Evaluation of a Revised Point-of-Care Test for the Detection of Feline Leukaemia p27 Antigen and Anti-p15E Antibodies in Cats.

The first point-of-care (PoC) test (v-RetroFel®; modified version 2021) determining the presence of FeLV p27 antigen and FeLV anti-p15E antibodies has become recently commercially available to identify different feline leukaemia virus (FeLV) infection outcomes. This study aimed to assess this PoC test's performance concerning FeLV p27 antigen and FeLV anti-p15E antibody detection. Sensitivity, specificity, positive and negative predictive values (PPV, NPV) were assessed after ten minutes (recommended) and 20 min (prolonged) incubation times. The test results were evaluated as either positive or negative. Serum samples from 934 cats were included, originating from Italy (n = 269), Portugal (n = 240), Germany (n = 318), and France (n = 107). FeLV p27 antigen and anti-p15E antibodies were measured by reference standard ELISAs and compared to the PoC test results. The PoC test was easy to perform and the results easy to interpret. Sensitivity and specificity for FeLV p27 antigen were 82.8% (PPV: 57.8%) and 96.0% (NPV: 98.8%) after both, ten and 20 minues of incubation time. Sensitivity and specificity for anti-p15E antibodies were 31.4% (PPV: 71.6%) and 96.9% (NPV: 85.1%) after ten minutes incubation time; sensitivity was improved by a prolonged incubation time (20 min) to 40.0% (PPV: 76.3%), while specificity remained the same (96.9%, NPV: 86.7%). Despite the improved sensitivity using the prolonged incubation time, lower than ideal sensitivities for both p27 antigen and especially anti-p15E antibodies were found, indicating that the PoC test in its current version needs further improvement prior to application in the field.

FeLIX is a restriction factor for mammalian retrovirus infection.

Endogenous retroviruses (ERVs) are remnants of ancestral viral infections. Feline leukemia virus (FeLV) is an exogenous and endogenous retrovirus in domestic cats. It is classified into several subgroups (A, B, C, D, E, and T) based on viral receptor interference properties or receptor usage. ERV-derived molecules benefit animals, conferring resistance to infectious diseases. However, the soluble protein encoded by the defective envelope (env) gene of endogenous FeLV (enFeLV) functions as a co-factor in FeLV subgroup T infections. Therefore, whether the gene emerged to facilitate viral infection is unclear. Based on the properties of ERV-derived molecules, we hypothesized that the defective env genes possess antiviral activity that would be advantageous to the host because FeLV subgroup B (FeLV-B), a recombinant virus derived from enFeLV env, is restricted to viral transmission among domestic cats. When soluble truncated Env proteins from enFeLV were tested for their inhibitory effects against enFeLV and FeLV-B, they inhibited viral infection. Notably, this antiviral machinery was extended to infection with the Gibbon ape leukemia virus, Koala retrovirus A, and Hervey pteropid gammaretrovirus. Although these viruses used feline phosphate transporter 1 (fePit1) and phosphate transporter 2 as receptors, the inhibitory mechanism involved competitive receptor binding in a fePit1-dependent manner. The shift in receptor usage might have occurred to avoid the inhibitory effect. Overall, these findings highlight the possible emergence of soluble truncated Env proteins from enFeLV as a restriction factor against retroviral infection and will help in developing host immunity and antiviral defense by controlling retroviral spread.IMPORTANCERetroviruses are unique in using reverse transcriptase to convert RNA genomes into DNA, infecting germ cells, and transmitting to offspring. Numerous ancient retroviral sequences are known as endogenous retroviruses (ERVs). The soluble Env protein derived from ERVs functions as a co-factor that assists in FeLV-T infection. However, herein, we show that the soluble Env protein exhibits antiviral activity and provides resistance to mammalian retrovirus infection through competitive receptor binding. In particular, this finding may explain why FeLV-B transmission is not observed among domestic cats. ERV-derived molecules can benefit animals in an evolutionary arms race, highlighting the double-edged-sword nature of ERVs.

Multiple recombination events between endogenous retroviral elements and feline leukemia virus.

