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In a 2019 Pan-European Study, Portugal exhibited the highest prevalence of Feline Leukemia Virus (FeLV) infection (8.8%). Following the coronavirus disease 2019 (COVID-19) pandemic, it is crucial to evaluate how the prevalence of FeLV has evolved. FeLV infection is associated with the highest morbidity rates, primarily due to the increased incidence of diseases that compromise the health of cat populations, which varies according to the lifestyle and background of the cats studied. This study aimed (1) to estimate the prevalence and temporal trends of FeLV and FIV infections among cats presented to a university veterinary hospital in the Lisbon metropolitan area, and (2) to evaluate the clinical associations between FeLV infection, health status, and FeLV-related conditions in cats. Conducted over 4.5 years, from January 2019 to July 2023, this cross-sectional study took place at a teaching hospital and involved 1,124 cats that were tested serologically and/or by qPCR and RT-qPCR for FeLV. Information was gathered on the intrinsic and extrinsic characteristics of the cats, their health status, and any related diseases. The overall prevalence of FeLV was found to be 11.3% (95% CI: 9.5%−13.3%), with 1.8% (95% CI: 1.1%−2.7%) of cats co-infected with FIV, and it peaked in 2020 at 14.1% (95% CI: 7.5%−23.4%), with 2.4% (95% CI: 0.03%−8.2%) co-infected with FIV. Over the 4.5-year period, an increasing number of cats were tested, and more quantification of proviral and viral loads was performed. This indicated a more progressive course in 47.0% (31/66), of sick FeLV-infected cats, who exhibited a higher incidence of FeLV-related diseases. Although there was no significant difference in the average age between positive and negative cats, FeLV-positive cats demonstrated a higher rate of sickness (74.8%, n = 95). To the best of the authors’ knowledge, this study represents the largest cross-sectional investigation of FeLV infection prevalence and its health implications conducted in Portugal. Overall, the available data suggest a possible increase in FeLV prevalence in Portugal, concurrent with a declining vaccination rate from 14.2% to 5.0%. The results also highlight notable differences in clinical status between progressive and regressive disease courses, reinforcing the necessity of staging the course of infection at diagnosis to ensure an informed medical approach and realistic prognosis. Efforts should focus on improving vaccination and screening activities, promoting neutering of indoor and outdoor cats, and isolating infected cats.

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.

Feline leukemia virus (FeLV) is widespread in domestic cats and frequently spills over into wild felid populations, causing severe outbreaks in nondomestic felid populations. Domestic cats carry both endogenous FeLV (enFeLV) and exogenous variants of FeLV (exFeLV), which can recombine to generate novel variants with alternate receptor usage. In contrast, most nondomestic felids, including the guigna, do not harbor enFeLV. This study applied amplification of the FeLV envelope gene combined with Illumina sequencing to characterize FeLV envelope gene diversity and transmission dynamics in guignas ( Leopardus guigna ), a small wild felid native to Chile and Argentina. Seven polymerase chain reaction (PCR )amplicons from five free-ranging guignas were sequenced. Illumina sequencing was successfully conducted, and subsequent phylogenetic analysis indicated that the detected infections were most closely related to strains circulating in Chilean domestic cats. However, a distinct guigna-specific cluster with unique sequence variations was identified, suggesting that FeLV transmission also occurs among guignas independent of domestic cats. Phylogenetic analysis showed that all guigna sequences formed a Chile-specific FeLV clade, closely related to domestic cat viruses but clearly separated from international FeLV-A strains.

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.

