The Life Histories of Intermediate Hosts and Parasites of Schistosoma haematobium and Schistosoma mansoni in the White Nile River, Sudan

Abstract

Background: The epidemiology of schistosomiasis transmission varies depending on the circumstances of the surrounding water bodies and human behaviors. We aimed to explore cercarial emergence patterns from snails that are naturally affected by human schistosomiasis and non-human trematodes. In addition, this study aimed to explore how schistosomiasis infection affects snail survival, reproduction, and growth.

Methods: We measured the survival rate, fecundity, and size of Biomphalaria pfeifferi snails and the cercarial rhythmicity of S. haematobium and S. mansoni. The number of egg masses, eggs per egg mass, and snail deaths were counted for 7 weeks. The survival rate and cumulative hazard were assessed for infected and non-infected snails.

Results: S. haematobium and S. mansoni cercariae peaked at 9:00-11:00 a.m. Infection significantly reduced the survival rate of B. pfeifferi, which was 35% and 51% for infected and non-infected snails, respectively (p = 0.02), at 7 weeks after infection. The hazard ratio of death for infected snails compared to non-infected snails was 1.65 (95% confidence interval: 1.35-1.99; p = 0.01).

Conclusions: An understanding of the dynamics of schistosomiasis transmission will be helpful for formulating schistosomiasis control and elimination strategies. Cercarial rhythmicity can be reflected in health education, and the reproduction and survival rate of infected snails can be used as parameters for developing disease modeling.

Keywords: Biomphalaria pfeifferi; Bulinus truncatus; Sudan; cercarial rhythmicity; cumulative hazard ratio; schistosomiasis; snail; survival rate.

Figure 1

Overall diurnal innate rhythmicity of cercariae liberated from Biomphalaria pfeifferi and Bulinus truncatus snails (y-axis: number of cercariae).

Figure 2

Weekly survival rates of Biomphalaria pfeifferi snails that were infected and non-infected with Schistosoma mansoni (black color, non-infected snails; red color, infected snails; dotted line, 95% confidence interval).

Figure 3

Cumulative hazard of Biomphalaria pfeifferi snails that were infected and non-infected with Schistosoma mansoni (black color, non-infected snails; red color, infected snails; dotted line, 95% confidence interval; cumulative hazard ratio, 1.65; 95% confidence interval, 1.35–1.99, p = 0.01).

Figure 4

Fecundity of Biomphalaria pfeifferi snails that were infected or non-infected with Schistosoma mansoni (p-value < 0.001 for number of egg masses; p-value < 0.001 for number of eggs; solid line, number of eggs; dotted line, number of egg masses).

Figure 5

The size of Biomphalaria pfeifferi snails exposed to Schistosoma mansoni compared to the non-infected control group (x-axis, week; y-axis, mm; * p-value < 0.001).