Comparison of six in-house tests for the rapid diagnosis of feline immunodeficiency and feline leukaemia virus infections

Six rapid tests for the diagnosis of feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV) infections which have recently been introduced in Europe for use in small animal practice were compared. Eight hundred serum samples were tested and those reacting FIV-positive in at least one of the tests were confirmed by Western blot, and those reacting FeLV-positive were confirmed by virus isolation. The specificity and sensitivity of each test and the quality of the results produced were compared.     

Evaluation of a new in‐clinic test system to detect feline immunodeficiency virus and feline leukemia virus infection

Background: Many in‐house tests for the diagnosis of feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) infection are licensed for use in veterinary practice. A new test with unknown performance has recently appeared on the market. Objectives: The aims of this study were to define the efficacy of a new in‐clinic test system, the Anigen Rapid FIV Ab/FeLV Ag Test, and to compare it with the current leading in‐clinic test, the SNAP Kombi Plus FeLV Antigen/FIB Antibody Test. Methods: Three‐hundred serum samples from randomly selected healthy and diseased cats presented to the Clinic of Small Animal Medicine at Ludwig Maximilian University were tested using both the Anigen Rapid Test and the SNAP Kombi Plus Test. Diagnostic sensitivity, specificity, and positive and negative predictive values were calculated for both tests using Western blot as the gold standard for verification of FIV infection and PCR as the gold standard for FeLV infection. Results: The presence of antibodies against FIV was confirmed by Western blot in 9/300 samples (prevalence 3%). FeLV DNA was detected by PCR in 15/300 samples (prevalence 5%). For FIV infection the Anigen Rapid Test had a sensitivity of 88.9%, specificity of 99.7%, positive predictive value of 88.9%, and negative predictive value of 99.7%. For FeLV infection, the Anigen Rapid Test had a sensitivity of 40.0%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 96.9%. Diagnostic accuracy was similar to that of the SNAP Kombi Plus Test. Conclusion: The new Anigen Rapid FIV Ab/FeLV Ag Test performed very well and can be recommended for use in veterinary practice.     

Epizootiologic association between feline immunodeficiency virus infection and feline leukemia virus seropositivity

Five hundred twenty-one feline serum samples submitted to the Texas Veterinary Medical Diagnostic Laboratory between Nov 1, 1988, and Jan 31, 1989 were tested for antibody to feline immunodeficiency virus (FIV) by use of an ELISA. The prevalence of FIV infection in this population was 11.3% (95% confidence interval: 8.6 to 14.0%). Serologic test results for FeLV were available for 156 of the 521 cats. A significant (P = 0.008) association between FIV infection and FeLV seropositivity was observed; FeLV-positive cats were nearly 4 times more likely to be seropositive for FIV than were FeLV-negative cats. The association remained statistically significant (P = 0.021) after adjusting for age and gender, using multiple-logistic regression analysis.     

Enzyme-linked immunosorbent assay methods for detection of feline leukemia virus and feline immunodeficiency virus.

Enzyme-linked immunosorbent assays have been widely used for diagnosis of FeLV and feline immunodeficiency virus (FIV) infections. Various ELISA kits for FeLV are available from several manufacturers. Although these tests are configured in a variety of formats, they are all direct antigen-detection systems for the viral core protein p27. On the other hand, ELISA for FIV exposure detects specific feline antibody to FIV. Basic immunoassay principles and the application of ELISA technology used in FeLV and FIV ELISA kits are described.     

Tumor necrosis factor alpha levels in cats experimentally infected with feline immunodeficiency virus: effects of immunization and feline leukemia virus infection.

