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.     

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.     

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.     

Suppression of feline bone marrow fibroblast colony-forming units by feline leukemia virus

Bone marrow fibroblast colony-forming units (CFU-F) were evaluated in cats experimentally infected with feline leukemia virus (FeLV). Cats that developed persistent viral infection and anemia (progressor cats) had a progressive decrease in the number of CFU-F at 2, 4, 6, 8, and 10 weeks after inoculation with FeLV. This suppression of CFU-F number in progressor cats ranged from 16 to 44% of the preinoculation CFU-F value. Cats that did not develop persistent viral infection or anemia (regressor cats) had decreased numbers of CFU-F (24% of the preinoculation CFU-F value) at 2 weeks after inoculation, but normal CFU-F numbers at 4, 6, 8, and 10 weeks after inoculation. In vitro incubation of bone marrow mononuclear cells from healthy cats with the 15,000-dalton envelope protein of FeLV resulted in decreased number of CFU-F (21% of that of untreated cultures). The number of CFU-F from bone marrow mononuclear cells incubated with the 27,000-dalton core protein of FeLV was similar to that from untreated cultures.     

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.     

A review of feline leukemia virus and feline immunodeficiency virus seroprevalence in cats in Canada

Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) are common and important infectious diseases of cats in Canada. Prevalence data are necessary to define prophylactic, management, and therapeutic measures for stray, feral and owned cats. Recently, comprehensive data on the seroprevalence of retrovirus infections of cats in Canada have become available and are reviewed. Further investigation into geographic variations in retrovirus seroprevalence within Canada is warranted, and may provide information to improve recommendations for testing and prevention. As well, more information is needed on FIV subtypes in Canada to improve diagnostics and vaccines, as well as to provide information on disease outcomes.     

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.     

Immunodeficiency in latent feline leukemia virus infections

Challenge of naive experimental animals with a retroviral inoculum may result in one of two broad sequelae. The first is the establishment of an appropriate humoral and cellular immune response leading to a condition of immunity to subsequent infection with the retrovirus. Alternatively, the host may fail to develop a successful immune response, resulting in a chronic viremia associated with immunosuppression and ultimately death due to secondary pathogens. An alternate disease course is the establishment of a latent infection characterized by the presence of neutralizing antibody and strong cellular immune reactivity. Recent data from the feline leukemia virus (FeLV) system suggest that cats infected with this virus may develop immunosuppression in the form of persistent neutrophil dysfunction. The potential effect of this cellular dysfunction is the possible susceptibility of the host to the same opportunistic pathogens which are responsible for the increased mortality noted in chronic FeLV infections. These data demonstrate that persistent retroviremia is not essential for the establishment of immunosuppression. This overview presents data accumulated from the feline model of the human acquired immunodeficiency syndrome (AIDS) and discusses its relationship to human retroviral infections.     

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.     

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.     

Relevance of feline calicivirus, feline immunodeficiency virus, feline leukemia virus, feline herpesvirus and Bartonella henselae in cats with chronic gingivostomatitis

Despite its common occurrence, the aetiology of chronic gingivostomatitis in cats remains uncertain. Aetiology is likely multifactorial, and several infectious agents may be associated with chronic gingivostomatitis. The purpose of this study was to investigate the prevalence of feline calicivirus (FCV), feline immunodeficiency virus (FIV), feline leukemia virus (FeLV), feline herpesvirus (FHV), and Bartonella henselae (B. henselae) in cats with chronic gingivostomatitis and in an age-matched control group. In addition, other factors, e. g., environmental conditions were investigated. In 52 cats with chronic gingivostomatitis and 50 healthy age-matched control cats, the presence of FCV ribonucleic acid (RNA), and FHV deoxyribonucleic acid (DNA) (polymerase chain reaction [PCR] from oropharyngeal swabs), and B. henselae DNA (PCR from oropharyngeal swabs and blood), as well as FeLV antigen (serum), and antibodies against FCV, B. henselae, and FIV (serum) were examined. FCV RNA was significantly more common in cats with chronic gingivostomatitis (53.8%, p < 0.001) than in controls (14.0%); a significant difference was also found in the prevalence of antibodies to FCV between the cats with chronic gingivostomatitis (78.8%, p = 0.023) and controls (58.0%). Of the other infectious agents investigated, there was no significant difference in the prevalence between the cats with chronic gingivostomatitis and the controls. The results of this study allow the conclusion that FCV, but no other infectious agents, is commonly associated with chronic gingivostomatitis in cats.