Cerebral toxoplasmosis in a cat with feline leukemia and feline infectious peritonitis viral infections

A diarrheic young cat died after neurological involvement. Biochemistry pointed to feline infectious peritonitis (FIP). The final diagnosis was severe multifocal meningoencephalitis due to Toxoplasma gondii. The presence of the parasite in the brain was confirmed using immunohistochemical staining. Concomitant feline leukemia virus (FeLV) and FIP were possible contributors to the clinical, fatal outcome.

Myeloma-related disorder with leukaemic progression in a cat

A 10-year-old American Shorthair cat with nasal discharge, anorexia, and weight loss was found to have pancytopenia and hyperproteinaemia. Bone marrow aspiration revealed atypical plasma cells that totalled 50% of the nucleated bone marrow cells. The number of atypical plasma cells progressively increased in the peripheral blood during the observation period of 64 days. The cat did not respond to treatments with melphalan, chlorambucil, and prednisolone, and died 71 days after the initial presentation. Clinical, cytological, histopathological, and immunohistochemical findings in this case supported the diagnosis of myeloma-related disorder (MRD) with leukaemic progression.

Chronic eosinophilic leukemia in a cat: cytochemical and immunophenotypical features

A 3-year-old, male, domestic shorthaired cat was presented with a 3-day history of anorexia and depression. The cat was moderately dehydrated, had pale, slightly icteric, mucous membranes, oral ulcerations, and mild hepatosplenomegaly. A feline leukemia virus (FeLV) antigen test was positive. CBC results obtained at initial presentation included severe normocytic, normochromic, nonregenerative anemia, severe thrombocytopenia, and marked leukocytosis (>100,000/microL) with 77% eosinophils. After 15 days of treatment with prednisone and doxycycline, the cat had persistent severe nonregenerative anemia (HCT 3.4%), thrombocytopenia (28,000/microL), and extreme eosinophilia (total eosinophils, 123.1 x 10(3)/microL; segmented 103.0 x 10(3)/microL; immature 20.1 X 10(3)/microL). Cytologic examination of aspirates from bone marrow, liver, lymph nodes, and spleen revealed a predominance of mature and immature eosinophils, many with dysplastic changes. The M:E ratio was 96.4. On histopathologic examination, multiple organs were infiltrated by eosinophilic granulocytes. Neoplastic cells in blood and bone marrow stained positive for alkaline phosphatase and were negative for myeloperoxidase, chloroacetate esterase, and alpha-naphthyl acetate esterase. On flow cytometric analysis of peripheral blood, the neoplastic cells were positive for CD11b and CD14. These findings were consistent with chronic eosinophilic leukemia. To our knowledge, this is the first report of chronic eosinophilic leukemia in a cat associated with naturally acquired FeLV infection, in which flow cytometry was used to characterize the neoplastic cells.

Effect of preexisting FeLV infection or FeLV and feline immunodeficiency virus coinfection on pathogenicity of the small variant of Haemobartonella felis in cats

OBJECTIVE

To investigate the effects of preexisting FeLV infection or FeLV and feline immunodeficiency (FIV) coinfection on the pathogenicity of the small variant of Haemobartonella felis (Hfsm, California variant) in cats.

ANIMALS

20 FeLV infected, 5 FeLV-FIV coinfected, and 19 retrovirus-free cats.

PROCEDURES

A client-owned cat, coinfected with FeLV and Hfsm, was the source for Hfsm. Inoculum 1 (FeLV free) was obtained by passage of source Hfsm through 4 FeLV-resistant cats. Inoculum 2 was obtained by further passage of Hfsm (inoculum 1) through 2 specific pathogen-free cats.

RESULTS

A mild-to-moderate anemia started 21 days after inoculation, with its nadir occurring at 35 to 42 days after inoculation. Infection with Hfsm induced greater decrease in hemoglobin concentration in FeLV infected cats, compared with retrovirus free cats. Reticulocytosis, macrocytosis, and polychromasia of erythrocytes developed in anemic cats regardless of retrovirus infection status. Mean neutrophil counts decreased during the hemolytic episode. For most cats, the anemia was transient. Four FeLV infected cats, 1 of which was also FIV infected, developed fatal FeLV-associated myeloproliferative diseases. Of the surviving cats, 8 died over the next 24 months from other FeLV-related diseases. Hemolysis did not recur after the initial episode. Inoculum 1 induced more severe anemia than inoculum 2.