Tumor necrosis factor alpha (TNF alpha) levels were determined by enzyme-linked immunosorbent assay (ELISA) and by cell culture bioassay in supernatants of lipopolysaccharide-stimulated feline monocyte cultures and in cat serum samples. There was a good correlation between the results obtained by the two methods. From the fact that TNF alpha was neutralized quantitatively by antibodies to human TNF alpha in feline monocyte supernatants and in feline sera, it was concluded that feline TNF alpha immunologically cross-reacts with human TNF alpha and that the human TNF alpha ELISA can be used to quantitate feline TNF alpha. During the first 6 months after experimental feline immunodeficiency virus (FIV) infection no differences in serum TNF alpha values were observed between infected and non-infected cats. TNF alpha levels increased significantly after primary vaccination with a feline leukemia virus (FeLV) vaccine in FIV infected cats over those in the non-infected controls. During secondary immune response TNF alpha levels rose transiently for a period of a few days in both the FIV positive and the FIV negative cats. After FeLV challenge, TNF alpha levels increased in all animals challenged with virulent FeLV for a period of 3 weeks. This period corresponded to the time necessary to develop persistent FeLV viremia in the control cats. It was concluded from these experiments that in the asymptomatic phase of FIV infection no increased levels of TNF alpha are present, similar to the situation in asymptomatic HIV infected humans. Activation of monocytes/macrophages in FIV infected cats by stimuli such as vaccination or FeLV challenge readily leads to increased levels of TNF alpha.     

Altered plasma concentrations of sex hormones in cats infected by feline immunodeficiency virus or feline leukemia virus

Gender differences may affect human immunodeficiency virus (HIV) infection in humans and may be related to fluctuations in sex hormone concentration. The different percentage of male and female cats observed to be infected by feline leukemia virus (FeLV) or feline immunodeficiency virus (FIV) has been traditionally explained through the transmission mechanisms of both viruses. However, sexual hormones may also play a role in this different distribution. To study this possibility, 17β-estradiol, progesterone, testosterone, and dehydroepiandrosterone (DHEA) concentrations were analyzed using a competitive enzyme immunoassay in the plasma of 258 cats naturally infected by FIV (FIV(+)), FeLV (FeLV(+)), or FeLV and FIV (F(-)F(+)) or negative for both viruses, including both sick and clinically healthy animals. Results indicated that the concentrations of 17β-estradiol and testosterone were significantly higher in animals infected with FIV or FeLV (P < 0.05) than in negative cats. Plasma concentrations of DHEA in cats infected by either retrovirus were lower than in negative animals (P < 0.05), and F(-)F(+) cats had significantly lower plasma values than monoinfected cats (P < 0.05). No significant differences were detected in the plasma concentration of progesterone of the four groups. No relevant differences were detected in the hormone concentrations between animal genders, except that FIV(+) females had higher DHEA concentrations than the corresponding males (P < 0.05). In addition, no differences were observed in the hormone concentrations between retrovirus-infected and noninfected animals with and without clinical signs. These results suggest that FIV and FeLV infections are associated with an important deregulation of steroids, possibly from early in the infection process, which might have decisive consequences for disease progression.     

Serological survey of Toxoplasma gondii,feline immunodeficiency virus and feline leukaemia virus in urban stray cats in Belgium

Three hundred and forty-six serum samples taken between 1998 and 2000 from urban stray cats in the city of Ghent were tested for antibodies to Toxoplasma gondii and feline immunodeficiency virus (FIV), and antigens of feline leukemia virus (FeLV). Of these 346 samples, 243 (70.2 per cent) were seropositive for Tgondii. Thirty-nine cats (11.3 per cent) had antibodies against FIV and 13 (3.8 per cent) had circulating antigens of FeLV. Fewer of the female cats had FIV and heavier cats had a higher seroprevalence of FIV. Exact logistic regression showed that cats that were infected with FIV were more likely to be infected with T gondii (P = 0.04), and the cats with FIV had a higher titre of Tgondii antibodies than FIV-negative animals. However, FeLV was not associated with either T gondii or FIV.     

Prevalence of feline immunodeficiency virus and other retroviral infections in sick cats in Italy.

