Analysis of FeLV-FAIDS provirus burden and productive infection in lymphocyte subsets in vivo

Hepadnavirus Infection in a Cat with Chronic Liver Disease: A Multi-Disciplinary Diagnostic Approach

A 3-year-old female stray, shorthair cat, with clinical signs and serum chemistry markers indicative of hepatic disease, was diagnosed with domestic cat hepadnavirus (DCH) infection. Coupling molecular and serological data, the infection was seemingly contextualized into a chronic phase, since IgM anti-core antibodies, a marker of early-stage Hepatitis B Virus (HBV) infection, were not detected. However, the cat possessed IgG anti-core, a common indicator of chronic HBV infection in human patients and did not show seroconversion to the anti-DCH surface antigen, considered protective during HBV infection and associated with long-term protective immunity. On genome sequencing, the DCH strain showed 98.3% nucleotide identity to strains previously identified in Italy.

An Outbreak of Limping Syndrome Associated with Feline Calicivirus

Feline calicivirus (FCV) is a common viral pathogen found in domestic cats. FCV is highly contagious and demonstrates a high genetic variability. Upper respiratory tract disease, oral ulcerations, salivation, and gingivitis-stomatitis have been regarded as typical clinical signs of FCV infection. Ulcerative dermatitis, abortion, severe pneumonia, enteritis, chronic stomatitis, and virulent systemic disease have been reported more sporadically. Limping syndrome has been also described either in naturally or experimentally FCV-infected cats. In this study, we monitored a small outbreak of FCV infection in two household cats, in which limping disease was monitored with a 12-day lag time. The complete genome sequence was determined for the viruses isolated from the oropharyngeal and rectal swabs of the two animals, mapping up to 39 synonymous nucleotide mutations. The four isolates were sensitive to low pH conditions and trypsin treatment, a pattern usually associated with viruses isolated from the upper respiratory tract. Overall, the asynchronous pattern of infections and the results of genome sequencing suggest that a virus of respiratory origin was transmitted between the animals and that the FCV strain was able to retain the limping disease pathotype during the transmission chain, as previously observed in experimental studies with FCV strains associated with lameness.

Phylogenetic identification of feline leukemia virus A and B in cats with progressive infection developing into lymphoma and leukemia

To date, only a few studies have examined the impacts of feline leukemia virus (FeLV) subgroups on disease development in spontaneously infected cats. The present study identified FeLV-A and FeLV-B subgroups in cats with lymphoma and leukemia and explored the phylogenetic relationships of env sequences. Twenty-six cats with lymphoma (n=16) or leukemia (n=10) were selected. FeLV p27 antigen positivity was determined using ELISA, and proviral DNA in blood samples was detected using nested PCR. Positive animals in both tests were classified as cases of FeLV progressive infection and subjected to a second nested PCR for env amplification and subgroup determination. Six samples of FeLV-A and five samples of FeLV-B were sequenced using the Sanger method, and the results were used to build a phylogenetic tree and estimate evolutionary divergence. Among cats with lymphoma, 68.8% carried FeLV-AB and 31.2% FeLV-A. Among cats with leukemia, 70% carried FeLV-AB and 30% FeLV-A. Regarding cat characteristics, 50% were young, 30.8% young adults, and 19.2% adults; 88.5% were mixed-breed and 11.5% pure breed; and 42.3% were males and 57.7% were females. Among lymphomas, 62.5% were mediastinal, 31.3% multicentric, and 6.3% extranodal. Regarding histological classification, lymphoblastic and small non-cleaved-cell lymphomas were the most frequently detected. Among leukemia cases, 30% were acute lymphoid, 30% chronic myeloid, and 40% acute myeloid. Phylogenetic analysis showed that FeLV-A SC sequences were closely related to the Arena, Glasgow-1, and FeLV-FAIDS variants. Meanwhile, FeLV-B SC sequences were divergent from one another but similar to the endogenous FELV env gene (enFeLV). In conclusion, FeLV-AB is prevalent in cats with lymphoma and leukemia, highlighting the genetic diversity involved in the pathogenesis of these neoplasms in Brazil.

