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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.

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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.

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Abstract Diseases such as those caused by feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) represent health problems for cats. Feline leishmaniasis (FL) has been reported in several cities across the country. The objective was to carry out a clinical-epidemiological and laboratory study of FIV, FeLV and FL in cats from shelters in Dourados, Mato Grosso do Sul, Brazil. Blood samples and swabs from the conjunctival and nasal mucosa were obtained from 75 cats, from four animal shelters. Serology for FIV and FeLV was performed. For Leishmania, polymerase chain reaction (PCR) was performed on blood, conjunctiva and nasal mucosa. In the immunochromatographic serological test, seven cats tested positive for FIV and none for FeLV. No samples was positive in PCR for Leishmania. The study showed that despite the presence of human and canine leishmaniasis in the studied region, Leishmania spp. were absent in the cats studied. To avoid an increase in contagion in shelters, it is essential isolate cats with FIV.

Resumo Doenças como as causadas pelos vírus da imunodeficiência felina (FIV) e vírus da leucemia felina (FeLV) representam problemas de saúde para os gatos. A leishmaniose felina (LF) tem sido relatada em diversas cidades do país. O objetivo deste trabalho foi realizar um estudo clínico-epidemiológico e laboratorial de FIV, FeLV e LF em gatos de abrigos em Dourados, Mato Grosso do Sul, Brasil. Amostras de sangue e swabs da mucosa conjuntival e da mucosa nasal foram obtidas de 75 gatos, dos quatro abrigos de animais. Foi feita a sorologia para FIV e FeLV. Para Leishmania foi realizada a reação em cadeia da polimerase (PCR) em sangue, conjuntiva e mucosa nasal. No teste sorológico imunocromatografico, sete gatos apresentaram resultado positivo para FIV e nenhum para FeLV. Nenhuma amostra foi positiva na PCR para Leishmania. O estudo demonstrou que apesar da presença de leishmaniose humana e canina, na região estudada, não foi encontrado Leishmania spp. nos gatos analisados. Para evitar o aumento do contágio em abrigos é fundamental isolar os gatos com FIV.

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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.

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The feline leukemia virus (FeLV) belongs to the Retroviridae family and Gammaretrovirus genus, and causes a variety of neoplastic and non-neoplastic diseases in domestic cats (Felis catus), such as thymic and multicentric lymphomas, myelodysplastic syndromes, acute myeloid leukemia, aplastic anemia, and immunodeficiency. The aim of the present study was to carry out the molecular characterization of FeLV-positive samples and determine the circulating viral subtype in the city of São Luís, Maranhão, Brazil, as well as identify its phylogenetic relationship and genetic diversity. The FIV Ac/FeLV Ag Test Kit (Alere™) and the commercial immunoenzymatic assay kit (Alere™) were used to detect the positive samples, which were subsequently confirmed by ELISA (ELISA - SNAP® Combo FeLV/FIV). To confirm the presence of proviral DNA, a polymerase chain reaction (PCR) was performed to amplify the target fragments of 450, 235, and 166 bp of the FeLV gag gene. For the detection of FeLV subtypes, nested PCR was performed for FeLV-A, B, and C, with amplification of 2350-, 1072-, 866-, and 1755-bp fragments for the FeLV env gene. The results obtained by nested PCR showed that the four positive samples amplified the A and B subtypes. The C subtype was not amplified. There was an AB combination but no ABC combination. Phylogenetic analysis revealed similarities (78% bootstrap) between the subtype circulating in Brazil and FeLV-AB and with the subtypes of Eastern Asia (Japan) and Southeast Asia (Malaysia), demonstrating that this subtype possesses high genetic variability and a differentiated genotype.

