Revisiting density-dependent fecundity in schistosomes using sibship reconstruction

Area of Science:

• Parasitology
• Epidemiology
• Mathematical Biology

Background:

• Parasite population stability is influenced by density-dependent processes.
• Density-dependent fecundity, reduced egg production at high worm burdens, is crucial for helminth infections.
• Understanding this in human schistosomiasis is vital for control but historically equivocal due to inaccessible adult worms.

Purpose of the Study:

• To investigate density-dependent fecundity in human Schistosoma haematobium and Schistosoma mansoni.
• To apply a novel statistical modeling approach combining molecular inference and parasitological data.
• To inform schistosomiasis elimination strategies and data interpretation.

Main Methods:

• Utilized a statistical modeling approach.
• Combined molecular inference of adult worm numbers with parasitological egg count data.
• Analyzed data from human hosts in mainland Tanzania and Zanzibar for Schistosoma spp.

Main Results:

• Provided the first clear evidence of density-dependent fecundity in Schistosoma haematobium.
• Observed a non-proportional relationship between S. haematobium egg counts and inferred female worm numbers.
• Did not find robust evidence for density-dependent fecundity in Schistosoma mansoni due to data limitations and model sensitivity.

Conclusions:

• Density-dependent fecundity is a key regulatory process for Schistosoma haematobium.
• The findings have implications for predicting intervention effectiveness and interpreting schistosomiasis monitoring data.
• The model-based approach offers potential for understanding density dependence in other helminthiases.