In vitro effects of the active metabolite of leflunomide, A77 1726, on feline herpesvirus-1.

OBJECTIVE: To determine whether the active metabolite of leflunomide, A77 1726 (A77), inhibits replication of feline herpesvirus-1 (FHV-1) in cell culture. STUDY POPULATION: Crandell Rees feline kidney (CRFK) cell cultures. PROCEDURES: Cell cultures were inoculated with FHV-1 and treated simultaneously with concentrations of A77 ranging from 0 to 200microM. The antiviral effect of A77 was determined by use of conventional plaque reduction assays. The effect of A77 on viral load was determined via real-time PCR analysis, and transmission electron microscopy was used to evaluate the effect of A77 on viral morphology. To determine whether the antiviral effect was attributable to alterations in CRFK cell viability and number, CRFK cells were treated with various concentrations of A77 and stained with Annexin V and propidium iodide to assess apoptosis and a mitochondrial function assay was used to determine cell viability. RESULTS: Concentrations of A77 > or = 20microM were associated with substantial reduction in plaque number and viral load. Concentrations > or = 100microM were associated with complete suppression of plaque formation. At low concentrations of A77, clusters of intracytoplasmic virus particles that appeared to lack tegument and an external membrane were detected. Treatment of uninfected CRFK cell monolayers with A77 was associated with reduction in mitochondrial function with minimal evidence of apoptosis. CONCLUSIONS AND CLINICAL RELEVANCE: Leflunomide may be an alternative to current calcineurin-based immunosuppressive protocols used in feline organ transplantation because of its antiherpesviral activity.

Virulent systemic feline calicivirus infection: local cytokine modulation and contribution of viral mutants.

Virulent systemic feline calicivirus (VS-FCV) is a novel, emerging pathogen with mortality up to 67% even in previously healthy adult cats; VS-FCV has resulted in at least six epidemics since 1998. Affected cats have systemic vascular compromise and hemorrhagic-fever like signs in part due to viral invasion of epithelium and endothelium, coupled with host cytokine responses. Affected skin tissues had, on average, 3.8 elevated cytokines compared with control tissue, with prominent upregulation in IL-10, TNF-alpha, and MIP-1alpha. Sequencing of most of the genomes of two VS-FCV strains documented patterns of virus relatedness and implicated changes in the capsid gene in the emerging phenotype, possibly through initiation of immune mechanisms manifest in the cytokine changes. Understanding the features contributing to the emergence of this disease is critical for management and prevention of this and similar outbreaks attributable to RNA viruses in animals and humans.

Feline coronavirus serotypes 1 and 2: seroprevalence and association with disease in Switzerland.

To determine the prevalence of antibodies to feline coronavirus (FCoV) serotypes 1 and 2 in Switzerland and their association with different disease manifestations, a serological study based on immunofluorescence tests was conducted with Swiss field cats using transmissible gastroenteritis virus (TGEV), FCoV type 1 and FCoV type 2 as antigens. A total of 639 serum samples collected in the context of different studies from naturally infected cats were tested. The current study revealed that, with an apparent prevalence of 83%, FCoV serotype 1 is the most prevalent serotype in Switzerland. FCoV type 1 viruses induced higher antibody titers than FCoV type 2, and were more frequently associated with clinical signs and/or feline infectious peritonitis. The antibody development in seven cats experimentally infected with FCoV type 1 revealed that, with progressing duration of infection, antibodies to FCoV type 1 significantly increased over those to FCoV type 2. There was a significant relationship between antibody titers against TGEV, FCoV 1, and FCoV 2 and TGEV antigen detected the highest proportion of seropositive cats. We conclude that a vaccine against FCoV should be based on FCoV type 1-related antigens and that for serodiagnosis of FCoV infection TGEV should be used to attain the highest diagnostic efficiency. When serology is used in addition to clinical signs, hematology, and clinical chemistry results as an aid to diagnose clinical FIP, TGEV shows a diagnostic efficiency equal to that of a FCoV antigen.

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.