- Feline Immunodeficiency
- What’s new?
- Passive immunity
- Active immune response
- Clinical signs
- Virus isolation
- Polymerase chain reaction (PCR)
- Disease management
- Prognosis for FIV-infected cats
- General management
- Vaccination of FIV-infected cats
- Supportive Treatment
- Antiviral therapy
- Immune modulators
- Control in specific situations
- Multi-cat households
- Breeding catteries
Edit October 15, 2015
The feline immunodeficiency guidelines that this article is updating were published in J Feline Med Surg 2009; 11: 575-584 and updated in J Feline Med Surg 2013; 15: 535; this update has been compiled by Margaret J Hosie.
It is generally accepted that FIV infection can induce clinical signs of immunodeficiency, leading to opportunistic infections or lymphomas, and clinical signs consistent with immunodeficiency in natural infection have been documented.1 However, in some cats the clinical signs are mild, which likely reflects heterogeneity amongst both circulating field isolates as well as host factors, and it has been reported that many FIV-infected cats have a normal life expectancy.2,3,4 Therefore surrogate markers are required to provide an objective assessment of FIV progression in individual cats. Recently it was shown that viruses dominating in early infection display a distinct receptor usage phenotype and that the emergence of viruses with an altered receptor usage phenotype coincides with the onset of immunodeficiency.5 Accordingly, viral phenotyping might assist in the clinical staging of individual cats diagnosed with FIV infection.
FIV infection was found to be prevalent in a survey of four large-scale hoarding situations; this high prevalence was probably related to the cats living in close confinement, under stressful conditions in which cats exhibited aggressive behavior.6 Therefore, it is recommended that cats should be tested for FIV infection at the time of seizure during hoarding investigations, as the results will influence housing decisions, medical care and adoption options.
FIV infection is also common in rescue shelters and it is recommended that all cats in rescue centres should be spayed or neutered and kept indoors, in order to reduce the risk of territorial aggression, which can result in penetrating bite wounds and consequently FIV transmission. This recommendation is supported by studies linking cat bite wounds and abscesses with FIV infection.7,8 A recent survey of cats in a rescue shelter in which FIV-infected cats were housed together with uninfected cats found no evidence of FIV transmission, in spite of the cats having unrestricted access and sharing food and water bowls, litter trays and bedding for several years.9 However, it is possibly significant that the cats had been spayed/neutered before entering this shelter and the median age of the uninfected cats was 4 months; kittens are a low risk group for FIV infection10 because territorial aggression has not yet developed. Similarly, neutered cats are less likely to display territorial aggression than intact cats and therefore FIV transmission might be more likely to occur in rescue centres housing older cats, especially if those cats exhibit aggressive behaviour.
Detailed information on the prevention and management of feline immunodeficiency virus infection was published in the ABCD guidelines.11
1 Barrs VR, Martin P, Nicoll RG, Beatty JA and Malik R. Pulmonary cryptococcosis and Capillaria aerophila infection in an FIV-positive cat. Australian Veterinary Journal 2000; 78: 154–158.
2 Addie DD, Dennis JM, Toth S, Callanan JJ, Reid S and Jarrett O. Long-term impact on a closed household of pet cats of natural infection with feline coronavirus, feline leukaemia virus and feline immunodeficiency virus. Vet Rec 2000; 146(159. 419-424.
3 Ravi M, Wobeser GA, Taylor SM and Jackson ML. Naturally acquired feline immunodeficiency virus (FIV) infection in cats from western Canada: Prevalence, disease associations, and survival analysis. Canad Vet Journal 2010; 51: 271–276.
4 Liem BP, Dhand NK, Pepper AE, Barrs VR and Beatty JA. Clinical findings and survival in cats naturally infected with feline immunodeficiency virus. J Vet Intern Med 2013; 27: 798–805.
5 Bęczkowski PM, Techakriengkrai N, Logan N, McMonagle E, Litster A, Willett BJ, et al., Emergence of CD134 cysteine-rich domain 2 (CRD2)-independent strains of feline immunodeficiency virus (FIV) is associated with disease progression in naturally infected cats. Retrovirology 2014; 11: 95.
6 Polak KC, Levy JC, Crawford PC, Leutenegger CM and Moreillo KA. Infectious diseases in large-scale cat hoarding investigations. Vet J 2014; 201: 189–195.
7 Goldkamp CE, Levy JK, Edinboro CH and Lachtara JL. Seroprevalences of feline leukemia virus and feline immunodeficiency virus in cats with abscesses or bite wounds and rate of veterinarian compliancewith current guidelines for retrovirus testing. J Amer Vet Med Assoc 2008; 232: 1152–1158.
