RESUMEN
Introduction: Exposure rates to Histoplasma species, the causative agent of equine epizootic lymphangitis (EL), are unknown amongst working equids in The Gambia. The primary aims of this study were to estimate anti-Histoplasma antibody seroprevalence in the equid population in rural The Gambia and to explore risk factors for seropositivity. Methods: A nationwide cross-sectional study was conducted (February-July 2022), representing baseline measurements of a longitudinal cohort study. Horses (n = 463) and donkeys (n = 92) without EL signs were recruited in 18 study sites. Following informed owner consent, equid clinical and management data were recorded. Blood samples were collected by jugular venepuncture, and sera were subject to the IMMY Latex Agglutination Histoplasma test (LAT). Seropositivity risk factors were explored by multi-level, multivariable logistic regression analysis. Study site and household variance were described using a latent-variable approach. Whole blood DNA extractions were subject to nested ITS-PCR to detect Histoplasma capsulatum var. farciminosum (HCF), and agreement with LAT results was measured using Cohen's kappa statistic. Results: Anti-Histoplasma antibody seroprevalence in horses and donkeys was 79.9% [95% confidence interval (CI) 76.0-83.5%] and 46.7% (95% CI 36.3-57.4%), respectively. In horses, two multivariable models explained the maximum amount of data variability. Model 1 demonstrated increased odds of seropositivity in mares [odds ratio (OR) = 2.90 95% CI 1.70-4.95, p < 0.001] and decreased odds in horses <2.5 years (OR = 0.46 95% CI 0.22-0.95, p = 0.04; reference: ≥4.5 years). Model 2 demonstrated increased odds in horses recruited during the rainy season (OR = 2.03 95% CI 1.08-3.84, p = 0.03) and those owned by farmers reporting previous EL in their equids (OR = 1.87 95% CI 1.04-3.37, p = 0.04). Decreased odds were measured in horses <2.5 years (OR = 0.37 95% CI 0.18-0.78, p = 0.01) and horses reported to transport firewood (OR = 0.45 95% CI 0.28-0.74, p = 0.001). On multivariable analysis of donkeys, decreased odds of seropositivity were demonstrated amongst donkeys owned by households which also owned horses (OR = 0.23 95% CI 0.06-0.85, p = 0.03). HCF infection prevalence in horses and donkeys was 22.0% (n = 102/463, 95% CI 18.3-26.1%) and 5.4% (n = 5/92, 95% CI 1.8-12.2%), respectively. No significant agreement was measured between LAT and nested ITS-PCR results (κ < 0.00). Conclusion: High Histoplasma spp. exposure was demonstrated amongst equids in The Gambia. Investigation of risk factors, including equid husbandry and management strategies, as well as geoclimatic variations, is warranted. Outcomes may inform sustainable and equitable EL control strategies in The Gambia and comparable settings worldwide.
RESUMEN
Robust surveillance of Histoplasma species is warranted in endemic regions, including investigation of community-level transmission dynamics. This cross-sectional study explored anti-Histoplasma antibody seroprevalence and risk factors for exposure in a general population in Upper River Region (URR), The Gambia. Study participants were recruited (December 2022-March 2023) by random household sampling across 12 Enumeration Areas (EAs) of URR. A questionnaire and clinical examination were performed; exploring demographic, clinical and environmental risk factors for Histoplasma exposure. One venous blood sample per participant was subject to IMMY Latex Agglutination Histoplasma test to determine presence of a recent IgM response to Histoplasma. Seropositivity risk factors were explored by multi-level, multivariable logistic regression analysis. The study population (n = 298) aged 5-83 years, demonstrated a positively skewed age distribution and comprised 55.4% females. An apparent seroprevalence of 18.8% (n = 56/298, 95% CI 14.5-23.7%) was measured using the LAT. A multivariable model demonstrated increased odds of Histoplasma seropositivity amongst female participants (OR = 2.41 95% CI 1.14-5.10); and participants reporting involvement in animal manure management (OR = 4.21 95% CI 1.38-12.90), and management of domestic animals inside the compound at night during the dry season (OR = 10.72 95% CI 2.02-56.83). Increasing age (OR = 0.96 95% CI 0.93-0.98) was associated with decreased odds of seropositivity. Clustering at EA level was responsible for 17.2% of seropositivity variance. The study indicates frequent recent Histoplasma exposure and presents plausible demographic and environmental risk factors for seropositivity. Histoplasma spp. characterisation at this human-animal-environment interface is warranted, to determine public health implications of environmental reservoirs in The Gambia. The study was supported by Wellcome Trust (206,638/Z/17/Z to CES) and a University of Liverpool-funded PhD studentship (to TRC).
RESUMEN
BACKGROUND: Despite recognition of histoplasmosis as a disease of national public health concern in Kenya, the burden of Histoplasma capsulatum in the general population remains unknown. This study examined the human seroprevalence of anti-Histoplasma antibody and explored associations between seropositivity and demographic and environmental variables, in Busia county, western Kenya. METHODOLOGY: Biobanked serum samples and associated data, from a previous cross-sectional survey, were examined. Latex agglutination tests to detect the presence of anti-Histoplasma antibody were performed on serum samples from 670 survey respondents, representing 178 households within 102 sub-locations. Potential epidemiologic risk factors for H. capsulatum exposure were explored using multi-level multivariable logistic regression analysis with household and sub-location included as random effects. PRINCIPAL FINDINGS: The apparent sample seroprevalence of anti-Histoplasma antibody was 15.5% (n = 104/670, 95% Confidence Interval (CI) 12.9-18.5%). A multivariable logistic regression model identified increased odds of H. capsulatum seropositivity in respondents reporting rats within the household within the previous 12 months (OR = 2.99 90% CI 1.04-8.55, p = 0.04). Compared to respondents aged 25-34 years, the odds of seropositivity were higher in respondents aged 15-24 years (OR = 2.70 90% CI 1.04-6.97, p = 0.04). CONCLUSIONS: The seroprevalence result provides a baseline for sample size approximations for future epidemiologic studies of the burden of H. capsulatum exposure in Busia county. The final model explored theoretically plausible risk factors for H. capsulatum exposure in the region. A number of factors may contribute to the complex epidemiological picture impacting H. capsulatum exposure status at the human-animal-environment interface in western Kenya. Focussed H. capsulatum research is warranted to determine the contextual significance of identified associations, and in representative sample populations.