A study of 194 cats found positive Leishmania test results in 12 of the 38 cats infected with FIV, FeLV, or both viruses. These data cannot establish a specific link with FeLV or show that one infection causes the other. In the laboratory, L. tarentolae remained for at least 72 hours in cells obtained from a single healthy cat. This finding does not demonstrate immune protection or an effect against FeLV, and whether infection can last long term and be transmitted from naturally infected cats remains unresolved.
The study published in Parasites & vectors in 2025 (doi: 10.1186/s13071-025-06983-w) combines observational screening of outdoor cats with an in vitro infection experiment using feline peripheral blood mononuclear cells (PBMCs). The results report 194 cats; the methods describe a calculated minimum sample size of 149 subjects, subsequently increased by 30%. Sample availability was convenience-based. The knowledge object's five empirical claims are classified as evidence level C; persistence and transmission remain an open question with no assigned evidence level.
Among 38 cats infected with FIV and/or FeLV, 12 were also serologically or molecularly positive for Leishmania spp. This finding documents co-occurrence in the sampled cats, but the combined FIV/FeLV category cannot isolate a FeLV-specific association, quantify immunosuppression, or establish causation. The estimated association between FIV and Leishmania positivity was not statistically significant: OR 2.359, 95% CI 0.901–6.179, and P = 0.081. This estimate concerns FIV, not FeLV; lack of statistical significance does not demonstrate absence of an association. FeLV proviral screening provides observational context for retroviral and Leishmania co-occurrence.
The PBMC experiment used blood from a single healthy cat. L. tarentolae infection persisted in feline-derived cells for at least 72 h; at that time, 41.6% of macrophages were infected, with an average of 2.1 parasites per infected cell. The result provides preliminary evidence of feline cellular susceptibility and short-term in vitro persistence in mononuclear phagocytes. The number of independent cell-culture replicates, independent biological replication, and an uninfected cell-culture control were not reported. The single-donor design does not provide population-level evidence or an experimental comparison between FeLV-infected and uninfected cats; it also does not establish parasite replication.
The authors identify the lack of validation of L. tarentolae IFAT in cats, possible serological cross-reactivity, limited cohort size for risk-factor assessment, and modest discrimination of the final multivariable model as limitations. Serological positivity does not independently establish species-specific infection or a protective immune response. Feline cytokine profiles, Th1 polarization, and FeLV-specific immune dysfunction were not measured or reported. The experiment therefore does not establish an effect of FeLV on immunity, a protective feline Th1 response, or an intervention against FeLV.
Whether L. tarentolae infection in mammals is transient or can persist, replicate, and subsequently infect sand flies remains unresolved. The authors call for confirmatory isolation efforts. The feline cell-culture findings do not resolve long-term persistence or transmission competence in naturally infected cats.
Level C evidence documents Leishmania positivity in 12 of 38 cats infected with FIV and/or FeLV, without isolating a FeLV-specific association. The FIV estimate was not statistically significant, which does not demonstrate absence of an association. In cells from a single healthy cat, L. tarentolae persisted for at least 72 h; 41.6% of macrophages were infected at that time, with an average of 2.1 parasites per infected cell. The cellular evidence is preliminary: uninfected culture controls and independent biological replication were not reported, and serological interpretation is limited by the lack of validation of L. tarentolae IFAT in cats and possible cross-reactivity.
These data do not establish a FeLV-specific association with Leishmania, causation, or the degree of immunosuppression. Feline cytokine profiles, Th1 polarization, and FeLV-specific immune dysfunction were not assessed. Immune protection and an effect against FeLV have not been established here. Whether L. tarentolae can persist and replicate in mammals and subsequently infect sand flies remains open; the experiment does not resolve long-term infection or transmission competence in naturally infected cats.
Excerpt verified in the source — verbatim, in the source's own language“In total, 38 cats (19.6%) were infected with FIV and/or FeLV, of which 12 were serologically or molecularly positive for Leishmania spp.”
This documents co-occurrence in the sampled cats. The combined retrovirus category does not isolate FeLV, quantify immunosuppression, or establish causation.
Excerpt verified in the source — verbatim, in the source's own language“The OR was calculated for FIV infection as a potential risk factor (OR 2.359; 95% CI 0.901–6.179), but with a P -value of 0.081, which is above the 0.050 threshold and therefore not considered statistically significant.”
This is an observational FIV estimate, not a FeLV estimate. Lack of statistical significance does not demonstrate absence of an association.
Excerpt verified in the source — verbatim, in the source's own language“A total of 4 mL of blood was collected from a healthy cat into ethylene diamine tetra acetic acid (EDTA) tubes (BD Vacutainer, San Diego, CA, USA).”
The experiment provides single-donor cellular evidence, not population-level evidence or an experimental comparison of FeLV-infected and uninfected cats.
Excerpt verified in the source — verbatim, in the source's own language“Cat PBMCs were successfully infected with L. tarentolae and the infection was sustained for at least 72 h post-infection (Fig. 2 ). At that timepoint, the rate of infected macrophages was 41.6%, with an average of 2.1 parasites per infected cell.”
This supports short-term in vitro persistence in feline mononuclear phagocytes. A single donor and absence of reported culture controls limit the evidence to preliminary status. It does not establish replication, immune protection, Th1 polarization, or FeLV-related effects.
Excerpt verified in the source — verbatim, in the source's own language“Although IFAT for L. tarentolae herein used was previously employed with feline sera [ 24 ], it is not yet validated for cats, which represents a limitation of the study that should be overcome in future work.”
Serological positivity must be interpreted in light of assay-validation uncertainty and possible cross-reactivity; it does not independently establish species-specific infection or a protective immune response.
The authors explicitly call for confirmatory isolation efforts. The feline cell-culture findings do not resolve long-term infection or transmission competence in naturally infected cats.
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