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.
ABCD Guidelines on Feline Immunodeficiency Virus 7/21 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].