8 Chang-Fung-Martel J, Gummow B, Burgess G, Fenton E and Squires R. A door-to-door prevalence study of feline immunodeficiency virus in an Australian suburb. J Feline Med Surg 2013; 15: 1070-1078.
9 Litster AL. Transmission of feline immunodeﬁciency virus (FIV) among cohabiting cats in two cat rescue shelters. Vet J 2014; 201: 184-188.
10 Levy JK, Scott HM, Lachtara JL and Crawford PC. Seroprevalence of feline leukemia virus and feline immunodeficiency virus infection among cats in North America and risk factors for seropositivity. J Amer Vet Med Assoc 2006; 228: 371–376.
11 Hosie MJ, Addie D, Bélak S, Boucraut-Baralon C, Egberink H, Frymus T, et al., Feline immunodeficiency. ABCD guidelines on prevention and management. J Feline Med Surg 2009; 11: 575-584.
Feline immunodeficiency virus (FIV) is a retrovirus of the genus Lentivirus that is closely related to HIV; however, humans are not susceptible to the cat virus, which occurs in 5 subtypes (clades) worldwide. Seroprevalence is highly variable geographically, with estimates of 1 to 14% in cats with no clinical signs and up to 44% in sick cats. Sick adult cats, male cats and entire cats are most likely to be infected, mostly through the inoculation of saliva during fighting. Most clinical signs are not caused by the virus, rather by secondary infections, a consequence of immunodeficiency and/or immune stimulation, which most frequently appears in the form of chronic gingivostomatitis, chronic rhinitis, lymphadenopathy, immune-mediated glomerulonephritis and weight loss. Routinely, FIV infection is diagnosed by detecting antibodies using ELISA and immunochromatography methods. Western blot is used to confirm questionable results.
Healthy seropositive cats should never be euthanized – they may live as long as uninfected ones. ABCD does not recommend the use of the vaccine available outside Europe, given the problems associated with serological diagnosis of infections and lack of evidence of efficacy against European isolates.
Since FIV was first isolated in 1986 (Pedersen 1987), serological studies have demonstrated that FIV is endemic in domestic cat populations worldwide; the seroprevalence of FIV is highly variable between regions, with estimates of 1 to 14% in cats with no clinical signs and up to 44% in sick cats (Hartmann 1998).
Sick adult cats, male cats and entire cats are most likely to be infected (Hosie et al., 1989). The major route of natural transmission is believed to be via the inoculation of saliva during fighting (Yamamoto et al., 1989). Vertical transmission and transmission between cats in stable households is relatively uncommon.
Most natural FIV infections are acquired by biting, presumably through the inoculation of virus, or virus-infected cells, from the saliva of persistently infected cats. Transmission from mother to kittens may occur but only a proportion of the offspring become persistently infected. The proportion of kittens infected depends on the viral load of the queen during pregnancy and birth. E.g. if the queen is acutely infected up to 70% of the kittens may be infected, but if the queen is clinically normal but chronically infected hardly any kittens will be infected (O’Neil et al., 1995a, 1995b, 1996).
Although neither oronasal nor venereal spread has been documented in nature, cats can be infected by experimental inoculation of virus into the nose, mouth, vagina and rectum (Moench et al., 1993) and virus can be recovered from semen following natural or experimental infection (Jordan et al., 1998). Queens however may still be infected at mating if bitten by an infected tomcat.
The major targets for FIV infection are activated CD4+ T-lymphocytes. These cells typically function as T-helper cells which have a central role in immune function, facilitating the development of humoral and cell-mediated immunity. The FIV envelope glycoprotein gp120 binds to a primary receptor on the cell surface, CD134 (Shimojima 2004, Willet 2006). A conformational change occurs in gp120 that enables a second interaction with the co-receptor, CXCR4, triggering membrane fusion and viral entry. The viral enzyme reverse transcriptase that mediates copying of its RNA genome into a DNA copy (or provirus) is error prone and lacks a proofreading function; thus FIV may mutate rapidly and exist as multiple strains. This genetic diversity results in variants that may evade immune detection and is an important consideration in the development of both molecular diagnostic techniques and vaccines.
Latent infection arises when a cell carries an integrated copy of provirus but does not produce new virus particles unless it becomes activated. Latently infected cells represent a “reservoir” of infection that is not susceptible to neutralising antibodies, posing an obstacle for effective vaccination.
