses, but hemorrhage is uncommonly reported. Virulent systemic FCV infection is suggested as an alternative description.

Pathogenesis and treatment of feline rhinitis

Diagnosis and treatment of feline rhinitis, like canine rhinitis, can be a frustrating experience for the veterinary practitioner. Having sound knowledge of the possible etiologies involved and using a systematic diagnostic approach makes the workup of these challenging cases much easier. Selection of appropriate therapy based on a definitive diagnosis makes treatment rewarding. This article discusses the pathogenesis and treatment of a variety of causes of feline rhinitis.

Infectious disease surveillance in captive and free-living cheetahs: An integral part of the species survival plan

During the formulative stages of developing the Species Survival Plan (SSP) for the cheetah, the impact of infectious disease upon its survival in captivity was of prime consideration, together with genetics, nutrition, physiology, and behavior. This paper summarizes the results of an infectious disease surveillance program, initially designed to monitor the infectious agents associated with clinically normal and clinically ill cheetahs in captivity, but subsequently supplemented with data from free‐living cheetahs. The focus was on two viral infections, feline infectious peritonitis (FIP) and feline rhinotracheitis virus. Results indicated that between 1989 and 1991, there was an increase in the seroprevalence (number antibody‐positive animals) of cheetahs to feline coronavirus from 41% to 64% in captivity. During this same time period, there were only two documented cases of FIP in cheetahs in the United States. The results suggest that feline coronavirus (feline enteric coronavirus‐‐feline infectious peritonitis group) or a closely related coronavirus of cheetahs is becoming endemic in the captive cheetah population.

Further serologic results from 39 free‐living cheetahs demonstrated that there was a high seroprevalence (61%) to feline coronavirus, although serum antibody titers were considerably lower than those encountered in captive cheetahs. The observation of a high percentage of free‐living cheetahs, which were seropositive to feline herpesvirus (44%), was unexpected, since it has been generally regarded that this infection is primarily associated with cheetahs in captivity. © 1993 Wiley‐Liss, Inc.