Feline Leukemia Virus Infection Research Articles

Evaluation of leukocyte ratios as survival prognostic markers in feline retrovirus infections

The utility of neutrophil-lymphocyte ratio (NLR), monocyte-lymphocyte ratio (MLR), and platelet-lymphocyte ratio (PLR) as prognostic markers in Feline Leukemia Virus (FeLV) and Feline Immunodeficiency Virus (FIV) infections has not yet been investigated. The aim of this study was to investigate these leukocyte ratios in retrovirus-positive cats and to evaluate their prognostic value for survival. This retrospective case-control study included 142 cats, 75 FIV-Antibodies (Ab)-positive, 52 FeLV-Antigen (Ag)-positive, and 15 FIV-Ab+FeLV-Ag-positive, and a control population of 142 retrovirus-negative age-, sex-, and lifestyle-matched cats. Signalment, complete blood count at the time of serological testing, and outcome were recorded. Leukocyte ratios were compared within the same case-control population, among the three retrovirus-seropositive populations, and were related to survival time.No significant difference was found in NLR, MLR, or PLR between FIV-Ab-positive and FIV-Ab+FeLV-Ag-positive cats and their cross-matched controls. In the FeLV-Ag-positive population, MLR was significantly lower than in the control population (0.05 and 0.14, respectively, P=0.0008). No ratio discriminated among the three infectious states. No ratio was significantly different between survivors and non-survivors in the population of FIV-Ab-positive cats. MLR at diagnosis was significantly higher in FeLV-Ag-positive cats that died 1-3 years after diagnosis than in FeLV-Ag-positive cats still alive at 3 years (P=0.0284). None of the three ratios could predict retroviruses-positive cats that would survive to the end of the study. Overall the results indicate that NLR, MLR, and PLR are not significantly different among retrovirus statuses evaluated and had a very limited prognostic value for the survival time in retrovirus-positive cats.

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.

Epidemiological Insights into Feline Leukemia Virus Infections in an Urban Cat (Felis catus) Population from Brazil.

Feline leukemia virus (FeLV) is a retrovirus distributed worldwide in domestic cats and with different outcomes (progressive, regressive, abortive, focal). The present study reports an epidemiological survey of FeLV frequency and the evaluation of some risk factors and the two main disease outcomes (progressive and regressive) in an urban cat population from Brazil. A total of 366 cats with sociodemographic information and p27 FeLV antigen test performed were included in the study. FeLV DNA (provirus) in the blood samples of all cats was detected via real-time polymerase chain reaction (qPCR). Plasma samples from 109 FeLV-positive and FeLV-negative cats were also submitted to reverse transcription (RT-qPCR) to determine the FeLV viral load. The results demonstrated that 112 (30.6%) cats were positive through the p27 antigen and/or qPCR. A risk factor analysis demonstrated that cats without vaccination against FeLV (OR 9.9, p < 0.001), clinically ill (OR 2.9, p < 0.001), with outdoors access (OR 2.7, p < 0.001), and exhibiting apathetic behavior (OR 3.1, p < 0.001) were more likely to be infected with FeLV. FeLV-infected cats were also more likely to present with anemia (OR 13, p < 0.001) and lymphoma (OR 13.7, p = 0.001). A comparative analysis of the different detection methods in a subset of 109 animals confirmed FeLV infection in 58 cats, including 38 (65.5%) with progressive, 16 (27.6%) with regressive, and 4 (6.9%) with probably focal outcome diseases. In conclusion, this study demonstrates a high prevalence of FeLV in this urban cat population from Brazil and highlights the need to establish more effective prevention strategies (such as viral testing, vaccination programs, specific care for FeLV-positive cats) to reduce diseases associated with this virus in Brazil.

