Wolbachia: endosymbiont of onchocercid nematodes and their vectors

Abstract

Background: Wolbachia is an obligate intracellular maternally transmitted, gram-negative bacterium which forms a spectrum of endosymbiotic relationships from parasitism to obligatory mutualism in a wide range of arthropods and onchocercid nematodes, respectively. In arthropods Wolbachia produces reproductive manipulations such as male killing, feminization, parthenogenesis and cytoplasmic incompatibility for its propagation and provides an additional fitness benefit for the host to protect against pathogens, whilst in onchocercid nematodes, apart from the mutual metabolic dependence, this bacterium is involved in moulting, embryogenesis, growth and survival of the host.

Methods: This review details the molecular data of Wolbachia and its effect on host biology, immunity, ecology and evolution, reproduction, endosymbiont-based treatment and control strategies exploited for filariasis. Relevant peer-reviewed scientic papers available in various authenticated scientific data bases were considered while writing the review.

Conclusions: The information presented provides an overview on Wolbachia biology and its use in the control and/or treatment of vectors, onchocercid nematodes and viral diseases of medical and veterinary importance. This offers the development of new approaches for the control of a variety of vector-borne diseases.

Keywords: Control; Endosymbionts; Onchocercid nematodes; Treatment; Vector; Wolbachia.

Fig. 1

Wolbachia in an embryo of the nematode Dirofilaria immitis (transmission electron microscopy observation). W: Wolbachia bacteria; n: nucleus; scale bar: 0.6 µm (Photograph of Luciano Sacchi and Claudio Bandi, Modified from Bergey's Manual of Systematic Bacteriology, volume 2: The Proteobacteria) [221]

Fig. 2

Role of Wolbachia in onchocecid nematode infections. Wolbachia induced changes in the host immune system such as immunomodulation for the survival of nematodes and various steps in the development of the immunopathology in filarial diseases are summarized

Fig. 3

Exploiting Wolbachia for vector control. Left panel: mosquito population replacement approach, in which Wolbachia-infected female and male mosquitoes are released; through CI, this strategy allows the spread of Wolbachia in the natural population. The presence of Wolbachia provides a fitness advantages (determined by CI) and can reduce the arbovirus transmission. Right panel: mosquito population reduction or suppression strategy. This approach involves the release of Wolbachia-infected males into an area; when these mosquitoes mate with wild Wolbachia-negative females (or female mosquitoes harbouring an incompatible strain of Wolbachia), a strong reduction in the rate of egg hatching is observed (CI incompatible matings). Thus, repeated releases of Wolbachia-infected males result in reduction or suppression of mosquito populations. CI cytoplasmic incompatibility, WT wild-type mosquitoes, Wolb + Wolbachia-infected mosquitoes