Prevalence of Spiroplasma and interaction with wild Glossina tachinoides microbiota.

Tsetse flies (Diptera: Glossinidae) are vectors of the tropical neglected diseases sleeping sickness in humans and nagana in animals. The elimination of these diseases is linked to control of the vector. The sterile insect technique (SIT) is an environment-friendly method that has been shown to be effective when applied in an area-wide integrated pest management approach. However, as irradiated males conserve their vectorial competence, there is the potential risk of trypanosome transmission with their release in the field. Analyzing the interaction between the tsetse fly and its microbiota, and between different microbiota and the trypanosome, might provide important information to enhance the fly's resistance to trypanosome infection. This study on the prevalence of Spiroplasma in wild populations of seven tsetse species from East, West, Central and Southern Africa showed that Spiroplasma is present only in Glossina fuscipes fuscipes and Glossina tachinoides. In G. tachinoides, a significant deviation from independence in co-infection with Spiroplasma and Trypanosoma spp. was observed. Moreover, Spiroplasma infections seem to significantly reduce the density of the trypanosomes, suggesting that Spiroplasma might enhance tsetse fly's refractoriness to the trypanosome infections. This finding might be useful to reduce risks associated with the release of sterile males during SIT implementation in trypanosome endemic areas.

Title: Prévalence de Spiroplasma et interaction avec le microbiote des Glossina tachinoides sauvages. Abstract: Les mouches tsé-tsé (Diptera : Glossinidae) sont les vecteurs de maladies tropicales négligées, la maladie du sommeil chez l'homme et la nagana chez les animaux. L'élimination de ces maladies est liée à la lutte contre le vecteur. La technique de l'insecte stérile (TIS) est une méthode respectueuse de l'environnement qui s'est révélée efficace lorsqu'elle est appliquée dans le cadre d'une approche de lutte antiparasitaire intégrée à l'échelle d'une zone. Cependant, comme les mâles irradiés conservent leur compétence vectorielle, il existe un risque potentiel de transmission des trypanosomes lors de la libération des mâles sur le terrain. L'analyse de l'interaction entre la mouche tsé-tsé et son microbiote, et entre différents microbiotes et le trypanosome, pourrait fournir des informations importantes pour améliorer la résistance de la mouche à l'infection trypanosomienne. Cette étude sur la prévalence de Spiroplasma dans les populations sauvages de sept espèces de glossines d'Afrique de l'Est, de l'Ouest, centrale et australe a montré que Spiroplasma est présent uniquement chez Glossina fuscipes fuscipes et Glossina tachinoides. Chez G. tachinoides, un écart significatif par rapport à l'indépendance dans la co-infection par Spiroplasma et Trypanosoma spp. a été observé. De plus, les infections à Spiroplasma semblent réduire considérablement la densité des trypanosomes, ce qui suggère que Spiroplasma pourrait renforcer le caractère réfractaire de la mouche tsé-tsé aux infections trypanosomiennes. Cette découverte pourrait être utile pour réduire le risque associé à la libération de mâles stériles lors de la mise en œuvre de la TIS dans les zones d'endémie trypanosomienne.

Hytrosaviruses: current status and perspective.

Salivary gland hytrosaviruses (SGHVs) are entomopathogenic dsDNA, enveloped viruses that replicate in the salivary glands (SGs) of the adult dipterans, Glossina spp (GpSGHV) and Musca domestica (MdSGHV). Although belonging to the same virus family (Hytrosaviridae), SGHVs have distinct morphologies and pathobiologies. Two GpSGHV strains potentially account for the differential pathologies in lab-bred tsetse. New data suggest incorporation of host-derived cellular proteins and lipids into mature SGHVs. In addition to within the SGs, MdSGHV undergoes limited replication in the corpora allata, potentially disrupting hormone biosynthesis, and GpSGHV replicates in the milk glands providing a transmission conduit to progeny tsetse. Whereas MdSGHV is a potential biocontrol agent, the vertically transmitted GpSGHV is unsuitable for tsetse vector control but does jeopardize tsetse mass rearing.

Antiviral drug valacyclovir treatment combined with a clean feeding system enhances the suppression of salivary gland hypertrophy in laboratory colonies of Glossina pallidipes.

BACKGROUND: Hytrosaviridae cause salivary gland hypertrophy (SGH) syndrome in some infected tsetse flies (Diptera: Glossinidae). Infected male and female G. pallidipes with SGH have a reduced fecundity and fertility. Due to the deleterious impact of the virus on G. pallidipes colonies, adding the antiviral drug valacyclovir to the blood diet and changing the feeding regime to a clean feeding system (each fly receives for each feeding a fresh clean blood meal) have been investigated to develop virus management strategies. Although both approaches used alone successfully reduced the virus load and the SGH prevalence in small experimental groups, considerable time was needed to obtain the desired SGH reduction and both systems were only demonstrated with colonies that had a low initial virus prevalence (SGH ≤ 10%). As problems with SGH are often only recognized once the incidence is already high, it was necessary to demonstrate that this combination would also work for high prevalence colonies. FINDINGS: Combining both methods at colony level successfully suppressed the SGH in G. pallidipes colonies that had a high initial virus prevalence (average SGH of 24%). Six months after starting the combined treatment SGH symptoms were eliminated from the treated colony, in contrast to 28 months required to obtain the same results using clean feeding alone and 21 months using antiviral drug alone. CONCLUSIONS: Combining valacyclovir treatment with the clean feeding system provides faster control of SGH in tsetse than either method alone and is effective even when the initial SGH prevalence is high.