Species of tsetse flies in and around QENP
Glossina fuscipes, G. pallidipes and G. brevipalpis are sub-species of tsetse flies previously reported to exist in Uganda (4, 8) (15, 16). The current study showed the presence of only two species of tsetse flies, G. fuscipes and G. pallidipes, in rangelands within and around QENP ecosystem and surroundings. Similar results have been reported in Uganda by Albert (4) and Waiswa et al. (17) in the Lake Victoria basin and eastern Uganda, respectively. Glossina pallidipes was the most predominantly caught species in communities around Queen Elizabeth national park, south western Uganda. The results are different from those of previous studies in Uganda (4, 17) and Ngonyoka et al (18) in Tanzania that all showed G. fuscipes as the dominant species.
Glossina pallidipes was predominantly found in the thickets and shrubs vegetation. The current study area was generally a savannah land dominated with invasive species of thickets and shrubs. Species, for example, Acacia spp, Eurphobia sp and Lantana camara among others, with small trees less than 3 metres above the ground, were the dominant species. This probably explains the presence of high numbers of G. pallidipes in the study area as such land cover provides unique ecological conditions ideal for survival and infestation of G. pallidipes (3, 4, 16, 19). The thickets and shrubs had the highest number of tsetse fly catches. The results agree with literature which suggests that G. pallidipes inhabits woodland savannas and thickets (16, 20, 21). Tsetse flies are very sensitive to changes in the environment and the ecology of an area. Factors such as temperature, humidity and vegetation cover are important in provision of shade and maintenance of suitable micro-climate and a habitat for hosts of tsetse flies (4, 19, 20, 22).
The sex ratio of caught tsetse flies indicated that higher numbers of females were recorded during the study. Similar results have been reported elsewhere (1, 4, 19). The high number of females present in the study area could result in future high population density of tsetse flies and ultimately infection rate (1). The high proportion of females in the current study can probably be attributed to the fact that females live longer than males (mean female fly life span is 8 weeks, but only 4 weeks for the males).
There was an existence of more biting flies each trap than tsetse flies. This is in agreement with previous literature which suggest that parts of south west and mid central Uganda have lower populations of tsetse flies than other biting flies (4). Presence of biting flies could pose a threat to livestock production since biting flies such as Stomoxys and Tabanids among others have been associated with mechanical transmission of some livestock diseases such as AAT (23, 24). Severe biting by these flies may be a nuisance to animals resulting in physical discomfort, wounds, reduced weight and milk production in livestock (23-25).
Different types of traps have been designed to catch different species of tsetse flies and these traps have been reported to have varying effectiveness in trapping different tsetse fly species (26-28). In this study, two different traps (Biconical and F3) were used in the capture of tsetse flies within and around QENP and their efficiency was determined. Generally, Biconical traps (BT) were more effective in trapping tsetse flies in the study area than F3 traps regardless of the tsetse fly species. Higher number of tsetse flies captured by biconical traps in this study could probably be explained by nearly twice the numbers of biconical traps deployed as compared to the F3 traps. Overall, 5003 tsetse flies were captured in the study with the calculated FTD of 20.6 which is comparable to that reported by Apaatah (1) and Salekwa et al. (21). However, it is higher than that previously reported by Albert (4).
Prevalence of Trypanosoma spp. in goats and cattle
The prevalence of Trypanosoma spp. in both cattle (37%) and goats (38.9%) for samples collected in 2015 based on PCR was higher than that reported by other studies in the same animal species in Uganda, Nigeria and Zambia (2, 5, 13, 14, 23). In addition, the overall prevalence of Trypanosoma spp. among cattle (38%) samples collected in 2017, based on PCR results was higher than what has been reported in previous studies in the country. For instance, the prevalence was 7.6% in Kasese, Rakai and Jinja districts of Uganda (14), 2.4% in Mbarara district, western Uganda (5) and 15.3% in Tororo district, eastern Uganda (11).This prevalence is also higher than in studies carried out in other tsetse fly endemic countries in Africa (1, 2, 25, 29, 30). However, some studies have reported almost similar prevalence of Trypanosoma spp. in cattle. For example, reports in Zambia and Ivory Coast showed prevalence of 33.5% and 22.31% in cattle in Zambia (2) and Ivory Coast (30) respectively. The higher prevalence of Trypanosoma spp. in this study could probably be explained by the close proximity of the study sites to the QENP savannah grasslands that hosts various wildlife species that are possible reservoirs of Trypanosoma spp. Wildlife has previously been reported to be important reservoir and maintenance hosts of Trypanosoma spp. (5, 8, 31). In addition, the difference in prevalence observed in Uganda could be due to variations in different geo-ecological zones and time of year for sampling (5, 14, 24, 30). The type of husbandry practices such as communal grazing, free range grazing and climatic variations across different geographical regions can influence the survival of both the parasites and vectors. Fishing communities within QENP keep goats that directly and indirectly interact with wildlife species. In addition, it is not uncommon to find wildlife interacting with cattle around QENP especially in communities that neighbour the national park.
