Parasites of invertebrates are poorly known because they typically cause little economic loss. Nevertheless, it is becoming apparent that many aquatic invertebrates are exploited by microparasite groups with simple, complex or unknown life cycles. Because infectious stages are typically released, screening for microparasite DNA in environmental samples offers a unique opportunity to gain insights on parasite distributions, diversities, and ecologies. Employing environmental DNA (eDNA) approaches is becoming critical in some cases due to emerging diseases of aquatic organisms, often in association with environmental stress. Since disease agents spread in water, hydrological connectivity is also likely to influence distributions and diversities. To determine how connectivity and stressors influence microparasite distributions, water and disturbed sediment samples were analysed from 17 UK lakes and rivers during the spring, summer and autumn, to characterise the presence and diversity of poorly known parasites of freshwater invertebrates - the Haplosporidia and the Myxozoa, (with unknown and complex life cycles, respectively). Genomic DNA was extracted and screened using PCR with specifically designed oligo primers targeting a region of the 18S rRNA gene along with appropriate controls.
Results/Conclusions
Haplosporidian DNA was detected in >90% of waterbodies. Haplosporidian incidence was highest in spring and lowest in autumn, perhaps reflecting mortality of infected hosts or seasonal variation in host or parasite populations. Presence of haplosporidian DNA was analysed with respect to hydrological connectivity, eutrophication, agricultural activity, urban land-use, water body volume and catchment size. Higher levels of connectivity were associated with higher probabilities of haplosporidian presence. Other factors had no significant effect on the likelihood of haplosporidian incidence. The myxozoan causative agent of salmonid Proliferative Kidney Disease (PKD) was only detected in rivers (in 2 of 3 sites). eDNA analyses of other myxozoans is ongoing.
In conclusion, distributions of poorly known parasite groups can be extensive (haplosporidians) and vary over time and space (haplosporidians, myxozoans). Drivers of distributions include hydrological connectivity but not environmental quality (haplosporidians) and water body type (PKD agent). The identification of such drivers may be relevant for the prediction and control of potential disease outbreaks. Ongoing analyses using Illumina MiSeq amplicon sequencing and Restriction Fragment Length Polymorphisms (RFLP analysis) will reveal further insights on haplosporidian and myxozoan diversities and distributions.