Expression of viral proteins in feline leukemia virus-associated enteritis

Fourteen cases of feline leukemia virus (FeLV)-associated enteritis were immunohistologically examined for the expression of FeLV proteins gp70, p27, and p15E in the jejunum, mesenteric lymph nodes, spleen, and bone marrow. Results were compared with those of FeLV-infected cats without intestinal alterations. Other viral infections and specific bacterial, fungal, and parasitic infections were excluded by standard microbiologic methods, histopathology, immunohistology, and in situ hybridization. In FeLV-associated enteritis, FeLV gp70 and p15E were strongly expressed in intestinal crypt epithelial cells. In contrast, FeLV-positive cats without intestinal alterations showed only faint staining for gp70 and p15E and comparatively strong p27 expression in these cells. Findings suggest a direct relation between FeLV infection and alterations in intestinal crypt epithelial cells that may be attributed to the envelope proteins gp70 and p15E and/or their precursor protein. Distinct similarities to the intestinal changes in the experimentally induced FeLV-feline AIDS syndrome are obvious, suggesting that naturally occurring feline AIDS variants may be responsible for FeLV-associated enteritis.     

Feline leukemia virus-associated enteritis--a condition with features of feline panleukopenia

Infection with feline leukemia virus (FeLV) was demonstrated immunohistologically in 218 necropsied cats suffering from enteritis. The animals were divided into three groups according to histopathological criteria. The first group exhibited the signs of feline panleukopenia in intestine, lymphoid tissues, and bone marrow. Only 1.6% of these animals were FeLV-infected. The animals of the second group had histopathological alterations as seen in cats suffering from feline panleukopenia, but these were found only in the intestine and not in lymphoid tissues or bone marrow. Of these 71.9% were infected with FeLV. The third group consisted of all other cats suffering from enteritis of which 6.3% were FeLV-positive. The association between FeLV infection and the lesions seen in the animals of group 1 (feline panleukopenia) and group 3 (other types of enteritis) is statistically not significant whereas the alterations exhibited by the cats of group 2 are significantly FeLV-associated. Cats with FeLV-associated enteritis (group 2) are of a mean age of about 2.5 years and are significantly older than animals with feline panleukopenia which are of a mean age of about half a year. Thus a FeLV-associated enteritis exists as a histopathologically recognizable condition which sometimes might be mistaken for feline panleukopenia in routine post-mortem investigations.     

Immunohistochemical identification of B and T lymphocytes in formalin-fixed, paraffin-embedded feline lymphosarcomas: relation to feline leukemia virus status, tumor site, and patient age.

The lymphocyte phenotype of 70 formalin-fixed, paraffin-embedded feline lymphosarcomas (LSAs) was determined immunohistochemically using a T cell polyclonal antibody, and a B cell monoclonal antibody. Forty-seven of 70 (67%) tumors were T cell, 19/70 (27%) were B cell, and 4/70 (6%) did not stain with either marker. Thirty-eight of 70 (54%) tumors were positive for feline leukemia virus (FeLV) antigen by immunohistochemistry (IHC), and 52/70 (74%) tumors were positive for FeLV DNA using the polymerase chain reaction (PCR). B cell tumors were as frequently FeLV-positive as T cell tumors using either IHC or PCR. Intestinal tumors were more likely to be B cell than T. The incidence of B and T cell tumors was not different among young (< or = 3 y), middle-aged (> 3 y to < or = 8 y), and old (> 8 y) cats. Both B and T cell tumors from old cats were FeLV-positive more often by PCR than by IHC. Feline leukemia virus DNA but not antigen, was detected in B cell tumors and intestinal tumors from cats > 8 y as often as it was detected in B cell tumors and intestinal tumors from cats < or = 8 y. Previously, most B cell and intestinal tumors from old cats were considered to be negative for FeLV. Here, the results suggest involvement of latent or replication-defective forms of the virus in such tumors from old cats. This study supports a role for FeLV in feline B cell as well as T cell tumorigenesis.     

