Haemadipsid leeches: Trypanosome vectors or an environmental blood source?

Knowledge of trypanosoma host species and vectors are critical in understanding disease transmission and spread. Vertebrate trypanosomes are transmitted by hematophagous vectors. Arthropods are the main vectors of transmission for terrestrial vertebrate trypanosomes, whereby aquatic leeches are the vectors for the aquatic clade of trypanosomes. Leeches are an environmental source of blood and feed unspecifically on vertebrate species. A previously undescribed trypanosome species closely related to Trypanosoma cyclops was identified in haemadipsid leeches in Victoria, Australia.Blood was collected from rodents and brown antechinus (Antechinus stuartii) in Dorrigo, North-coast NSW for PCR detection of Trypanosoma using primers specific to the small subunit ribosomal RNA (SSU rRNA). Both antechinus (n=2) and no rodents (n=9) sampled positive for Trypanosoma at the Dorrigo site. The two positive samples were then sequenced in a commercial lab by bidirectional Sanger sequencing using amplification primers to determine the specific trypanosome species. The sequencing matched a previously identified Trypanosoma sp. in two haemadipsid leeches in Victoria, Australia. Using a Fisher’s exact test, our study found that Antechinus were significantly more likely to be infected withTrypanosoma than rodents (p=0.0278). Our results suggest that haemadipsid leeches are unlikely to be the vectors for this Trypanosoma sp. as they are not host specific, and thus would expect to see similar infection rates between Antechinus and rodents. Morphological detection of amastigotes and epimastigotes in a vector would be required to confirm its role in disease transmission.