Freshwater ecosystems - an underexplored reservoir of zoonotic parasites

Abstract

Freshwater ecosystems are understudied reservoirs of zoonotic parasites. Previously, Pelophylax esculentus complex frogs were revealed to be carriers of a dematiaceous hyphomycete - Fonsecaea sp., the causative agent of chromoblastomycosis and phaeohyphomycosis, neglected diseases in humans, and a rare basidiomycete - Quambalaria cyanescens, an opportunistic pathogen. To gain insight into the role of freshwater ecosystems in the transmission of zoonotic parasites to terrestrial hosts, copepods and branchiopods and surface water from the Sava and Danube rivers and the floodplains around Belgrade were sampled and screened for the presence of Toxoplasma gondii and Giardia spp. gDNA by PCR. Surface water (10 L) was concentrated by filtration through a 1.2 μm polycarbonate filter. Crustaceans were collected using nets. Total DNA was extracted from the water pellet and crustaceans using Trizol reagent and the 529bp RE and β-giardin were amplified using specific primers. T. gondii was detected in 6/8 freshwater samples, and in 1/4 crustacean samples (Cyclops sp.). Giardia spp. gDNA was not detected. All samples originated from freshwater ecosystems from areas which are heavily used for commercial and recreational purposes around Belgrade and are habitats for wildlife, thus providing opportunities for parasite exchange. Surface water in some areas is contaminated with T. gondii oocysts while copepods may be an underappreciated link in their transmission. As frogs carry pathogenic fungi, they could be important as vectors for zoonotic parasites due to their biphasic life cycle, and an investigation of frogs in the transmission of Spirometra spp. is underway.