FeLV and haemoplasma IgM positivity in a hospital sample of cats in Portugal

Companion animal health and genetics · 2026

In plain language

In a hospital study in Portugal, 32 of 134 cats tested positive for IgM antibodies against haemoplasmas. No statistically significant link was found between having FeLV and testing positive, but only six cats had FeLV: the results do not show that there is no link or that FeLV has a protective effect. A positive test was the study's criterion for classifying acute mycoplasmosis, not independent confirmation of active clinical disease in each cat. The study did not evaluate interventions targeting FeLV or the course of FeLV disease.

Scientific detail

The clinical study, published in 2026 in Companion animal health and genetics, used an analytical cross-sectional observational design in a hospital sample of 134 cats in Portugal. It classified acute feline mycoplasmosis using a positive haemoplasma IgM result. There were 32 IgM-positive and 102 IgM-negative cats; the reported observed prevalence of positivity was 23.8%, with a 95% confidence interval of 0.169–0.320. This frequency applies to the screened hospital patients; it is neither a representative estimate for all cats in Portugal nor a measure of FeLV prevalence. The operational definition also does not independently confirm active clinical disease in every IgM-positive cat.

FeLV status was available for 124 cats, including six FeLV-positive cats, one of whom was IgM-positive. Univariate analysis identified no statistically significant association between FeLV status and haemoplasma IgM positivity: OR 0.587, 95% CI 0.066–5.22, p = 1. The small FeLV-positive subgroup and wide confidence interval do not establish a protective effect of FeLV or the absence of an association. The FIV finding is distinct and cannot substitute for a FeLV finding. Prognostic analyses included the 32 IgM-positive cats; the study did not evaluate FeLV-directed interventions or FeLV disease progression.

The authors could not identify the Mycoplasma species affecting individual cats or distinguish single haemoplasma infections from coinfections. The reported associations therefore cannot be assigned to a particular species or to single versus mixed infections; this limitation does not mean that recorded FIV or FeLV status was unavailable for every cat. They also reported a lack of laboratory standardization and missing information in retrospective records. The abstract acknowledges that direct causality cannot be inferred. The claims presented are assigned evidence level C and derive from an observational hospital sample, not a controlled experiment.

What we know

In this hospital sample, 32 of 134 cats were haemoplasma IgM-positive; the reported observed prevalence was 23.8% (95% CI 0.169–0.320). The study used this positivity to classify acute mycoplasmosis. Among the 124 cats with recorded FeLV status, six were FeLV-positive and one of those six was IgM-positive. Univariate analysis detected no statistically significant association between FeLV and IgM positivity (OR 0.587; 95% CI 0.066–5.22; p = 1). This is level C observational evidence.

What we don't know

These data do not establish whether an association exists between FeLV and haemoplasma IgM positivity, nor do they demonstrate a protective effect of FeLV. The Mycoplasma species involved were not identified, and single haemoplasma infections were not distinguished from coinfections. IgM-based classification does not independently confirm active clinical disease in each positive cat. Direct causality cannot be inferred, and the observed frequency cannot be extrapolated to all cats in Portugal. The study provides no evaluation of FeLV-directed interventions or FeLV disease progression.

Evidence

Provenance

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