Detection and Characterization of Feline Calicivirus Associated with Paw and Mouth Disease

Feline calicivirus (FCV) infection in cats can led to several diverse clinical presentations, ranging from mild upper respiratory signs to virulent systemic disease. Herein, we report a paw and mouth disease case in a 7-year-old household cat due to an FCV infection. An asymptomatic cat living in the same household was also infected with FCV. Clinical and pathological investigations were combined with the molecular and phenotypical characterization of the FCV strains. The RNA of the FCV was detected using qualitative and quantitative reverse transcription (RT)-PCR assays, and FCV antigen was confirmed by immunohistochemistry. After the whole genome analysis, the strains detected in the two cats appeared to be genetically diverse from FCVs previously detected in association with paw and mouth disease and with virulent systemic disease. Interestingly, the isolates obtained in this study were resistant to low pH conditions and slightly susceptible to bile salts, but they were susceptible to a trypsin treatment, revealing a phenotype pattern that is different from that which has been observed for respiratory FCVs.

The outcomes of polyparasitism in stray cats from Brazilian Midwest assessed by epidemiological, hematological and pathological data

We evaluated the epidemiological, hematological, and pathological data of Leishmania spp., Toxoplasma gondii, Platynosomum illiciens, feline immunodeficiency virus (FIV), and feline leukemia virus (FeLV) infections and the coinfections in stray cats of an endemic area for leishmaniasis. The diagnosis was performed by serological tests and necropsy. We described gross lesions and histopathological findings. We used immunohistochemistry and chromogenic in situ hybridization for L. infantum detection. We found infection in 27 out of 50 sampled cats, among them, 14 presented coinfections. A strong correlation between splenomegaly and lymphadenomegaly with FeLV, and an association between hepatic lesions and cachexia with parasitism due to P. illiciens were observed. Moreover, we found a significant increase in the monocyte count in the FeLV-infected and a decrease in the red blood cell count in the FIV-infected animals. Amastigote forms of Leishmania spp. and tissue changes were detected in lymphoid organs of an animal coinfected with P. illiciens, T. gondii, and FIV. Polyparasitism recorded in stray cats of the Brazilian Midwest should be considered in effective control strategies for public health diseases. Moreover, stray cats of Campo Grande may be a source of infection of FIV, FeLV and P. illiciens for populations of domiciled cats.

Frecuencia de la leucemia felina (vilef): refugio municipal Rionegro, Colombia 2020

La leucemia viral felina (ViLeF) es una enfermedad retroviral letal, de una elevada prevalencia en Colombia, que afecta a felinos de diferentes edades y sexos. El objetivo de esta investigación fue determinar la frecuencia por serodiagnóstico de ViLeF en felinos del centro integral de bienestar animal Ceiba, ubicado en Rionegro, Antioquia (Colombia), en 2020. Para ello, se realizó un estudio descriptivo longitudinal de serofrecuencia de ViLeF desde enero hasta diciembre de 2020. Fueron muestreados 92 gatos, a los cuales se les efectuó una prueba p27 por inmunoensayo comercial Elisa (Idexx©, Snap Combo Plus®, Maine, EE. UU.). La frecuencia de felinos positivos fue 30/92 (32,60%) y el mes de mayo fue el de mayor frecuencia (9,78%). Los machos positivos fueron 17/92 (18,47%) y las hembras 13/92 (14,13%). La edad promedio de seropositividad fue 2,14 años. La frecuencia de ViLeF en 2020 para Ceiba, Rionegro (Colombia) es de 32,60%, un valor elevado con respecto a descripciones en otros albergues para felinos. ViLeF es una enfermedad que está siendo reportada con mayor frecuencia en Colombia, debido a que las medidas de prevención no se están adoptando rutinariamente.