Epidemiological and clinicopathological findings of feline immunodeficiency virus and feline leukemia virus infections in domestic cats from the Brazilian semiarid region

Feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) are retroviruses of great importance for domestic cats with a worldwide distribution. A retrospective study was conducted to determine the epidemiological and clinicopathological aspects of the infection by FIV and FeLV in cats from the Brazilian semiarid region. Cats treated between 2011 and 2021 at the teaching veterinary hospital of the Federal Rural University of the Semi-Arid Region that were submitted to a point-of-care (POC) test to detect anti-FIV IgG antibodies and FeLV antigen were enrolled in the study. Overall, 454 cats were selected, of which 30.2% [95% CI = 26.0% – 34.3%] were FIV-positive, 1.1% [95% CI = 0.9% – 1.2%] were FeLV-positive, and 0.7% [95% CI = 0.1% – 1.3%] were coinfected by both retroviruses. No statistical association was found between the studied retroviruses (P = 0.144). Multivariable analysis detected significant associations between FIV infection and male sex [OR = 5.7, 95% CI = 3.0–10.7, P < 0.0001), age between 19 and 78 months [OR = 5.2, 95% CI = 2.2–12.1, P < 0.0001], age greater than 78 months [OR = 12.8, 95% CI = 5.1–31.9, P < 0.0001], crossbreed [OR = 4.1, 95% CI = 1.2–13.4, P = 0.021], the presence of oral disease [OR = 2.1, 95% CI = 1.3–3.4, P = 0.004], reduced red blood cell (RBC) count [OR = 3.7, 95% CI = 1.9–7.2, P < 0.0001], and an albumin:globulin (A:G) ratio lower than 0.6 [OR = 3.4, 95% CI = 1.6–7.1, P = 0.001]. No statistical analyses were performed for FeLV infection due to the low number of positive animals. In the quantitative analyses of hematological parameters, FIV-positive cats presented lower values for RBC, hemoglobin, hematocrit, lymphocytes, and platelets compared to the negative animals. In the biochemical profile, cats infected with FIV showed higher creatinine, urea, total protein, and globulin values, while lower values for albumin and A:G ratio were observed (P < 0.05). The findings of this study characterized the prevalence, clinicopathological findings, and risk factors associated with FIV and FeLV in cats from the Brazilian semiarid region. They may help support veterinary practitioners in diagnosing feline retroviruses. The FIV prevalence observed is among the highest reported in Brazil, demonstrating the need for prevention and control strategies for this retrovirus.

Long-term surveillance of the feline leukemia virus in the endangered Iberian lynx (Lynx pardinus) in Andalusia, Spain (2008–2021)

Feline leukemia virus (FeLV) infection is considered one of the most serious disease threats for the endangered Iberian lynx (Lynx pardinus) Over 14 years (2008–2021), we investigated FeLV infection using point-of-care antigen test and quantitative real-time TaqMan qPCR for provirus detection in blood and tissues in lynxes from Andalusia (Southern Spain). A total of 776 samples from 586 individuals were included in this study. The overall prevalence for FeLV antigen in blood/serum samples was 1.4% (5/360) (95% CI: 0.2–2.6), FeLV proviral DNA prevalence in blood samples was 6.2% (31/503) (95% CI: 4.1–8.6), and FeLV proviral DNA in tissues samples was 10.2% (34/333) (95% CI: 7–13.5). From a subset of 129 longitudinally sampled individuals, 9.3% (12/129) PCR-converted during the study period. Our results suggest that FeLV infection in the Andalusian population is enzootic, with circulation of the virus at low levels in almost all the sampling years. Moreover, since only one viremic individual succumbed to the infection, this study suggests that lynxes may therefore control the infection decreasing the possibility of developing a more aggressive outcome. Although our results indicate that the FeLV infection in the Iberian lynx from Andalusia tends to stay within the regressive stage, continuous FeLV surveillance is paramount to predict potential outbreaks and ensure the survival of this population.

Prospective Investigation of Feline Leukemia Virus Infection in Stray Cats Subjected to a Trap-Neuter-Return Program in Switzerland.