Two hundred and seventy-seven sick pet cats living in Italy were tested for antibodies to feline immunodeficiency virus (FIV) and for feline leukemia virus (FeLV) antigen. Overall, 24% of the cats resulted positive for anti-FIV antibody and 18% for FeLV antigen. FIV was isolated from the peripheral mononuclear blood cells of ten out of 15 seropositive cats examined and from one out of eight saliva samples. No FIV isolations were obtained from six serum samples cultured. Feline syncytium forming virus (FeSFV) could be isolated from blood and/or saliva in ten out of 11 FIV seropositive cats examined, in six out of nine FeLV antigen positive cats, in two cats found positive for both infection markers, and in three out of 11 cats negative for both markers. Thus, the probability of isolating FeSFV was enhanced by infection with other exogenous retroviruses.     

Diagnosis of feline leukemia virus and feline immunodeficiency virus infections

Feline leukemia virus is an oncogenic retrovirus that can result in a wide variety of neoplastic and non-neoplastic diseases, including immunosuppression. Diagnosis of FeLV infection can be achieved by several methods, including virus isolation; IFA assay of a peripheral blood smear; and detection of a viral protein (called p27) by ELISA testing of whole blood, plasma, serum, saliva, or tears. Commercially available ELISA kits have revolutionized FeLV testing and have become very popular as "in-house" procedures. This article discusses the interpretation of ELISA results and compares them with IFA assay findings. Feline immunodeficiency virus is a lentivirus that causes immunosuppression, but not neoplasia, in cats. It originally was called feline T-lymphotropic lentivirus. Differentiating FIV infection from the immunosuppressive type of FeLV infection requires virus isolation or serology. The most rapid method for diagnosis of FIV infection is ELISA testing for antiviral antibody.     

Prevalence of feline leukaemia virus and antibodies to feline immunodeficiency virus in cats in the United Kingdom

A representative sample of the pet cat population of the United Kingdom was surveyed. Blood samples from 1204 sick and 1007 healthy cats of known breed, age and sex were tested for antibodies to feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV). The prevalence of FIV was 19 per cent in sick cats and 6 per cent in healthy cats, and the prevalence of FeLV was 18 per cent in sick cats and 5 per cent in healthy cats; both infections were more common in domestic cats than in pedigree cats. Feline immunodeficiency virus was more prevalent in older cats but FeLV was more prevalent in younger cats. There was no difference between the prevalence of FeLV in male and female cats but male cats were more likely to be infected with FIV than female cats. No interaction was demonstrated between FIV and FeLV infections. Of the cats which were in contact with FIV in households with more than one cat, 21 per cent had seroconverted. The prevalence of FeLV viraemia in cats in contact with FeLV was 14 per cent. The clinical signs associated with FIV were pyrexia, gingivitis/stomatitis and respiratory signs, and with FeLV, pyrexia and anaemia. It was concluded that both viruses were significant causes of disease, and that the cats most likely to be infected with FIV were older, free-roaming male cats and for FeLV, younger, free-roaming cats.     

Use of western blot and radioimmunoprecipitation for diagnosis of feline leukemia and feline immunodeficiency virus infections.

The uses and limitations of the western blot (WB) and radioimmunoprecipitation assay (RIPA) techniques for study of feline immunodeficiency virus (FIV) and FeLV were evaluated. Western blot analysis was used to detect antigenic relatedness between the 2 lentiviruses. Using a rabbit serum directed against p26 of the equine infectious anemia virus (EIAV) and anti-EIAV horse serum obtained from an infected horse, cross-reactivity with p24 of FIV was revealed. Cat sera obtained late after experimentally induced FIV infection recognized p26 of EIAV, which indicates reciprocal cross-reactivity. For RIPA, FIV was metabolically labeled, and virus-coded proteins were identified, using immunoprecipitation. Polypeptides with apparent molecular mass of about 15, 24, 43, 50, 120, and 160 kilodaltons were detected. An additional polypeptide of 10 kilodaltons was found only by use of WB analysis.     