Steroid-responsive neutropenia in a cat with progressive feline leukemia virus infection

An 8-month-old female domestic shorthair cat was presented to the Animal Medical Center with anorexia, lethargy, and mild gastrointestinal signs. A CBC revealed a profound neutropenia, and serologic testing with an in-house test kit (SNAP FIV/FeLV Combo, IDEXX) was positive for feline leukemia virus (FeLV) antigen. Serial hematologic examinations during hospitalization showed a persistent neutropenia with occasionally severe anemia and thrombocytopenia. Prednisolone administration afforded complete hematologic remission within 3 days. Four weeks after the premature discontinuation of prednisolone, the patient relapsed; however, complete and prolonged hematologic remission was achieved after prednisolone was re-induced. Bone marrow aspiration cytology was consistent with immune-mediated destruction of the mature myeloid cells. steroid-responsive (likely immune-mediated) cytopenias rarely occur in cats with progressive FeLV infection. Although only a few cases of FeLV-positive, severely neutropenic cats that responded to immunosuppressive therapy have been reported, this case highlights that a grave prognosis should not always be given to these FeLV-positive cats.     

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.     

The presence of leukaemia (lymphosarcoma) and feline leukaemia virus (FeLV) in cats in The Netherlands

To study the presence and spread of feline leukaemia virus (FeLV) in The Netherlands, seven different groups of cats were examined. The indirect fluorescent antibody (IFA) test was used to detect FeLV-antigen in blood smears. Of cats with lymphosarcoma/leukaemia 73.2% were positive and 32.4% with infectious peritonitis were positive. Only one of sixty-six cats with other tumours–a cat with mammary carcinoma–was positive.
Forty-two (7.5%) of 557 cats with various complaints were positive for FeLV-antigen. The IFA-test appeared to be an important diagnostic supplement.
Of all stud males which had had contact with FeLV-positive cats 24.7% were positive for FeLV-antigen, whereas all stud males which had not had this contact, were negative.
There was a distinct difference between the percentages of FeLV-positive individuals in the groups of cats which had had (20.6%) and which had not had (0.4%) contact with FeLV-positive cats.
From the follow-up study it was found that 67.3% of the FeLV-positive cats died from, or were destroyed because of, FeLV-associated diseases within a period of 20 months.     

Prevalence and risk factors for hemoplasmas in domestic cats naturally infected with feline immunodeficiency virus and/or feline leukemia virus in Rio de Janeiro--Brazil

The aim of this study was to determine the prevalence and risk factors for Mycoplasma haemofelis (Mhf) and 'Candidatus Mycoplasma haemominutum' (Mhm) infections in domestic cats tested for feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) with a commercial enzyme-linked immunosorbent assay (ELISA) kit. Based on serological testing, cats were grouped as i) FIV-positive (n=25); ii) FeLV-positive (n=39); iii) FIV/FeLV-positive (n=8); and iv) FIV/FeLV-negative (n=77). Complete blood counts were followed by DNA extraction, species-specific polymerase chain reaction (16S rRNA gene) for Mhf and Mhm and Southern blotting for all animals. Mhf DNA was found in 4.0, 2.6, 12.5 and 7.8% of the cats from groups i, ii, iii and iv, respectively, while 32, 5.1, 50 and 5.2% of these animals had an Mhm infection. Cats with FIV (OR=4.25, P=0.009) and both FIV and FeLV (OR=7.56, P=0.014) were at greater risk of being hemoplasma infected than retroviral-negative cats, mainly due to Mhm infection (OR=8.59, P=0.001 and OR=18.25, P=0.001, respectively). Among pure-breed cats, FIV-positive status was associated with hemoplasma infection (OR 45.0, P=0.001).     

