FIV antibody ELISA

FIV antibody ELISA

Species: Feline

Specimen: Serum, plasma

Container: Red top or gel tube for serum, EDTA or heparin tube for plasma

Collection protocol: Venepuncture

Special handling/shipping requirements: Standard

General information about the disease:

Feline immunodeficiency virus (FIV) is a lentivirus in the family Retroviridae. It contains RNA and its life cycle involves the integration of its RNA into the DNA of the genome of the host using the enzyme reverse transcriptase. This proviral DNA is then replicated as the cell divides. The proviral DNA is then translated back into viral RNA, and viruses are released from the host cell, the virus receiving its envelope from the host cell membrane. It shows many similar features to HIV, but is unrelated. A number of different subtypes or clades of FIV have been identified by sequencing the gene involved with the viral envelope. Isolates have been divided into five phylogenetic subtypes designated A, B, C, D and E. New Zealand has been found to have subtype C as the predominant subtype, fewer numbers of subtype A, and a novel, as yet unknown subtype. There is also a putative A/C recombinant strain. Transmission is mostly associated with biting/fighting, hence free roaming male cats are more at risk than others. All kittens born to infected queens will have maternal antibody present, although only one third will be infected with FIV. Maternally derived antibodies may persist for up to 3 months. Then it may be a further two months before infected kittens seroconvert.

Stages of Infection

1. The acute phase: This stage lasts several weeks. May see fever, diarrhoea, gingivitis, jaundice, uveitis, conjunctivitis, generalized lymphadenopathy and neutropenia. The severity depends on age. Young kittens have a more florid lymphadenopathy during the acute phase and there is increased severity in adolescents, while geriatric cats show minimal signs but progress more rapidly to the next stages of disease.

2. Asymptomatic carrier: This stage lasts from months to years with no obvious signs, and the cats appear apparently healthy. This stage may last up to 5 years but cats infected at >10 years of age progress through this stage faster than younger cats.

3. Persistent generalised lymphadenopathy and AIDS related complex: Lasts for 6 months to several years. It is characterized by vague, non-specific signs of illness, weight loss, enlarged lymph nodes, stomatitis, anorexia, anaemia, leucopoenia, neurological signs and apathy. This is the stage at which the majority of cats are presented to veterinarians.

4. Terminal AIDS-like phase: Lasts less than a year. Cats are emaciated. There are opportunistic infections, lymphoid depletion and miscellaneous disorders including neurologic, renal, immunologic and neoplastic disease.

General information about when this test is indicated:

Antibody to FIV appears at about 2-4 weeks post infection. The majority of commercial tests test for presence of antibody against membrane and core proteins (ELISA and immunodiffusion test kits). In New Zealand the majority of FIV positive results are true positive results because of the high prevalence and the excellent sensitivity and specificity of the tests available. However false negative results may occur early in the disease before there is a sufficient antibody response. They may also occur late in the disease when the cat is severely immunosuppressed. False positive results may occur in cats that have been vaccinated with the FIV vaccine. Currently vaccinated cats cannot be differentiated from naturally infected cats by routine serological means such as the ELISA test kits, because both classes of cats will have antibody present. Antibody may also be present in kittens that are born to cats that have been either infected or vaccinated and have transferred maternal antibody to their kittens. The presence of these maternal antibodies can interfere with serological testing for FIV in kittens <6m of age.

Comparison with other related tests: FIV PCR testing is another option for disease status investigation