Nutrient Dynamics in Schistosomiasis Transmission: Examining snail ingestion rates under varying resource conditions Open Access

Abstract

Schistosomiasis is a parasitic disease caused by trematode worms that relies on an intermediate

aquatic snail host for transmission to humans. Infected snails release cercariae, the free-living

larval stage of the parasite, which penetrates human skin to initiate infection. With no vaccine

and limited treatment options, mitigating the burden of schistosomiasis may be more effectively

achieved by through directly modifying the intermediate snails host communities. Traditional

epidemiological models have assumed that infection risk is directly correlated with the density of

infected snails, but recent research has suggested that cercarial production is significantly

impacted by resource availability. Endemic regions of schistosomiasis frequently face

fluctuations in resource availability, driven by both natural causes and human activities, which

contribute to an excess of nutrients in the environment. If snail resource availability drives

human infection risk, it is important to integrate ecological factors into current schistosomiasis

control strategies. This study examined whether snails modify their ingestion based on the

quality of food that is provided with the hypothesis that snails would ingest lesser quantities of

nutrient-rich foods. We fed uninfected Biomphalaria glabrata snails varying nutrient enriched

foods through a randomized block feeding design. Data was collected on their size, survival, and

ingestion. We then created a model for ingestion that incorporated size, ingestion rate, food

dissolution, and food availability. Fitting this model to our data indicated that uninfected snails

had similar ingestion rates across all food treatments. This study seeks to determine how snail

ingestion is modified in response to nutrient-enriched foods, to better understand how nutrient

availability influences feeding patterns and potential implications for schistosomiasis control.

Table of Contents

INTRODUCTION ............................................................................................................................... 1

METHODS......................................................................................................................................... 9

SNAIL SELECTION, MAINTENANCE, AND FEEDING SCHEDULE ................................................................................ 9

DATA COLLECTION ......................................................................................................................................... 9

CONTROL EXPERIMENT ................................................................................................................................. 10

DATA ANALYSIS ............................................................................................................................................ 11

MODEL FITTING........................................................................................................................................... 12

RESULTS ........................................................................................................................................ 14

DISCUSSION ................................................................................................................................... 16

FIGURES ......................................................................................................................................... 19

FIGURE 1: THE LIFE CYCLE OF THE SCHISTOSOMA PARASITE. ...................................................................... 19

FIGURE 2: CONTROL MASSES OF EXPERIMENTAL FOODS IN SOAKED AND UNSOAKED CONDITIONS. ................ 20

FIGURE 3: NUTRIENT ENRICHMENT WITH +N AND +NP INCREASES FOOD INGESTION. .................................. 21

TABLE 1: RANDOMIZED BLOCK DESIGN FEEDING SCHEDULE. ....................................................................... 22

TABLE 2: EXPERIMENTAL FOOD RECIPES. ................................................................................................... 22

TABLE 3: CALCULATED AIC VALUES RESULTING FROM THE TWO MODELS RUN. .......................................... 23

REFERENCES ................................................................................................................................. 24

SUPPLEMENTARY FIGURES .......................................................................................................... 28

SUPP. FIGURE 1: NUTRIENT SUPPLEMENTATION ALTERS SNAIL GROWTH, REPRODUCTION, AND PARASITE

OUTPUT. .................................................................................................................................................... 28

SUPP. FIGURE 2: STATISTICAL OUTPUT FROM A GENERALIZED LINEAR MIXED MODEL (GLMM). .................. 29

About this Honors Thesis

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School	Emory College
Department	Biology
Degree	B.A.
Submission	Honors Thesis
Language	English
Research Field	Biology, Parasitology Biology, Ecology
Keyword	SCHISTOSOMIASIS SCHISTOSOMA MANSONI
Committee Chair / Thesis Advisor	Dr. Julie Clennon, Emory University Dr. Arri Eisen, Emory University Dr. David Civitello, Emory University

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