Feline leukemia virus (FeLV) remains a serious concern in some countries despite advances in diagnostics and vaccines. FeLV-infected cats often have reduced lifespans due to FeLV-associated diseases. The infection is transmitted through social interactions. While Northern European countries have reported a decrease in FeLV among pet cats, Switzerland's rates remain stagnant at 2.7% (2016/17: 95% CI 1.4-5.2%). Research on FeLV in Swiss stray cats has been lacking, even though these animals could serve as a virus reservoir. Sampling stray cats that do not receive regular veterinary care can be challenging. Collaboration with the Swiss Network for Animal Protection (NetAP) allowed for the prospective collection of saliva samples from 1711 stray cats during a trap-neuter-return program from 2019 to 2023. These samples were tested for FeLV RNA using RT-qPCR as a measure for antigenemia. Viral RNA was detected in 4.0% (95% CI 3.1-5.0%) of the samples, with 7.7% (95% CI 4.9-11.3%) in sick cats and 3.3% (95% CI 2.4-4.4%) in healthy ones. We identified three geographically independent hotspots with alarmingly high FeLV infection rates in stray cats (up to 70%). Overall, including the previous data of privately owned cats, FeLV-positive cats were scattered throughout Switzerland in 24/26 cantons. Our findings underscore welfare concerns for FeLV infections among stray cats lacking veterinary attention, highlighting the potential risk of infection to other free-roaming cats, including those privately owned. This emphasizes the critical significance of vaccinating all cats with outdoor access against FeLV and developing programs to protect cats from FeLV infections.

Status Quo of Feline Leukaemia Virus Infection in Turkish Cats and Their Antigenic Prevalence

Feline leukaemia virus (FeLV) is a member of the Gammaretrovirus genus, which has two genotypes in cats: endogenous (replication-defective provirus) and exogenous (replication-competent). In this study, 550 cats were examined, and 112 of them (20.36%) were found to have the endogenous FeLV (enFeLV) genotype. EnFeLV-positive animals were also tested for additional viral infections, and 48 cats (42.85%) were discovered to be co-infected with other viruses. According to co-infection data, these cats were infected with feline coronavirus (FCoV) (27/112, 24.1%), feline panleukopenia virus (FPV) (14/112, 12.5%), feline immunodeficiency virus (FIV) (0/112, 0%), and domestic cat hepadnavirus (DCH) (13/112, 11.6%). Their age, sex, breed, clinical state, lifestyle (in/outdoor), and immunization data against FeLV were also evaluated. In line with our results, the prevalence of enFeLV and co-infection with other pathogens in cats admitted to the clinic for various reasons were discussed. The majority of positive animals in terms of FeLV (94/112, 83.93%) had clinical findings. We emphasized that the FeLV-positive situation of cats should be taken into consideration by veterinarians when planning treatment and vaccination programs. Additionally, in this study, we questioned the group in which our enFeLVs were phylogenetically located. Therefore, we performed a phylogenetic analysis based on a comparison with global FeLV sequences obtained from the GenBank database. The sequenced positive samples were in the AGTT subgroup within Group-II.

Epidemiology of Pathogenic Retroviruses and Domestic Cat Hepadnavirus in Community and Client-Owned Cats in Hong Kong.