Epidemiology of feline leukaemia and feline immunodeficiency virus infections in the Czech Republic

Commercial serological sets were used for the examination of 727 cats kept in larger towns of the Czech Republic. FeLV antigen and antibodies to FIV were demonstrated in 96 (13.2%) and 42 (5.8%) of the animals, respectively. Seven (0.96%) animals were positive for both FeLV and FIV. Most of the FeLV and/or FIV positive patients were intact rambling males aged 1-4 years. Chronic gastrointestinal and respiratory diseases were found in 54.2% and 43.8% of the FeLV-positive patients, respectively. Chronic urinary tract diseases and generalized lymphadenopathy were found in 47.6% and 45.2% of the FIV-positive patients, respectively. The results of this first survey in the Czech Republic have shown prevalence values and clinical patterns similar to those reported formerly from other European countries.     

Diseases associated with spontaneous feline leukemia virus (FeLV) infection in cats

More than 2000 cats sent for necropsy in order to provide a diagnosis were investigated immunohistologically using paraffin sections for the presence of a persistent infection with feline leukemia virus (FeLV). The spectrum of neoplastic and non-neoplastic diseases associated significantly with FeLV infection was determined statistically. Three-quarters of the cats with persistent FeLV infections died of non-neoplastic diseases and about 23% died of tumors, nearly exclusively those of the leukemia/lymphoma disease complex. A strong association with liver degeneration, icterus and a FeLV-associated enteritis was found in addition to the known association with non-neoplastic diseases and conditions such as anemia, bacterial secondary infections and respiratory tract inflammations due to the immunosuppressive effect of FeLV, hemorrhages and feline infectious peritonitis. Surprisingly, diseases and conditions like feline infectious panleukopenia, enteritis (of other types than FeLV-associated enteritis and feline infectious panleukopenia), glomerulonephritis, uremia and hemorrhagic cystitis were not associated with persistent FeLV infection. Another unexpected finding was that most pathogenic infectious agents demonstrated in the cats were not FeLV-associated either. Thus, immunosuppression due to FeLV infection seems to make the animals susceptible to certain pathogenic infectious agents, but not to the majority.     

Assessment of feline blood for transfusion purposes in the Dublin area of Ireland

The prevalence of A, B and AB blood types and of feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV) infection was determined in cats in Ireland, in order to determine risk factors for blood taken for transfusion purposes. EDTA blood samples were available from 137 non-pedigree cats and 39 pedigree cats (91 females and 85 males, aged four months to 15.0 years) in the Dublin area of Ireland. Of the 176 EDTA blood samples obtained, 112 (from 92 healthy cats and 20 sick cats) were tested for the presence of both FIV antibodies and FeLV antigens. Blood typing was performed using an immunochromatographic cartridge (CHROM; Alvedia). Testing for FIV and FeLV was performed by ELISA (SNAP FIV/FeLV Combo Test; Idexx Laboratories). Of the 39 pedigree cats, the majority (38 [97.4 per cent]) was type A, and only one (2.6 per cent) was type B. Of the 137 non-pedigree cats, the majority (116 [84.7 per cent]) was type A, 20 (14.6 per cent) were type B, and one (0.7 per cent) was type AB. Of the 92 healthy cats tested, the prevalence of FIV and FeLV positivity was 4.35 and 1.09 per cent, respectively. None of the 20 sick cats tested was FIV-positive; two (10 per cent) of the 20 sick cats were FeLV-positive.     

