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.     

Prevalence of feline leukemia virus and antibodies to feline immunodeficiency virus in cats in Norway.

Serum samples from 224 Norwegian cats were analyzed for the presence of feline leukemia virus (FeLV) p27 common core antigen, and for antibodies to feline immunodeficiency virus (FIV). Ninety specimens originated from the serum bank at the central referral clinic at the Norwegian College of Veterinary Medicine, which had been collected during the years 1983-1989; 67 sera were submitted from veterinarian practitioners; while 67 sera originated from cats presented for euthanasia. The cats were classified into one "healthy" and one "sick" group. Only 2.2% of sick cats and 1.2% of healthy cats showed FeLV antigenemia, a finding which is lower than which has been reported from many other countries. The prevalence of FIV antibodies was 10.1% in sick cats and 5.9% in healthy cats. Antibodies to FIV was most prevalent in male cats (14.7%) than in female cats (2.1%), and more prevalent among domestic cats (12.0%) compared to pedigree cats (2.4%). Antibodies to FIV in the cats demonstrated increasing prevalence with increasing age. It may be concluded that FeLV causes minor problems in Norwegian cats, while FIV is present in a similar prevalence to what is reported from other countries.     

Prevalence of feline leukemia virus infection and serum antibodies against feline immunodeficiency virus in unowned free-roaming cats

OBJECTIVE: To determine prevalence of FeLV infection and serum antibodies against feline immunodeficiency virus (FIV) in unowned free-roaming cats. DESIGN: Cross-sectional serologic survey. ANIMALS: 733 unowned free-roaming cats in Raleigh, NC, and 1,143 unowned free-roaming cats in Gainesville, Fla. RESULTS: In Raleigh, overall prevalence of FeLV infection was 5.3%, and overall seroprevalence for FIV was 2.3%. In Gainesville, overall prevalence of FeLV infection was 3.7%, and overall seroprevalence for FIV was 4.3%. Overall, FeLV prevalence was 4.3%, and seroprevalence for FIV was 3.5%. Prevalence of FeLV infection was not significantly different between males (4.9%) and females (3.8%), although seroprevalence for FIV was significantly higher in male cats (6.3%) than in female cats (1.5%). CONCLUSIONS AND CLINICAL RELEVANCE: Prevalence of FeLV infection and seroprevalence for FIV in unowned free-roaming cats in Raleigh and Gainesville are similar to prevalence rates reported for owned cats in the United States. Male cats are at increased risk for exposure to FIV, compared with female cats.     

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.     

Accuracy of polymerase chain reaction assays for diagnosis of feline immunodeficiency virus infection in cats

OBJECTIVE: To determine the sensitivity, specificity, and overall diagnostic accuracy of polymerase chain reaction (PCR) assays offered by commercial diagnostic laboratories for diagnosis of FIV infection in cats. DESIGN: Prospective clinical trial. ANIMALS: 124 cats. PROCEDURE: Blood was collected from cats that were neither infected with nor vaccinated against FIV, uninfected cats that were vaccinated with a licensed FIV vaccine, and cats experimentally and naturally infected with FIV representing subtypes A, B, and C. Coded blood samples were submitted to 3 laboratories in the United States and Canada offering PCR assays for diagnosis of FIV infection to veterinary practitioners. All laboratories tested fresh blood samples, and 1 laboratory also tested samples submitted as dried blood smears. The FIV infection status in all cats was confirmed by virus isolation. Sensitivity, specificity, and correct results were calculated for each PCR assay. RESULTS: Sensitivity ranged from 41% to 93%. Specificity ranged from 81% to 100% in unvaccinated cats and 44% to 95% in cats vaccinated against FIV. Correct results were obtained in 58% to 90% of 124 cats tested. All tests misidentified both uninfected and infected cats. False-positive results by all laboratories were higher in cats vaccinated against FIV than in unvaccinated cats, suggesting that vaccination interferes with the performance or interpretation of PCR assays used for diagnosis of FIV infection. CONCLUSIONS AND CLINICAL RELEVANCE: PCR assays used for diagnosis of FIV infection presently marketed to veterinary practitioners in North America vary significantly in diagnostic accuracy and did not resolve the diagnostic dilemma resulting from vaccination of cats against FIV.     

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 and feline coronavirus in stray cats sent to an RSPCA hospital

A total of 517 stray cats at an RSPCA veterinary hospital were tested for feline leukaemia virus (FeLV), feline coronavirus (FCoV) and feline immunodeficiency virus (FIV). The prevalence of FeLV was 3.5 per cent in all the cats, 1.4 per cent in healthy cats and 6.9 per cent in sick cats. FeLV positivity was associated only with disease of non-traumatic origin. Antibodies to FCoV were present in 22.4 per cent of the cats, and their prevalence was significantly higher in cats over two years old and in feral/semiferal cats. The prevalence of antibodies to FIV was 10.4 per cent in all the cats, 4.9 per cent in healthy cats and 16.7 per cent in sick cats. The prevalence of FIV antibodies was significantly higher in entire males and neutered males than in females, in cats over two years old compared with younger cats, and in cats suffering disease of non-traumatic origin rather than in healthy cats or cats suffering only from trauma. Sex, age and health status were each independently highly associated with FIV antibodies.     

Husbandry practices for cats infected with feline leukemia virus or feline immunodeficiency virus.

Cats that are persistently infected with FeLV or feline immunodeficiency virus but are not manifesting clinical signs of disease are at risk for developing a wide variety of immunosuppressive, degenerative, or neoplastic diseases. Infected cats should be isolated to prevent transmission of virus to healthy cats, and to protect infected cats from exposure to pathogens that can cause life-threatening secondary infections. Iatrogenic transmission of virus from infected cats in isolation to healthy cats may be reduced by strict adherence to handling, sanitation, and disinfection procedures. Husbandry practices that may delay the complications of infection include regular vaccination, provision of high-quality diets, reduction of stress, control of endoparasites and ectoparasites, and early and aggressive treatment of clinical signs of disease.     