Feline leukemia virus (FeLV) is an exogenous retrovirus that causes malignant hematopoietic disorders in domestic cats, and its virulence may be closely associated with viral sequences. FeLV is classified into several subgroups, including A, B, C, D, E, and T, based on viral receptor interference properties or receptor usage. However, the transmission manner and disease specificity of the recombinant viruses FeLV-D and FeLV-B remain unclear. The aim of this study was to understand recombination events between exogenous and endogenous retroviruses within a host and elucidate the emergence and transmission of recombinant viruses. We observed multiple recombination events involving endogenous retroviruses (ERVs) in FeLV from a family of domestic cats kept in one house; two of these cats (ON-T and ON-C) presented with lymphoma and leukemia, respectively. Clonal integration of FeLV-D was observed in the ON-T case, suggesting an association with FeLV-D pathogenesis. Notably, the receptor usage of FeLV-B observed in ON-T was mediated by feline Pit1 and feline Pit2, whereas only feline Pit1 was used in ON-C. Furthermore, XR-FeLV, a recombinant FeLV containing an unrelated sequence referred to the X-region, which is homologous to a portion of the 5'-leader sequence of Felis catus endogenous gammaretrovirus 4 (FcERV-gamma4), was isolated. Genetic analysis suggested that most recombinant viruses occurred de novo; however, the possibility of FeLV-B transmission was also recognized in the family. This study demonstrated the occurrence of multiple recombination events between exogenous and endogenous retroviruses in domestic cats, highlighting the contribution of ERVs to pathogenic recombinant viruses.IMPORTANCEFeline leukemia virus subgroup A (FeLV-A) is primarily transmitted among cats. During viral transmission, genetic changes in the viral genome lead to the emergence of novel FeLV subgroups or variants with altered virulence. We isolated three FeLV subgroups (A, B, and D) and XR-FeLV from two cats and identified multiple recombination events in feline endogenous retroviruses (ERVs), such as enFeLV, ERV-DC, and FcERV-gamma4, which are present in the cat genome. This study highlights the pathogenic contribution of ERVs in the emergence of FeLV-B, FeLV-D, and XR-FeLV in a feline population.

Convergent evolution of antiviral machinery derived from endogenous retrovirus truncated envelope genes in multiple species.

Host genetic resistance to viral infection controls the pathogenicity and epidemic dynamics of infectious diseases. Refrex-1 is a restriction factor against feline leukemia virus subgroup D (FeLV-D) and an endogenous retrovirus (ERV) in domestic cats (ERV-DC). Refrex-1 is encoded by a subset of ERV-DC loci with truncated envelope genes and secreted from cells as a soluble protein. Here, we identified the copper transporter CTR1 as the entry receptor for FeLV-D and genotype I ERV-DCs. We also identified CTR1 as a receptor for primate ERVs from crab-eating macaques and rhesus macaques, which were found in a search of intact envelope genes capable of forming infectious viruses. Refrex-1 counteracted infection by FeLV-D and ERV-DCs via competition for the entry receptor CTR1; the antiviral effects extended to primate ERVs with CTR1-dependent entry. Furthermore, truncated ERV envelope genes found in chimpanzee, bonobo, gorilla, crab-eating macaque, and rhesus macaque genomes could also block infection by feline and primate retroviruses. Genetic analyses showed that these ERV envelope genes were acquired in a species- or genus-specific manner during host evolution. These results indicated that soluble envelope proteins could suppress retroviral infection across species boundaries, suggesting that they function to control retroviral spread. Our findings revealed that several mammalian species acquired antiviral machinery from various ancient retroviruses, leading to convergent evolution for host defense.

Rapid characterization of feline leukemia virus infective stages by a novel nested recombinase polymerase amplification (RPA) and reverse transcriptase-RPA.

Feline leukemia virus (FeLV) is a major viral disease in cats, causing leukemia and lymphoma. The molecular detection of FeLV RNA and the DNA provirus are important for staging of the disease. However, the rapid immunochromatographic assay commonly used for antigen detection can only detect viremia at the progressive stage. In this study, nested recombinase polymerase amplification (nRPA) was developed for exogenous FeLV DNA provirus detection, and reverse transcriptase polymerase amplification (RT-RPA) was developed for the detection of FeLV RNA. The approaches were validated using 108 cats with clinicopathologic abnormalities due to FeLV infection, and from 14 healthy cats in a vaccination plan. The nRPA and RT-RPA assays could rapidly amplify the FeLV template, and produced high sensitivity and specificity. The FeLV detection rate in regression cats by nRPA was increased up to 45.8% compared to the rapid immunochromatographic assay. Hence, FeLV diagnosis using nRPA and RT-RPA are rapid and easily established in low resource settings, benefiting FeLV prognosis, prevention, and control of both horizontal and vertical transmission.

Endogenous Feline Leukemia Virus (FeLV) siRNA Transcription May Interfere with Exogenous FeLV Infection.

