Reduced variation in Wolbachia density of larval stages in comparison with adults of Onchocerca volvulus: implications for clinical outcome of infection?

Background Wolbachia are important endosymbionts of filarial parasites. The Wolbachia of Onchocerca volvulus , the filarial pathogen responsible for the human disease onchocerciasis, is implicated in the immunopathology of the disease and may be associated with disease severity dependent on the density of Wolbachia . However, little is known in regards to the density and heterogeneity of Wolbachia in microfilariae, the life stage that is thought to be responsible for the pathology. Results We used a real-time qPCR relative copy number assay to estimate the number of Wolbachia genome(s) per nuclear genome of skin microfilariae (Mf), vector L1 and iL3, and nodulectomy adult male and female O. volvulus worms sampled in Ghana and the Democratic Republic of the Congo. Relatively low median Wolbachia copy numbers and variation was observed in the Mf and vector stages, in contrast to significantly higher median and more variable Wolbachia copy number from the iL3 stage to the adult worm stages. Conclusions This study provides the first insight into variation in Wolbachia density between the major life stages of the parasite. The relatively invariant ratios observed for Mf and vector stages is in strong contrast to the high degree of variability of Wolbachia to nuclear ratios in adults and may indicate that the mutualistic relationship between the nematode and Wolbachia in these earlier stages is regulated differently, and certainly more stringently, than the relationship in adults.