Persistent infection with feline immunodeficiency virus (FIV) is fairly common, particularly among free-ranging cats. The virus can cause very serious disease resulting from a state of immunodeficiency that is produced over a period of time. Although many cats survive in good health with the infection, they can transmit the virus to other cats.
The disease conditions associated with FIV infection are relatively non-specific. During the primary phase of infection (first two to four months) some cats may show short-term signs of illness involving malaise, pyrexia and possibly generalised lymph node enlargement. Most cats recover from this early phase and enter a second phase when they appear to be healthy.
Eventually in the third phase of infection, other signs of disease may develop. Signs can arise as a direct effect of the virus. Thus, infection of nervous tissues can lead to neurological or behavioural signs, and infection of the intestinal tract may be associated with some cases of chronic diarrhoea. However, in most cases clinical disease results from secondary problems associated with the immunodeficiency that the virus may ultimately cause. These conditions can take many forms and therefore the clinical signs are quite variable. However, the combination of multiple persistent or recurrent signs of disease may point to immunodeficiency. Common signs include malaise, weight loss, inappetence, pyrexia, lymphadenopathy and gingivitis. There may be a predisposition to other chronic problems such as rhinitis, conjunctivitis, chronic abscessation or cellulitis and skin problems. Cats with immunosuppression associated with FIV have a higher risk of developing neoplasia, particularly lymphoma, and are more vulnerable to other infectious agents that may be unusual, or of little/less consequence in otherwise healthy cats.
Biting is considered to be the most important method of transmission for FIV. Infection appears also to occur by close social contact of cats living in groups where there is no overt aggression, but this method is thought to be a less efficient method of spread. It is suspected that, as for FeLV, ingestion of saliva plays an important role in this situation. A small proportion of kittens (possibly around one in five) born to FIV-infected queens may be found to be infected.
The overall prevalence of FIV in the healthy UK cat population is three to six per cent. Surveys of sick cats presented to veterinary practices have shown a higher prevalence of 12 to 18 per cent.
The prevalence varies in different areas and between different groups of cats such as feral and farm cats, but where the virus is present the prevalence may be high. Infection is rare in pedigree breeding colonies. Important risk factors are recognised for FIV that are related to the most common method of transmission, which is biting. Entire male cats carry a higher risk of infection and a free-living life style increases the prevalence. Cats can be infected at any age so that the prevalence of infection increases with age. There is often a considerable delay between infection and development of clinical signs. Consequently, the appearance of disease is more common in middle aged or older cats. In contrast to FeLV, many FIV-infected cats remain healthy throughout their lives.
There are several test systems available for FIV including inpractice test kits. In-practice tests detect anti-virus antibody, usually directed against a viral core protein (p24), the transmembrane envelope protein (gp40) or a combination of both. The most common test systems are based on enzyme-linked immunosorbent assays (ELISA) or immunochromatography (IC). Combination tests that enable simultaneous testing for FIV and FeLV are widely used.
The more specialised tests include immunofluorescence and western blotting for the detection of antibodies to FIV, and virus isolation and polymerase chain reaction (PCR) for the detection of the virus itself. These tests can be considered as confirmatory tests although several laboratories use immunofluorescence as their first-line test, as it is very sensitive and detects antibody to all of the viral proteins. Western blotting is a second sensitive test, which allows the detection of antibodies to individual viral proteins. Virus isolation is sensitive but is limited by practical considerations (expense, facilities and time) and is not suitable for routine use.
PCR tests, which detect the FIV nucleic acids (genetic material) are now more readily available and are very sensitive. As discussed below, PCR is very useful in the diagnosis of infection in young kittens which may have maternally-derived antibodies. Similar issues of accuracy and the potential for errors apply to the in-practice test kits for anti-FIV antibody as for FeLV antigen. Providing the test has been performed correctly with an appropriate sample, and the specificity of the test is very high, positive results are generally reliable. However, it is strongly recommended that a positive result on an in-practice test should be confirmed by another type of test, such as immunofluorescence or western blotting, particularly in the case of a healthy cat. The in-practice test kits require blood samples and are best performed with serum or plasma, rather than whole blood. As with all test kits, there is a possibility for false positive and false negative results. In cats with a high suspicion of infection but which are negative on in-practice test kits, use of another test system to confirm the negative result is also highly recommended.