Endogenous retroviruses (ERVs) are increasingly recognized for biological impacts on host cell function and susceptibility to infectious agents, particularly in relation to interactions with exogenous retroviral progenitors (XRVs). ERVs can simultaneously promote and restrict XRV infections using mechanisms that are virus and host specific. The majority of endogenous-exogenous retroviral interactions have been evaluated in experimental mouse or chicken systems, which are limited in their ability to extend findings to naturally infected outbred animals. Feline leukemia virus (FeLV) has a relatively well-characterized endogenous retrovirus with a coexisting virulent exogenous counterpart and is endemic worldwide in domestic cats. We have previously documented an association between endogenous FeLV (enFeLV) long terminal repeat (LTR) copy number and abrogated exogenous FeLV in naturally infected cats and experimental infections in tissue culture. Analyses described here examine limited FeLV replication in experimentally infected peripheral blood mononuclear cells, which correlates with higher enFeLV transcripts in these cells compared to fibroblasts. We further examine NCBI Sequence Read Archive RNA transcripts to evaluate enFeLV transcripts and RNA interference (RNAi) precursors. We find that lymphoid-derived tissues, which are experimentally less permissive to exogenous FeLV infection, transcribe higher levels of enFeLV under basal conditions. Transcription of enFeLV-LTR segments is significantly greater than that of other enFeLV genes. We documented transcription of a 21-nucleotide (nt) microRNA (miRNA) just 3' to the enFeLV 5'-LTR in the feline miRNAome of all data sets evaluated (n = 27). Our findings point to important biological functions of enFeLV transcription linked to solo LTRs distributed within the domestic cat genome, with potential impacts on domestic cat exogenous FeLV susceptibility and pathogenesis. IMPORTANCE Endogenous retroviruses (ERVs) are increasingly implicated in host cellular processes and susceptibility to infectious agents, specifically regarding interactions with exogenous retroviral progenitors (XRVs). Exogenous feline leukemia virus (FeLV) and its endogenous counterpart (enFeLV) represent a well-characterized, naturally occurring XRV-ERV dyad. We have previously documented an abrogated FeLV infection in both naturally infected cats and experimental fibroblast infections that harbor higher enFeLV proviral loads. Using an in silico approach, we provide evidence of miRNA transcription that is produced in tissues that are most important for FeLV infection, replication, and transmission. Our findings point to important biological functions of enFeLV transcription linked to solo-LTRs distributed within the feline genome, with potential impacts on domestic cat exogenous FeLV susceptibility and pathogenesis. This body of work provides additional evidence of RNA interference (RNAi) as a mechanism of viral interference and is a demonstration of ERV exaptation by the host to defend against related XRVs.

Adeno-Associated Vector-Delivered CRISPR/SaCas9 System Reduces Feline Leukemia Virus Production In Vitro.

Feline leukemia virus (FeLV) is a retrovirus of cats worldwide. High viral loads are associated with progressive infection and the death of the host, due to FeLV-associated disease. In contrast, low viral loads, an effective immune response, and a better clinical outcome can be observed in cats with regressive infection. We hypothesize that by lowering viral loads in progressively infected cats, using CRISPR/SaCas9-assisted gene therapy, the cat's immune system may be permitted to direct the infection towards a regressive outcome. In a step towards this goal, the present study evaluates different adeno-associated vectors (AAVs) for their competence in delivering a gene editing system into feline cells, followed by investigations of the CRISPR/SaCas9 targeting efficiency for different sites within the FeLV provirus. Nine natural AAV serotypes, two AAV hybrid strains, and Anc80L65, an in silico predicted AAV ancestor, were tested for their potential to infect different feline cell lines and feline primary cells. AAV-DJ revealed superior infection efficiency and was thus employed in subsequent transduction experiments. The introduction of double-strand breaks, using the CRISPR/SaCas9 system targeting 12 selected FeLV provirus sites, was confirmed by T7 endonuclease 1 (T7E1), as well as Tracking of Indels by Decomposition (TIDE) analysis. The highest percentage (up to 80%) of nonhomologous end-joining (NHEJ) was found in the highly conserved gag and pol regions. Subsequent transduction experiments, using AAV-DJ, confirmed indel formation and showed a significant reduction in FeLV p27 antigen for some targets. The targeting of the FeLV provirus was efficient when using the CRISPR/SaCas9 approach in vitro. Whether the observed extent of provirus targeting will be sufficient to provide progressively FeLV-infected cats with the means to overcome the infection needs to be further investigated in vivo.

