Immunologic, genetic and social human risk factors associated to histoplasmosis: studies in the State of Guerrero, Mexico

Abstract

Immunologic and occupational aspects of the susceptible population exposed to Histoplasma capsulatum, the causative agent of histoplasmosis were analyzed in the Mexican State of Guerrero. Three areas were studied, Juxtlahuaca, Olinala, and Coyuca; in the first two, their populations refer contact with bat guano and/or avian excreta, which contain nutrients for fungal growth, while the Coyuca population referred no contact with the above mentioned excreta. Previous infection with H. capsulatum was determined by histoplasmin-skin test, and the response was higher in men than in women (93.87, 85.71, and 6.6% for men, and 78.94, 66.6, and 0% for women) in Juxtlahuaca, Olinala, and Coyuca, respectively. Labor activities related to a persistent contact with the fungus were considered as an occupational risk factor, histoplasmin-skin test reached 88.57 and 36.36% of positive response in individuals with high and low risk activities. A high percentage of histoplasmin responses was observed in subjects with constant contact with H. capsulatum, such as, cave-tourist guides, peasants, and game-cock handlers, and generally they developed the largest diameter of skin reactions. Genetic risk factor was determined by studying the gene frequency of the Major Histocompatibility Complex antigens in a sample of individuals and their degree relatives in Juxtlahuaca, Olinala, and Coyuca. Significant differences were found for HLA-B22 and B17 antigens in Juxtlahuaca, and for HLA-B22 in Olinala, in comparison to the usual gene frequency observed in the normal Mexican population. HLA results were important, considering that HLA-B22 was previously found to be possibly related to pulmonary histoplasmosis in Guerrero.