Control of feline leukaemia virus

Feline leukaemia virus (FeLV) usually occurs in its natural species, the domestic cat. FeLV is also important to human individuals as a comparative model, as it may cause a variety of diseases, some malignant and some benign, such as immunosuppression, which bears a resemblance to AIDS (acquired immune deficiency syndrome) in man. FeLV is transmitted among cats by contagion. The main sources of infection are persistently infected carrier cats which continuously excrete virus. Dissemination of FeLV among cats may be prevented by identifying infected carrier cats and removing them from contact with non-infected cats. Removal programmes using indirect immunofluorescence antibody tests were applied successfully in The Netherlands. The proportion of FeLV-positive cats decreased from 9% in 1974 to approximately 3% in 1985 during such a programme. The results of a removal programme carried out in a catbreeders' society were even better: the incidence of cats positive for FeLV decreased from 11% in 1974 to less than 2% within 4 years. None of the cats tested in this society has been found to be positive for FeLV since 1984. Besides removal programmes, other methods of control, such as pre-exposure treatment, were developed to prevent the spread of FeLV. We attempted to protect kittens against oronasal infection with FeLV by treatment with virus-neutralizing (VN) monoclonal antibodies (MoAbs) directed against an epitope on the viral glycoprotein gp70. However, no protection was achieved. It is unlikely that the amount of VN antibodies, the mode and route of their application or the infectious dose of FeLV used can account for this failure. Other possible explanations for the lack of protective effect are that (i) the restricted epitope specificity of the MoAb preparation used may have led to selection of neutralization-resistant virus mutants, or (ii) other mechanisms than virus neutralization (complement-mediated lysis, antibody-dependent cell cytotoxicity), that may be involved in protection, function less efficiently with MoAb. However, in the light of our finding that an early anti-idiotypic response is observed in all cats following administration of the MoAb preparation, the rapid clearance of anti-FeLV MoAb from the circulation is a more likely explanation. Efforts were further made to develop a vaccine for controlling FeLV infection. The immunostimulating complex vaccine (FeLV-ISCOM vaccine), a subunit vaccine in which FeLV gp70 is presented in a particular manner, looks promising. The protective effect of FeLV-ISCOM vaccine was studied by vaccinating six 8-week-old SPF cats with ISCOM, followed by oronasal challenge with FeLV.(ABSTRACT TRUNCATED AT 400 WORDS)     

Comparison of four test kits for feline leukemia virus antigen.

The sensitivity and specificity of 4 commercial FeLV ELISA kits, using blood, were compared with results of virus isolation from blood and immunofluorescent antibody (IFA) testing on blood. Significant differences were not found among the 4 ELISA kits. Marked decrease in sensitivity of the ELISA kits was detected when virus isolation was used as the standard of positivity rather than the IFA test. Virus isolation was a more sensitive indicator of early infection, with marked discrepancy among results obtained by virus isolation, ELISA, and the IFA test. Results became progressively more concordant as infection became fully established. Cats FeLV-positive by virus isolation alone were more likely to eliminate viremia. All cats FeLV-positive by IFA testing remained persistently viremic. Virus isolation, ELISA, and IFA testing appear to differ in their prognostic value. The use of blood rather than serum for the ELISA resulted in several discordant results. Six cats were FeLV-positive by ELISA when blood was tested but were FeLV-negative when serum was tested. Positive ELISA results were obtained for 4 of these cats when serum was tested, using extended incubation to increase sensitivity. It is possible that blood may actually be more sensitive than serum for use of the ELISA method.     

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.     

Detection of feline leukaemia virus in blood and bone marrow of cats with varying suspicion of latent infection

The purpose of this study was to determine if polymerase chain reaction (PCR) could be used to detect FeLV proviral DNA in bone marrow samples of cats with varying suspicion of latent infection. Blood and bone marrow samples from 50 cats and bone marrow from one fetus were collected, including 16 cats with diseases suspected to be FeLV-associated. Serum enzyme-linked immunosorbent assay (ELISA), blood and bone marrow immunofluorescent antibody test (IFA), and blood and bone marrow PCR were performed on each cat, and IFA and PCR on bone marrow of the fetus. Forty-one cats were FeLV negative. Five cats and one fetus were persistently infected with FeLV. Four cats had discordant test results. No cats were positive on bone marrow PCR only. It appears persistent or latent FeLV infection is not always present in conditions classically associated with FeLV.     

Year two of follow-up evaluation of a randomized, blind field trial of a commercial feline leukemia virus vaccine.

A blind randomized field trial of a commercial FeLV vaccine was conducted. Cats on study were vaccinated with either a commercial FeLV vaccine or a placebo, then housed with FeLV-positive cats in a ratio of approximately 2 study cats to 1 infected cat (results of the first 12 months of the study have been reported). All surviving placebo-treated and FeLV-vaccinated cats were re-vaccinated 1 year after initial exposure to FeLV-infected cats. Exposure continued for an additional 12 months, and the viremia status of the cats was monitored by immunofluorescent antibody (IFA) and ELISA testing at 4-month intervals. During the second year of observation, 1 additional FeLV-vaccinated cat had positive results of 2 consecutive ELISA tests, but remained IFA negative. Classifying this cat as persistently viremic reduced the estimate of the preventable fraction, but did not alter the conclusions drawn earlier, viz, that vaccination appreciably reduces the number of cats that become persistently viremic after long-term natural exposure.     

