Pubertal development predicts resistance to infection and reinfection with Schistosoma japonicum.

BACKGROUND: In communities where Schistosoma species are endemic, the prevalence and intensity of schistosomiasis is disproportionately high among children, compared with adults. This epidemiologic pattern is consistent with either the slow development of resistance or the requirement of host developmental changes for the expression of resistance. METHODS: We enrolled 87 individuals aged 7-18 years who did not have Schistosoma japonicum infection and 641 individuals aged 7-30 years with S. japonicum infection, all of whom reside in 3 villages in Leyte, Philippines. At baseline, S. japonicum infection was assessed by Kato-Katz thick-smear stool examination, and the levels of the pubertal hormone dehydroepiandrosterone sulfate (DHEA-S) in serum were determined. Individuals with S. japonicum infection were treated with praziquantel, after which stool examination and DHEA-S level measurement were performed every 3 months for 18 months. RESULTS: In cross-sectional analyses, the intensity of infection among individuals with high DHEA-S levels was 43% lower (28 eggs per g, n = 243), compared with individuals with low DHEA-S levels (50 eggs per g, n = 242), even after adjusting for age, sex, and village (P = .01). Following praziquantel treatment, increased DHEA-S levels were associated with resistance to reinfection (P = .006). The intensity of reinfection among individuals with high DHEA-S levels was 42% lower, compared with individuals with low DHEA-S levels, even after adjusting for age, baseline intensity of S. japonicum infection, village, sex and water contact (P < .001). CONCLUSIONS: Increased DHEA-S levels in serum, a marker for adrenal development, is associated with reduced S. japonicum infection and reinfection, even after adjusting for age and, by proxy, cumulative exposure. These data suggest that an intrinsic property of host pubertal development mediates, in part, the resistance to infection observed in older individuals.

Seroprevalence of cysticercosis in children and young adults living in a helminth endemic community in leyte, the Philippines.

Cysticercosis is a significant public health problem in countries where pigs are raised for consumption and remains an important cause of neurological disease worldwide. The Philippines is considered an endemic area for cysticercosis because cases in both humans and pigs have been reported; however, epidemiologic information stays limited. We conducted a pilot survey of the seroprevalence of human cysticercosis in a village in Leyte, the Philippines, by measuring antibody specific for Taenia solium cyst-fluid antigen. There were 497 subjects aged 7-30 years in our study and most subjects were infected with one or more helminths. The overall cysticercosis seroprevalence in this population was 24.6% (95% CI: 20.82% ~ 28.58%) with no significant difference based on age, sex, or other helminth coinfection status. Although the sample may not be representative of the whole community, the findings suggest that cysticercosis is a significant, but underrecognized public health concern in the Philippines.

T-helper-2 cytokine responses to Sj97 predict resistance to reinfection with Schistosoma japonicum.

Although schistosomiasis is effectively treated with Praziquantel, rapid reinfection with rebound morbidity precludes effective control based on chemotherapy alone and justifies current efforts to develop vaccines for these parasites. Using a longitudinal treatment-reinfection study design with 616 participants 7 to 30 years of age, we evaluated the relationship between cytokine responses to Schistosoma japonicum soluble adult worm extract (SWAP), Sj97, Sj22.6, and Sj67, measured 4 weeks after treatment with Praziquantel, and resistance to reinfection in a population from Leyte, The Philippines, where S. japonicum is endemic. S. japonicum transmission was high: 54.8% and 91.1% were reinfected within 6 and 18 months, respectively. A Th2 bias in the following cytokine ratios, interleukin-4 (IL-4)/IL-12, IL-5/IL-12, IL-13/IL-12, IL-4/gamma-IFN (IFN-gamma), IL-5/IFN-gamma, and IL-13/IFN-gamma, in response to SWAP predicted a 1.4- to 2.9-month longer time to reinfection (P < 0.05) and a 27 to 55% lower intensity of reinfection (P < 0.05). Similarly, a Th2 bias in response to Sj97 predicted a 1.6- to 2.2-month longer time to reinfection (P < 0.05) and a 30 to 41% lower intensity of reinfection (P < 0.05). Only a high IL-5/IL-10 ratio in response to Sj22.6 predicted a 3.0-month-longer time to reinfection (P = 0.03). Cytokine responses to Sj67 were not associated with protection. In a large population-based treatment-reinfection study we found that Th2 responses to SWAP and Sj97 consistently predicted resistance to reinfection. These findings underscore Th2-type immune responses as central in human resistance to S. japonicum and support Sj97 as a leading vaccine candidate for this parasite.