Histoplasma capsulatum seroprevalence in free-roaming cats from 2 endemic regions

The aim of this study was to investigate Histoplasma seroprevalence and associated risk factors in free-roaming cats from 2 endemic regions: north central Oklahoma and eastern Tennessee. Seroprevalence was determined using frozen serum samples from trap, neuter, release programs in Tennessee (n = 426) and Oklahoma (200) from 2013 to 2024. For Tennessee samples, those with complete signalment information were included. For Oklahoma samples, no demographic information was available. An anti-Histoplasma immunoglobulin G antibody enzyme immunoassay was used to evaluate for the presence of anti-Histoplasma immunoglobulin G, and results were categorized as positive, intermediate, or negative. The Fisher exact test was used to assess risk factor associations. In total, 51 of 626 (8.1%) tested positive or intermediate, and 575 of 626 (91.9%) were negative. Of the samples from Tennessee, 24 of 403 (6.0%) were seropositive. From Oklahoma, 4 of 200 (2.0%) were seropositive. Of 47 Tennessee samples with positive or intermediate results, the median was 10.3 ELISA units/mL (EU; range, 8 to 31.1; positive, ≥ 10.0 EU), and of 4 Oklahoma samples with positive or intermediate results, the median was 20.3 EU (range, 18.8 to 22.6). There was no association between retrovirus infection, sex, pregnancy status, or presence of injury/disease and Histoplasma seropositivity. Our study is the first to document seropositivity of this regionally endemic fungus in free-roaming cats. Additional studies are encouraged to evaluate if similar seroprevalence is seen in indoor cats and if seropositivity is associated with clinical infection. Given the reported seroprevalence of histoplasmosis in felines, continued monitoring for Histoplasma infection by veterinary practitioners is warranted.