A longitudinal observational study in two cats naturally-infected with hepadnavirus

Hepatitis B virus (HBV) is a major cause of liver disease in humans including chronic hepatitis and hepatocellular carcinoma. Domestic cat hepadnavirus (DCH), a novel HBV-like hepadnavirus, was identified in domestic cats in 2018. From 6.5 %-10.8 % of pet cats are viremic for DCH and altered serological markers suggestive of liver damage have been identified in 50 % of DCH-infected cats. DCH DNA has been detected in association with characteristic lesions of chronic hepatitis and with hepatocellular carcinoma in cats, suggesting a possible association. In this study longitudinal molecular screening of cats infected with DCH was performed to determine if DCH can cause chronic infections in cats. Upon re-testing of sera from five DCH-positive animals, 2-10 months after the initial diagnosis, three cats tested negative for DCH on two consecutive occasions using quantitative PCR. Two other cats remained DCH-positive, including an 8-month-old female cat re-tested four months after the initial positive result, and a 9-year-old male cat, which tested positive for DCH on six occasions over an 11-month period. The latter had a history of chronic hepatopathy with jaundice, lethargy and elevated serum alanine transaminase levels (ALT). During the period of observation, DCH titers ranged between 1.64 × 10⁵ and 2.09 × 10⁶ DNA copies/mL and ALT was persistently elevated, suggesting chronic infection. DCH DNA was not detected in oral, conjunctival, preputial and rectal swabs from the two animals collected at several time points. Long-term (chronic) infection would be consistent with the relatively high number of viremic cats identified in epidemiological investigations, with the possible association of DCH with chronic hepatic pathologies and with what described with HBV in human patients.

What's New in Feline Leukemia Virus Infection

Feline leukemia virus (FeLV) is a retrovirus with global impact on the health of domestic cats that causes tumors (mainly lymphoma), bone marrow disorders, and immunosuppression. The importance of FeLV is underestimated due to complacency associated with previous decline in prevalence. However, with this comes lowered vigilance, which, along with potential for regressively infected cats to reactivate viremia and shed the virus or develop clinical signs, can pose a risk to feline health. This article summarizes knowledge on FeLV pathogenesis, courses of infection, and factors affecting prevalance, infection outcome, and development of FeLV-associated diseases, with special focus on regressive FeLV infection.

Prevalence and risk factors for Felis catus gammaherpesvirus 1 detection in domestic cats in Italy

Felis catus gammaherpesvirus 1 (FcaGHV1), a novel gammaherpesvirus of domestic cats identified in 2014, has been detected in different countries demonstrating a worldwide distribution. The aim of this study was to establish the prevalence of FcaGHV1 in Italy using a molecular epidemiological approach. FcaGHV1 DNA was detected with virus-specific real-time PCR in ≃1% of 2659 feline blood samples tested. Analysis of risk factors showed that being male and coinfection with feline immunodeficiency virus (FIV) increase the likelihood of FcaGHV1 detection. One-third of FcaGHV1-positive cats also tested positive for FIV provirus, whereas coinfections with feline panleukopenia virus were not demonstrated. Further studies are necessary to confirm the risk factors for FcaGHV1 detection and the pathobiology of the virus.

Novel Orthopoxvirus and Lethal Disease in Cat, Italy

We report detection and full-genome characterization of a novel orthopoxvirus (OPXV) responsible for a fatal infection in a cat. The virus induced skin lesions histologically characterized by leukocyte infiltration and eosinophilic cytoplasmic inclusions. Different PCR approaches were unable to assign the virus to a defined OPXV species. Large amounts of typical brick-shaped virions, morphologically related to OPXV, were observed by electron microscopy. This OPXV strain (Italy_09/17) was isolated on cell cultures and embryonated eggs. Phylogenetic analysis of 9 concatenated genes showed that this virus was distantly related to cowpox virus, more closely related to to ectromelia virus, and belonged to the same cluster of an OPXV recently isolated from captive macaques in Italy. Extensive epidemiologic surveillance in cats and rodents will assess whether cats are incidental hosts and rodents are the main reservoir of the virus. The zoonotic potential of this novel virus also deserves further investigation.