Feline Leukemia Virus (FeLV) Endogenous and Exogenous Recombination Events Result in Multiple FeLV-B Subtypes during Natural Infection.

Feline leukemia virus (FeLV) is associated with a range of clinical signs in felid species. Differences in disease processes are closely related to genetic variation in the envelope (env) region of the genome of six defined subgroups. The primary hosts of FeLV are domestic cats of the Felis genus that also harbor endogenous FeLV (enFeLV) elements stably integrated in their genomes. EnFeLV elements display 86% nucleotide identity to exogenous, horizontally transmitted FeLV (FeLV-A). Variation between enFeLV and FeLV-A is primarily in the long terminal repeat (LTR) and env regions, which potentiates generation of the FeLV-B recombinant subgroup during natural infection. The aim of this study was to examine recombination behavior of exogenous FeLV (exFeLV) and enFeLV in a natural FeLV epizootic. We previously described that of 65 individuals in a closed colony, 32 had productive FeLV-A infection, and 22 of these individuals had detectable circulating FeLV-B. We cloned and sequenced the env gene of FeLV-B, FeLV-A, and enFeLV spanning known recombination breakpoints and examined between 1 and 13 clones in 22 animals with FeLV-B to assess sequence diversity and recombination breakpoints. Our analysis revealed that FeLV-A sequences circulating in the population, as well as enFeLV env sequences, are highly conserved. We documented many recombination breakpoints resulting in the production of unique FeLV-B genotypes. More than half of the cats harbored more than one FeLV-B variant, suggesting multiple recombination events between enFeLV and FeLV-A. We concluded that FeLV-B was predominantly generated de novo within each host, although we could not definitively rule out horizontal transmission, as nearly all cats harbored FeLV-B sequences that were genetically highly similar to those identified in other individuals. This work represents a comprehensive analysis of endogenous-exogenous retroviral interactions with important insights into host-virus interactions that underlie disease pathogenesis in a natural setting. IMPORTANCE Feline leukemia virus (FeLV) is a felid retrovirus with a variety of disease outcomes. Exogenous FeLV-A is the virus subgroup almost exclusively transmitted between cats. Recombination between FeLV-A and endogenous FeLV analogues in the cat genome may result in emergence of largely replication-defective but highly virulent subgroups. FeLV-B is formed when the 3' envelope (env) region of endogenous FeLV (enFeLV) recombines with that of the exogenous FeLV (exFeLV) during viral reverse transcription and integration. Both domestic cats and wild relatives of the Felis genus harbor enFeLV, which has been shown to limit FeLV-A disease outcome. However, enFeLV also contributes genetic material to the recombinant FeLV-B subgroup. This study evaluates endogenous-exogenous recombination outcomes in a naturally infected closed colony of cats to determine mechanisms and risk of endogenous retroviral recombination during exogenous virus exposure that leads to enhanced virulence. While FeLV-A and enFeLV env regions were highly conserved from cat to cat, nearly all individuals with emergent FeLV-B had unique combinations of genotypes, representative of a wide range of recombination sites within env. The findings provide insight into unique recombination patterns for emergence of new pathogens and can be related to similar viruses across species.

Measuring the Humoral Immune Response in Cats Exposed to Feline Leukaemia Virus.

Retroviruses belong to an important and diverse family of RNA viruses capable of causing neoplastic disease in their hosts. Feline leukaemia virus (FeLV) is a gammaretrovirus that infects domestic and wild cats, causing immunodeficiency, cytopenia and neoplasia in progressively infected cats. The outcome of FeLV infection is influenced by the host immune response; progressively infected cats demonstrate weaker immune responses compared to regressively infected cats. In this study, humoral immune responses were examined in 180 samples collected from 123 domestic cats that had been naturally exposed to FeLV, using a novel ELISA to measure antibodies recognizing the FeLV surface unit (SU) glycoprotein in plasma samples. A correlation was demonstrated between the strength of the humoral immune response to the SU protein and the outcome of exposure. Cats with regressive infection demonstrated higher antibody responses to the SU protein compared to cats belonging to other outcome groups, and samples from cats with regressive infection contained virus neutralising antibodies. These results demonstrate that an ELISA that assesses the humoral response to FeLV SU complements the use of viral diagnostic tests to define the outcome of exposure to FeLV. Together these tests could allow the rapid identification of regressively infected cats that are unlikely to develop FeLV-related disease.

Feline Leukemia Virus p27 Antigen Concentration and Proviral DNA Load Are Associated with Survival in Naturally Infected Cats.