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

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The aim of this study was to investigate the coinfection of feline retroviruses (feline immunodeficiency virus-FIV, and the feline leukemia virus-FeLV) with Leishmania infantum and Toxoplasma gondii and the factors associated with these pathogens in domestic cats from Mossoró, a city endemic for canine and human leishmaniasis situated in the semiarid region of Northeast Brazil. Blood samples from 120 cats were collected, and an epidemiological questionnaire was applied to investigate the risk factors associated with the infections. Retroviruses, L. infantum, and T. gondii infections were assessed using a point-of-care ELISA and quantitative PCR (qPCR), indirect fluorescent antibody test (IFAT) and qPCR, and IFAT, respectively. The overall seroprevalences observed were 35% (95% CI = 27.0-43.8%) for FIV, 0.8% (95% CI = 0.1-4.5%) for FeLV, 25.8% (95% CI = 18.8-34.3%) for T. gondii, and 4.2% (95% CI = 1.7-9.3%) for L. infantum. Coinfection with FIV and L. infantum was observed in 2.5% (3/120) of the assessed cats, while 12.5% (15/120) were coinfected with FIV and T. gondii. No significant association was found among the investigated agents (p > 0.05). The factors associated with FIV infection in the multivariable analysis were male sex and age above 78 months. The findings of this study demonstrated a high rate of FIV infection in cats from the Brazilian semiarid region and the exposure of these animals to zoonotic and opportunistic agents. Due to the immunosuppressive potential of FIV, cats infected with this retrovirus should be screened for coinfections with L. infantum and T. gondii, and preventative measures should be adopted.

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The surface envelope (SU) protein determines the cell tropism and consequently the pathogenesis of the feline leukemia virus (FeLV) in felids. Recombination of exogenous FeLV (exFeLV) with endogenous retroviruses (enFeLV) allows the emergence of more pathogenic variants. Currently, phenotypic testing through interference assays is the only method to distinguish among subgroups-namely, FeLV-A, -B, -C, -E, and -T. This study proposes a new method for FeLV classification based on molecular analysis of the SU gene. A total of 404 publicly available SU sequences were used to reconstruct a maximum likelihood tree. However, only 63 of these sequences had available information about phenotypic tests or subgroup assignments. Two major clusters were observed: (a) clade FeLV-A, which includes FeLV-A, FeLV-C, FeLV-E, and FeLV-T sequences, and (b) clade enFeLV, which includes FeLV-B and enFeLV strains. We found that FeLV-B, FeLV-C, FeLV-E, and FeLV-T SU sequences share similarities to FeLV-A viruses and most likely arose independently through mutation or recombination from this strain. FeLV-B and FeLV-C arose from recombination between FeLV-A and enFeLV viruses, whereas FeLV-T is a monophyletic subgroup that has probably originated from FeLV-A through combined events of deletions and insertions. Unfortunately, this study could not identify polymorphisms that are specifically linked to the FeLV-E subgroup. We propose that phylogenetic and recombination analysis together can explain the current phenotypic classification of FeLV viruses.

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In this retrospective and prospective study, histopathological and immunohistochemical analyses of 62 cases of lymphomas in cats were performed to classify the anatomic forms and subtypes, according to the WHO guidelines, and correlate it to FeLV proviral DNA detected using PCR. The most common anatomical form was gastrointestinal (40.3%, 25/62), followed by multicentric (29%, 18/62), mediastinal (17.7%, 11/62) and extranodal (12,9%, 8/62). Among the lymphoma subtypes, diffuse large B-cell lymphoma (DLBCL) (30.6%, 19/62) was the most commonly diagnosed followed by peripheral T-cell lymphoma (PTCL) (29%, 18/62) and enteropathy associated T-cell lymphoma type 2 (14.5%, 9/62). DNA extraction from paraffin-embedded neoplastic tissue was obtained in 28 cases and FeLV proviral DNA was detected by PCR, in 23 of these. Of the cases presenting with FeLV proviral DNA, nine (32%) were of the multicentric form, five (22%) of the mediastinal and extranodal forms and four (17%) of the gastrointestinal form. The most frequent subtypes with FeLV proviral DNA, independent of the anatomical form, were DLBCL (39.1%, 9/23) and PTCL (34.7%, 8/23). The presence of the FeLV proviral DNA in 23 cats of this study, probably had association with the multicentric form of lymphoma and higher occurrence in the DLBCL and PTCL subtypes.

