Comparative mitogenomics of Spirocerca lupi from South Africa and China: Variation and possible heteroplasmy.

The complete mitochondrial genome of Spirocerca lupi isolated from a dog in South Africa was sequenced using next generation sequencing (NGS) technology and the 12 protein coding genes along with the two rRNA genes were compared to 18 other nematode species as well as S. lupi from China. The mitochondrial genome of S. lupi South Africa had a mean genetic diversity of 6.1 % compared to S. lupi China with some variation in nucleotide composition, gene positioning and size. Pairwise distance results indicated slightly higher variation when compared to the pairwise distances of other closely related species, however, this variation was not high enough for it to be considered a cryptic species. Phylogenetic analysis indicated that S. lupi from the two continents are very similar. In addition, single nucleotide polymorphisms were detected in the nad2 gene with ten sequence variants identified from 10 clones from a single nematode, suggesting possible heteroplasmy. The origin of the heteroplasmy is currently unknown but it is speculated to have arisen from accumulated mutations in the mitochondria during somatic replication.

Population genetic structure of the parasitic nematode Spirocerca lupi in South Africa.

Spirocerca lupi is a parasitic nematode of canids and occurs in most tropical and subtropical regions around the world. While its life cycle is well known, insight is lacking about its mating structure within-hosts, genetic variability and long-distance dispersal ability. These characteristics contribute significantly to the dynamics and spread of potential resistance genes, which impacts on the control of S. lupi. To evaluate the population structure and infer potential mating behaviour of S. lupi, we genotyped 130 samples at nine microsatellite loci from three geographical locations in South Africa, between 600 and 1000 km apart. These loci identified unique individuals with high levels of polymorphism suggesting that these are not newly established S. lupi populations in South Africa and that effective population sizes must be large. Population genetic analyses showed that populations are not very distinct, that worms within dogs are more similar to each other than random worms from each population, and that mating is at random within dogs. We can thus infer that the parasite is frequently transported over great distances. Even so, two genetically distinct populations could be identified. Relatedness of worms within dogs were significantly higher than between dogs and together with F-statistics suggests some non-random transmission of parasites between hosts. While mating is random within a host, parasites from a host are more likely to be related and hence an increase in homozygosity is seen. The implications of this genetic structure on parasite control are considered.

Diversity of Spirocerca lupi in domestic dogs and black-backed jackals (Canis mesomelas) from South Africa.

Spirocerca lupi is a parasitic nematode that causes spirocercosis predominantly in domestic dogs. Spirocerca lupi nematode samples were collected from four regions around South Africa and analyzed to compare the genetic diversity among the regions. A total of 56 S. lupi nematodes were obtained by necropsy from domestic dogs and wild black-backed jackals (Canis mesomelas). Sixteen different haplotypes of cox1 were identified some of which are shared between regions as well as with black-backed jackal. The genetic similarity between S. lupi in domestic dogs and black-backed jackals indicates transmission between these canid species and may have potential conservation implications.

Molecular genomics resource for the parasitic nematode Spirocerca lupi: Identification of 149 microsatellite loci using FIASCO and next generation sequencing.

Understanding genetic diversity and movement patterns in parasitic organisms is paramount to establish control and management strategies. In this study we developed a microsatellite resource as well as a diagnostic multiplex for the cosmopolitan parasitic nematode Spirocerca lupi, known to cause spirocercosis in canids. A combination of microsatellite enrichment and 454 sequencing was used to identify 149 unique microsatellite loci in S. lupi. Twenty loci were characterized further in two sampling sites in South Africa, with 10 loci identified as polymorphic (allele ranges from 4 to 17). These loci were designed into a single diagnostic multiplex suitable for species identification and population genetics studies. The markers were also successful in cross-species amplification in Cylicospirura felineus, Philonema oncorhynchi and Gongylonema pulchrum. Our resource provides a large set of candidate loci for a number of nematode studies as well as loci suitable for diversity and population genetics studies of S. lupi within the South African context as well as globally.

High within-host genetic variation of the nematode Spirocerca lupi in a high-density urban dog population.

The nematode worm Spirocerca lupi has a cosmopolitan distribution and can cause the death of its final canid host, typically dogs. While its life cycle, which involves a coprophagous beetle intermediate host, a number of non-obligatory vertebrate paratenic hosts and a canid final host, is well understood, surprisingly little is known about its transmission dynamics and population genetic structure. Here we sequenced cox1 to quantify genetic variation and the factors that limit gene flow in a 300 km(2) area in South Africa. Three quarters of the genetic variation, was explained by differences between worms from the same host, whereas a quarter of the variation was explained by differences between worms from different hosts. With the help of a newly derived model we conclude that while the offspring from different infrapopulations mixes fairly frequently in new hosts, the level of admixture is not enough to homogenize the parasite populations among dogs. Small infrapopulation sizes along with clumped transmission may also result in members of infrapopulations being closely related.