Understanding the local epidemiology of feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV) in Hong Kong will inform retrovirus prevention strategies. Domestic cat hepadnavirus (DCH), a novel hepatitis-B-like virus, is commonly detected among client-owned cats in Hong Kong, but community cats have not been studied. The aims of this study were to investigate the frequency and potential risk factors for (i) FeLV and FIV among community and client-owned cats and (ii) perform molecular detection of DCH among community cats in Hong Kong. Blood samples from 713 cats were obtained from client-owned (n = 415, residual diagnostic) and community cats (n = 298, at trap-neuter-return). Point-of-care (POC) testing for FeLV antigen and feline immunodeficiency virus (FIV) anti-p15 and p24 antibodies was performed. FeLV-positive samples were progressed to p27 sandwich enzyme-linked immunosorbent assay. Whole blood DNA was tested with qPCRs for FeLV U3 and gag, and nested PCRs where additional information was required. DCH qPCR was performed on a subset of community cats (n = 193). A single, regressive, FeLV infection was detected in a client-owned cat (1/415 FeLV U3 qPCR positive, 0.2%, 95% CI 0.0-1.3%). Five/415 client-owned cats tested presumably false FeLV-antigen positive (qPCR negative). No markers of FeLV infection were detected in community cats (0/298; 0%). FIV seroprevalence was much higher in community cats (46/298, 15.4%) than in client-owned cats (13/415, 3.1%) (p < 0.001). Mixed breed was a risk factor for FIV infection in client-owned cats. Neither sex nor age were associated with FIV infection. DCH DNA was detected in 34/193 (17.6%) community cats (median viral load 6.32 × 103 copies/reaction). FeLV infection is rare in Hong Kong, negatively impacting the positive predictive value of diagnostic tests. FeLV-antigen testing remains the screening test of choice, but confirmation of a positive result using FeLV qPCR is essential. FIV infection is common in community cats and the absence of a sex predisposition, seen previously in cats managed similarly, raises questions about virus-transmission dynamics in these groups. DCH infection is very common in Hong Kong, both in client-owned and community cats, highlighting the importance of understanding the pathogenic potential of this virus for cats.

Status of selected feline infectious diseases in Gwangju, Korea

From 2008 to 2017, blood samples from 280 and fecal samples from 149 stray cats in Gwangju, South Korea, were examined for feline immunodeficiency virus (FIV), feline leukemia virus (FeLV), Dirofilaria immitis, and Giardia infections using commercial diagnostic tests. Overall, the combined prevalence of FeLV, FIV, D. immitis, and Giardia was 8.6%, 1.4%, 0.4%, and 2.0%, respectively. FeLV exhibited the highest prevalence rate among the 4 pathogens surveyed, both in the 2008–2009 (9.6%) and 2015–2017 (6.3%) surveys. The results of the feline Giardia study represent the first prevalence report of Giardia infection among stray cats in Korea.

Prevalence of feline leukemia virus and feline immunodeficiency virus in cats from southern Italy: a 10-year cross-sectional study.

Feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) are well-known retroviruses causing important infections in domestic cats worldwide. The goal of this study was to determine the prevalence of FeLV and FIV infections in cat living indoor and outdoor in southern Italy. The survey was conducted on 1322 stray and owned cats from the regions of Campania, Basilicata, and Calabria. It was carried out over a 10-year period to obtain a more realistic picture of the prevalence of these retroviral diseases in the country. FIV and FeLV status was determined by enzyme-linked immunosorbent assay (ELISA) using a commercial kit (SNAP Combo Plus FeLV/FIV, IDEXX). Risk factors were analysed by logistic regression. The results showed that 101/1322 (7.64%) cats were positive for FeLV antigen and 110/1322 (8.32%) cats were positive for FIV antibody. Twenty-six of the 1322 cats (1.97%) were positive for both FIV and FeLV infection. Our results are similar to those published in recent studies in Europe. A statistically significant association (p < 0.05) was found between year, province, region, lifestyle and risk of FeLV infection. FIV positivity was instead statistically associated only with year and lifestyle.

Anti-Leishmania spp. antibody detection in domestic cats from a visceral leishmaniasis transmission area.

Feline leishmanial infection is reported worldwide, but the epidemiological role of domestic cats in the leishmaniasis cycle remains unclear, and cats might act as cryptic reservoir hosts in endemic areas with no feline leishmaniosis cases. Considering that, a serological screening for anti-Leishmania spp. antibodies was performed by indirect immunofluorescence antibody test (IFAT) in 389 necropsied cats' serum samples from a new visceral leishmaniasis transmission area with no feline leishmanial infection reported to unveil if the cats are being exposed to the parasite. The overall seroprevalence for Leishmania spp. was 11.05% (43/389). No association was found between sex, neutering status, age group, breed, coat length, feline immunodeficiency virus (FIV) infection, and Leishmania spp. antibody detection. A positive association was found with coat color (cats within the orange spectrum with white [particolor]) (OR = 2.47, CI 95% 1 - 6.13, P = 0.044) and a negative association (OR = 0.38, CI 95% 0.18 - 0.79, P = 0.01) between feline leukemia virus (FeLV) infection and IFAT positivity for Leishmania spp. Therefore, it is concluded that the seroprevalence found was greater than 10%, indicating contact of the protozoan with cats in the region served.

