Glossina Hytrosavirus Control Strategies in Tsetse fly Factories: Application of Infectomics in Virus Management

Abstract

African trypanosomosis is a fatal zoonotic disease transmitted by tsetse flies (Diptera; Glossinidae); blood-sucking insects found only in sub-Saharan Africa. Two forms of trypanosomoses occur: the animal African trypanosomosis (AAT; nagana), and the human African trypanosomosis (HAT; sleeping sickness). Since there are no effective vaccines against trypanosomosis, tsetse fly eradication is the most effective disease control method. Tsetse flies can be effectively eradicated by the sterile insect technique (SIT), which is applied in an area-wide integrated pest management approach. SIT is an environmentally benign method with a long and solid record of accomplishments. SIT requires large-scale production of sexually sterilized male flies (by exposure to a precise and specific dose of ionizing radiation, usually from a 60(0 or 137(e source), which are sequentially released into a target wild insect population to out-compete wild type males in inseminating wild virgin females. Once inseminated by sterile males, the virgin females do not produce viable progeny flies. Importantly, these females do not typically re-mate. Ultimately, the target wild insect population can decrease to extinction. However, tsetse SIT programs are faced with a unique problem: laboratory colonies of many tsetse species are infected by the Glossina pallidipes salivary gland hypertrophy virus (GpSGHV; family Hytrosaviridae). GpSGHV-infected flies have male aspermia or oligospermia, underdeveloped female ovarioles, sterility, salivary gland hypertrophy syndrome (SGH), distorted sex ratios, and reduced insemination rates. Without proper management, symptomatic GpSGHV infections (characterized by SGH symptoms) can cause collapse of Glossina colonies. To ensure colony productivity and survival, GpSGHV management strategies are required. This will ensure a sustained supply of sterile males for SIT programs. The aim of this PhD research was to investigate the functional and structural genomics and proteomics (infectomics) of GpSGHV as a prerequisite to development of rationally designed viral control strategies. A series of experiments were designed to: (i) investigate epidemiology and diversity of GpSGHV; (ii) identify GpSGHV proteome and how viral and host proteins contribute to the pathobiology of the virus; and (iii) investigate the interplay between GpSGHV, the microbiome and the host, and how these interactions influence the outcomes of viral infections. By relating GpSGHV and host infectomics data, cost-effective viral management strategies were developed. This resulted in significant reduction of GpSGHV loads and elimination of SGH from laboratory colonies of G. pallidipes.