# Genetic analysis of cercarial release in schistosomes

> **NIH NIH R01** · TEXAS BIOMEDICAL RESEARCH INSTITUTE · 2020 · $503,600

## Abstract

SUMMARY
Identification of the parasite genes that influence transmission, virulence and host specificity is of central interest
for understanding host/parasite interactions. The central aim of this proposal is to identify the genetic basis of two
such traits in Schistosoma mansoni, a parasitic fluke that infects 67 million people in South America, Middle-East
and Africa. We will focus on the larval stage of the parasite lifecycle in aquatic snails. Following penetration of the
snail host, schistosome larvae reproduce clonally, castrating their snail host, and hundreds to tens of thousands of
motile cercariae larvae are released into the water where they infect humans or rodents. Two key transmission-
related traits show high levels of heritable genetic variation among parasites. First, the timing of cercarial release
from the snail varies among populations and overlaps with the water contact patterns of their vertebrate hosts. Most
S. mansoni populations that primarily infect humans shed cercariae larvae in late morning, while parasite
populations that primarily infect rodents shed cercariae in late afternoon or night. Late shedding has evolved at least
three times in S. mansoni populations. Laboratory crosses demonstrate a simple genetic basis for this trait, but the
genetic architecture of late shedding is different in the three populations where it has been documented. Second, the
number of cercariae larvae shed from the intermediate aquatic snail host varies ≥7-fold among individual
schistosome genotypes. High shedding parasites have greater potential for transmission but also castrate and kill
their intermediate snails more rapidly than low shedding parasites. Laboratory experiments demonstrate that this
trait responds rapidly to selection and is highly heritable.
Schistosome parasites are unusual among parasites of humans because the complete lifecycle can be easily
maintained in the laboratory, so genetic crosses can be staged and thousands of progeny isolated, while a complete
genome sequence and a growing molecular toolkit now allows genomic and functional characterization. In
preliminary work, we conducted genetic crosses between diurnal and nocturnal shedding parasites from Oman and
identified a region on chr.1 that determines cercarial shedding time (LOD=6.1). In Aim 1, we will exploit the
growing schistosome molecular toolkit to fine map and functionally analyze the gene(s) that determine shedding
time in the Omani cross, and we will conduct additional crosses to determine the genetic basis of this trait in other
parasite populations where late shedding is observed. In Aim 2, we will use RNAseq to examine rhythms in
expression of nocturnal and diurnal shedding parasites from Oman across the 24 hr light/dark cycle, to investigate
the metabolic pathways underlying control of cercarial release. Finally, in Aim 3, we will analyze genetic crosses
between parasites showing 7-fold differences in numbers of cercariae shed from infected snail...

## Key facts

- **NIH application ID:** 9962286
- **Project number:** 5R01AI133749-04
- **Recipient organization:** TEXAS BIOMEDICAL RESEARCH INSTITUTE
- **Principal Investigator:** Tim J Anderson
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $503,600
- **Award type:** 5
- **Project period:** 2017-07-03 → 2022-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9962286

## Citation

> US National Institutes of Health, RePORTER application 9962286, Genetic analysis of cercarial release in schistosomes (5R01AI133749-04). Retrieved via AI Analytics 2026-05-21 from https://api.ai-analytics.org/grant/nih/9962286. Licensed CC0.

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