BET Inhibitor JQ1 Attenuates Feline Leukemia Virus DNA, Provirus, and Antigen Production in Domestic Cat Cell Lines.

Feline leukemia virus (FeLV) is a cosmopolitan gammaretrovirus that causes lifelong infections and fatal diseases, including leukemias, lymphomas, immunodeficiencies, and anemias, in domestic and wild felids. There is currently no definitive treatment for FeLV, and while existing vaccines reduce the prevalence of progressive infections, they neither provide sterilizing immunity nor prevent regressive infections that result in viral reservoirs with the potential for reactivation, transmission, and the development of associated clinical diseases. Previous studies of murine leukemia virus (MuLV) established that host cell epigenetic reader bromodomain and extra-terminal domain (BET) proteins facilitate MuLV replication by promoting proviral integration. Here, we provide evidence that this facilitatory effect of BET proteins extends to FeLV. Treatment with the archetypal BET protein bromodomain inhibitor (+)-JQ1 and FeLV challenge of two phenotypically disparate feline cell lines, 81C fibroblasts and 3201 lymphoma cells, significantly reduced FeLV proviral load, total FeLV DNA load, and p27 capsid protein expression at nonlethal concentrations. Moreover, significant decreases in FeLV proviral integration were documented in 81C and 3201 cells. These findings elucidate the importance of BET proteins for efficient FeLV replication, including proviral integration, and provide a potential target for treating FeLV infections.

Prevalence of Different Courses of Feline Leukaemia Virus Infection in Four European Countries.

Prevalence of progressive feline leukaemia virus (FeLV) infection is known to still be high in cats in Europe, especially in Southern Europe, but the prevalence of other outcomes of FeLV infection has not been determined in most countries. The present study aimed to investigate the prevalence of progressive, regressive, abortive, and focal infection in four European countries, two with a high (Italy, Portugal) and two with a low expected prevalence (Germany, France). Blood samples of 934 cats (Italy: 269; Portugal: 240; France: 107; Germany: 318) were evaluated for the p27 antigen, as well as anti-whole virus, anti-SU, and anti-p15E antibodies by enzyme-linked immunosorbent assay (ELISA) in serum and for proviral DNA by quantitative polymerase chain reaction (qPCR) in whole blood. Positive p27 antigen ELISA results were confirmed by reverse transcriptase-qPCR (RT-qPCR) detecting viral RNA in saliva swabs and/or blood. The outcome of FeLV infection was categorised as progressive (antigen-positive, provirus-positive), regressive (antigen-negative, provirus-positive), abortive (antigen- and provirus-negative, antibody-positive), and focal (antigen-positive, provirus-negative) infection. Overall FeLV prevalence was 21.2% in Italy, 20.4% in Portugal, 9.5% in Germany, and 9.3% in France. Prevalence of progressive, regressive, abortive, and focal infection in Italy was 7.8%, 4.5%, 6.3%, and 2.6%; in Portugal 3.8%, 8.3%, 6.7%, and 1.7%; in Germany 1.9%, 1.3%, 3.5%, and 2.8%; in France 1.9%, 3.7%, 2.8%, and 0.9%, respectively. In conclusion, overall FeLV prevalence is still very high, especially in Southern European countries. Therefore, testing, separation of infected cats, and vaccination are still important measures to reduce the risk of FeLV infection.

