Feline Immunodeficiency virus (clade A) QPCR
The Molecular Diagnostic Unit run the UK’s only QPCR tests for the detection of feline immunodeficiency virus (FIV). The tests detect integrated viral DNA (provirus) within the host’s blood lymphocytes. A limitation of current FIV tests, including ELISAs and the in-practice tests, is that they detect antibody rather than virus in the blood. Some FIV infected cats are negative with certain antibody testing systems, and kittens born to FIV infected queens can be FIV antibody positive without having true FIV infection due to the acquisition of maternally derived FIV antibodies. Now FIV DNA testing is available to provide an alternative method of FIV diagnosis and help you monitor FIV infection in cats by measuring the amount of FIV DNA (provirus) in the blood.
FIV has a worldwide distribution and five different subtypes (or clades) exist in different geographical locations:
- Clades A and B are present in Europe
- Clades A, B and C are present in the USA and Canada
- Clade A is present in Australia and Africa
- Clades B and E are present in South America
- Clades A, B, C and E are present in Japan and Asia
In Europe clade A virus isolates are found mainly in Northern countries (such as the UK and the Netherlands), whilst clade B isolates primarily occur in Southern countries (such as Italy and Spain).
The only FIV subtype that has been reported in the UK is clade A.
Due to the RNA sequence variation present between and within different clades of FIV it is highly unlikely that any single FIV PCR assay will be able to reliably detect all five clades. The Molecular Diagnostic Unit has developed QPCR assays that are reliable for the detection of clade A FIV isolates. Two QPCR tests are required to maximise detection of all known clade A isolates, and these QPCRs are able to quantify FIV proviral DNA in the blood of cats. These QPCRs are appropriate for use in cats in the UK where thus far only clade A FIV isolates have been found. The use of these QPCRs allows you to indirectly assess the cat’s FIV viral load, which may be useful when monitoring the course of infection in your FIV-infected patients.
The sample required for the FIV QPCR tests is 0.5 ml of EDTA anticoagulated blood.
Additionally, each FIV QPCR includes an internal amplification control to ensure that a valid diagnostic result is produced for every submitted sample.
The Molecular Diagnostic Unit recommendations for FIV testing: ELISA testing to detect FIV antibody is still indicated for routine FIV infection screening. The FIV DNA PCR test can be used to provide evidence of FIV infection in cats suspected of having FIV but which are antibody negative and in kittens born to FIV infected queens in which antibody testing may be misleading. The PCR test can also be used to monitor proviral loads in those cats found to be FIV-infected.
For more information about this assay please see our publications