Feline calicivirus infection in cats with virulent systemic disease, Italy

Feline calicivirus (FCV) is a contagious viral pathogen that usually causes a mild, self-limiting respiratory disease. More recently, highly virulent FCV strains have emerged and have been associated with severe systemic infection, referred to as virulent systemic disease (VSD). The objective of this study is to report VSD cases in Italian cats along with the molecular characterization of two detected FCV strains. Three client-owned cats showed clinical signs resembling to those described for VSD cases. The cats were subjected to molecular investigations for detection of FCV and other feline pathogens. Histopathology and immunohistochemistry were performed on internal organs of one cat; molecular characterization of two detected FCV strains was obtained through sequence and phylogenetic analyses. Putative VS-FCV strains were detected in all three cats, which were co-infected with feline panleukopenia virus. The cat submitted to histopathology and immunohistochemistry displayed severe histological changes and FCV antigens in internal organs. Two Italian FCV strains, for which amplification of ORF2 was successful, were strictly related and formed a unique phylogenetic cluster. These viruses did not show consistent changes in the amino acid sequences with respect to reference VS-FCVs. The results of our study confirm that VS-FCV strains are circulating in Italy and that VSD diagnosis is complicated since both genetic and clinical markers have not been identified so far.

Canine parvovirus type 2c infection in a kitten associated with intracranial abscess and convulsions

A case of canine parvovirus type 2c (CPV-2c) infection in a 3-month-old feral kitten with a cerebral abscess and neurological disease is reported. The cat displayed ataxia and convulsions together with signs of gastroenteritis and profound alteration of the total and differential white blood cell counts. A parvovirus strain was detected by a TaqMan assay in the blood and faeces of the affected kitten, which was characterised as CPV by means of molecular assays but did not react with any of the CPV type-specific probes. By sequence and phylogenetic analyses of the VP2-protein gene, the CPV-2c strain displayed a non-coding mutation in the probe-binding region. Although the role of CPV-2c in this particular case is unclear, it is possible that it predisposed the kitten to the clinical signs seen. Continuous surveillance is needed to monitor future spreading of this CPV-2c mutant, and any associated clinical signs, in the dog and cat population.

Feline leukemia virus immunity induced by whole inactivated virus vaccination

A fraction of cats exposed to feline leukemia virus (FeLV) effectively contain virus and resist persistent antigenemia/viremia. Using real-time PCR (qPCR) to quantitate circulating viral DNA levels, previously we detected persistent FeLV DNA in blood cells of non-antigenemic cats considered to have resisted FeLV challenge. In addition, previously we used RNA qPCR to quantitate circulating viral RNA levels and determined that the vast majority of viral DNA is transcriptionally active, even in the absence of antigenemia. A single comparison of all USDA-licensed commercially available FeLV vaccines using these modern sensitive methods has not been reported. To determine whether FeLV vaccination would prevent nucleic acid persistence, we assayed circulating viral DNA, RNA, antigen, infectious virus, and virus neutralizing (VN) antibody in vaccinated and unvaccinated cats challenged with infectious FeLV. We identified challenged vaccinates with undetectable antigenemia and viremia concomitant with persistent FeLV DNA and/or RNA. Moreover, these studies demonstrated that two whole inactivated virus (WIV) adjuvanted FeLV vaccines (Fort Dodge Animal Health's Fel-O-Vax Lv-K) and Schering-Plough Animal Health's FEVAXYN FeLV) provided effective protection against FeLV challenge. In nearly every recipient of these vaccines, neither viral DNA, RNA, antigen, nor infectious virus could be detected in blood after FeLV challenge. Interestingly, this effective viral containment occurred despite a weak to undetectable VN antibody response. The above findings reinforce the precept of FeLV infection as a unique model of effective retroviral immunity elicited by WIV vaccination, and as such holds valuable insights into retroviral immunoprevention and therapy.

Cellular segregation of feline leukemia provirus and viral RNA in leukocyte subsets of long-term experimentally infected cats

Cats exposed to feline leukemia virus (FeLV) may develop different outcomes of the infection. However, during acute infection blood proviral and viral RNA loads of cats with progressive and regressive infection are not significantly different. Thus, not the overall loads but rather those of specific leukocyte subsets may influence the infection outcome. By combining fluorescence activated cell sorting (FACS) with sensitive real-time TaqMan PCR and reverse transcriptase (RT) PCR, we established in the present study the methods to determine FeLV proviral and viral RNA loads in specific leukocyte subsets. In addition, they were applied to analyze long-term persistently FeLV-infected (p27-positive) and FeLV exposed but nonantigenemic (p27-negative), nonviremic cats. In the latter animals, CD4(+) and B lymphocytes exhibited the highest proviral loads, whereas in p27-positive cats, all leukocyte subsets showed similar high loads. In p27-positive cats, monocytes and granulocytes bore the highest viral RNA loads, whereas only one p27-negative cat was positive for viral RNA in T lymphocytes. To our knowledge, this is the first study to investigate FeLV proviral and viral RNA loads in leukocyte subsets of FeLV exposed cats. The herein described methods are important prerequisites to gain a deeper insight into the pathogenesis of FeLV infection.