Onset of Protection of FeLV Vaccine Containing Purified P45 FeLV-Envelope Antigen after One Single Injection of Primary Vaccination in Cats

Feline Leukaemia Virus (FeLV) is a viral pathogen causing fatal disease in cat populations worldwide, mainly in young kittens with outdoor access. This study aimed to assess the protection against feline leukaemia virus (FeLV), provided by a FeLV vaccine containing purified p45 FeLV-envelope antigen (Leucogen®) after one single injection of primary vaccination in kittens. Twenty-five 9-week-old cats, negative for FeLV antibodies and antigens the day of vaccination, were randomized into two groups. One group of 10 kittens was not vaccinated and kept as control, and one group of 15 animals received one dose of Leucogen® vaccine. The serological response was measured 14 and 21 days post vaccination. Three weeks after the vaccination, all kittens were inoculated by oronasal route with a virulent FeLV-A strain. The development of persistent viraemia was monitored for 15 weeks following inoculation. The animals were clinically monitored closely during the experimental phase. All cats remained in good health, presented physiological growth along the study and did not show any unexpected reaction after vaccination. In the control group, 90% of cats (9/10 cats) developed a persistent infection, confirming that this experimental infection model was valid, since the minimum of 80% required by the European monograph was achieved. On the other side, 73% of the vaccinated cats (11/15 cats) did not develop a persistent infection following the challenge strain inoculation. In the FeLV vaccinated group, 73% of cats were protected from the first vaccine injection. The first injection of primary vaccination with Leucogen® vaccine provided complete protection against FeLV persistent viraemia in 73% of the kittens. The second injection of the primary vaccination is necessary to ensure a complete protection of the whole population and a long lasting immunity. The early protection against FeLV infection conferred after one single injection of primary vaccination with FeLV vaccine containing purified p45 FeLV-envelope antigen could be a contributing factor in the reduction of prevalence of FeLV infection.

Feline osteochondromatosis in a 12-year-old feline leukaemia virus-negative cat

Feline osteochondromatosis is a spontaneous osteocartilaginous exostosis associated with feline leukaemia virus (FeLV) infection or due to a frameshift variant in the exostosin glycosyltransferase 1 (EXT1) gene. Osteochondromatosis was diagnosed in an indoor-only, 12-year-old, neutered female, Russian Blue cat. Radiographs revealed bilateral calcified proliferations in the elbow, costochondral and sternochondral joints, which distorted the normal skeletal structure. Grossly, the proliferated joints presented with consistent, rounded masses, causing complete ankylosis. The main histopathological finding was an osteocartilaginous proliferation composed of multiple irregular islands of well-differentiated hyaline cartilage surrounded and delimited by osteoid tissue. Immunohistochemistry of the osteochondromas, bone marrow and mediastinal lymph nodes, using a primary anti-FeLV gp70 antibody, and FeLV proviral DNA real-time polymerase chain reaction on bone marrow were negative. Sequencing of exon 6 of the EXT1 gene was performed and nucleotide BLAST analysis demonstrated the absence of a frameshift variant. This study reports the only case of spontaneous feline osteochondromatosis in an animal more than 10 years old.

The detection and full genomic characterization of domestic cat Orthohepadnaviruses from Türkiye.

Domestic cat hepadnaviruses (DCHs) have been described as a novel virus that can infect cats. The aim of our study is the first identification and molecular characterizations of DCH infection in Turkish domestic cats. The blood, organ and ascites fluid samples from 550 cats were randomly sampled. The presence of DCH nucleic acid was investigated by using both in the literature and newly designed primers. It was found that the hepadnavirus positivity rate is 4% (22/550) in Türkiye. The full genomic characterization was performed on 13 of 22 samples, and others were characterized as nearly full genome. In this study, we highlight that whole blood samples should be also screened for DCH, not only serum samples as has frequently been done in other studies. DCH-infected cats were also found positive (54.54%, 12/22) for Feline leukaemia virus infection. BLAST results revealed that Turkish DCHs have 86.32%-99.08% homology with strains in the GenBank database, enabling us to construct phylogenetic trees. According to this study's results, it is suggested that this infection should be added to veterinary diagnostic panels worldwide. Additionally, we suggest that our new synthesized primers for the amplification of X gene can also be used for diagnosis.