This study aimed to classify the Feline leukaemia virus (FeLV) infection outcomes in domestic cats in Thailand and determine the accuracy of conjunctival swabs for FeLV proviral DNA detection by comparing results to PCR testing of blood samples. Whole blood and conjunctival swabs were collected from 126 cats with and without clinical signs. Blood specimens were evaluated for p27 FeLV antigen using the SNAP Feline Immunodeficiency Virus (FIV)/FeLV Combo Test, IDEXX Laboratories. The 3'-LTR region of the proviral FeLV was amplified from both blood and conjunctival samples. The prevalence rates of progressive and regressive FeLV infections in this study were 14.3% (95% CI: 8.69-21.63) and 36.5% (95% CI: 28.12-45.55), respectively. Cats older than 12 months of age had a higher probability of being regressively infected than cats younger than 1 year (p-value = 0.039, OR =0.294, 95% CI: 0.092-0.942). Conjunctival swabs used for detecting FeLV proviral DNA demonstrated a sensitivity of 95.3% (95% CI: 86.91-99.02) and a specificity of 100% (95% CI: 94.22-100.00) compared to conventional blood samples. The observed kappa value of 0.956 indicates that conjunctival swabs are reliable and can be used as an alternative to blood venipuncture. What is the context? Feline leukaemia virus (FeLV) is a common, fatal disease affecting cats worldwide. It belongs to the family Retroviridae. Cats can easily become infected through close contact, such as grooming, sharing feeding bowls and fighting. FeLV causes immunosuppressive diseases, neoplasia, anaemia and ultimately death in cats. FeLV infection stages are categorised as abortive, regressive, progressive and focal/atypical. Various tests have been used to detect this virus. Diagnosis typically relies on blood samples for specific antigen tests, which can cause stress for cats, veterinarians and cat owners. Some studies suggest using non-invasive samples, such as tears or saliva, which are less stressful for the cat than blood samples. However, the results from these samples are not always consistent with those from blood samples. In this study, we use conjunctival tissue obtained via conjunctival swabs to detect proviral DNA antigen and identify regressive FeLV. This sampling method is easy and non-invasive for the cat and the results are reliable and consistent with conventional blood sampling tests. What is new? This study introduces a less invasive and simpler conjunctival swab that makes the sample collection easier and less stressful for cats, veterinarians and cat owners compared to blood samples. This method also allows cat owners to perform sample collection at home. The conjunctival sample provides reliable and accurate results when using proviral detection PCR and is easy to administer. What is the impact? This study offers an alternative, reliable sample collection method for FeLV detection using a simpler technique that yields the same accurate results, reducing stress for cats, owners and veterinarians. The outcomes for the regressive, progressive and abortive or non-infected stages of FeLV infection are reported for the first time in Thailand.

This study aimed to characterize the clinical presentations and effects of progressive and regressive outcomes of feline leukemia virus (FeLV) infection on the life expectancy of cats. In total, 176 cats were selected: 116 with progressive infection (FeLV + P), 30 with regressive infection (FeLV + R), and 30 FeLV-negative cats (Control). The cats underwent testing using ELISA to detect the FeLV p27 antigen and nested polymerase chain reaction to identify U3-LTR region and gag proviral DNA. The cats were clinically monitored until their death or for a period ranging 12–54 months. Survival analysis was performed using Kaplan–Meier analysis and Cox regression. The median survival time following FeLV diagnosis was 30 days for the FeLV + P group. The median survival time was not reached for the other groups. The cats’ health status (sick) at the time of inclusion in the study and the progression status of the FeLV infection led to a 4–5-fold increase in the Hazard Ratio (HR) for death in the general population. The primary causes of death among cats in the FeLV + P group were lymphoma, leukemia, anemia, and other diseases. In the FeLV + R group, the causes of death included leukemia, anemia, and other diseases. Progressive FeLV infection reduced life expectancy, whereas regressive FeLV infection had no direct impact on the survival curve.

Feline leukemia virus (FeLV) was the first feline retrovirus discovered, and is associated with multiple fatal disease syndromes in cats, including lymphoma. The original research conducted on FeLV employed classical virological techniques. As methods have evolved to allow FeLV genetic characterization, investigators have continued to unravel the molecular pathology associated with this fascinating agent. In this review, we discuss how FeLV classification, transmission, and disease-inducing potential have been defined sequentially by viral interference assays, Sanger sequencing, PCR, and next-generation sequencing. In particular, we highlight the influences of endogenous FeLV and host genetics that represent FeLV research opportunities on the near horizon.

The aim of this study was to describe the seroprevalence, presenting complaint, clinicopathological changes, co-morbidities and outcomes of feline leukemia virus positive cats presented to a specialty referral center in Florida, USA. In this retrospective study, medical records of 8050 cats presented to a private referral center from August 2008 to September 2019 were reviewed. Inclusion criteria required was a positive result for feline leukemia virus by point-of-care antigen testing or immunofluorescence assay. Forty-one cases met the inclusion criteria. Of 2002 cats that were tested, 41 cats (2%) met the inclusion criteria. One cat had a negative point of care antigen test result and positive bone marrow IFA result. The mean age at diagnosis was 9 years. The main reasons for presentation were abnormal complete blood cell count results (35%), followed by pleural effusion (18%), and anorexia (15%). The most common laboratory abnormalities included anaemia (71%), of which 74% had a nonregenerative anemia, thrombocytopenia (52%), elevated aspartate aminotransferase (50%), hyperbilirubinemia (35%), and hypokalemia (35%). Seven percent of cats (3/41) were also positive for feline immunodeficiency virus. The most common diagnoses were neoplasia (76%) and bone marrow disorders (12%). Cats with neoplasia were significantly younger. Survival to discharge was 88%. Results of this study show that feline leukemia virus is uncommon in secondary referral center, even if this represents a population of unhealthy cats. The most common associated diagnosis was neoplasia, which was more likely to be seen in younger cats (< 4 years of age). The mean age of cats positive for feline leukemia virus was also older than previously published data. These findings support the current guidelines which indicate that cats presented with clinical illness should be tested for FeLV at the time of presentation.

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.

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.