Evaluation of a novel nested PCR for the routine diagnosis of feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV)

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.     

Prevalence of canine distemper virus, feline immunodeficiency virus and feline leukemia virus in captive African lions (Panthera leo) in Japan

Sero-prevalences of canine distemper virus (CDV), feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) were evaluated in 20 captive lions in two Japanese zoos. Anti-CDV antibody was detected in 13 of 20 lions. We could pursue antibody responses against CDV in three lions back to 1996. Sera collected in 1996 were negative for anti-CDV antibody, therefore, all of them showed sero-conversion in 2000. This result suggested that the epidemic of CDV infection in this zoo might have happened between 1996 and 2000. The lions were also examined for FIV and FeLV infections. We had no evidence for FeLV infection but eight lions were sero-positive for anti-FIV antibody.     

Prevalences of feline leukaemia virus and feline immunodeficiency virus infections in cats in Sydney

Objective To determine prevalences of feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV) infections in ‘healthy’ cats that, through acute misadventure or other circumstance, were presented to veterinary practitioners. Prevalences of FeLV and FIV in this population were compared to those in a population of predominantly sick cats. Design and procedures Serum specimens were obtained over a 2-year period from 200 cats oldeer than 1 year of age presented to veterinary clinics for routine procedures, including cat fight injuries or abscesses, vehicular trauma, neutering, dental scaling, vaccination, grooming or boarding. An additional 894 sera were obtained over approximately the same period from specimens submitted by veterinarians to a private clinical pathology laboratory, mainly from sick cats suspected of having immune dysfunction, but including some sera from healthy cats being screened prior to FeLV vaccination. FIV antibody and FeLV antigen were detected in samples using commercial enzyme immunoassays. Results Amongst 200 ‘healthy’ cats, the prevalence of FeLV infection was 0 to 2%, and the prevalence of FIV was 6.5 to 7.5%, depending on the stringency of the criteria used to define positivity. FIV infection was significantly more prevalent in cats which resided in an inner city environment (P = 0.013). Of the 894 serum specimens submitted to the laboratory by practitioners, 11/761 (1.4%) were FeLV positive, while 148/711 (20.8%) were FIV positive. The prevalence of FIV was significantly higher in these predominantly ‘sick’ cats than in cats seen for routine veterinary procedures (P < 0.00001), while there was no difference in the prevalence of FeLV (P = 0.75) Conclusions The prevalence of FeLV and FIV in healthy cats may have been substantially overestimated in some previous Australian surveys. FeLV infection would appear to be a rare cause of disease in Australian cats. The higher prevalence of FIV positivity in sick as opposed to healthy cats infers that FIV infection contributes to the development of disease.     

Vaccination of cats experimentally infected with feline immunodeficiency virus, using a recombinant feline leukemia virus vaccine.

A group of 15 cats experimentally infected with a Swiss isolate of feline immunodeficiency virus (FIV) and a group of 15 FIV-negative control cats were inoculated with an FeLV vaccine containing recombinant FeLV-envelope. High ELISA antibody titer developed after vaccination in FIV-positive and FIV-negative cats. Vaccinated and nonvaccinated controls were later challenge exposed by intraperitoneal administration of virulent FeLV subtype A (Glasgow). Although 12 of 12 nonvaccinated controls became infected with FeLV (10 persistently, 2 transiently), only 1 of 18 vaccinated (9 FIV positive, 9 FIV negative) cats had persistent and 2 of 18 had transient viremia. From these data and other observations, 2 conclusions were drawn: In the early phase of FIV infection, the immune system is not depressed appreciably, and therefore, cats may be successfully immunized; a recombinant FeLV vaccine was efficacious in protecting cats against intraperitoneal challenge exposure with FeLV.     