Progressive and regressive infection with feline leukemia virus (FeLV) in cats in southern Brazil: Prevalence, risk factors associated, clinical and hematologic alterations.

Enzyme-linked immunosorbent assay (ELISA) for viral antigen is commonly used for the diagnosis of progressive feline leukemia virus (FeLV) infection but is not able to determine the true prevalence of infection when used as the sole test. Additional testing to detect proviral DNA will identify regressive (antigen negative) FeLV infections as well as progressive infections. Therefore, this study aimed to determine the prevalence of progressive and regressive FeLV infection, outcome-associated factors, and hematologic changes. A cross-sectional study was performed on 384 cats selected from routine hospital care. Blood samples were subjected to complete blood count, ELISA for FeLV antigen and FIV antibody, and nested PCR amplifying the U3- LTR region and gag gene, which are conserved in most exogenous FeLV. The prevalence of FeLV infection was 45.6% (CI95% 40.6-50.6%). The prevalence of progressive infection (FeLV+P) was 34.4% (CI95% 29.6-39.1%), that of regressive infection (FeLV+R) was 10.4% (CI95% 7.4-13.4%), for discordant but positive results 0.8% (CI95% 0.75-0.84%), for FeLV+P coinfected with FIV 2.6% (CI95% 1.2-4.0%), and FeLV+R coinfected with FIV 1.5% (CI95% 0.3-2.7%). Male cats were three times more likely to be in the FeLV+P group. Cats coinfected with FIV were 4.8 times more likely to belong to the FeLV+R group. In the FeLV+P group, the main clinical changes were lymphoma (38.5%), anemia (24.4%), leukemia (17.9%), concomitant infections (15.4%), and feline chronic gingivostomatitis - FCGS (3.8%). In the FeLV+R group, the main clinical signs were anemia (45.4%), leukemia (18.2%), concomitant infections (18.2%), lymphoma (9.1%), and FCGS (9.1%). Cats in the FeLV+P and FeLV+R groups showed mainly thrombocytopenia (56.6% and 38.2%), non-regenerative anemia (32.8% and 23.5%), and lymphopenia (33.6% and 20.6%). Hemoglobin concentration, packed cell volume (PCV), platelet count, lymphocytes, and eosinophils in the FeLV+P and FeLV+R groups had lower medians than the control group (FeLV/FIV-uninfected, healthy). Erythrocyte and eosinophil counts were statistically different among the three groups, with the medians of the FeLV+P and FeLV+R groups being lower than those of the control group. In addition, the median PCV and band neutrophil counts were higher in FeLV+P than in FeLV+R. Our results show a high prevalence of FeLV, different factors associated with the course of infection, and more frequent and severe hematologic changes in progressive infections compared with regressive infections.

Discordant FeLV p27 immunoassay and PCR test results in 21 cats with hematologic disorders.

A total of 1692 medical records from a primary care feline practice and a veterinary referral hospital were evaluated retrospectively to assess discordant feline leukemia virus (FeLV) test results. In total, 73 cats were positive for FeLV using serum in a lateral flow immunoassay (LFI) or laboratory-based ELISA. Of these cats, 21 subsequently tested negative for FeLV proviral DNA by non-quantitative PCR on EDTA whole blood (16/21, 76.2%), bone marrow (4/21, 19%) or both (1/21, 4.7%). The proportional morbidity (an estimate of prevalence in a sample of the total population) for FeLV by LFI/ELISA and PCR assays was 3.1%, consistent with that reported in previous studies for cats in North America. Cats with discordant LFI/ELISA and PCR results had either primary bone marrow disease (18 autoimmune, one neoplastic), a bone marrow insult (hemotrophic mycoplasmosis) or systemic inflammation (pyothorax with a marked neutrophilic leukocytosis). The percentage of cats with a positive LFA/ELISA result and negative PCR assay surviving to discharge was 85.7% (18/21). Of these, 88.9% (16/18) survived 4 months to 6 years. Seven cats (33.3%) were re-tested with LFI or ELISA once primary disease was controlled, and all tested negative. These findings indicate that in cats with bone marrow disease that shares features of progressive FeLV infection, positive LFI and ELISA FeLV test results should be followed up with FeLV proviral DNA PCR testing, particularly in populations where disease prevalence is low.

