Genetic Variation among Isolates of Sarcocystis neurona , the Agent of Protozoal Myeloencephalitis, as Revealed by Amplified Fragment Length Polymorphism Markers

Abstract

Sarcocystis neurona causes serious neurological disease in horses and other vertebrates in the Americas. Based on epidemiological data, this parasite has recently emerged. Here, the genetic diversity of Sarcocystis neurona was evaluated using the amplified fragment length polymorphism (AFLP) method. Fifteen S. neurona taxa from different regions collected over the last 10 years were used; six isolates were from clinically diseased horses, eight isolates were from wild-caught opossums (Didelphis virginiana), and one isolate was from a cowbird (Molothrus ater). Additionally, four outgroup taxa were also fingerprinted. Nine primer pairs were used to generate AFLP patterns, with a total number of amplified fragments ranging from 30 to 60, depending on the isolate and primers tested. Based on the presence/absence of amplified AFLP fragments and pairwise similarity values, all the S. neurona isolates tested were clustered in one monophyletic group. No significant correlation could be found between genomic similarity and host origin of the S. neurona isolates. AFLP revealed significant intraspecific genetic variations, and S. neurona appeared as a highly variable species. Furthermore, linkage disequilibrium analysis suggested that S. neurona populations within Michigan have an intermediate type of population structure that includes characteristics of both clonal and panamictic population structures. AFLP is a reliable molecular technique that has provided one of the most informative approaches to ascertain phylogenetic relationships in S. neurona and its closest relatives, allowing them to be clustered by relative similarity using band matching and unweighted pair group method with arithmetic mean analysis, which may be applicable to other related protozoal species.

Limited genetic diversity among Sarcocystis neurona strains infecting southern sea otters precludes distinction between marine and terrestrial isolates

“…Previous studies have concluded that S. neurona possesses an intermediate population structure that exhibits both clonal propagation and recombination (Asmundsson et al, 2006; Elsheikha et al, 2006; Sundar et al, 2008). Analysis of markers in the current study supports these conclusions.…”

An update on Sarcocystis neurona infections in animals and equine protozoal myeloencephalitis (EPM)

“…The initial efforts to generate nucleic acid sequence data for S. neurona were conducted in the context of phylogenetic analyses, development of diagnostic probes, and included the use of RAPD assays and sequence analysis of the 18S rRNA locus (Fenger et al, 1994; Granstrom et al, 1994; Dame et al, 1995; Marsh et al, 1999; Tanhauser et al, 1999a, b; Elsheikha et al, 2005a; Elsheikha et al, 2005b; Elsheikha et al, 2006a; Elsheikha et al, 2006b; Elsheikha and Mansfield, 2007; Elsheikha, 2009) to identify species-specific genetic markers. Some of these investigations led to PCR-based tests that detect S. neurona and/or distinguish it from other closely-related species (Fenger et al, 1995; Tanhauser et al, 1999a, b).…”

Equine Protozoal Myeloencephalitis

“…[45][46][47] However, efforts to increase stress by use of a second transport and treatment with immunosuppressive steroids did not exacerbate disease, 48,49 so it is apparent that the interplay between immune suppression and infection is more complex than currently understood. Modest genetic and antigenic diversity exist among strains of S neurona that have been isolated, [50][51][52] and there is some suggestion that particular parasite genotypes may be more virulent than others. 53 This finding was Equine Protozoal Myeloencephalitis based on a large collection of S neurona isolates from marine mammals, however, and the association between parasite genotype and disease was not apparent in the more limited sample set of isolates from horses suffering from EPM.…”