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

Setaria digitata is an animal filarial parasite with natural hosts of cattle and buffaloes that causes mild disease conditions. Infection of non-permissive hosts such as goats, sheep and horses, by this nematode can cause cerebrospinal nematodiasis that leads to lumbar paralysis and the eventual death of the animals and inflicts considerable economic losses on livestock farmers. Wolbachia are obligate mutualistic endosymbionts for some filarial nematodes and are currently being targeted for the control of diseases caused by these parasites. However, little is known about the occurrence of this endosymbiont in the Setariidae family. In this work, worms collected from infected cattle in Sri Lanka were morphologically identified as S. digitata and tested for the presence of Wolbachia by PCR screening using the WSP- and Wolbachia-specific 16S rRNA and multilocus sequence typing primers that were designed to amplify the gatB, coxA, hcpA, ftsZ and fbpA sequences of Wolbachia. The presence of endobacteria in S. digitata was also examined by whole-mount immunofluorescence staining of the parasites and transmission electron microscopic studies. These analyses did not produce evidence of presence of Wolbachia or any other endosymbiotic bacteria in S. digitata, whereas such evidence was found in Brugia malayi, which was used as a positive control in this study.