Longitudinal studies of cats naturally infected with feline leukemia virus (FeLV) are important for understanding disease outcomes. Levels of p27 antigen and copy numbers of proviral DNA have been associated with FeLV-infection courses. The purpose of this prospective study was to establish cutoff values for p27 antigen concentration and proviral DNA load that distinguished high positive from low positive groups of cats and to evaluate an association with survival. At enrollment, 254 cats were tested by point-of-care and microtiter plate enzyme-linked immunosorbent assays (ELISAs) for p27 antigen and real-time polymerase chain reaction (PCR) for proviral DNA. The 127 positive cats were retested monthly for six months and monitored for survival over the four-year study. A receiver operating characteristic-based analysis of samples with concordant or discordant qualitative results for p27 antigen and proviral DNA was used to establish cutoff values, and when applied to test results at enrollment for classifying cats as high positive or low positive, a significant difference in survival was observed. High positive cats had a median survival of 1.37 years (95% CI 0.83-2.02) from time of enrollment, while most low positive cats were still alive (93.1% survival). Quantitative results for p27 antigen concentration and proviral DNA load were highly correlated with survival times in FeLV-infected cats.

Presence of Endogenous Viral Elements Negatively Correlates with Feline Leukemia Virus Susceptibility in Puma and Domestic Cat Cells.

While feline leukemia virus (FeLV) has been shown to infect felid species other than the endemic domestic cat host, differences in FeLV susceptibility among species has not been evaluated. Previous reports have noted a negative correlation between endogenous FeLV (enFeLV) copy number and exogenous FeLV (exFeLV) infection outcomes in domestic cats. Since felids outside the genus Felis do not harbor enFeLV genomes, we hypothesized absence of enFeLV results in more severe disease consequences in felid species lacking these genomic elements. We infected primary fibroblasts isolated from domestic cats (Felis catus) and pumas (Puma concolor) with FeLV and quantitated proviral and viral antigen loads. Domestic cat enFeLV env and long terminal repeat (LTR) copy numbers were determined for each individual and compared to FeLV viral outcomes. FeLV proviral and antigen levels were also measured in 6 naturally infected domestic cats and 11 naturally infected Florida panthers (P. concolor coryi). We demonstrated that puma fibroblasts are more permissive to FeLV than domestic cat cells, and domestic cat FeLV restriction was highly related to enFeLV-LTR copy number. Terminal tissues from FeLV-infected Florida panthers and domestic cats had similar exFeLV proviral copy numbers, but Florida panther tissues have higher FeLV antigen loads. Our work indicates that enFeLV-LTR elements negatively correlate with exogenous FeLV replication. Further, Puma concolor samples lacking enFeLV are more permissive to FeLV infection than domestic cat samples, suggesting that endogenization can play a beneficial role in mitigating exogenous retroviral infections. Conversely, presence of endogenous retroelements may relate to new host susceptibility during viral spillover events.IMPORTANCE Feline leukemia virus (FeLV) can infect a variety of felid species. Only the primary domestic cat host and related small cat species harbor a related endogenous virus in their genomes. Previous studies noted a negative association between the endogenous virus copy number and exogenous virus infection in domestic cats. This report shows that puma cells, which lack endogenous FeLV, produce more virus more rapidly than domestic cat fibroblasts following cell culture challenge. We document a strong association between domestic cat cell susceptibility and FeLV long terminal repeat (LTR) copy number, similar to observations in natural FeLV infections. Viral replication does not, however, correlate with FeLV env copy number, suggesting that this effect is specific to FeLV-LTR elements. This discovery indicates a protective capacity of the endogenous virus against the exogenous form, either via direct interference or indirectly via gene regulation, and may suggest evolutionary outcomes of retroviral endogenization.

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.

Outcome of cats referred to a specialized adoption program for feline leukemia virus-positive cats.

