= Feline immunodeficiency virus
= FIV
{c}
{synonym}
<Feline immunodeficiency virus> is a <Lentivirus> of <cats>, classified within <Orthoretrovirinae>. Its connection to immune dysfunction made it a useful subject for studying persistent <retrovirus> infection in a host distinct from the human host of <human immunodeficiency virus>.<Lentivirus report by the International Committee on Taxonomy of Viruses>[Biological properties, feline lentiviruses and hosts]{ref}
The 1987 report by <N. C. Pedersen> and colleagues described isolation of a T-cell-associated <virus> from a cattery with an immunodeficiency-like syndrome. The animals had tested seronegative for feline leukemia virus, and the newly isolated agent was antigenically distinct from <human immunodeficiency virus>. These comparisons addressed whether an already recognized agent accounted for the observations; a shared disease description alone would not establish viral identity.<Isolation of a T-lymphotropic virus from domestic cats with an immunodeficiency-like syndrome by N. C. Pedersen and others>[Science 235, 790–793, Abstract; original initial-only byline]{ref}
The same report found <antibodies> to the new agent in 10 of 25 cats showing signs of ill health and in 1 of 18 apparently normal cats. Those proportions are $40\%$ and approximately $5.6\%$. Their difference motivates investigating an association, while the positive apparently normal animal shows why infection and observed illness cannot be treated as identical categories.<Isolation of a T-lymphotropic virus from domestic cats with an immunodeficiency-like syndrome by N. C. Pedersen and others>[Abstract, serologic comparison of the two cattery groups]{ref}
These are counts from selected groups in one investigation, not a population-wide prevalence estimate. <Serology> measures evidence of a host response under an assay's criteria; establishing the complete causal sequence of a disease calls for further observations.
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