Specificity in receptor usage by T-cell-tropic feline leukemia viruses: implications for the in vivo tropism of immunodeficiency-inducing variants

Cytopathic, T-cell-tropic feline leukemia viruses (FeLV-T) evolve from FeLV-A in infected animals and demonstrate host cell specificities that are distinct from those of their parent viruses. We recently identified two cellular proteins, FeLIX and Pit1, required for productive infection by these immunodeficiency-inducing FeLV-T variants (M. M. Anderson, A. S. Lauring, C. C. Burns, and J. Overbaugh, Science 287:1828-1830, 2000). FeLV-T is the first example of a naturally occurring type C retrovirus that requires two proteins to gain entry into target cells. FeLIX is an endogenous protein that is highly related to the N-terminal portion of the FeLV envelope protein, which includes the receptor-binding domain. Pit1 is a multiple-transmembrane phosphate transport protein that also functions as a receptor for FeLV-B. The FeLV-B envelope gene is derived by recombination with endogenous FeLV-like sequences, and its product can functionally substitute for FeLIX in facilitating entry through the Pit1 receptor. In the present study, we tested other retrovirus envelope surface units (SUs) with their cognate receptors to determine whether they also could mediate infection by FeLV-T. Cells were engineered to coexpress the transmembrane form of the envelope proteins and their cognate receptors, or SU protein was added as a soluble protein to cells expressing the receptor. Of the FeLV, murine leukemia virus, and gibbon ape leukemia virus envelopes tested, we found that only those with receptor-binding domains derived from endogenous FeLV could render cells permissive for FeLV-T. We also found that there is a strong preference for Pit1 as the transmembrane receptor. Specifically, FeLV-B SUs could efficiently mediate infection of cells expressing the Pit1 receptor but could only inefficiently mediate infection of cells expressing the Pit2 receptor, even though these SUs are able to bind to Pit2. Expression analysis of feline Pit1 and FeLIX suggests that FeLIX is likely the primary determinant of FeLV-T tropism. These results are discussed in terms of current models for retrovirus entry and the interrelationship among FeLV variants that evolve in vivo.

Feline leukaemia provirus load during the course of experimental infection and in naturally infected cats

Feline leukaemia virus (FeLV) infection in domestic cats can vary in its outcome (persistent, transient, no infection) for reasons that are not entirely known. It was hypothesized that the initial virus and provirus load could significantly influence the course of retrovirus infection. To determine the role of provirus loads, two methods of PCR, a nested PCR and a fluorogenic probe-based (TaqMan) real-time quantitative PCR, which were specific to the U3 region of FeLV-A were established. FeLV provirus in naturally and experimentally infected cats was then measured. Only 3 weeks after experimental FeLV-A infection, persistently infected cats demonstrated higher provirus loads and lower humoral immune responses than cats that had overcome antigenaemia. Lower initial provirus loads were associated with successful humoral immune responses. Unexpectedly, provirus in the buffy-coat cells of two cats that tested negative for the p27 antigen (a marker for viraemia) was also detected. In 597 Swiss cats, comparison of p27 antigen levels with PCR results revealed broad agreement. However, similar to the experimental situation, a significant number of animals (10%) was negative for the p27 antigen and FeLV-positive by PCR. These cats had a mean provirus load 300-fold lower than that of animals testing positive for the p27 antigen. In conclusion, an association between the provirus load and the outcome of FeLV infection was found. Detection of provirus carriers should contribute to further the control of FeLV. In addition, quantification of provirus loads will lead to a better understanding of FeLV pathogenesis and anti-retrovirus protective mechanisms.