OBJECTIVES: The purpose of this retrospective study was to assess outcomes of cats referred to a specialized adoption program for feline leukemia virus (FeLV)-positive cats. METHODS: Cats referred to an FeLV-specific adoption program between January 2018 and July 2019 at an animal shelter in Austin, TX, USA, were first identified based on their putative FeLV status as reported by the referring shelter, rescue group, veterinarian or individual. Each cat was re-screened for FeLV upon admission and subsequently deemed infected or uninfected. Data on cat source, admission date, outcome date, outcome type, signalment and comorbidities at the time of admission were extracted from the shelter database. Outcomes were recorded up to 15 December 2019. RESULTS: In total, 801 cats suspected to be infected with FeLV were referred to the FeLV adoption program. Of these, 149 (18.6%) were ultimately deemed uninfected, and infection was confirmed in 652 (81.4%) cats. Adoption was the most common outcome for FeLV-infected cats (n = 514 cats; 78.8%), followed by euthanasia or death in care (n = 109; 16.7%). Upper respiratory infection (URI) was the most common comorbidity in FeLV-infected cats (n = 106; 16.3%) at the time of admission, which was not significantly different than URI in the cats that were deemed not to be infected with FeLV (n = 29; 19.5%). CONCLUSIONS AND RELEVANCE: This study demonstrated high national demand for a lifesaving option for cats diagnosed with FeLV. FeLV infections could not be confirmed in approximately one in five cats referred to the FeLV adoption program, a reminder of the risk behind basing the fate of a cat on a single positive test result. The majority of cats referred to the FeLV program were adopted, demonstrating that programs centered on adopter education and post-adoption support can create lifesaving outcomes for most FeLV-infected cats, despite uncertainty regarding their long-term prognosis.

Prevalence and Genomic Diversity of Feline Leukemia Virus in Privately Owned and Shelter Cats in Aburrá Valley, Colombia.

The feline leukemia virus (FeLV) belongs to the family Retroviridae; it is the first feline retrovirus discovered and one of the agents that has a great impact on cats' health and the ecology of the feline population worldwide. It is associated with the occurrence of several syndromes of fatal diseases, including the development of lymphomas. Studies on FeLV have been reported in Colombia, and most of them have been approached from a clinical point of view. However, only a few studies have focused on the prevalence of the infection, while none have clarified which variant or FeLV viral subgroup is presently circulating in our country. Therefore, the present study investigated the prevalence of the infection associated with the molecular characterization of FeLV present in cats in Aburrá Valley, Colombia. The sampling of privately owned and shelter cats was performed in female (n = 54) and male (n = 46) felines; most of them were seemingly healthy according to the owner's report, with nonspecific clinical history. Immunoassay confirmed that 59.44% (95% confidence interval (CI) = 49.81-69.06%) of felines were FeLV seropositive. The molecular testing of felines using reverse transcription-polymerase chain reaction and sequencing showed that 30% (30/100) of felines were positive, and the most prevalent subgroup in the Aburrá Valley was FeLV-A. In conclusion, the frequency of leukemia virus, as revealed by molecular and serological tests, is one of the highest reported frequencies to date, and a high molecular variation is shown in the Colombian population. More studies on the behaviour of the virus in feline populations in Columbia are warranted to determine its prevalence throughout the country.

Feline Leukaemia Virus Associated with Leukaemia in Cats in Santa Catarina, Brazil.

Leukaemia is a haemopoietic neoplasm originating from myeloid or lymphoid precursors in the bone marrow and may be either acute or chronic. These tumours are rare, but occur more frequently in cats because of an association with the feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV). To the best of our knowledge, no studies conducted in Brazil to date have analysed the association between leukaemia and FeLV and FIV infection in cats. The aim of this study was to perform a histopathological analysis of feline leukaemia and evaluate the association between leukaemia and FeLV and FIV infection in cats. The study evaluated 37 cats with leukaemia diagnosed between 2009 and 2017. The animals underwent necropsy examination, histopathology and immunohistochemistry with anti-FeLV gp70 and anti-FIV p24 gag antibodies. Of the evaluated animals, 54% (20/37) were males and 43.2% (16/37) were females. With respect to the life stage of the animals, 24.3% (9/37) were junior, 32.4% (12/37) were prime, 18.9% (7/37) were mature and 10.8% (4/37) were senior, and five animals were of unknown age. Myeloid leukaemia occurred in 56.8% (21/37) of the cases and lymphocytic leukaemia occurred in 43.2% (16/37) of the cases. Acute leukaemia (73%, 27/37) was more common than chronic leukaemia (27%, 10/37). The positivity for FeLV (78.4%, 29/37) and FIV (16.2%, 6/37) indicated a high association between FeLV infection and tumour development in the study region.

The Diagnosis of Feline Leukaemia Virus (FeLV) Infection in Owned and Group-Housed Rescue Cats in Australia.