A serologic survey of Oklahoma cats for antibodies to feline immunodeficiency virus, coronavirus, and Toxoplasma gondii and for antigen to feline leukemia virus

A serologic survey was done on 618 cat sera submitted to the Oklahoma Animal Disease Diagnostic Laboratory between July 1, 1987 and June 30, 1988. The samples were collected from clinically normal and sick cats. The sera were tested for the presence of antibodies to feline immunodeficiency virus by a commercial immunoassay, to a coronavirus by an indirect fluorescent antibody test, and to Toxoplasma gondii by a commercial latex agglutination test and for the presence of feline leukemia virus antigen with one of 3 different commercial assay kits. Ten percent of the sera had antibodies to feline immunodeficiency virus, 35% had antibodies to a coronavirus, and 22% had antibodies to Toxoplasma gondii. Feline leukemia virus antigen was detected in 15% of the sera. Thirty-two percent of the sera had evidence of exposure to 2 or more of the agents.     

Low-dose interferon-alpha treatment for feline immunodeficiency virus infection

Feline immunodeficiency virus sustains an AIDS-like syndrome in cats, which is considered a relevant model for human AIDS. Under precise enrolment requirements, 30 naturally infected cats showing overt disease were included in a trial of low-dose, oral human interferon-alpha treatment. Twenty-four of them received 10 IU/Kg of human interferon-alpha and 6 placebo only on a daily basis under veterinary supervision. The low-dose human interferon-alpha treatment significantly prolonged the survival of virus-infected cats (p<0.01) and brought to a rapid improvement of disease conditions in the infected hosts. Amelioration of clinical conditions was neither correlated with plasma viremia, nor with proviral load in leukocytes. A good survival of CD4+ T cells and a slow increase of CD8+ T cells were also observed in human interferon-alpha-treated cats. Interestingly, the improvement of the total leukocyte counts showed a much stronger correlation with the recovery from serious opportunistic infections. As shown in other models of low-dose interferon-alpha treatment, there was a rapid regression of overt immunopathological conditions in virus-infected cats. This hints at a major role of interferon-alpha in the control circuits of inflammatory cytokines, which was probably the very foundation of the improved clinical score and survival despite the unabated persistence of virus and virus-infected cells.     

Quality of different in-clinic test systems for feline immunodeficiency virus and feline leukaemia virus infection

Many new diagnostic in-house tests for identification of feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV) infection have been licensed for use in veterinary practice, and the question of the relative merits of these kits has prompted comparative studies. This study was designed to define the strengths and weaknesses of seven FIV and eight FeLV tests that are commercially available. In this study, 536 serum samples from randomly selected cats were tested. Those samples 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. In addition, a random selection of samples testing negative in all test systems was re-tested by Western blot (100 samples) and by virus isolation (81 samples). Specificity, sensitivity, positive and negative predictive values of each test and the quality of the results were compared.     

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.     

Association between feline immunodeficiency virus antibodies and host characteristics in Finnish cats.

Toward the end of 1989 the largest private veterinary laboratory in Finland (Vet/lab) began using a commercial combined ELISA test for Feline Immunodeficiency Virus (FIV) antibodies and Feline Leukemia Virus (FeLV) antigens (Cite Combo). The overall proportion of FIV seropositive feline samples was 5% during the 22 month study period. The number of tests performed increased slowly while the positive test results decreased with time (7% in 1990 and 4% in 1991). The decrease in prevalence was assumed to reflect a change in the sample population rather than an actual change in the general cat population. There were more symptomatic and domestic cats tested in 1990 than 1991. The lower-risk groups in the second year of the study may simply be an indication that the cat owners became more aware of FIV and the motivation to send samples switched from the veterinarian's interest to diagnose the disease in a symptomatic cat to the owner's interest to survey their cats for possible FIV infection. In a multivariable analysis, breed, symptoms, age and sex were associated with the risk of FIV seropositivity. The risk increased faster with age in males than in females (i.e., the age effect was not constant between sexes). The cats with symptoms had a higher risk than those without symptoms and non-purebred cats were at a higher risk than purebred cats. FeLV infection was not associated with FIV.     

Clinical aspects of feline immunodeficiency and feline leukemia virus infection

Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) are retroviruses with a global impact on the health of domestic cats. The two viruses differ in their potential to cause disease. FIV can cause an acquired immunodeficiency syndrome that increases the risk of developing opportunistic infections, neurological diseases, and tumors. In most naturally infected cats, however, FIV itself does not cause severe clinical signs, and FIV-infected cats may live many years without any health problems. FeLV is more pathogenic, and was long considered to be responsible for more clinical syndromes than any other agent in cats. FeLV can cause tumors (mainly lymphoma), bone marrow suppression syndromes (mainly anemia) and lead to secondary infectious diseases caused by suppressive effects of the virus on bone marrow and the immune system. Today, FeLV is less important as a deadly infectious agent as in the last 20 years prevalence has been decreasing in most countries.     

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.     

Feline leukemia virus and feline immunodeficiency virus.

Ophthalmic manifestations of FeLV or FIV infection can occur in all ocular tissues and may be manifestations of direct viral effects or secondary to viral-related malignant transformation. Additionally, the manifestations of common feline ophthalmic pathogens may be more severe and poorly responsive to therapy because of the immunosuppressive effects of FeLV or FIV infection. Prompt diagnosis of underlying viral infection in cats with ophthalmic disease is paramount for accurate diagnosis and prognosis and is required for appropriate therapeutic decision making.