Type-I interferons (IFNs) are cytokines that have non-specific antiviral activity, participating mostly in innate defense mechanisms. Their administration has been proposed to treat several viral and immunomediated diseases as an immunomodulatory therapy. Due to its availability, recombinant human interferon-alpha (rHuIFN-α) has been studied in relation to feline retrovirosis, both in vitro and in vivo. However, IFNs are species-specific and antibodies have been shown to develop in response to the high rHuIFN-α doses necessary for an effective therapy. A recombinant feline IFN has been developed, which has been characterized as interferon-omega (rFeIFN-ω), designed to overcome these problems. Nonetheless, very few studies have been undertaken to evaluate its efficacy in cats naturally infected with FIV or FeLV. In an initial study, we here demonstrated that rFeIFN-ω can dramatically improve the clinical condition of infected cats, and induce improvement of hematologic parameters. Minor changes or no change was observed for hypergammaglobulinemia, CD4/CD8 ratio, proviral load, viremia and RT activity, suggesting that the overall effect of IFN was on innate immunity. More studies are needed in order to better understand its in vivo mechanisms.

Laboratory diagnosis of feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) usually involves both viruses, as the clinical signs are similar and coinfection may occur. Serological methods may not represent an accurate diagnosis: maternal antibodies or cross-reactions may give false positive results to FIV, and false negative results may occur in latent FeLV status, or in certain FIV infection stages. A nested polymerase chain reaction (PCR) technique was designed to detect FeLV, FIV and feline endogenous retrovirus simultaneously. The detection of endogenous sequences was considered indicative of successful DNA extraction. The technique was used to diagnose FIV and FeLV in the blood cells of 179 cats. The kappa value with the serological data was 0.69 for FeLV and 0.87 for FIV. The joint detection of FeLV and FIV by this novel nested PCR is sensitive, specific, fast and convenient, and its applicability for clinical diagnosis is promising, as the direct evidence of the presence of the virus is more realistic than the indirect data provided by the serological detection.

Infections produced by feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV), two of the most prevalent pathogens in cats, range from passing unnoticed to presenting a wide variety of clinical signs. Different epidemiological, clinical, hematological and virological parameters were analyzed in 78 FIV-and/or FeLV-infected cats. FeLV-infected (FeLV + ) cats were considerably younger than FIV-infected (FIV + ) cats, and in general were seen to have a more severe disease than FIV + cats. Around one third of the cats presented anemia, and neutropenia was also frequently observed. Though a higher percentage of FIV + than FeLV + cats had altered leukocyte counts, FeLV + cats had altered counts of both neutrophils and lymphocytes more frequently than FIV + , which usually presented only either altered neutrophils or lymphocyte counts. Virological markers were only detected in FeLV + cats, either as mono-or dual-infection, and correlated with the severity of the disease, but not in FIV + cats. In conclusion, these results suggest that FeLV affects more blood cell types and provokes death of affected animals at a much earlier age than FIV and that the severity of the disease seemed to depend on the viral status of the cat.

(132 words)The efficacy of interferons (IFNs), used empirically to treat retrovirus-infected cats has been shown in vivo, but the direct effect on infected cells is largely unknown.

The electrophoretogram of 89 cats, including those infected by feline immunodeficiency virus (FIV+), feline leukaemia virus (FeLV+) and non-infected, showed statistically significant differences in several of the fractions. FIV+ cats had very high protein values (mean, 8.10 g/dl), mostly because of hypergammaglobulinemia (mean, 2.81 g/dl) as compared with non-infected animals and FeLV+. In addition, in these FIV+ animals, the albumin/globulins ratio (A/G) was very low (mean, 0.72). Statistically significant differences in A/G and alpha2-globulin fraction were observed in FeLV+ group (A/G mean, 0.88 +/- 0.08; alpha2-globulin, mean, 0.84 +/- 0.07 g/dl) when compared with non-infected group (A/G mean, 1.06 +/- 0.08; alpha2-globulin mean, 0.68 +/- 0.04 g/dl). The alpha1-globulin fraction was higher in double infected animals (FIV and FeLV positive, F-F) (3.55 g/dl), than in FeLV+ or FIV+ cats (3.10 and 3.07 g/dl respectively), but no statistical conclusions may be drawn from this fact because of the low number of F-F animals. This technique may help to assess the initial clinical status of retrovirus-infected cats, and the clinical course of these chronic diseases, specifically during and after suitable therapy.