Feline Immunodeficiency Virus

Also known as: FIV

Description

Feline immunodeficiency virus is a retrovirus that cuases immunodeficiency disease in the domestic cat.

Agent

FIV is prevalent in cat populations throughout the world and is an important cause of feline disease. FIV belongs to the lentivirus family of the retrovirus group. Seroepidemiological surverys of the prevalence of FIV in the UK have shown that 13-19% of sick cats may be infected with FIV compared to 2-3% of healthy cats.

Transmission and Epidemiology

The major route of transmission is via saliva, especially through bting, and those cats exhibiting territorial aggression are most at risk of infection. Vertical transmission can also occur byt the importance of this is not known. Venereal transmission has not been reported. Within households horizontal transmission can occur but the level of infection can be very variable. In some househilds only a single cat in a group may be FIV positive, wherease in others nearly every cat may be infected. However, overall it appears that if fighting among cats housed together is rare, the prevalence of FIV is likely to be low. Feline Immunodeficiency Virus is commonly abbreviated to FIV.

Pathogenesis

• Receptor: CD134, found on monocyte-derived macrophages and activated T cells
  • Net effect: disruption of acquired immune response
• Infected cats develop antibody whether or not they are able to clear the virus

Two versions:

• Avirulent:
  • Transient infection with no CD4 decline
• Virulent:
  • Progressive CD4 decline with three stages (may present indistinct)
    1. High circulating virus for 1-10 weeks with resulting lymphoid depletion and CD8CD4 double positive Tcell destruction, thymic aplasia esp in kittens
    2. Remission: decrease in circulating virus as immune response increases, followed by immune exhaustion
       • Increase in CD8+ production and antibody response
       • Paracortical T cells and lymphoid follicles expand in primary and secondary lymph tissue and may be visible as white nodules
    3. Rapidly progressing infection with high virus present
       • Feline AIDS presents in a minority of cases
       • Nonregenerative anemia
       • Leucopenia
       • Neutropenia
       • Skin infections
       • Usually followed by secondary infection as a result of immunosuppression
       • Virus-ridden T cell destroy normal T cells, causing chronic immunosuppression

Signalment

FIV infection increases in prevalence in older cats, and is more often found in male cats compared to females. It is the older male cat that is free to roam outdoors that is most likely to be infected with FIV.

Diagnosis

Laboratory Tests

• ELISA for serum antibody
  • False positives occur, particularly in the presence of maternal Ab
• Positives can be confirmed by lab work (Western blotting)

Pathology

On post-mortem examination, lymphadenopathy is seen. Intestinal lesions similar to those seen in feline panleukopenia virus infection may be apparent^fmc.

In early disease, lymphadenopathy is seen histologically to be due to follicular hyperplasia and infiltration of plasmacytes to surround the cortex. Later in disese, a mixutre of follicular hyperplasia and follicular depletion may exist, and in the terminal stages of FIV infection, follicular involution is the key feature^fmc. Lymphoplasmacytic infiltrates are seen in the gingiva, lymphoid tissues, spleen, kidney, liver and brain. Brain lesions also include perivascular cuffing, gliosis, neuronal loss, vacuolation of the white matter and, occasionally, the presence of giant cells.

Prognosis

The long-term prognosis for FIV-infected cats is guarded, but some cats will survive for many years following diagnosis. Around 20% of affected cats die within the first two years after diagnosis; this equates to a 20% mortality rate in the first 4.5-6 years after the estimated time of infection^fmc. In generally, the more chronic and severe the clinical signs, the worse the prognosis is.

Control

• No UK vaccine
• Healthy positive cats should have diagnose confirmed by further testing
• Isolate and castrate
• Preventative neutering of males

Links

• Feline Advisory Bureau FIV Factsheet

References

1. Tilley, L P and Smith, F W K (2004) The 5-minute Veterinary Consult (Fourth Edition),Blackwell.
2. Caney, S (2000) Feline immnunodeficiency virus: an update. In Practice, 22(5), 255-260.
3. Johnson, C M (2005) Transmission of Feline Immunodeficiency Virus. Proceedings of the 56th Annual Meeting of the American College of Veterinary Pathologists and 40th Annual Meeting of the American Society for Veterinary Clinical Pathology.
4. Merck & Co (2008) The Merck Veterinary Manual (Eight Edition), Merial.
5. Morrision, W B (2002) Cancer in dogs and cats: medical and surgical management, Teton NewMedia.
6. Rand, J (2006) Problem-based feline medicine, Elsevier Health Sciences.