Feline leukemia virus-induced thrombocytopenia and macrothrombocytosis in cats

Erythroleukemia in a retrovirus-negative cat

CASE DESCRIPTION

A 5-year-old spayed female cat was evaluated because of lethargy of 3 days' duration, acute respiratory distress, and anemia.

CLINICAL FINDINGS

Physical examination revealed the cat was in good body condition but had pale mucous membranes and elevated heart and respiratory rates. Results of hematologic analysis indicated the cat had severe anemia (Hct, 0.07 L/L; reference range, 0.28 to 0.49 L/L) and marked rubricytosis (19.0 × 10(9) cells/L; reference value, 0 cells/L). Results of serologic and PCR assays for detection of FeLV and FIV and PCR assays for detection of Mycoplasma spp were negative. Cytologic evaluation of a bone marrow aspirate and histologic evaluation of a biopsy specimen revealed a predominance of rubriblasts and rubricytes with granulocytopenia. Cytologic evaluation of fine-needle aspirates of the spleen and liver also revealed numerous rubriblasts.

TREATMENT AND OUTCOME

The cat received transfusions of packed RBCs, and supportive treatment was administered. Analysis of test results yielded a diagnosis of acute myeloid leukemia (erythroid subtype). Because of continued hemolysis and anemia in combination with the diagnosis of erythroleukemia (which has a poor prognosis), the cat was euthanized.

CLINICAL RELEVANCE

To the authors' knowledge, erythroleukemia has only been reported in cats infected with FeLV. However, results of all diagnostic assays for FeLV were negative in the cat reported here, which suggested that erythroleukemia can develop in cats in the absence of FeLV infection.

Primary Immune-Mediated Thrombocytopenia in Cats

Feline primary immune-mediated thrombocytopenia (pIMT) is a rare condition, and only a few cases have been described in veterinary literature. Five cats with severe thrombocytopenia most likely due to pIMT are described. A flow cytometry platelet-bound antibody test was positive in all cats; underlying diseases or triggering factors causing thrombocytopenia were not detected. Three cats were transfused with blood type-compatible fresh whole blood; one cat received Oxyglobin as well. All cats were treated with prednisolone; one cat received chlorambucil in addition. Four cats responded to treatment and were discharged from the hospital. One cat was euthanized due to dyspnea. Primary immune-mediated thrombocytopenia is rarely diagnosed in cats, but it is important as a differential diagnosis in cats presented with surface bleeding.

Seroreactivity to A-type retrovirus proteins in a subset of cats with hyperthyroidism

The thyroid gland is afflicted in several endocrine, autoimmune, and malignant diseases. Previous studies detected immunoreactivity against proteins of a human intracisternal A-type retroviral particle type-I (HIAP-I) in serum samples from the majority of patients with Graves' disease, an autoimmune disease of the thyroid that can also affect other organs, most prominently the eyes. To determine whether hyperthyroid animals might provide a model for the retroviral involvement in thyroid autoimmunity, serum samples from 32 cats (21 hyperthyroid and 11 controls) and 10 hypothyroid dogs were examined for immunoreactivity with HIAP-I using a Western blot technique. Of the 21 hyperthyroid cats 15 (71.4%) were HIAP-I positive, while only 2 of 11 (11.8%) control animals without endocrine pathology were positive. No significant correlations were seen between HIAP seroreactivity and serum thyroid hormone levels (T3 and T4), age, gender, treatment history, vaccination status, or weight. No seroreactivity to HIAP-I was detected in hypothyroid dogs. An examination of HIAP-I reactivity in feline leukemia virus (FeLV)-seroconverting cats found that 7/9 (78%) animals viremic for FeLV-A showed an alteration in HIAP serology, whereas only 1/7 (14%) nonviremic animals showed a change in HIAP-I serology. These results suggest that it may be possible to develop an animal (feline) model for the role of retroviruses in thyroid autoimmune diseases.

Feline leukemia virus-associated myelopathy in cats

Feline leukemia virus (FeLV) infection is associated with distinct neoplastic, hematologic, and immunosuppressive diseases. Here we report on a novel neurologic syndrome in 16 cats infected with FeLV for more than 2 years. Clinical signs consisted of abnormal vocalization, hyperesthesia, and paresis progressing to paralysis. The clinical course of affected cats involved gradually progressive neurologic dysfunction invariably resulting in euthanasia. Microscopically, white-matter degeneration with dilation of myelin sheaths and swollen axons was identified in the spinal cord and brain stem of affected animals. Neither neoplastic nor hematologic diseases commonly associated with FeLV infection were present. Fungal and protozoal infection in one animal was suggestive of impaired immune competence. Immunohistochemical staining of affected tissues revealed consistent expression of FeLV p27 antigens in neurons, endothelial cells, and glial cells. Furthermore, proviral DNA was amplified from multiple sections of spinal cord as well as intestine, spleen, and lymph nodes. These findings suggest that in a proportion of chronically FeLV-infected cats, a virus evolved with cytopathic potential for cells in the central nervous system.

Hemostatic disorders in cats: a retrospective study and review of the literature

Hemostasis profiles from 101 cats presented for medical or surgical evaluation to The Ohio State University Veterinary Teaching Hospital from 1986 through 1991 were reviewed retrospectively; 69% were abnormal. Commonly identified abnormalities included a mixed hemostatic defect compatible with disseminated intravascular coagulation, thrombocytopenia, isolated prolongation of the activated partial thromboplastin time (APTT), and prolongation of both the APTT and one-stage prothrombin time. The most common disorders associated with abnormal hemostasis profiles in this study were liver disease, neoplasia, and feline infectious peritonitis.

