Abstract
ObjectiveTo estimate the degree of synergism between helminth species in their combined effects on anemia.MethodsQuantitative egg counts using the Kato–Katz method were determined for Ascaris lumbricoides, hookworm, Trichuris trichiura, and Schistosoma japonicum in 507 school-age children from helminth-endemic villages in The Philippines. Infection intensity was defined in three categories: uninfected, low, or moderate/high (M+). Anemia was defined as hemoglobin <11 g/dL. Logistic regression models were used to estimate odds ratios (OR), 95% confidence intervals (CI), and synergy index for pairs of concurrent infections.ResultsM+ co-infection of hookworm and S. japonicum (OR = 13.2, 95% CI: 3.82–45.5) and of hookworm and T. trichiura (OR = 5.34, 95% CI: 1.76–16.2) were associated with higher odds of anemia relative to children without respective M+ co-infections. For co-infections of hookworm and S. japonicum and of T. trichiura and hookworm, the estimated indices of synergy were 2.9 (95% CI: 1.1–4.6) and 1.4 (95% CI: 0.9–2.0), respectively.ConclusionCo-infections of hookworm and either S. japonicum or T. trichiura were associated with higher levels of anemia than would be expected if the effects of these species had only independent effects on anemia. This suggests that integrated anti-helminthic treatment programs with simultaneous deworming for S. japonicum and some geohelminths could yield a greater than additive benefit for reducing anemia in helminth-endemic regions.
Highlights
The high prevalence of polyparasitic infections of geohelminth and schistosomiasis infections has received considerable attention in epidemiologic literature [1,2,3,4,5,6,7]
Seven children were simultaneously uninfected by hookworm, S. japonicum and trichuris in the analytic sample; all seven children were free of anemia
Our study suggests that for children in helminth endemic regions, contemporaneous infections with hookworm and either S. japonicum or trichuris may result in higher levels of anemia than would be expected if the effects of these species on anemia were additive
Summary
The high prevalence of polyparasitic infections of geohelminth and schistosomiasis infections has received considerable attention in epidemiologic literature [1,2,3,4,5,6,7] This profile of infection is recognized to be the norm for many residents of parasite endemic regions [3,5,6,7,8,9]. One possible form of interaction is synergism, which implies that the adverse health effect associated with multiple species infection is greater than the sum of adverse effects for individual species. This has been observed in mice coinfected with Trichinella spiralis and Heligmosomoides polygyrus [11]. Understanding the morbidity implications of polyparasitism, including any evidence of synergism between helminths in their cumulative health impacts, could provide valuable information for healthcare providers in many developing countries who must decide how aggressively to screen and treat children for polyparasitism in their resource limited settings
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