Novel ribonucleic acid species in Eimeria nieschulzi are associated with RNA-dependent RNA polymerase activity

Transcriptome mining of RNA viruses (family Totiviridae ) in Eimeria necatrix and Eimeria stiedai

Coccidian protozoa from the genus Eimeria are widespread parasites of vertebrates, causing serious disease (coccidiosis) and economic loss most notably in poultry. Several species of Eimeria are themselves infected with small RNA viruses assigned to the family Totiviridae . In this study, the sequences of two such viruses were newly determined, one of which represents the first complete protein-coding sequence of a virus from E. necatrix , an important pathogen of chickens, and the other of which is from E. stiedai , an important pathogen of rabbits. Sequence features of the newly identified viruses, compared with those of ones reported previously, provide several insights. Phylogenetic analyses suggest that these eimerian viruses constitute a well-demarcated clade, probably deserving of recognition as a distinct genus.

Eimeria necatrix virus: intracellular localisation of viral particles and proteins

The presence of the Eimeria necatrix virus was investigated in the following life cycle stages: sporocysts, sporozoites, merozoites, and macrogametes. Electron microscopy revealed virus-like particles (VLPs) in sporozoites, which were purified from sporozoite extracts and used to raise polyclonal antibodies. Viral proteins were identified as RNA polymerase (95 kDa) and the major capsid protein (80 kDa). Polyclonal antibody was used to detect the intracellular localisation of VLPs and proteins. Immunoelectron microscopy and immunohistochemistry identified a viral protein of 95 kDa in all the E. necatrix stages studied, whereas the 80 kDa protein was found only in sporocysts and sporozoites. In addition, no VLPs were found in sporocysts. These results indicate that the synthesis of viral capsid proteins takes place during the early events of sporulation, and is then packaged into novel viruses during the late events. No VLPs were seen and no capsid proteins were found in the merozoites and macrogametes, whereas the 95 kDa RNA polymerase was present in both these stages. In addition, no VLPs or proteins were detected in chicken tissues.

High-temperature inducible cell-free transcription and replication of double-stranded RNAs within the parasitic protozoan Cryptosporidium parvum

Sporozoites of the protozoan parasite, Cryptosporidium parvum, were found to contain free, full-size plus strands transcribed from two extrachromosomal, cytoplasmic, virus-like double-stranded RNAs (dsRNAs). Cell-free transcription and replication of both dsRNAs were observed in crude sporozoite lysates. RNA polymerase activity was found to be dependent upon addition of Mg2+ or Mn2+, as well as the four ribonucleoside triphosphates, and was insensitive to inhibitors of cellular DNA-dependent RNA polymerase. Semiconservative transcription of the dsRNAs (plus strand synthesis) was observed at a wide range of temperatures, with an optimum of 50 degrees C. In contrast, replication (minus strand synthesis) was detected only at 50 and 60 degrees C.

Virus-like particles in Eimeria nieschulzi are associated with multiple RNA segments

RNA preparations from sporulated oocysts of Eimeria nieschulzi were found to contain 2 double-stranded RNA segments of 5.0 kb and 5.7 kb that were not present in other species of Eimeria. Treatment of crude lysates with RNase A revealed that in addition to these two segments, 3 other segments of 0.57 kb, 0.72 kb and 11.5 kb were protected from digestion, suggesting that they were enclosed within particles. Virus-like particles with a diameter of approximately 39 nm were purified by caesium chloride buoyant density centrifugation. Four of the five RNA segments copurified with these particles. In keeping with the nomenclature generally adopted for protozoan viruses, we have named this new isolate ENV 1. The largest RNA segment does not cosediment with ENV 1 particles and may be derived from another RNA-protein complex that is unstable under the conditions used. The particle size and genome structure of ENV 1 both differ from that of the Eimeria stiedae virus (ESV), which is the only other virus to have been isolated from Eimeria to date. Short cDNA clones derived from ENV 1 show significant homology to a region of the Leishmania virus (LRV 1) genome that encodes an RNA-dependent RNA polymerase. The polymerase sequences from ENV 1 and LRV 1 are more closely related to each other than to any other protein sequences in the GenEMBL Database. This raises intriguing questions about the origins of the two viruses, since Eimeria and Leishmania normally infect different hosts and also show different cell tropisms within these hosts.