Incidence of persistent viraemia and latent feline leukaemia virus infection in cats with lymphoma

In the past, feline leukaemia virus (FeLV) infection, and also latent FeLV infection, were commonly associated with lymphoma and leukaemia. In this study, the prevalence of FeLV provirus in tumour tissue and bone marrow in FeLV antigen-negative cats with these tumours was assessed. Seventy-seven diseased cats were surveyed (61 antigen-negative, 16 antigen-positive). Blood, bone marrow, and tumour samples were investigated by two polymerase chain reaction (PCR) assays detecting deoxyribonucleic acid (DNA) sequences of the long terminal repeats (LTR) and the envelope (env) region of the FeLV genome. Immunohistochemistry (IHC) was performed in bone marrow and tumour tissue. None of the antigen-negative cats with lymphoma was detectably infected with latent FeLV. The prevalence of FeLV viraemia in cats with lymphoma was 20.8%. This suggests that causes other than FeLV play a role in tumorigenesis, and that latent FeLV infection is unlikely to be responsible for most feline lymphomas and leukaemias.     

Frequency and significance of feline leukemia virus infection in necropsied cats

Feline leukemia virus (FeLV) infection was diagnosed immunohistologically on paraffin-embedded tissues obtained from 1,095 necropsied cats. Significant association of FeLV infection was demonstrated by chi 2 and Fisher's tests with various conditions and diseases (ie, anemia, tumors of the leukemia/lymphoma complex, feline infectious peritonitis, bacterial infections, emaciation, FeLV-associated enteritis, lymphatic hyperplasia, and hemorrhage). Unexpected findings associated with FeLV infection were icterus, several types of hepatitis, and liver degeneration. A negative association with FeLV infection was found for most parasitic and viral infections, including feline panleukopenia. Neither positive nor negative associations were established for FeLV infection and most forms of nephritis, including severe glomerulonephritis. Feline leukemia virus-infected cats were significantly (Kruskal-Wallis test) older than were FeLV-negative cats with the same nonneoplastic FeLV-associated diseases.     

Ocular disease in FeLV-positive cats: 11 cases (1981-1986).

A total of 147 cats positive for FeLV were retrospectively studied to determine the incidence of ocular disease. Of those cats, 97 had clinical cases of the disease and 50 were artificially infected with the virus. The incidence of ocular disease among FeLV-positive cats with clinical signs of disease was less than 2%, and represented less than 0.1% of the total feline cases for the 5-year period studied. The only ocular findings that could be associated with FeLV were pupillary and motility abnormalities. Retinal hemorrhage and subsequent degeneration found in experimentally infected and naturally infected cats were secondary to profound anemia, which was secondary to FeLV infection. On the basis of the literature and our findings, FeLV is not a major cause of primary or secondary ocular disease in the cat. Anterior uveal disease (iris bombé) was detected in 1 of 147 FeLV-positive cats, and the incidence of secondary infectious disease was zero.     

Infections with feline leukaemia virus detected upon post-mortem examination

Cats submitted for post-mortem examination have been studied for persistent FeLV infection using immune histological methods. Persistent FeLV infection turned out to cause the most frequent lethal infectious disease of the cat. In the post-mortem material, 16 per cent of the cats were found positive whereas 3 per cent can be assumed for the normal feline population. FeLV-positive animals die from FeLV-associated non-tumourous conditions in 75 per cent of the cases rather than from leucosis. The most important non-tumourous conditions are anaemia, feline infectious peritonitis, inflammation of the respiratory tract and liver degeneration. Important differences have been found between the various forms of leucosis which can also be distinguished in the small animal practice concerning their association with FeLV infection. Variations between 20 and 90 per cent have been found.     

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.