Molecular Detection of Totiviruses in Medically Important Arthropods and Parasites

Abstract

The Totiviridae is a family of unsegmented, icosahedral, small dsRNA viruses in the realm of Riboviria, which has been historically characterised by host diversity, morphology and host impact on differences in strategies for transmission. Human hosts include parasites like Leishmania, the cause of leishmaniasis a widespread and sometimes fatal disease, Trichomonas, the cause of trichomoniasis, the most common non-viral sexually transmitted infection, and Giardia, which causes giardiasis - an acute or chronic gastrointestinal disease. Eimeria causes serious diseases of domestic animals, particularly chickens, cattle and rabbits. Hosts from which they have been isolated included plant parasitic oomycetes, many yeasts and fungi, red macroalgae (seaweeds), diatoms (single celled algae), woodlice (terrestrial crustaceans), many insects such as flies, mosquitoes, ants and wasps and shrimp (marine crustaceans). However, also fish, freshwater snails that are intermediate hosts to parasites, and plants like papaya, notoginseng, maize, and wild petunias. The totiviruses increase the virulence of the parasites in Leishmania and Trichomonas (hypervirulence) and sometimes decreases fungal virulence (hypovirulence) such as in oats. Totivirus is myocarditis and myonecrosis in salmon, smelt and shrimp, and is asymptomatic in golden shiners. It is not infectious and vertically transmitted in Leishmania, Trichomonas, and other fungi and plants, while in Giardia it is transmitted horizontally by fish, shrimps, papaya. Totiviruses evolve so fast that there is currently no systematic method to search for them. The commercial antibody J2, specific for dsRNA, has been evaluated as such a tool to detect totivirus. While the sensitivity of the antibody was promising, the lack of specificity for dsRNA rendered it useless. To enable a systematic survey, conserved regions in the RNA-dependent RNA polymerase gene of individual virus species and lineages were identified and primers developed for Leishmaniavirus1, Leishmaniavirus2, Leishmania aethiopica virus, Giardiavirus, Eimeriavirus, and Trichomonasvirus. Outside of Leishmaniaviruses, PCR results were limited by the absence of available virus-positive host samples, and the reasons for failures to detect virus in test samples is discussed. The following viruses new to science were discovered: Leishmania infantum virus, Leishmania major virus, Leishmania panamensis virus, Leishmania hertigi virus, Leishmania mexicana virus, Leishmania amazonensis virus, Leishmania venezuelensis virus, Leishmania chagasi virus, Leishmania donovani virus, Leishmania gerbilli virus, and Leishmania tarentolae virus. Outside the current taxonomic grouping of parasites, Totiviruses new to science were discovered in the genus Endotrypanum, in the species Herpetomonas megaseliae, and in the species Blastocrithidia culicis of the Trypanosomatidae. In addition, the first totivirus was discovered in Bodo caudatus (Bodonida: Kinetoplastida), widely expanding the range of vertically transmitted totiviruses and the probable time when these viruses entered their host lineage. Sandflies as most common vectors of Leishmania parasites were investigated with next generation whole genome sequencing for arthropod derived Totiviridae to resolve where the infection came from to Leishmania. Using alignments of all available sequences, a new conserved motif of the RNA-dependent RNA polymerase of dsRNA viruses was discovered. Based on these alignments, a new phylogeny of the totiviruses was reconstructed and generic and whole-family delineations discussed.