Diseases associated with feline leukemia virus and feline immunodeficiency virus infection: A retrospective study of 1470 necropsied cats (2010-2020).

Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) are retroviruses affecting cats worldwide, and the prevalence of infection varies considerably according to the geographic area. We retrospectively described FIV- and FeLV-associated diseases in a population of 1470 necropsied cats, of which 396 (26.9%) were infected with FeLV, 199 (13.5%) with FIV, and 134 (9.1%) with FeLV and FIV concomitantly. Cats infected with FeLV (OR 3.4) and co-infected with FeLV and FIV (OR 1.9) were more likely to have neoplasms. The diagnosis of lymphoma and leukemia was higher in cats infected with FeLV (OR 3.9 and 19.4, respectively) and coinfected with FeLV and FIV (OR 1.9 and 19.3, respectively). The odds of diagnosing bacterial diseases were higher in cats coinfected with FeLV and FIV (OR: 2.8), whereas the odds of viral diseases were higher in those infected with FeLV (OR: 2.8), with 2.2 times more diagnoses of feline infectious peritonitis. Neoplastic and infectious diseases in FIV-infected cats did not differ significantly from those in uninfected cats. According to our results, a high prevalence of retroviral infections was observed in southern Brazil, mainly in relation to FeLV. Infected cats were significantly younger than uninfected cats. The main causes of death associated with FeLV infection and FeLV and FIV coinfection were neoplastic and infectious diseases. In contrast, FIV infection was not associated with any specific condition.

The first study on clinicopathological changes in cats with feline infectious peritonitis with and without retrovirus coinfection.

Feline infectious peritonitis (FIP) is an infectious, immune-mediated, and fatal disease in cats caused by a mutant feline coronavirus (FCoV) infection. Feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) are two common retroviruses that play a role in reducing feline immune function with opportunistic retrovirus infection being a predisposing factor for the development of FIP. This study aimed to evaluate the clinicopathological parameters of FIP in cats with and without retrovirus coinfection. In total, 62 cats presenting with pleural and/or peritoneal effusion at the Kasetsart University Veterinary Teaching Hospital, Bangkok, Thailand, were selected for the study. Effusion samples were collected and a reverse transcriptase-polymerase chain reaction (RT-PCR) assay was performed on all samples using the 3' untranslated region primer. All FCoV-positive cats were tested for retrovirus infection using a commercial kit (Witness FeLV-FIV [Zoetis]; United States). Clinical signs, hematological, and biochemical parameters of these cats were investigated and grouped. Of the 62 cats with pleural and/or peritoneal effusion, FCoV was detected in 32, of which 21 were highly suspicious for FIP. The cats suspected of FIP were divided into three subgroups following viral detection. A total of 14 had only FCoV infection (Group A), four had FCoV and FeLV infection (Group B), and three had FCoV, FeLV, and FIV infection (Group C). Of the rest, 11 had definitive diagnoses, which included three being FCoV and FeLV-positive (Group D), and eight were retrovirus-negative (Group E). Mild anemia and lymphopenia were found in cats infected with these three viruses. An albumin-to-globulin ratio lower than 0.5 was found in FIP cats with only FCoV infection. Typically, cats with clinical effusion and FIP, with and without retrovirus coinfection, had similar hematological findings. Clinical signs, blood parameters, fluid analysis with cytological assessment, and RT-PCR assays could identify better criteria to diagnose FIP with and without retrovirus coinfection.