Experimental feline panleucopenia in the conventional cat

Persistent viremia by a novel parvovirus in a slow loris (Nycticebus coucang) with diffuse histiocytic sarcoma

Cancer is one of the leading health concerns for human and animal health. Since the tumorigenesis process is not completely understood and it is known that some viruses can induce carcinogenesis, it is highly important to identify novel oncoviruses and extensively study underlying oncogenic mechanisms. Here, we investigated a case of diffuse histiocytic sarcoma in a 22 year old slow loris (Nycticebus coucang), using a broad spectrum virus discovery technique. A novel parvovirus was discovered and the phylogenetic analysis performed on its fully sequenced genome demonstrated that it represents the first member of a novel genus. The possible causative correlation between this virus and the malignancy was further investigated and 20 serum and 61 organ samples from 25 animals (N. coucang and N. pygmaeus) were screened for the novel virus but only samples collected from the originally infected animal were positive. The virus was present in all tested organs (intestine, liver, spleen, kidneys, and lungs) and in all banked serum samples collected up to 8 years before death. All attempts to identify a latent viral form (integrated or episomal) were unsuccessful and the increase of variation in the viral sequences during the years was consistent with absence of latency. Since it is well known that parvoviruses are dependent on cell division to successfully replicate, we hypothesized that the virus could have benefitted from the constantly dividing cancer cells and may not have been the cause of the histiocytic sarcoma. It is also possible to conjecture that the virus had a role in delaying the tumor progression and this report might bring new exciting opportunities in recognizing viruses to be used in cancer virotherapy.

Prognostic factors in cats with feline panleukopenia

BACKGROUND

Feline panleukopenia is a highly contagious and often lethal disease.

OBJECTIVE

The purpose of the study was to identify prognostic factors for survival of cats with panleukopenia.

ANIMALS

Between 1990 and 2007, 244 cats were diagnosed with panleukopenia in the Clinic of Small Animal Medicine, LMU University of Munich, Germany. Diagnosis was established by electron microscopy, polymerase chain reaction of feces or blood, antigen ELISA of feces, pathognomonic histopathological lesions at necropsy, or some combination of these procedures.

METHODS

Medical records of each cat were evaluated retrospectively.

RESULTS

Survival rate was 51.1%. No significant correlation was found between outcome and living conditions, age, vaccination status (unvaccinated versus one or more vaccines administered), or severity of clinical signs. However, of the vaccinated cats, none had received a vaccine later than 12 weeks of age as a kitten. Nonsurvivors had significantly lower leukocyte and thrombocyte counts at presentation compared with survivors. The relative risk of death for patients with <1,000/μL leukocytes was 1.77 times as high as in patients with a leukocyte count of 1,000-2,500/μL (P=.038), and 1.85 times as high as in patients with >2,500/μL leukocytes (P=.001). The likelihood of a fatal outcome was higher when serum albumin concentration was <30 g/L or serum potassium concentration <4 mmol/L.

CONCLUSIONS AND CLINICAL IMPORTANCE

Vaccination strategies that do not include vaccination of kittens beyond 12 weeks of age may not be adequate to prevent panleukopenia. Leukopenia, thrombocytopenia, hypoalbuminemia, and hypokalemia are negative prognostic factors in cats with panleukopenia.

Comparative examination of cats with feline leukemia virus-associated enteritis and other relevant forms of feline enteritis

