Absence of Wolbachia endobacteria in Sri Lankan isolates of the nematode parasite of animals Setaria digitata

Reduction of Wolbachia in Diaphorina citri (Hemiptera: Liviidae) increases phytopathogen acquisition and decreases fitness

Wolbachia pipientis is a maternally inherited intracellular bacterium that infects a wide range of arthropods. Wolbachia can have a significant impact on host biology and development, often due to its effects on reproduction. We investigated Wolbachia-mediated effects in the Asian citrus psyllid, Diaphorina citri Kuwayama, which transmits Candidatus Liberibacter asiaticus (CLas), the causal agent of citrus greening disease. Diaphorina citri are naturally infected with Wolbachia; therefore, investigating Wolbachia-mediated effects on D. citri fitness and CLas transmission required artificial reduction of this endosymbiont with the application of doxycycline. Doxycycline treatment of psyllids reduced Wolbachia infection by approximately 60% in both male and female D. citri. Psyllids treated with doxycycline exhibited higher CLas acquisition in both adults and nymphs as compared with negative controls. In addition, doxycycline-treated psyllids exhibited decreased fitness as measured by reduced egg and nymph production as well as adult emergence as compared with control lines without the doxycycline treatment. Our results indicate that Wolbachia benefits D. citri by improving fitness and potentially competes with CLas by interfering with phytopathogen acquisition. Targeted manipulation of endosymbionts in this phytopathogen vector may yield disease management tools.

Molecular identification and genetic diversity of equine ocular setariasis in Thailand based on the COI, 12S rDNA, and ITS1 regions

Equine ocular setariasis is mainly caused by Setaria digitata, and the identification of this filarial nematode is based on morphology. However, morphological characterization alone is insufficient for the detection and differentiation of S. digitata from its congeners. In Thailand, the molecular detection of S. digitata is lacking and its genetic diversity is still unknown. This study aimed to phylogenetically characterize equine S. digitata from Thailand based on sequences derived from the mitochondrial cytochrome c oxidase subunit 1 (COI), the mitochondrial small subunit ribosomal DNA (12S rDNA), the nuclear internal transcribed spacer 1 (ITS1) and Wolbachia surface protein (wsp). Five samples of S. digitata were characterized, submitted to the NCBI database, and used for phylogenetic analysis as well as the assessment of similarity, entropy, and haplotype diversity. Phylogenetic analyses revealed that the S. digitata Thai strain was similar to S. digitata from China and Sri Lanka, with 99 to 100% similarity. The entropy and haplotype diversity indicated that the S. digitata Thai isolate was conserved and closely related to S. digitata worldwide. This is the first report on the molecular detection of equine ocular setariasis caused by S. digitata in Thailand.

First Molecular Confirmation of Equine Ocular Setaria digitata in China

A 5-year-old Mongolian mare (Equus caballus Linnaeus, 1758) was observed to have corneal opacity and excessive ocular discharge. An ophthalmic examination revealed a moving thread-like cylindrical worm in the anterior chamber of the right eye. The parasite was successfully removed surgically. The worm was observed under light microscopy and confirmed as Setaria digitata by 12S rRNA gene amplification and sequencing. Phylogenetic analysis demonstrated similarity with Setaria digitata in the National Center for Biotechnology Information (NCBI) GenBank database isolated from other Asian countries. This report is the first confirmed case of equine ocular setariasis by molecular diagnosis in China, which may indicate its presence in livestock and promote research on its epidemiology.

The Genome of Setaria digitata: A Cattle Nematode Closely Related to Human Filarial Parasites

Here we present the draft genome sequence of Setaria digitata, a parasitic nematode affecting cattle. Due to its similarity to Wuchereria bancrofti, the parasitic nematode that causes lymphatic filariasis in humans, S. digitata has been used as a model organism at the genomic level to find drug targets which can be used for the development of novel drugs and/or vaccines for human filariasis. Setaria digitata causes cerebrospinal nematodiasis in goats, sheep, and horses posing a serious threat to livestock in developing countries. The genome sequence of S. digitata will assist in finding candidate genes to use as drug targets in both S. digitata and W. bancrofti. The assembled draft genome is ∼90 Mb long and contains 8,974 genomic scaffolds with a G+C content of 31.73%.

Characterization of the complete mitochondrial genome of Setaria digitata (Nematoda: Setariidae) from China

Setaria digitata is a filarial parasite that causes fatal cerebrospinal nematodiasis in goats, horses and sheep, resulting in substantial economic losses to livestock farmers. In the present study, the complete mitochondrial (mt) genome of S. digitata from China was determined, characterized and compared with that of S. digitata from Sri Lanka. The identity of the mt genomes was 98.3% between S. digitata from China and Sri Lanka, and the complete mt genome sequence of S. digitata from China was slightly shorter (25 bp) than that from Sri Lanka. For the 12 protein genes, this comparison revealed sequence differences at both the nucleotide (1.4%) and amino acid (2.2%) levels. The present study determined the complete mt genome sequence of S. digitata from China, providing novel genetic markers for the study of the population genetics and molecular epidemiology of S. digitata in animals.

Draft genome of neurotropic nematode parasite Angiostrongylus cantonensis, causative agent of human eosinophilic meningitis

Angiostrongylus cantonensis is a bursate nematode parasite that causes eosinophilic meningitis (or meningoencephalitis) in humans in many parts of the world. The genomic data from A. cantonensis will form a useful resource for comparative genomic and chemogenomic studies to aid the development of diagnostics and therapeutics. We have sequenced, assembled and annotated the genome of A. cantonensis. The genome size is estimated to be ∼260 Mb, with 17,280 genomic scaffolds, 91X coverage, 81.45% for complete and 93.95% for partial score based on CEGMA analysis of genome completeness. The number of predicted genes of ≥300 bp was 17,482. A total of 7737 predicted protein-coding genes of ≥50 amino acids were identified in the assembled genome. Among the proteins of known function, kinases are the most abundant followed by transferases. The draft genome contains 34 excretory-secretory proteins (ES), a minimum of 44 Nematode Astacin (NAS) metalloproteases, 12 Homeobox (HOX) genes, and 30 neurotransmitters. The assembled genome size (260 Mb) is larger than those of Pristionchus pacificus, Caenorhabditis elegans, Necator americanus, Caenorhabditis briggsae, Trichinella spiralis, Brugia malayi and Loa loa, but smaller than Haemonchus contortus and Ascaris suum. The repeat content (25%) is similar to H. contortus. The GC content (41.17%) is lower compared to P. pacificus (42.7%) and H. contortus (43.1%) but higher compared to C. briggsae (37.69%), A. suum (37.9%) and N. americanus (40.2%) while the scaffold N50 is 42,191. This draft genome will facilitate the understanding of many unresolved issues on the parasite and the disorder it causes.

Setaria digitata in advancing our knowledge of human lymphatic filariasis

Setaria digitata is a filarial parasite that causes fatal cerebrospinal nematodiasis in goats, sheep and horses, resulting in substantial economic losses in animal husbandry in the tropics. Due to its close resemblance to Wuchereria bancrofti, this nematode is also frequently used as a model organism to study human lymphatic filariasis. This review highlights numerous insights into the morphological, histological, biochemical, immunological and genetic aspects of S. digitata that have broadened our understanding towards the control and eradication of filarial diseases.