The prognosis for FIV-infected cats is more unpredictable but generally better than for FeLV-infected cats. The outlook for cats that show severe, chronic, multiple signs of disease is poor. If clinical signs have developed only recently and are not severe, there is a reasonable prospect of improvement with treatment, which may be maintained for some time. Treatment usually consists of supportive therapy, often antibiotics, possibly coupled with antiviral therapy. A proportion of FIV-positive cats that have shown no clinical signs related to infection may remain healthy for extended periods, if not indefinitely.
A vaccine for FIV has been licensed in the USA , but its efficacy in the field is unknown at this point. The vaccine is not available in the UK . A problem is that the vaccine induces anti-FIV antibodies so that vaccinated cats cannot readily be distinguished from infected cats by the most commonly used diagnostic methods. Healthy FIV-infected cats should continue to be vaccinated against other infectious diseases.
1. The pet cat
Single indoor/outdoor cats
Single cats should be tested for FIV if they are sick and showing signs compatible with infection. The cat infected with FIV poses a risk to other cats and in order to prevent it transmitting the virus it would need to be kept in isolation from others. Additionally, isolating healthy FIV-infected cats indoors can be of benefit in protecting against exposure to other feline infectious agents which might provoke more serious disease in immunodeficient cats than in normal cats. On welfare grounds isolation may not be applicable to some cats that will not tolerate being kept indoors permanently. Therefore, owners must weigh up the risks (to their own and other cats) with the welfare implications. It may be possible to fence in the garden or provide a run where cats can go out and present no risk to themselves or others.
Single cats confined indoors
Single cats confined indoors are at no risk of exposure to FIV. However, since there can be a long delay between infection and development of disease, there is a possibility that a cat has acquired an infection as a young kitten, despite having spent its whole life since then isolated from other cats.
2. Multicat households
The same considerations about possible risk to neighbouring cats apply to infected cats from multicat households as from single cat households. The issue of possible spread of infection within a household of cats must also be addressed since FIV appears to spread even among cats that show no overt aggression to each other.
In a household in which a cat with FIV infection has been identified, testing is indicated to determine the status of the individual cats. Test results can allow segregation of infected and uninfected cats if this is practical within the households. A good general health care programme should be maintained which may help both to reduce transfer of infection and progression of disease.
Testing of cats before introducing new individuals into a multicat household should be done to prevent inadvertent spread to incoming cats, or to cats already established in the household.
3. The rescue situation
What should be the test protocol for cats coming into the rescue facility?
In an ideal world, all cats would be tested for FIV. However the costs for this would be very high. The prevalence of FIV infection in the general cat population is about three to six per cent. However, this increases with age and within certain ‘at risk' groups of cats. All ‘at risk' cats should be tested for FIV. These include entire males, sick cats, those with visual evidence of fighting, and feral cats. Fractious cats may be tested and neutered at the same time to allow for blood sampling under anaesthetic.
What are the responsibilities/legal considerations for the rescue facility?
Rescue facilities have a duty of care and should undertake what is reasonable in the circumstances. As outlined above, it may not be financially possible to test every cat or kitten, but whether they have been tested or not should be explained to the new owner, along with any results if tests have been undertaken. No cat that has tested positive for FIV should be rehomed without the new owner being fully informed of the risks.
What is the suggested protocol for kittens?
There are complications in identifying FIV infection in young kittens based on antibody testing because kittens from FIVinfected dams may have obtained anti-FIV antibodies but may not be infected themselves. There is also a chance of kittens born to infected queens becoming actively infected from their mother. If screening is to be performed by antibody testing, this should be delayed until 20 weeks of age, by which time maternally-derived antibodies may no longer be present. If it is infected, by then the kitten should have antibodies of its own (ie, a positive result will indicate true infection). It is suggested that kittens less than 20 weeks old which test FIV-positive should remain at the rescue facility and be re-tested after 20 weeks of age. An alternative is to test for the presence of virus using PCR or virus isolation. This can be done at any age.
What about positive cats?
An FIV-positive cat which is very unwell with signs indicative of severe immunodeficiency should be euthanased. If an FIV-positive cat shows minor clinical signs, it should receive appropriate treatment, and may recover clinically. Any adult cat that tests positive for FIV and appears otherwise healthy may have a good life expectancy and should be considered for rehoming. However, in view of the risks to other cats, this must be to a home where there are no other cats and where the new owners can guarantee that the cat will not go outside. It may be that such requirements cannot be fulfilled. In these circumstances the cat should be euthanased.
