Environmental source of histoplasmosis in India: An unsolved One Health enigma

Histoplasmosis is an emerging mycosis in India. Although clinical cases are increasingly recognized, the environmental niche of the Histoplasma (H.) capsulatum fungus remains poorly defined, with only a single soil isolation reported from India in 1975.

To investigate the presence of H. capsulatum in soil samples from endemic regions of West Bengal using conventional culture and sensitive molecular methods.

Forty-five soil samples were collected from Nadia and Bardhaman districts, targeting sites enriched with high nitrogen content, such as areas under the trees, uprooted soil, and abandoned houses. The soil samples were cultured on Sabouraud's dextrose agar with antibiotics and incubated for four weeks. DNA extracted from soil suspensions using a commercial kit was analyzed by TaqMan-based real-time PCR targeting the internal transcribed spacer region of H. capsulatum.

None of the samples were positive for H. capsulatum using conventional culture and/or RT-PCR. Nevertheless, the samples were positive for other saprophytic fungi, including Penicillium, Zygomycetes, and Acremonium spp. Real-time PCR demonstrated high sensitivity (10 fg of H. capsulatum DNA/μl). However, no amplification was observed in any of the soil samples, indicating no detectable presence of H. capsulatum DNA in the sampled locations in India.

The absence of H. capsulatum detection may reflect limited sample size, sampling bias, or patchy distribution of the fungus, suggesting the need for large-scale surveys combined with sensitive molecular methods. Therefore, strengthening environmental surveillance within a One Health framework will be crucial for better understanding and control of histoplasmosis in endemic regions.