Abstract
Neospora caninum is an apicomplexan parasite responsible for neosporosis, a disease causing hind limb paralysis in dogs and abortion in cattle, resulting in substantial economic losses to beef and dairy industries. Marked differences in pathogenicity exist between N. caninum strains suggesting that intrinsic genetic differences exist between them. These differences likely exist in genes expressed during the tachyzoite lifecycle stage which is responsible for the pathogenesis of neosporosis. An improved understanding of these genetic differences is essential to understanding N. caninum virulence, though such knowledge is scarce. Using a variant detection workflow we compared the tachyzoite transcriptomes of two N. caninum strains with different virulence properties: NC-Liverpool (virulent) and NC-Nowra (avirulent). This workflow identified 3130 SNPs and 6123 indels between the strains, and nine markers capturing 30 variants were Sanger sequenced for both strains. Sequencing of these loci was extended to an additional eight strains and subsequent phylogenetic analysis supported a genetic population structure comprised of two major clades with no geographical segregation. Sequence polymorphisms within coding regions of tachyzoite-associated genes were concentrated on chromosomes XI and XII, with 19 distinct tachyzoite-associated SNP hotspot regions identified within coding regions of the N. caninum nuclear genome. The variants were predominantly located in loci associated with protein binding, protein–protein interactions, transcription, and translation. Furthermore, 468 nonsynonymous SNPs identified within protein-coding genes were associated with protein kinase activity, protein binding, protein phosphorylation, and proteolysis. This work may implicate these processes and the specific proteins involved as novel effectors of N. caninum tachyzoite virulence.
Highlights
Neospora caninum is a cyst forming coccidian of the phylum Apicomplexa first described as the cause of a potentially fatal neurological disease of dogs (Dubey et al 1988a)
These differences likely exist in genes expressed during the tachyzoite lifecycle stage which is responsible for the pathogenesis of neosporosis
Sequence polymorphisms within coding regions of tachyzoiteassociated genes were concentrated on chromosomes XI and XII, with 19 distinct tachyzoite-associated SNP hotspot regions identified within coding regions of the N. caninum nuclear genome
Summary
Neospora caninum is a cyst forming coccidian of the phylum Apicomplexa first described as the cause of a potentially fatal neurological disease of dogs (Dubey et al 1988a). Its economic importance is primarily due to its role as the etiological agent of bovine neosporosis, a reproductive disease characterized by abortion and stillbirths in cows that is recognized as the leading global cause of bovine reproductive failure (Dubey and Lindsay 1996; Dubey 1999; Reichel and Ellis 2002; Dubey and Dubey 2003; Dubey et al 2006; Reichel et al 2007). The combined annual losses due to N. caninum for the Australian and New Zealand dairy and beef industries are estimated to be greater than AU $110 million annually (Miller et al 2002; Reichel and Ellis 2002).
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