Neste estudo retrospectivo e prospectivo, análises histopatológicas e imuno-histoquímicas de 62 casos de linfomas em gatos foram realizadas para classificar as formas anatômicas o e subtipos do linfoma, de acordo com as diretrizes da OMS. Além disso, foi realizada a extração de DNA dos tumores incluídos na parafina para obtenção de DNA pró-viral do FeLV por PCR, e relacionada com os exames anteriores. A forma anatômica mais comum foi a gastrointestinal (40.3%, 25/62), seguida pela multicêntrica (29%, 18/62), mediastinal (17,7%, 11/62) e extranodal (12,9%, 8/62). Entre os subtipos de linfoma, o linfoma difuso de grandes células B (DLBCL) (30.6%, 19/62) foi o mais comumente diagnosticado, seguido por linfoma de células T periférico (PTCL) (29%, 18/62) e o linfoma de células T associado a enteropatia tipo 2 (14.5%, 9/62). A extração de DNA de tecido neoplásico emblocado em parafina foi obtida em 28 casos e o DNA pró-viral de FeLV foi detectado por PCR, em 23 deles. Dos casos com DNA pró-viral do FeLV, nove (32%) eram da forma multicêntrica, cinco (22%) das formas mediastinal e extranodal e quatro (17%) da forma gastrointestinal. Os subtipos mais frequentes com DNA pró-viral do FeLV, independente da forma anatômica, foram DLBCL (39.1%, 9/23) e PTCL (34.7%, 8/23). A presença do DNA pró-viral do FeLV em 23 gatos deste estudo, provavelmente teve associação com a forma multicêntrica do linfoma e maior ocorrência nos subtipos DLBCL e PTCL.

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Background: Erythroid leukemia is a myeloproliferative hematopoietic disorder considered acute when there is a predominance of blasts in the bone marrow. It is frequently reported in cats infected with feline leukemia virus, but it is unclear whether this virus is involved in the oncogenesis. The clinical signs in cats are anorexia, apathy, weight loss, with evolution from 2 weeks to 2 months, pale mucous membranes, hemorrhages, ascites, salivation, and dyspnea due to pleural effusion. This affection responds little to chemotherapy with an unfavorable prognosis. The aim of this study is to report a case of a feline leukemia virus infected cat with the onset of severe hemolytic anemia. Case: A 8-year-old male mixed breed cat was attended with a history of anorexia, oligodipsia, apathy, progressive weight loss, and yellowish color of urine for 7 days. Laboratorial exams showed anemia (with metarubricytes, acanthocytes and ghost cells), leukocytosis and FeLV reagent test. The cat underwent treatment with methylprednisolone acetate and supportive care. One day later, the animal returned with icteric mucous membranes, and emesis. A blood count was performed that found worsening anemia, increased leukocytosis, and lymphocytosis. Abdominal ultrasound showed cholangiohepatitis and lymphadenomegaly in mesenteric lymph nodes. Treatment was started with ondansetron, metronidazole, and amoxicilin with potassium clavulanate. The cat returned after 3 days and laboratorial exams revealed worsening of blood parameters, so blood transfusion was performed. After 2 days, the patient started with dyspnea and hypothermia, that evolved to cardiorespiratory arrest. The body was sent to necropsy and histopathology, where blast cells and rubricytes were found in blood vessels of various organs. The bone marrow was markedly cellular with complete disappearance of adipose tissue. Most of the cells were blasts with abundant and eosinophilic cytoplasm, central nucleus with finely dotted chromatin and a large nucleolus. There were rubricytes, which made possible to confirm acute erythroid leukemia as a morphological diagnosis. Discussion: The clinical signs observed in acute erythroid leukemia are lethargy, inappetence, fever, splenomegaly, mild lymphadenomegaly, associated with leukocytosis, severe anemia, and thrombocytopenia. The reported animal presented signs similar to those described in the literature except that there was no change in platelet counts. The diagnosis of leukemia was reached after histopathology, and it is made when is observed more than 30% of myeloblasts and monoblasts together or when the blast cells count including rubriblasts is greater than 30%. Although chemotherapy, the prognosis is usually poor. It is essential to perform the myelogram for the diagnosis of myeloid leukemias in vivo. In this report, we only achieve final diagnosis after the cat's death, due to the aggressive behavior of the disease. Clinicians must be aware of the likely development of acute erythroid leukemia whenever a feline leukemia virus infected cat presents hemolytic anemia to get an early diagnosis, since this is an extremely aggressive disease, to propose prompt chemotherapy and give the patient a longer survival period.

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