CONCLUSIONS AND CLINICAL RELEVANCE

Our results support the clinical observation that cats coinfected with FeLV and H felis develop more severe anemia than cats infected with H felis alone. Infection with Hfsm may induce myeloproliferative disease in FeLV infected cats. The small variant of H felis may lose pathogenicity by passage through FeLV-free cats.

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.

Inhibition of feline leukemia virus subgroup A infection by coinoculation with subgroup B

Feline leukemia virus (FeLV) subgroup B arises de novo through recombination between the env genes of exogenous FeLV subgroup A and endogenous FeLV-like sequences. FeLV-B, which by itself is poorly infectious, will increase to high titer in the presence of FeLV-A, and is associated with FeLV-related neoplastic disease. Although the participation of FeLV-B in disease progression has not been definitively proven, circumstantial evidence supports the hypothesis that the generation of FeLV-B is linked to disease progression. The present study was designed to evaluate whether increasing the levels of FeLV-B early in FeLV-A infection could result in reduction of the incubation period for development of neoplastic disease. For this study, an isolate of FeLV-B, designated FeLV-1B3, was biologically cloned, partially sequenced, and subgroup typed. In in vivo studies, none of the neonatal cats inoculated with FeLV-1B3 alone converted to viremia positive, and all remained healthy throughout the observation period. All of the kittens inoculated with FeLV-A alone became chronically viremic, and those held for long-term observation all developed either neoplastic disease or anemia. However, kittens inoculated with the combination of FeLV-1B3 and FeLV-A showed attenuated infections whereby the majority of cats failed to develop chronic viremia. The apparent interference of FeLV-A infection by FeLV-B was time and titer dependent. This unexpected result suggests that FeLV-B may act as an attenuated virus, causing inhibition of FeLV-A possibly through an immune-mediated mechanism. Partial support for this view was provided by postmortem examination of cats inoculated with FeLV-1B3 alone. Even though none of these cats became viremic, FeLV antigen was detected as focal infections in select tissues, especially salivary gland epithelium, where enough antigen may be expressed to provide an immunizing dose against gag and pol cross-reacting antigens. This work may also provide another approach to vaccine development based on endogenous retrovirus vector systems.

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.

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.

Acute feline leukemia virus infection causes altered energy balance and growth inhibition in weanling cats

Naturally occurring retroviral infections cause progressive weight loss, immune suppression, invasion by opportunistic organisms, and eventual death. Feline leukemia virus (FeLV) inhibited growth and decreased energy intake in seven experimentally infected weanling cats compared with age- and sex-matched controls. Remarkably, changes in energy intake, energy expenditure, and weight gain occurred in the acute phase of infection prior to the systemic/productive bone marrow phase of FeLV infection. In other words, growth inhibition developed before FeLV infection was clinically detectable with use of standard enzyme-linked immunosorbent assay or fixed-cell immunofluorescence assays of circulating neutrophils and platelets. Acutely infected, previremic cats consumed 25% less energy [Day 4 postinoculation to Day 16 postinoculation (p < 0.05)] and expended 20% less energy [Day 8 postinoculation to Day 18 postinoculation (p < 0.05)] compared with control cats. Growth stunting of inoculated cats began by Day 11 postinoculation (p < 0.05) and was not corrected during the remaining 4 months of the study. Thus, experimental FeLV infection causes perturbations of metabolism and energy balance resulting in permanent growth impairment. Secondly, detrimental metabolic effects begin in the acute phase of retroviral infection, prior to the clinically detectable phase of FeLV infection.

Erythroleukemia in two cats naturally infected with feline leukemia virus in the same household

Erythroleukemia was observed in two unrelated cats infected with feline leukemia virus (FeLV) from the same household. Case 1, a 1-year-old neutered male cat developed erythroleukemia (M6) after a diagnosis of myelodysplastic syndrome (MDS-Er) on the criteria of FAB classification of acute leukemias. Case 2, a 1-year-old neutered female cat, which had close contact with Case 1, also developed erythroleukemia (M6Er). In both cases, marked proliferation of erythroid progenitor cells with disproportionally large numbers of immature forms was observed in the bone marrow. In Case 1, neoplastic proliferation of myeloid cells in the bone marrow was also noted at the terminal stage. Combination chemotherapy with daunomycin was partially effective for treatment of these erythroid neoplasias, but did not induce complete remission. Southern blot analysis using exogenous FeLV-specific probes indicated the clonal origin of these hematopoietic tumor cells. Furthermore, the erythroid and myeloid tumor cells in Case 1 were shown to be derived from independent transformed clones. A variant FeLV was shown to be integrated into the tumor cells in Case 1, while a full-length FeLV was found in both cases. Because these erythroid neoplastic diseases occurred in two unrelated cats kept in the same household and these diseases are rare, they may both have been associated with the same FeLV strain.