4. Feral cats
Feral kittens young enough to be rehomed can be considered as rescue kittens above. All feral cats should be tested and positive cats euthanased rather than returned to the colony.
5. Breeding/show cats
Risk of spread at cat shows is minimal. Positive cats should not be bred from, and new owners and other breeders should enquire about the FIV status of the cats. Most breeders test for FIV on a regular basis and most breeding cats are kept indoors or in runs where FIV cannot be contracted from outside cats.
Review of FIV biology and associated diseases
Pedersen NC , Yamamoto JK, Ishida T, Hansen H (1989) Feline immunodeficiency virus infection. Veterinary Immunology and Immunopathology 21, 111-129
Sellon RK, Hartmann K (2006) Feline Immunodeficiency Virus Infection In Infectious Diseases of the Dog and Cat. Third Edition, pp131-143. Ed. CE Greene. Pub Saunders Elsevier
Sparkes AH, Hopper CD, Millard WG, Gruffydd-Jones TJ, Harbour DA (1993) Feline immunodeficiency virus infection. Clinicopathologic findings in 90 naturally occurring cases. Journal of Veterinary Internal Medicine 7, 85-90
Hosie MJ, Robertson C, Jarrett O (1989) Prevalence of feline leukaemia virus and antibodies to feline immunodeficiency virus in cats in the United Kingdom. Veterinary Record 125, 293-297
Muirden A. (2002) Prevalence of feline leukaemia virus and antibodies to feline immunodeficiency virus and feline coronavirus in stray cats sent to an RSPCA hospital. Veterinary Record 150, 621-625
Barr MC (1996) FIV, FeLV, and FIPV: interpretation and misinterpretation of serological test results. Seminars in Veterinary Medicine and Surgery (Small Animal) 11, 144-153.
Bienzle D, Reggeti F, Wen X, Little S, Hobson J, Kruth S. (2004) The variability of serological and molecular diagnosis of feline immunodeficiency virus infection. Canadian Veterinary Journal 45, 753-757.
Reid RW, Barr MC, Scott FW. (1992) Retrospective serologic survey for the presence of feline immunodeficiency virus antibody: a comparison of ELISA and IFA techniques. Cornell Veterinarian 82, 359-369
Richards JR. (2005) Feline immunodeficiency virus vaccine: implications for diagnostic testing and disease management. Biologicals 33, 215-217
Addie DD, Dennis JM, Toth S, Callanan JJ, Reid S, Jarrett O (2000) Long-term impact on a closed household of pet cats of natural infection with feline coronavirus, feline leukaemia virus and feline immunodeficiency virus. Veterinary Record 146, 419-424
Goto Y, Nishimura Y, Baba K, Mizuno T, Endo Y, Masuda K, Ohno K, Tsujimoto H (2002) Association of plasma viral RNA load with prognosis in cats naturally infected with feline immunodeficiency virus. Journal of Virology 76, 1079-1083.
Andersen PR, Tyrrell P (2004) Feline immunodeficiency virus diagnosis after vaccination. Animal Health Research Reviews 5, 327-330
Huang C, Conlee D, Loop J, Champ D, Gill M, Chu HJ (2004) Efficacy and safety of a feline immunodeficiency virus vaccine. Animal Health Research Reviews 5, 295-300
Kahler SC; American Association of Feline Practitioners. (2002) Deluge of questions prompts AAFP to develop FIV vaccine brief. American Association of Feline Practitioners Journal of the American Veterinary Medical Association 221, 1231-1234.
Levy JK, Crawford PC, Slater MR. (2004) Effect of vaccination against feline immunodeficiency virus on results of serologic testing in cats. Journal of the American Veterinary Medical Association 225, 1558-1561
Matteucci D, Poli A, Mazzetti P, Sozzi S, Bonci F, Isola P, Zaccaro L, Giannecchini S, Calandrella M, Pistello M, Specter S, Bendinelli M. (2000) Immunogenicity of an anti-clade B feline immunodeficiency fixed-cell irus vaccine in field cats. Journal of Virology 74, 10911-10919
Updated May 2006