Abstract
Many species of tsetse flies (Diptera: Glossinidae) are infected with a virus that causes salivary gland hypertrophy (SGH), and flies with SGH symptoms have a reduced fecundity and fertility. The prevalence of SGH in wild tsetse populations is usually very low (0.2%–5%), but higher prevalence rates (15.2%) have been observed occasionally. The successful eradication of a Glossina austeni population from Unguja Island (Zanzibar) using an area-wide integrated pest management approach with a sterile insect technique (SIT) component (1994–1997) encouraged several African countries, including Ethiopia, to incorporate the SIT in their national tsetse control programs. A large facility to produce tsetse flies for SIT application in Ethiopia was inaugurated in 2007. To support this project, a Glossina pallidipes colony originating from Ethiopia was successfully established in 1996, but later up to 85% of adult flies displayed symptoms of SGH. As a result, the colony declined and became extinct by 2002. The difficulties experienced with the rearing of G. pallidipes, epitomized by the collapse of the G. pallidipes colony originating from Ethiopia, prompted the urgent need to develop management strategies for the salivary gland hypertrophy virus (SGHV) for this species. As a first step to identify suitable management strategies, the virus isolated from G. pallidipes (GpSGHV) was recently sequenced and research was initiated on virus transmission and pathology. Different approaches to prevent virus replication and its horizontal transmission during blood feeding have been proposed. These include the use of antiviral drugs such as acyclovir and valacyclovir added to the blood for feeding or the use of antibodies against SGHV virion proteins. In addition, preliminary attempts to silence the expression of an essential viral protein using RNA interference will be discussed.
Highlights
Tsetse flies (Glossina spp.) are the only cyclical vectors of two debilitating diseases in Africa, sleeping sickness in humans and the cattle disease nagana (African animal trypanosomosis [AAT] caused by T. b. brucei, Trypanosoma congolense, and Trypanosoma vivax) [1,2]
As a consequence of this success, programs were developed to apply this approach on the African mainland and, in 1996, the government of Ethiopia embarked on such a program with the aim of creating a zone free of Glossina pallidipes in the Southern Rift Valley of Ethiopia [8,9]
Investigations revealed that up to 85% of both male and female flies had salivary gland hypertrophy (SGH), a syndrome first described in wild populations of G. pallidipes [10,11], but later detected in many tsetse species from different African countries [12,13,14,15,16,17,18,19]
Summary
Tsetse flies (Glossina spp.) are the only cyclical vectors of two debilitating diseases in Africa, sleeping sickness in humans (human African trypanosomosis [HAT] caused by Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense) and the cattle disease nagana (African animal trypanosomosis [AAT] caused by T. b. brucei, Trypanosoma congolense, and Trypanosoma vivax) [1,2]. As a consequence of this success, programs were developed to apply this approach on the African mainland and, in 1996, the government of Ethiopia embarked on such a program with the aim of creating a zone free of Glossina pallidipes in the Southern Rift Valley of Ethiopia [8,9]. This project included the establishment of a laboratory colony of the target species at the Insect Pest Control Laboratory (former Entomology Unit) of the Joint FAO/IAEA Programme of Nuclear Techniques in Food and Agriculture, Seibersdorf, Austria. The limitations that hinder the use of this virus as a biological control agent for tsetse control are likewise discussed
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