Schistosomiasis Burden and Its Association With Lower Measles Vaccine Responses in School Children From Rural Cameroon

Abstract

Background and Methods: Schistosomiasis is debilitating and reported to impair immune responsiveness of infected hosts. In Cameroon, mass drug administration (MDA) is used in schoolchildren to reduce transmission of S. haematobium and S. mansoni. The effects of MDA and the impact of schistosomiasis on the titers of antibodies in vaccinated children have been poorly studied. We therefore assessed the prevalence of schistosomiasis in schoolchildren, eight months after MDA, in two locations: Barombi Koto (BK), endemic for S. haematobium (N = 169) and Yoro (Y), endemic for S. mansoni (N = 356). Age, gender, residence time and frequency of contact with river water were assessed as risk factors for infection and morbidity in both localities. In 70 schoolchildren from BK and 83 from Y, ultrasound was used to assess morbidity according to the WHO guidelines. Evaluation of measles antibodies was performed in previously vaccinated schoolchildren (14 with S. haematobium and 12 egg-negative controls from BK and 47 with S. mansoni and12 egg-negative controls from Y). Principal Findings and conclusions: The prevalence of S. haematobium was 25. 4% in BK (43/169) and 34.8% for S. mansoni in Y (124/356), indicating the persistent transmission of schistosomiasis despite MDA. Older age (AOR 1.31; 95%CI 1.12-1.54) and higher frequencies of exposure to river water (AOR 1.99; 95%CI 1.03-3.86) were identified as risks for infection in BK whereas only older age (OR 1.15; 95%CI 1.04-1.27) was a risk for infection in Y. Bladder pathology (score 2 to 5) was observed in 29.2% (7/24) of egg-positive children in BK and liver pathology (pattern C) in 31.1% (19/61) of egg-positive children in Y. There was a positive correlation between S. haematobium egg burden and bladder pathology (AOR 1.01; 95% CI 0.99-1.02) and positive correlation between S. mansoni-driven liver pathology and female gender (AOR 3.01; 95% CI 0.88-10.26). Anti-measles antibodies in vaccinated children were significantly lower in S. mansoni-infected when compared to egg-negative controls (p = 0.001), which was not observed in the S. haematobium-infected group from BK. Our results demonstrate a questionable efficacy of MDA alone in halting schistosomiasis transmission and confirm a possible immunomodulatory effect of S. mansoni on response to vaccines.

Keywords: Cameroon; fibrosis; infection; measles; risk factors; schistosomiasis; vaccine responses.

Figure 1

Study flow diagrams. (A). Barombi-Kotto. (B). Yoro.

Figure 2

Age distribution & schistosomiasis prevalence in the two endemic communities studied. (A). Distribution of children by infection status and age in Barombi-Kotto. (B). Distribution of children by infection status and age in Yoro. (C). Prevalence of infected children in Barombi-Kotto. (D). Prevalence of infected children in Yoro.

Figure 3

Effect of Schistosomiasis infections on vaccine-induced anti-measles responses in schoolchildren from Barombi Kotto and around Yoro river. (A) Influence of S. haematobium (BK) infection on serum anti-measles IgG levels. N = 26 with 14 egg (–) and 12 egg (+) (B) Age distribution in children tested for vaccine responses in BK. (C) Influence of S. mansoni (Y) infection on serum anti-measles IgG levels. N = 59 with 12 egg (–) and 47 egg (+). (D). Age distribution in children tested for vaccine responses in Y. (E) Correlation between S. mansoni egg burdens and serum anti-measles IgG levels in Yoro. (F) Egg burdens and anti-measles antibody titers in examined children from Yoro. Low / equivocal (< 12 U/ml); positive titers (≥12 U/ml). Bars represent the medians and vertical lines represent the interquartile ranges.