Reassessment of feline leukaemia virus (FeLV) vaccines with novel sensitive molecular assays.

We previously described antigen negative, provirus positive cats. Subsequently, we hypothesized that efficacious FeLV vaccines cannot prevent minimal viral replication. Thus, we vaccinated cats with either a canarypox-vectored live or a killed virus vaccine and analyzed the challenge outcome with quantitative PCR and a newly established real-time RT-PCR. When judged by conventional parameters (antigenaemia, virus isolation), most of the vaccinated cats were, as expected, protected from persistent viraemia. However, all cats were found to be plasma viral RNA positive. The loads were significantly associated with the infection outcome. Thus, commonly used FeLV vaccines understood to be successful model antiretroviral vaccines protecting against FeLV-related diseases do not confer sterilizing immunity.

Quantitation of feline leukaemia virus viral and proviral loads by TaqMan real-time polymerase chain reaction.

Feline leukaemia virus (FeLV) infection in cats is not only of veterinary importance but also a well-acknowledged animal model for studying the pathogenesis of retroviral disease. After virus exposure, different courses and outcomes of FeLV infection may prevail; they have been associated with cellular and humoral immune responses and the FeLV proviral load in peripheral blood. We hypothesized that the plasma viral RNA load might be an additional relevant indicator for the infection outcome. To quantify these loads, a real-time reverse transcriptase (RT) polymerase chain reaction (PCR) assay was developed. The assay amplifies FeLV-A, -B, and -C as some naturally infected cats could not be identified with a FeLV-A-based assay previously. The assay was applied to determine plasma FeLV RNA loads in cats infected both naturally and experimentally with FeLV. In addition, an improved real-time PCR assay for quantitation of FeLV proviral loads is described. The assays developed were more sensitive than ELISA and virus isolation in the early phase of infection. In addition, PCR allows the identification of provirus carriers that have overcome antigenaemia. Thus, for most effective detection of FeLV exposure and characterization of the infection in a cat, PCR assays are recommended as diagnostic tools.

Risk factors for feline coronavirus seropositivity in cats relinquished to a UK rescue charity.

Two thousand, two hundred and seven cats from 14 shelters of a major UK cat charity were blood tested for feline coronavirus (FCoV) antibodies. Data was collated on breed, sex, age, number of cats at original location, outdoor access, health status, and time spent in the shelter prior to sampling (range 0 to 4 years). Some cats were also tested for feline leukaemia virus antigen, feline immunodeficiency virus, and Toxoplasma gondii antibodies. The effect of these variables on FCoV seropositivity was explored by multivariable logistic regression. FCoV seropositivity in cats that had spent 5 days or less in a shelter at sampling was significantly associated with a multi-cat origin, cats aged 3 years or less, and Persian breed. Whether pet, stray or feral, health status, indoor/outdoor access, and sex had no significant effect. Overall FCoV seropositivity was associated with time spent in a shelter but this association was not linear. Cats that had spent more than 60 days in a shelter were over five times as likely to be seropositive. This may be the result of a change in husbandry from solitary to communal housing for cats remaining in shelters long term. Rescue of cats for less than 60 days was not associated with a significant increasing risk of seropositivity. Significant variation existed in seropositivity between individual shelters overall and in cats rescued for less than 5 days. These findings may reflect inter-shelter variation in cat husbandry and variation in seropositivity of shelter intake respectively.