A field study was undertaken to (i) measure the prevalence of feline leukaemia virus (FeLV) exposure and FeLV infection in a cross-section of healthy Australian pet cats; and (ii) investigate the outcomes following natural FeLV exposure in two Australian rescue facilities. Group 1 (n = 440) consisted of healthy client-owned cats with outdoor access, predominantly from eastern Australia. Groups 2 (n = 38) and 3 (n = 51) consisted of a mixture of healthy and sick cats, group-housed in two separate rescue facilities in Sydney, Australia, tested following identification of index cases of FeLV infection in cats sourced from these facilities. Diagnostic testing for FeLV exposure/infection included p27 antigen testing using three different point-of-care FeLV kits and a laboratory-based ELISA, real-time polymerase chain reaction (qPCR) testing to detect FeLV proviral DNA in leukocytes, real-time reverse-transcription PCR (qRT-PCR) testing to detect FeLV RNA in plasma, and neutralising antibody (NAb) testing. Cats were classified as FeLV-uninfected (FeLV-unexposed and presumptively FeLV-abortive infections) or FeLV-infected (presumptively regressive and presumptively progressive infections). In Group 1, 370 FeLV-unexposed cats (370/440, 84%), 47 abortive infections (47/440, 11%), nine regressive infections (9/440, 2%), and two progressive infections (2/440, 0.5%) were identified, and 12 FeLV-uninfected cats (12/440, 3%) were unclassifiable as FeLV-unexposed or abortive infections due to insufficient samples available for NAb testing. In Groups 2 and 3, 31 FeLV-unexposed cats (31/89, 35%), eight abortive infections (8/89, 9%), 22 regressive infections (22/89; 25%), and 19 progressive infections (19/89; 21%) were discovered, and nine FeLV-uninfected cats (9/89; 10%) were unclassifiable due to insufficient samples available for NAb testing. One of the presumptively progressively-infected cats in Group 3 was likely a focal FeLV infection. Two other presumptively progressively-infected cats in Group 3 may have been classified as regressive infections with repeated testing, highlighting the difficulties associated with FeLV diagnosis when sampling cats at a single time point, even with results from a panel of FeLV tests. These results serve as a reminder to Australian veterinarians that the threat of FeLV to the general pet cat population remains high, thus vigilant FeLV testing, separate housing for FeLV-infected cats, and FeLV vaccination of at-risk cats is important, particularly in group-housed cats in shelters and rescue facilities, where outbreaks of FeLV infection can occur.

Prevalence of and factors associated with feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) in cats of the state of Santa Catarina, Brazil.

A cross-sectional study was conducted in 274 cats for determination of FeLV antigenemia and FIV seropositivity and factors associated with those infections in cats presented at the Veterinary Hospital of the Santa Catarina State University - UDESC (Brazil). Apparent prevalence for sick cats at the hospital population was 28.41% (95%CI 21.88-34.94%) for FeLV, 7.65% (95%CI 3.71-11.50%) for FIV and 2.18% (95%CI 0.56-5.47%) for both viruses. For healthy cats, the apparent prevalence was 9.89% (95%CI 3.75-16.02%) for FeLV, 2.20% (95%CI 0.34-7.75%) for FIV by immunoassay (ELISA). Average age for FeLV- and FIV-positive individuals was 38.32 and 64.25 months, respectively. Behavior such as aggressiveness and sex (male) were both associated with increased odds of result positivity test for FeLV and FIV; older animals were also associated with FIV test results. A very small proportion of the animals were vaccinated against FeLV and none against FIV. Most of the animals were adopted from shelters or rescued from streets, living with multiple cats that had access to outdoors. The high prevalence of FeLV suggests a need for better control strategies against this disease.

Reduced Folate Carrier: an Entry Receptor for a Novel Feline Leukemia Virus Variant.

