SURVEILLANCE OF ZOONOTIC PARASITES IN SEDIMENT, WATER, AND INVASIVE BIVALVES AT THE LAND-WATER INTERFACE

Abstract

Climate-driven shifts in precipitation, paired with human activity, increasingly mobilize terrestrial pathogens into aquatic systems, where filter-feeding bivalves such as Corbicula fluminea can acquire and retain waterborne contaminants. Because the parasites Toxoplasma gondii and Cryptosporidium spp. persist in the environment and are closely tied to hydrologic variability, the Tar-Pamlico River Basin offers an ideal system for examining how precipitation-driven transport shapes pathogen presence across soil, water, and clam tissue. To investigate this, soil, surface water, and C. fluminea tissue were collected seasonally from five sites spanning a freshwater-to-brackish environmental gradient, alongside USGS (US Geological Survey) stream gage height data used to characterize hydrologic variability. Samples were screened for T. gondii and Cryptosporidium spp. the molecular method quantitative PCR (qPCR), and pathogen occurrence was estimated using bias-reduced logistic regression and generalized linear mixed-effects models to assess how sample type, hydrology, and water quality predicted detection. Cryptosporidium spp. was detected frequently in soil (up to 97.8%) and water (up to 93.3%) across all seasons, but rarely in clam tissue, while soil and water samples were significantly more likely to test positive than clams (OR = 92.65 and 26.59, respectively). T. gondii was detected far less often overall and never in clams. Nonetheless, both parasites showed positive associations with stream gage height and salinity, with this relationship considerably stronger for Cryptosporidium than T. gondii. This contrast suggests that although parasites are clearly present and mobilized within the watershed, their environmental availability does not consistently lead to bivalve uptake. The rarity of detections in C. fluminea likely suggests intermittent, low-level exposure, behavioral constraints on filtration, and the limits of whole-tissue qPCR rather than true parasite absence.