Cats with feline leukemia virus (FeLV)-associated enteritis (FAE), enteritis of other known viral etiology (parvovirus [PV], enteric coronavirus [CoV]), and enteritis of unknown etiology with histologic features similar to those of FAE and PV enteritis (EUE) and FeLV-negative and FeLV-positive cats without enterocyte alterations were examined. Amount and types of infiltrating leukocytes in the jejunum and activity and cellular constituents of mesenteric lymph nodes, spleen, and bone marrow were determined. PV and CoV infections were confirmed by immunohistologic demonstration of PV and CoV antigen, ultrastructural demonstration of viral particles in the intestinal content, and in situ hybridization for PV genome. FeLV infection was detected by immunohistology for gp70, p27, and p15E. Latent FeLV infection was excluded by polymerase chain reaction methods for exogenous FeLV DNA. Enterocyte lesions involved the crypts in cats with PV enteritis, FAE, and EUE and the villous tips in cats with CoV enteritis. Inflammatory infiltration was generally dominated by mononuclear cells and was moderate in the unaltered intestine and in cats with PV enteritis and marked in cats with FAE, CoV enteritis, and EUE. In cats with EUE, myeloid/histiocyte antigen-positive macrophages were relatively numerous, suggesting recruitment of peripheral blood monocytes. Lymphoid tissues were depleted in cats with PV enteritis and with EUE but were normal or hyperplastic in cats with FAE. Bone marrow activity was decreased in cats with PV enteritis; in cats with FAE or EUE and in FeLV-positive cats without enterocyte alterations, activity was slightly increased. In cats with FAE and PV enteritis, a T-cell-dominated response prevailed. EUE showed some parallels to human inflammatory bowel disease, indicating a potential harmful effect of infiltrating macrophages on the intestinal epithelium.

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.

Severe leukopenia and dysregulated erythropoiesis in SCID mice persistently infected with the parvovirus minute virus of mice

Parvovirus minute virus of mice strain i (MVMi) infects committed granulocyte-macrophage CFU and erythroid burst-forming unit (CFU-GM and BFU-E, respectively) and pluripotent (CFU-S) mouse hematopoietic progenitors in vitro. To study the effects of MVMi infection on mouse hemopoiesis in the absence of a specific immune response, adult SCID mice were inoculated by the natural intranasal route of infection and monitored for hematopoietic and viral multiplication parameters. Infected animals developed a very severe viral-dose-dependent leukopenia by 30 days postinfection (d.p.i.) that led to death within 100 days, even though the number of circulating platelets and erythrocytes remained unaltered throughout the disease. In the bone marrow of every lethally inoculated mouse, a deep suppression of CFU-GM and BFU-E clonogenic progenitors occurring during the 20- to 35-d.p.i. interval corresponded with the maximal MVMi production, as determined by the accumulation of virus DNA replicative intermediates and the yield of infectious virus. Viral productive infection was limited to a small subset of primitive cells expressing the major replicative viral antigen (NS-1 protein), the numbers of which declined with the disease. However, the infection induced a sharp and lasting unbalance of the marrow hemopoiesis, denoted by a marked depletion of granulomacrophagic cells (GR-1(+) and MAC-1(+)) concomitant with a twofold absolute increase in erythroid cells (TER-119(+)). A stimulated definitive erythropoiesis in the infected mice was further evidenced by a 12-fold increase per femur of recognizable proerythroblasts, a quantitative apoptosis confined to uninfected TER-119(+) cells, as well as by a 4-fold elevation in the number of circulating reticulocytes. Therefore, MVMi targets and suppresses primitive hemopoietic progenitors leading to a very severe leukopenia, but compensatory mechanisms are mounted specifically by the erythroid lineage that maintain an effective erythropoiesis. The results show that infection of SCID mice with the parvovirus MVMi causes a novel dysregulation of murine hemopoiesis in vivo.

Myeloid depression follows infection of susceptible newborn mice with the parvovirus minute virus of mice (strain i)

The in vivo myelosuppressive capacity of strain i of the parovirus minute virus of mice (MVMi) was investigated in newborn BALB/c mice inoculated with a lethal intranasal dose. MVMi infection reached maximum levels of DNA synthesis and infectious titers in lymphohemopoietic organs at 4 to 6 days postinoculation and was restricted by an early neutralizing humoral immune response. After viral control (by 10 days postinoculation), a significant decrease in femoral and splenic cellularity, as well as in granulocyte-macrophage colony-forming unit and erythroid burst-forming unit hemopoietic progenitors, was observed in most inoculated animals. This delayed myeloid depression, although it may be not a major cause of the lethality of the infection, implies indirect pathogenic mechanisms induced by MVMi infection in a susceptible host.