In the first few days following experimental inoculation, FIV grows in dendritic cells, macrophages and CD4+ T lymphocytes, and may be detected in the plasma within two weeks. The level of virus in the plasma and proviral DNA in the blood mononuclear cells increases, reaching a peak 8 to 12 weeks post infection. During this period mild to moderate clinical signs such as anorexia, depression, and pyrexia may be observed. These conditions generally subside rapidly; in contrast signs such as generalised lymphadenopathy, due to increased numbers and size of active germinal centres in the lymph nodes, may persist for weeks or months. The decrease in plasma viral load marks the beginning of the so-called ‘asymptomatic’ phase that can last for many years, or may be lifelong. It is assumed that viral replication is controlled by the immune response during this phase while the infected cat remains relatively free of clinical signs.
The final outcome of FIV infection is variable. During the asymptomatic phase the plasma virus load is stable but there is a progressive decline in CD4+ T lymphocyte numbers which results in a decreased CD4:CD8 T lymphocyte ratio (Torten et al., 1991). In a proportion of infected cats this leads to a functional immunodeficiency, clinical signs of AIDS and death.
Active immune response
Most clinical signs that FIV-infected cats present with are not directly caused by the FIV itself, so it is vital to check for the underlying cause of the presenting clinical signs. In many cases, the clinical signs will be caused by a secondary infection that should be identified and treated (see below). FIV itself is responsible for immunodeficiency (making the cat more susceptible to secondary infections and neoplasia) or immune stimulation (resulting in immune-mediated disease). In rare cases, the virus can cause neurological disease.
In the first weeks to months post FIV infection, transient clinical signs lasting a few days to a few weeks may be seen during the primary phase of FIV infection. These may include mild pyrexia, lethargy and peripheral lymphadenopathy (del Fierro et al., 1995). Haematology may show a neutropenia (Pedersen et al., 1989).
Infected cats then generally remain free of clinical signs for an extended period of time before problems associated with immunodeficiency develop (Ishida et al., 1992). This asymptomatic period will generally last for years in most cases (Addie et al., 2000), but some cats will never develop FIV-related clinical signs in their lives. Clinical disease is therefore not seen until later in life – generally 4-6 years of age or older.
Immunodeficiency and/or immunostimulation most frequently appears in the form of chronic gingivostomatitis, chronic rhinitis, lymphadenopathy, immune-mediated glomerulonephritis and weight loss.
Many concurrent viral (Brown et al., 1989), bacterial (Hughes et al., 1999), fungal (Schubach et al., 2003 ) and protozoal (Pennisi, 2002) infections have been reported in FIV-infected cats. Unusual clinical presentations, such as unusual or severe parasitic skin disease (e.g. demodecosis, pediculosis), or tumours should also alert the clinical to the possibility of FIV infection. B cell lymphosarcomas (Callanan et al., 1996), myeloproliferative disease and squamous cell carcinoma (Hutson et al., 1991) have been reported in association with FIV infection.
Because it impairs cats’ life quality, feline chronic gingivostomatitis is one the most common presenting signs of FIV-infected cats (Tenorio et al., 1991).
As confirmed by experimental infections with neurovirulent strains, CNS involvement (Ryan et al., 2005) and peripheral neuropathy (Kennedy et al., 2004) are early subclinical events, often associated only with altered forebrain or peripheral nerve electrical activity. Behavioural changes, seizures, disrupted sleep patterns, impaired learning and paresis have also been reported (Phillips et al., 1996).
Reproductive failure is described in infected cats and associated with PCR-positive placental and foetal tissues (Weaver et al., 2005). Renal involvement due to glomerular and tubulo-interstitial lesions associated with severe proteinuria is a frequent occurrence in FIV-infected cats (Poli et al., 1993). A direct role of FIV in the induction of the renal damage is possible (Poli et al., 1995a) together with that of renal immune deposits (Poli et al., 1995b). Polyclonal B cell activation actually sustains hyperglobulinaemia and a high level of circulating immune complexes (Matsumoto et al., 1997) and autoantibodies (Pennisi et al., 1994, Masucci et al., 2006).
Polymerase chain reaction (PCR)
Prognosis for FIV-infected cats
Vaccination of FIV-infected cats
Control in specific situations
FIV is an important consideration in rescue shelters. A high prevalence of infection is found in this population of cats, particularly those with a feral background and if male and entire. The prevalence of infection may not be significantly higher in pre-owned cats that have recently been relinquished compared to the local household pet cat population, but may be higher if it is a stray cat.
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