Feline leukemia virus (FeLV) is horizontally transmitted among cats and causes a variety of hematopoietic disorders. Five subgroups of FeLV, A to D and T, each with distinct receptor usages, have been described. Recently, we identified a new FeLV Env (TG35-2) gene from a pseudotyped virus that does not belong to any known subgroup. FeLV-A is the primary virus from which other subgroups have emerged via mutation or recombination of the subgroup A env gene. Retrovirus entry into cells is mediated by the interaction of envelope protein (Env) with specific cell surface receptors. Here, phenotypic screening of a human/hamster radiation hybrid panel identified SLC19A1, a feline reduced folate carrier (RFC) and potential receptor for TG35-2-phenotypic virus. RFC is a multipass transmembrane protein. Feline and human RFC cDNAs conferred susceptibility to TG35-2-pseudotyped virus when introduced into nonpermissive cells but did not render these cells permissive to other FeLV subgroups or feline endogenous retrovirus. Moreover, human cells with genomic deletion of RFC were nonpermissive for TG35-2-pseudotyped virus infection, but the introduction of feline and human cDNAs rendered them permissive. Mutation analysis of FeLV Env demonstrated that amino acid substitutions within variable region A altered the specificity of the Env-receptor interaction. We isolated and reconstructed the full-length infectious TG35-2-phenotypic provirus from a naturally FeLV-infected cat, from which the FeLV Env (TG35-2) gene was previously isolated, and compared the replication of the virus in hematopoietic cell lines with that of FeLV-A 61E by measuring the viral RNA copy numbers. These results provide a tool for further investigation of FeLV infectious disease.IMPORTANCE Feline leukemia virus (FeLV) is a member of the genus Gammaretrovirus, which causes malignant diseases in cats. The most prevalent FeLV among cats is FeLV subgroup A (FeLV-A), and specific binding of FeLV-A Env to its viral receptor, thiamine transporter feTHTR1, is the first step of infection. In infected cats, novel variants of FeLV with altered receptor specificity for viral entry have emerged by mutation or recombination of the env gene. A novel FeLV variant arose from a subtle mutation of FeLV-A Env, which altered the specific interaction of the virus with its receptor. RFC, a folate transporter, is a potential receptor for the novel FeLV variant. The perturbation of specific retrovirus-receptor interactions under selective pressure by the host results in the emergence of novel viruses.

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.

Toxoplasmose cérébrale chez un chat atteint des infections virales de leucémie féline et de péritonite infectieuse féline. Un jeune chat diarrhéique est mort après des symptômes neurologiques. La biochimie a signalé une péritonite infectieuse féline (FIP). Le diagnostic final a été une méningo-encéphalite multifocale grave causée par Toxoplasma gondii. La présence du parasite dans le cerveau a été confirmée à l'aide de la coloration immunohistochimique. La présence concomitante du virus de la leucémie féline (FeLV) et de la FIP sont des facteurs possibles ayant contribué au résultat clinique mortel.(Traduit par Isabelle Vallières).

Feline Leukemia Virus (FeLV) Disease Outcomes in a Domestic Cat Breeding Colony: Relationship to Endogenous FeLV and Other Chronic Viral Infections.

Exogenous feline leukemia virus (FeLV) is a feline gammaretrovirus that results in a variety of disease outcomes. Endogenous FeLV (enFeLV) is a replication-defective provirus found in species belonging to the Felis genus, which includes the domestic cat (Felis catus). There have been few studies examining interaction between enFeLV genotype and FeLV progression. We examined point-in-time enFeLV and FeLV viral loads, as well as occurrence of FeLV/enFeLV recombinants (FeLV-B), to determine factors relating to clinical disease in a closed breeding colony of cats during a natural infection of FeLV. Coinfections with feline foamy virus (FFV), feline gammaherpesvirus 1 (FcaGHV-1), and feline coronavirus (FCoV) were also documented and analyzed for impact on cat health and FeLV disease. Correlation analysis and structural equation modeling techniques were used to measure interactions among disease parameters. Progressive FeLV disease and FeLV-B presence were associated with higher FeLV proviral and plasma viral loads. Female cats were more likely to have progressive disease and FeLV-B. Conversely, enFeLV copy number was higher in male cats and negatively associated with progressive FeLV disease. Males were more likely to have abortive FeLV disease. FFV proviral load was found to correlate positively with higher FeLV proviral and plasma viral load, detection of FeLV-B, and FCoV status. Male cats were much more likely to be infected with FcaGHV-1 than female cats. This analysis provides insights into the interplay between endogenous and exogenous FeLV during naturally occurring disease and reveals striking variation in the infection patterns among four chronic viral infections of domestic cats.IMPORTANCE Endogenous retroviruses are harbored by many animals, and their interactions with exogenous retroviral infections have not been widely studied. Feline leukemia virus (FeLV) is a relevant model system to examine this question, as endogenous and exogenous forms of the virus exist. In this analysis of a large domestic cat breeding colony naturally infected with FeLV, we documented that enFeLV copy number was higher in males and inversely related to FeLV viral load and associated with better FeLV disease outcomes. Females had lower enFeLV copy numbers and were more likely to have progressive FeLV disease and FeLV-B subtypes. FFV viral load was correlated with FeLV progression. FFV, FcaGHV-1, and FeLV displayed markedly different patterns of infection with respect to host demographics. This investigation revealed complex coinfection outcomes and viral ecology of chronic infections in a closed population.