Pathogenesis of feline panleukopenia virus and canine parvovirus

Feline panleukopenia virus (FPV) and canine parvovirus (CPV) are autonomous parvoviruses which infect cats or dogs, respectively. Both viruses cause an acute disease, with virus replicating for less than seven days before being cleared by the developing immune responses. The viruses have a broad tropism for mitotically active cells. In neonatal animals the viruses replicate in a large number of tissues, and FPV infection of the germinal epithelium of the cerebellum leads to cerebellar hypoplasia, while CPV may infect the hearts of neonatal pups, causing myocarditis. In older animals the virus replicates systemically, primarily in the primary and secondary lymphoid tissues, and also in the rapidly replicating cells of the small intestinal epithelial crypts. A transient panleukopenia or relative lymphopenia is often observed after FPV or CPV infection, respectively. Whether the reduction in cell numbers in vivo is due to virus replicating in and killing cells, or due to other indirect effects, is not known. However, FPV kills both erythroid and myeloid colony progenitors in in vitro bone marrow cultures, and it has been suggested that virus replication in the myeloid cells in vivo could lead to the reduced neutrophil levels seen after FPV infection of cats.

Cytotoxic infection of hematopoietic stem and committed progenitor cells by the parvovirus minute virus of mice. Propagation of an acute myelosuppression in culture

We have investigated the ability of two strains of the parvovirus minute virus of mice to impair mouse hematopoiesis in vitro. We found that the BFU-E and CFU-GM committed progenitors, CFU-Mix pluripotent progenitor, as well as the CFU-S12d, one of the most primitive hematopoietic precursors of the stem cell compartment detectable by colony technique, were similarly inhibited in their proliferative capacity by the immunosuppressive strain MVMi, but not by the prototype virus MVMp. The inhibitory effect correlated with the input of purified MVMi and was reversed by neutralizing MVM antiserum, showing that cytotoxic mechanisms underlying infectious MVMi replication and not operating in MVMp-infected cells were responsible for the reproductive death of hematopoietic precursors. In agreement with this, myeloid nonadherent cells of long-term bone marrow cultures were selectively permissive for MVMi but not for MVMp replication, as judged by viral DNA synthesis, the expression of the nonstructural cytotoxic NS-1 protein, and virus propagation in these cells. Altogether, the suppressive effects mediated by the MVMi cytotoxic infection define a wide lympho-myelotropism not previously reported for this virus. The MVM-mouse model highlights the role that unsuspected virus-hematopoietic compartment interactions may play in bone marrow failures of immunocompromised animal or human hosts.

Emergence, natural history, and variation of canine, mink, and feline parvoviruses

This chapter discusses the emergence of canine parvovirus (CPV), the evidence concerning the previous emergence of mink enteritis virus (MEV) as the cause of a new disease in minks in the 1940s, and the mechanisms that determine the host ranges and other specific properties of the viruses of cats, minks, and dogs. The viruses are classified as the feline parvovirus subgroup of the genus Parvovirus, within the family Parvoviridae. Feline panleukopenia virus (FPV), MEV, and CPV are classified as “host range variants.” In addition to the viruses of cats, minks, and dogs, similar viruses naturally infect many species within the families Felidae, Canidae, Procyonidae, Mustelidae, and possibly the Viverridae. The differences in virulence for minks observed after inoculation of MEV or FPV suggests that there are subtle differences between FPV and MEV that have yet to be defined. Genetic mapping studies indicate that only three or four sequence differences between the FPV and CPV-2 isolates within the VP-1 lVP-2 gene determine all of the specific properties of CPV that have been defined: the pH dependence of hemagglutination, the CPV-specific epitope, and the host range for canine cells and dogs.

Viruses and bone marrow failure

Some generalizations can be drawn from a review of virus-associated bone marrow failure. The story of B19 parvovirus illustrates that viral infection may be an occult cause of marrow failure. Although the epidemiology of transient aplastic crisis suggested a viral aetiology, the implication of a single virus was surprising; the sporadic appearance of chronic bone marrow failure in immunosuppressed persons has had none of the features of a viral illness. The incrimination of parvovirus in these cases required development of specific immunological and molecular assays. Human and animal retrovirus studies have shown that small changes in the virus genome can have dramatic effects on the biology of the infectious agent and its pathogenicity in infected hosts. In Epstein-Barr virus infection, the host's immune response may play a more important role in mediating disease than virus cytotoxicity. Finally, the association of aplastic anaemia with hepatitis may be underestimated because of the inability to diagnose virus infection without obvious liver disease. The true spectrum of bone marrow disease due to virus infection is not known.