Hemostatic disorders in feline immunodeficiency virus-seropositive cats

The hemostatic function of 40 feline immunodeficiency virus (FIV) seropositive and 8 FIV and feline leukemia virus (FeLV) seropositive cats was evaluated and compared with reference values from 30 clinically healthy cats. The FIV-positive cats were divided into 3 groups: group I included asymptomatic carriers; group II comprised sick FIV-infected cats with illnesses not likely to influence the hemostatic system; and group III included FIV-positive cats with diseases potentially associated with coagulopathies. Platelet counts in FIV/FeLV-infected cats were significantly lower than in healthy cats (P < .003), whereas the differences in the 3 groups of FIV-positive cats were variable (group I, P = .009; II, P = .05; III, P = .09). Thrombocytopenia (< 145,000 platelets/microL) was present in 4 FIV-positive and 3 FIV/FeLV-positive cats. Platelet aggregation induced by collagen (0.5 and 0.25 micrograms/mL), adenosine diphosphate (ADP) (1 and 0.6 mumol/L), and thrombin (0.4 and 0.25 IU/mL) was not significantly different from that of healthy cats. The plasma coagulation system was evaluated by measuring one-stage prothrombin time (OSPT), activated partial thromboplastin time (APTT), thrombin time, fibrinogen concentration, coagulation factor assays, fibrinogen and fibrin degradation products (FDP), and plasma exchange test. The OSPT was similar in FIV-seropositive cats and in the healthy control group. Cats with FIV infection, however, had markedly shorter clotting times than healthy cats when using a modified test system (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Thrombocytopenia in cats: a retrospective study of 41 cases

The prevalence of feline thrombocytopenia (< 200,000 platelets/microL) at North Carolina State University, College of Veterinary Medicine Teaching Hospital, from January 1985 to March 1990, was 1.2% (41/3300). Cats were divided into six categories based on clinical diagnoses: 29% (12/41) had infectious disease, 20% (8/41) had neoplasia, 7% (3/41) had cardiac disease, 2% (1/41) had primary immune-mediated disease, 22% (9/41) had multiple diseases, and 20% (8/41) had disorders of unknown etiology. The mean platelet count for all thrombocytopenic cats was 52,000/microL +/- 46,000/microL (1 SD) with a range of 1000-190,000/microL. No significant differences were found between groups with respect to platelet count, packed cell volume, or white blood cell count, though anemia and leukopenia were common among the cats as a whole. Bleeding disorders (hemorrhage or thrombosis) were observed in 29% (12/41) of thrombocytopenic cats and were more likely to be associated with neoplasia, cardiac disease, and platelet counts less than or equal to 30,000/microL. Disseminated intravascular coagulopathy was diagnosed in 12% (5/41) of the cats. Infections and/or neoplasia affecting the bone marrow were the most common diseases associated with thrombocytopenia. Feline leukemia virus and myeloproliferative neoplasia accounted for approximately 44% (18/41) of the specific diagnoses in thrombocytopenic cats.

Feline leukemia/sarcoma viruses and immunodeficiency

This chapter discusses the structure feline leukemia virus (FeLV) and pathogenesis of lymphomas and leukemias BY FeLV. FeLV is quite similar to the better-studied murine leukemia viruses in structure and genetic map. The virus particles bud from cytoplasmic membranes into either extracellular spaces or into vacuoles. FeLV has long been considered a typical noncytopathogenic, longlatency leukemia virus based on its behavior in fibroblasts in vitro . Recent evidence suggests that its in vivo behavior in critical target hemolymphatic tissues is as likely to be cytopathic as transforming. The type of FeLV-related disease that occurs and the disease-free interval probably are influenced by viral envelope proteins and glycoproteins and the consequences of proviral integration. FeLV subgroup specificity apparently determines when and what type of disease will occur. The ecotropic FeLV-A is the most frequent subgroup found in pet cats and is transmitted contagiously. Immunosuppression is the most frequent and the most devastating manifestation of FeLV viremia in clinical and experimental studies. It seems that multiple cell types and multiple processes are involved in the development of feline retrovirus-induced immunosuppression. Although no solid evidence is available for the malfunctioning of cat T helper cells because of the paucity of T-cell specific markers, the circumstantial evidence provided thus far indicates an impaired T helper function in FeLV-infected cats similar to that observed in humans infected with HIV. Studies on the pathogenesis of FeLV-induced immunosuppression might provide a valuable mode for a better understanding and means of control of human AIDS.

Size referenced electronic leukocyte counting threshold and lysed leukocyte size distribution of common domestic animal species

Using a single channel electronic cell counter and attached particle size analyzer, leukocyte size distribution histograms were determined on canine, feline, bovine, and equine blood diluted with chloride-based diluent and treated with a conventional stromatolysin. Histograms were usually unimodal, but a few were bimodal. Mean values for mean lysed leukocyte particle volume were 49.2, 51.1, 55.4, and 65.0 fl for canine, feline, equine, and bovine blood, respectively. From inspection of histograms, a lower threshold of 30 fl referenced to latex spheres was interpreted to be appropriate for counting leukocytes of these four species simultaneously. Debris below the threshold was seen in many samples and was usually separated from the leukocyte population by a valley touching the histogram baseline at the threshold channel. Debris resulted in a visually detectable threshold failure by extending considerably into the leukocyte size range in 9% of feline, 9% of canine, and 7% of bovine samples. It is recommended that careful establishment of the lower counting threshold will minimize frequency and severity of leukocyte count error associated with failure to exclude debris.