Feline Leukemia Virus Infection: Age-Related Variation in Response of Cats to Experimental Infection2

Abstract

Sixty-seven specific-pathogen-free cats of various ages (newborn, 2 wk, 1 mo, 2 mo, 4 mo, and 1 yr) were inoculated ip with either the Rickard (R) or the Kawakami-Theilen (KT) strain of feline leukemia virus (FeLV). Susceptibility to FeLV was judged by induction of a) FeLV group-specific antigens (gsa) in leukocytes, b) FeLV-related disease, c) antibody to feline oncornavirus-associated cell membrane antigen (FOCMA), and d) virus-neutralizing (VN) antibody. Susceptibility to FeLV-decreased with age. Persistent viremia and FeLV-related disease developed in 100% of cats inoculated as newborns, in 85% of cats inoculated at 2 weeks to 2 months of age, and in 15% of cats inoculated at 4 months or 1 year of age. Cats susceptible to FeLV leukemogenesis became persistently FeLV gsa-positive (viremic) at 4 weeks post inoculation and thereafter and produced little or no FOCMA or VN antibody. Cats that resisted leukemogenesis by FeLV all developed persistent FOCMA and VN titers and never became FeLV gsa-positive. The disease in inoculated cats was influenced by virus strain; FeLV-R induced predominantly thymic lymphosarcoma, whereas FeLV-KT caused fatal nonregenerative anemia without concurrent neoplasia.

Feline Leukemia Virus DNA Vaccine Efficacy Is Enhanced by Coadministration with Interleukin-12 (IL-12) and IL-18 Expression Vectors

“…It had been expected that all of the control cats would become persistently infected following the intraperitoneal challenge. The recovery from viremia may have been due to the innate resistance of 20-week-old cats (23). Indeed it was in an attempt to overcome this potential resistance that the intraperitoneal method of administration of the challenge was used (45).…”

“…Persistent viremia was defined as the presence of virus in the plasma at the end of the trial, i.e., 15 weeks after challenge. Virus-neutralizing antibody titers were determined at each time point, since a significant postchallenge antibody titer usually correlates with protection (23). Virus isolation was also performed on cultured bone marrow samples, collected 15 weeks postchallenge, when the trial ended.…”

Longitudinal Analysis of Feline Leukemia Virus-Specific Cytotoxic T Lymphocytes: Correlation with Recovery from Infection

“…Following experimental exposure to FeLV, the majority of cats over 16 weeks of age either recover completely from infection or develop a latent infection (16). A proportion of cats develop a persistent infection, and these animals ultimately develop FeLV-associated diseases.…”

Feline oncornavirus-associated cell-membrane antigen (FOCMA): distinction between FOCMA and the major virion glycoprotein.

“…This occurs both following laboratory inoculation with concentrated live virus preparations (6-10) and after horizontal contact exposure to virus under laboratory (6,9,11,12) and field conditions (13)(14)(15). The levels of FOCMA antibody detected in sera of virus-exposed cats have been shown to be predictive of tumor occurrence and growth.…”