Experimentally induced severe canine parvoviral enteritis

Severe enteritis was produced in recently weaned, 8-week old pups 3 to 9 days after being given parvovirus by mouth. The most severe manifestations of disease were observed 7 days after infection, when one pup died. Viraemia was detected on days 4 and 5 and a severe leucopenia was present 6 to 8 days after infection. Antibody was demonstrated in serum 4 days after infection, high titres being present 3 days later. Sequential pathological studies revealed necrosis of Peyer's patches on day 3. Between days 5 and 7 typical lesions of the disease became widespread with necrosis of tonsil and thymus being prominent. By the fifth day after infection viral inclusion bodies were numerous. Virus isolation from tissues was greatest at this stage and had diminished by the seventh day. Although tissue repair was well advanced by the tenth day thymic necrosis remained prominent and villous atrophy was still present on day 13. Based on these findings a possible pathogenesis is discussed.

Canine parvoviral disease: experimental reproduction of the enteric form with a parvovirus isolated from a case of myocarditis

Five 7-week-old pups and four 4-week-old pups, all seronegative to canine parvovirus, were inoculated intravenously with 1000 haemagglutinating units of canine parvovirus originally isolated from the myocardium of a dog with naturally occurring myocarditis. After three days, pups in both litters became pyrexic, anorectic and depressed, with vomiting and diarrhoea. The 4-week-old pups were killed on day 4, and the 7-week-old pups died or were killed on day 5 post-inoculation. Histological examination showed degeneration and necrosis of intestinal crypt epithelial cells and villous atrophy. All pups had thymic atrophy caused by lymphoid depletion. Peyer's patches, mesenteric lymph node and spleen also had lymphoid depletion. Lymphoid necrosis was present occasionally in these tissues. In the bone marrow, granulocytes and granulocyte and erythroid precursors were depleted. Amphophilic intranuclear inclusion bodies were abundant in crypt epithelial nuclei, less so in myocardial nuclei. Canine parvovirus was isolated from intestinal contents, thymus, spleen, mesenteric lymph node and liver in most pups, but not from kidney or myocardium.

Light and electron microscopic evaluation of thymuses from feline leukemia virus-infected kittens

Light microscopic and electron microscopic findings in thymuses from 4-week old feline leukemia virus-infected and 4- and 9-week old noninfected kittens were evaluated and found to be morphologically similar to each other. Thymuses from 9-week old feline leukemia virusinfected kittens were markedly atrophied and individual lobules within each thymus varied in the severity of atrophy. Loubules having the least severe atrophy had a moderate thinning of the cortex and a heterogeneous thymuses included intense eosinopoiesis at the corticomedullary junction, increased prominence of vasculature, and enlarged Hassal's corpuscles. In addition to these changes lobules of thymus having the most severe atrophy had a marked cortical thymocyte depletion, lobule collapse, and increased numbers of mast cells. Degeneration of epithelial cells in most lobules was indicated by electronlucency of the cytoplasmic matrix and often greatly dilated rough endoplasmic reticulum.

Feline panleukopenia. III. Development of lesions in the lymphoid tissues

Germfree and specific pathogen-free cats were inoculated with feline panleukopenia virus. Cats were necropsied 2 to 6 days after inoculation and tissues from the thymus, lymph nodes and spleen taken for histological and immunofluorescence studies. Necrosis of lymphoid cells in the thymic cortex began 3 days after inoculation and continued for 5 to 6 days after inoculation when the thymus was nearly depleted of lymphocytes. Immunofluorescence studies showed the lesions to be caused by virus. There was gross and histological involution of the thymus in both germfree and specific pathogen-free cats. The lymph nodes and spleen of uninoculated germfree cats looked "inactive" and lacked well developed lymphoid follicles and paracortical areas. In both germfree and specific pathogen-free cats there was necrosis in both follicular and paracortical areas of the lymph nodes and follicular and periarteriolar areas of the spleen 3 to 4 days after inoculation. Immunofluorescence showed these areas had virus infection. By 5 to 6 days after inoculation, these areas were populated by many lymphoblastoic cells. Even though significant destruction of lymphoid cells occurred, subsequently, in cats that develop mild clinical illness, these lymphoid tissues seemed stimulated rather than depleted of lymphocytes.