Skin and serum reactivity among humans to histoplasmin in the vicinity of a natural focus of Histoplasma capsulatum var. duboisii

Abstract

The epidemiology of histoplasmosis duboisii (African histoplasmosis) is not well understood. The present study was carried out to investigate the prevalence of skin sensitivity and to determine by immunodiffusion the presence of antibodies among humans to histoplasmin around a recently discovered natural focus of Histoplasma capsulatum var. duboisii in a bat cave in Ogbunike in the Anambra State of Nigeria. Out of the 40 subjects, all young adults aged 18-30 years, comprising cave guides, traders and farmers examined in the immediate vicinity of the cave, 14 (35.0%) gave a positive skin test. In another population of the same age group, comprising 620 persons, viz. traders, farmers, palm oil workers and some patients attending rural clinics, examined in other nearby areas in Anambra State, 55 (8.8%) reacted positively to histoplasmin. In the immunodiffusion tests, 2 (2.08%) of the 96 school children and 17 (9.4%) of the 181 young adults, including farmers, palm oil workers and traders tested amongst the population around the cave, demonstrated precipitating antibodies to histoplasmin in their sera. Only 5 (0.79%) of the 630 adults of the same age group with similar occupations examined from other areas in Anambra State had precipitating antibodies. Out of another 50 subjects examined, viz.; wood workers, traders, farmers, and school teachers in Nsukka in the Enugu State, two (4.0%) demonstrated antibodies. It is suggested that asymptomatic infections due to the duboisii variety of H. capsulatum may be common in the human population around the cave. A diligent search with the help of local hospitals and public health officials may reveal clinical cases of histoplasmosis duboisii with cutaneous and systemic lesions.

Literature Review and Case Histories ofHistoplasma capsulatumvar.duboisiiInfections in HIV-infected Patients

“…Skin reaction to histoplasmin in histoplasmosis-endemic areas showed a 3% prevalence ( 10 ), but variety capsulatum and variety duboisii were not able to be differentiated. Higher prevalence (≈35%) was found in rural populations, especially among farmers, traders, and cave guides ( 11 ). Histoplasmosis due to variety duboisii may be misdiagnosed in those areas because of physicians’ lack of awareness.…”

Histoplasmosis Infections Worldwide: Thinking Outside of the Ohio River Valley

“…The distribution of histoplasmosis in Africa is probably the most puzzling due to the lack of solid epidemiologic studies coupled with the limited laboratory capacity available in much of the continent 55,58,59,80,81 . Complicating matters, there is the coexistence of two varieties of the fungus: H. capsulatum var.…”

Antibodies to antigens of Histoplasma, Blastomyces and Candida in HIV patients and carriers in Nigeria

“…Investigations on the prevalence of antibodies to fungal antigens in the normal and HIV‐negative population in Nigeria have been lacking. In a recent study that we carried out [12], 2.7% of 958 subjects comprising different population groups tested showed precipitating antibodies to both capsulatum and duboisii histoplamins. However, the prevalence of antibodies in population in the vicinity of a natural focus of H. capsulatum var.…”

“…We prepared the antigen of H. capsulatum var . duboisii (duboisii histoplasmin) using a ten‐fold concentration of the mycelial cultural filtrate of the fungus as described earlier [12]. The Candida antigen in the study was the homogenate‐supernatant antigen of the yeast cells of Candida albicans prepared in our laboratory following the method described by Mackenzie et al .…”

“…Control sera for C. albicans were prepared by immunization of rabbits with the prepared antigen. Immunodiffusion tests were carried out essentially according to a procedure described earlier [12].…”