Chromosome abnormalities and oncogenesis in cat leukemias

Chromosome abnormalities are found in feline leukemia virus (FeLV)-infected tumor cells as well as in tumor cells free of the virus. Three cell lines derived from tumors in the domestic cat (Felis catus), two of thymic origin and one of multicentric lymphoma origin, were analyzed cytogenetically to determine whether the FeLV virus was associated with chromosomal abnormalities in these tumor cell lines. One thymic tumor and the multicentric lymphoma were FeLV infected. The other thymic tumor cell line was FeLV-free. The normal diploid number in the domestic cat is 38. All three cell lines had numerical chromosome abnormalities with modal numbers of 37, 38 (pseudodiploid), and 39, respectively and had consistent structural chromosome abnormalities. Three markers in the virus-free cell line (S markers) were shared with one or the other of the virus-positive cell lines. The two FeLV-positive cell lines did not have S markers in common. The finding of chromosome abnormalities in both the virus-infected and the virus-free cell lines suggests that these abnormalities may be important in oncogenesis. The FeLV virus could not be considered the only causative agent of the abnormalities observed.

Lymphocytotoxic strains of feline leukemia virus induce apoptosis in feline T4-thymic lymphoma cells

Feline leukemia retrovirus (FeLV) strains with subgroup C env genes kill feline T4 lymphoma 3201 cells by 7 to 12 days after in vitro inoculation, whereas FeLV strains with subgroup A env genes do not. Neither FeLV-A nor FeLV-C kill feline fibroblasts. FeLV-C, but not FeLV-A, is replicated to higher titer by 3201 cells and productive infection precedes death by 3 to 7 days. Transcriptional activity of the FeLV-C long terminal repeat, as assessed by chloramphenicol acetyltransferase activity, is high in feline lymphoid cells but low in feline fibroblasts. Activity of the FeLV-A long terminal repeat is moderate in both cell types. FeLV-C-infected cells form aggregates 1 to 4 days before dying; ultrastructurally, virus particles can be seen approximating the clustered cells. Dying cells demonstrate nuclear condensation, surface blebbing, and fragmentation. DNA fragmentation and laddering compatible with apoptosis occur 1 to 2 days before massive cell death. In FeLV-C-infected 3201 cells, a shift from phospholipid to neutral lipid incorporation of [14C]oleic acid, increases in palmitic acid proportions and decreases in linoleic acid proportions occur 1 to 2 days before peak killing. Exposure of 3201 cells to ultraviolet-inactivated FeLV-KT (200-800 micrograms/10(6) cells) causes cytostasis within 2 days and death within 4 days. Blebbing and nuclear condensation occur but clusters do not form. The induction of programmed cell death in feline thymic lymphoma cells by subgroup C feline retroviruses may be relevant to the pathogenesis of FeLV-induced thymic atrophy, paracortical lymphoid depletion and acquired immunodeficiency in vivo.

Some viral and protozool diseases in the European wildcat (Felis silvestris)

Ten European wildcats (Felis silvestris) were examined at necropsy and an additional 23 were examined clinically for evidence of viral diseases in Scotland. Two plasma samples taken from live free-living wildcats showed positive ELISA reactions to feline leukemia antigen. A feline leukemia virus of subgroup A was isolated from one of these samples, taken from a wildcat in north-western Scotland. No antibodies to feline coronavirus or feline immunodeficiency virus were detected in any sample. Three of the live wildcats and one of the dead had chronic mucopurulent rhinotracheitis suggestive of "cat flu." One other dead wildcat had diffuse enlargement of anterior lymph nodes. The findings indicated that feline leukemia virus infection can occur in free-living Felis silvestris. It is possible that the disease exists as a sustained infection in some wildcat populations, although the close interaction between wildcat and the domestic cat means that the latter could act as a continual source of infection.