Vectorial competence of Glossina brevipalpis in the transmission of Trypanosoma congolense in the Matutuíne District, Maputo Province, Mozambique

Abstract

African Animal Trypanosomoses (AAT) are a group of parasitic diseases that are considered a major constraint to animal health and production in Africa, where they are associated with vast economic losses. AAT is caused by protozoa parasites of the genus Trypanosoma. In Mozambique, T. congolense is the predominant trypanosome species in regions affected by AAT. The epidemiology of AAT is largely determined by the distribution and vectorial competence of its cyclic vector, the tsetse fly. In southern Mozambique, there is a high prevalence of AAT in the Matutíne District, where the tsetse fly species Glossina brevipalpis is abundant. Based on existing studies, there is currently a lack of clarity on the vectorial competence of Glossina brevipalpis in the transmission of T. congolense. Therefore, this study aimed to assess the competence of G. brevipalpis as a vector of T. congolense using wild flies captured in Matutuíne District, Mozambique. In an initial experiment, 234 G. brevipalpis flies were captured in the Maputo National Park, and their survival under experimental conditions was evaluated. These flies were transferred to entomological cages, fed every 48 hours on one bovine and kept in a room for 30 days at the Tintigala Research Station, where temperature and relative humidity (Rh) were regularly monitored. The vectorial competence and possible mechanical transmission of T. congolense to susceptible cattle were then evaluated. For this experiment, 915 G. brevipalpis flies (41 females and 874 males) were fed six times in two cattle that had previously been infected with T. congolense (isolated from Matutuíne - TCM2018), followed by two meals in a clean animal to mechanically remove the remnant trypanosomes from previous blood meals. Lastly, they were fed for 30 days on four cattle that were susceptible to infection. These five susceptible animals were monitored for the development of parasitaemia for 60 days based on body temperature, PCV, buffy coat and PCR. In the meantime, flies were dissected weekly to observe the development of trypanosomes in the midgut and proboscis. Regarding the evaluation of mechanical transmission by G. brevipalpis, 97 teneral flies from a colony were fed once on two infected cattle (three days after emergence) and once on a susceptible bovine (48 hours after the first meal). Under experimental conditions, a survival rate of 77% was recorded within a period of 30 days among captured G. brevipalpis flies. Weekly dissection of flies that fed on infected animals revealed that 89% were positive for T. congolense, based on microscopy and 100% based on PCR (midgut and proboscis). The four susceptible cattle tested positive for T. congolense infection. However, no trypanosome infection was observed in the cattle used for cleaning the proboscis and evaluation of mechanical transmission. The current results indicate that G. brevipalpis is a competent vector for the transmission of T. congolense. Additionally, these results demonstrate the inability of G. brevipalpis to mechanically transmit T. congolense after 48 hours of an infected blood meal.