Genetic and epidemiologic assessment of Schistosoma haematobium induce kidney and bladder pathology in rural Zimbabwe

Disease outcome in persons infected with Schistosoma haematobium can vary dramatically, ranging from mild symptoms to severe damage of the kidneys and/or bladder. This study explores the relationship of a number of epidemiological, parasitological, and genetic parameters with urinary tract pathology in children from rural Zimbabwe.;We surveyed 551 primary school students (9–16 years old) from three schools in the Chikwaka Communal Lands for schistosomiasis; of these, 59.7% were infected with Schistosoma haematobium. Ultrasound examinations of urinary tract organs were performed on 221 of the students. Kidney and bladder pathology were significantly linked to current S. haematobium infection status (P = 0.04 and P < 0.001 respectively). Among those infected, 49.7% had bladder damage and 33.7% had dilation of the pyelon of at least one of their kidneys.;In order to characterize the nature of transmission in the area and compare epidemiological parameters with morbidity, 247 of the students were administered a questionnaire concerning water exposure and other activities. Intensity of infection, certain water contact behaviors, and male gender were associated with bladder damage, with disease intensity accounting for most of the pathology. Kidney pathology was more prevalent in students from the schools closest to the major rivers in the area. No other parasitological or demographic characteristics were associated with kidney damage.;For 25 students, 12 with mild and 13 with severe infections, additional urine specimens were taken to enable characterization of the parasite genotypes composing their infections. By performing monomiracidial infections of host snails to replicate the parasite, we were able to obtain sufficient quantities of parasite DNA while minimizing the selection normally seen during passaging of the parasite through a rodent host. Using four RAPD primers on each of 133 miracidial isolates, allelic frequencies at 53 loci were scored. Mean heterozygosity of the population was 0.116 ± .043. Analysis of molecular variance revealed that parasite diversity was high within hosts but comparatively low between hosts. Using a cluster analysis, 13 parasite families were found to circulate in the area, with the occurrence of three significantly linked to pathology.;Our work suggests that intensity of infection and the presence of particular parasite strains may influence disease outcome with urinary schistosomiasis. The high level of S. haematobium diversity within persons reflects the chronic nature of exposure to the parasite, while low interhost diversity suggests panmixia. To improve understanding of risk factors for kidney pathology, it may be necessary to conduct long term studies which take into account the pattern of parasite exposure. Further characterization of the parasite families that were linked with more severe disease outcome may reveal a possible genetic mechanism for parasite virulence.