High rate of feline immunodeficiency virus infection in cats in the Brazilian semiarid region: Occurrence,associated factors and coinfection with Toxoplasma gondii and feline leukemia virus

To evaluate the occurrence of feline immunodeficiency virus (FIV) and factors associated with this and to demonstrate occurrences of coinfection with Toxoplasma gondii and feline leukemia virus (FeLV) in cats, a total of 103 blood samples were collected from owned cats, during home visits. To diagnose FIV and FeLV, immunochromatographic kit was used and serological diagnoses of T. gondii, the indirect immunofluorescence test was performed. The occurrence of FIV-seropositive cats was 23.3% (24/103) and the factor associated with infection was male sex. T. gondii seropositivity of 53.4% (55/103) was observed and 75% of FIV cases (18/24) were positive for T. gondii coinfection. Only 0.9% (1/103) was positive for FeLV. It can be concluded that the seroprevalence of FIV in cats in the Brazilian semiarid region is high and that FIV positive cats were also likely to be T. gondii seropositive, while FeLV had very low occurrence in the study region.     

Long-term impact on a closed household of pet cats of natural infection with feline coronavirus, feline leukaemia virus and feline immunodeficiency virus

A closed household of 26 cats in which feline coronavirus (FCoV), feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV) were endemic was observed for 10 years. Each cat was seropositive for FCoV on at least one occasion and the infection was maintained by reinfection. After 10 years, three of six surviving cats were still seropositive. Only one cat, which was also infected with FIV, developed feline infectious peritonitis (FIP). Rising anti-FCoV antibody titres did not indicate that the cat would develop FIP. The FeLV infection was self-limiting because all seven of the initially viraemic cats died within five years and the remainder were immune. However, FeLV had the greatest impact on mortality. Nine cats were initially FIV-positive and six more cats became infected during the course of the study, without evidence of having been bitten. The FIV infection did not adversely affect the cats' life expectancy.     

Hematologic abnormalities preceding apparent recovery from feline leukemia virus infection

A 5-month-old domestic short-haired cat was referred to the Western College of Veterinary Medicine because of hemorrhage from the mouth. Neutropenia and bone marrow dyscrasia developed within 2 weeks, and results of a fluorescent antibody test for feline leukemia virus (FeLV) were positive. During the next 6 months, the feline oncornavirus cell membrane-associated antibody titer increased, the hematologic abnormalities regressed, and the cat became negative to the FeLV fluorescent antibody test (FeLV test). The results of 3 consecutive FeLV tests were negative, and the cat has been clinically normal for the past 18 months.     

A prospective epidemiological,clinical, and clinicopathologic study of feline leukemia virus and feline immunodeficiency virus infection in 435 cats from Greece

Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) are retroviruses causing significant morbidity and mortality in cats. The aim of this study was to describe the epidemiological, clinical and clinicopathologic aspects of FeLV and FIV infections in different populations of cats in Greece, including client-owned cats, stray cats and cats who live in catteries.A total of 435 cats were prospectively enrolled. Serological detection of FeLV antigen and FIV antibody was performed using a commercial in-house ELISA test kit.The results showed that 17 (3.9 %) and 40 (9.2 %) of the 435 cats were positive for FeLV antigen and FIV antibody, respectively, whereas 5 (1.1 %) had concurrent infection with FeLV and FIV. Factors that were associated with FeLV antigenemia, based on multivariate analysis, included vomiting, rhinitis, infection with FIV, neutropenia, decreased blood urea nitrogen and increased serum cholesterol and triglyceride concentrations. Factors associated with FIV seropositivity included male gender, older age, outdoor access, weight loss, fever, gingivostomatitis, skin lesions and/or pruritus and hyperglobulinemia.Various clinical signs and laboratory abnormalities were found to be significantly associated with retroviral infections, suggesting that current guidelines to test all sick cats should be followed, taking into particular consideration the high-risk groups of cats found in this study.