The prevalence of Trypanosoma spp. was higher in cattle than in goats, for samples collected in 2015. The chances of an animal being infected with Trypanosoma spp. vary with the geographical location, the rate at which the host is being fed on by the infected tsetse fly (2, 14), the detection of carbon dioxide emitted by potential vertebrate host, the short-range visual and olfactory stimuli by a tsetse, and the behavior of a particular host (2). Cattle have larger body sizes compared to goats and therefore are most likely to emit more odor (carbon dioxide) and therefore likely to attract more tsetse flies than goats (2, 14).
The study confirmed presence of T. congolense, T. vivax and T. brucei in both goats and cattle for years 2015 and 2017. However, T. vivax was the least prevalent of all the species. This is contrary to other studies that have reported T. vivax as the most predominant species in the endemic parts of Uganda (5, 11, 14, 24). However, the results are consistent with studies in Zambia (2, 32, 33), Nigeria (25, 34), Ghana (1) and some parts of Uganda (35) where T. congolense was reported to be the most prevalent species. The high prevalence of T. congolense could be attributed to the complementary roles played by major cyclic vectors like G. pallidipes. In addition, this could be due to high sensitivity and specificity of PCR methods used in the current study that can detect even extremely low parasitaemia. Trypanosoma congolense and T. vivax species may also be mechanically transmitted by biting flies (36). The low prevalence of T. vivax could be attributed to the low densities of G. fuscipes in the current study. Glossina fuscipes fuscipes is well known to be a good vector for T. vivax (37, 38).
Mixed infections for all the species for T. brucei and T. vivax were only in cattle and goats sampled in 2015. In both years, there was mixed infections for all species of Trypanosoma in both cattle and goats though it was less prevalent in cattle samples of 2017. Trypanosoma brucei and T. congolense mixed infections was most prevalent for both years in all animals. Presence of mixed infection was consistent with the findings by Apaatah (1), Kouadio et al. (30) and Samdi (25). Presence of biting flies such as Stomoxys, Tabanids, G. fuscipes and G. pallidipes may explain the mixed infection in cattle and goats. Mixed infections may also be due to close interaction between wildlife and domestic animals. Tsetse flies may be getting blood meals from cattle, goats and wildlife leading to mixed infections.
For samples collected in 2015, there was no major variations in the prevalence of Trypanosoma spp. infections in all the study sites. The results were consistent with those reported in a previous report (1). This could suggest that climatic and ecological conditions which influence tsetse fly distribution in these communities sampled may be homogeneous. However, for samples collected in 2017, there was a statistically significant difference in the prevalence of Trypanosoma spp. by location with Muhokya and Lake Katwe, that are closely bordering the national park, having higher prevalence compared to other sites. The results are consistent with studies elsewhere which showed that prevalence of Trypanosoma species are higher in sites that are in close proximity with wildlife areas (14, 30). The pastoralists around QENP practice similar traditional husbandry management practices such as communal grazing and sometimes graze near or inside the national park. They expose their animals to tsetse flies that are more common inside than outside the national park. The occurrence of Trypanosoma species causing AAT directly corresponds to the availability of the vector (especially tsetse fly) (1, 26).
The survey for tsetse fly distribution was not conducted widely nor done in both the years to allow for comparison. The infection rates of tsetse flies captured was not investigated as well for seasonal variations in the tsetse fly abundance. The prevalence of T. brucei and T. congolense was high for samples collected in 2015 and 2017 respectively. This may be a true picture of prevalence since we tested the samples using same method of PCR. In this study, there was a time lag between sample collection and direct examination in the laboratory which could easily affect the results of this study. In addition, we neither sampled the same farms nor households for cattle in Years 2015 and 2017. Goats were sampled only in 2015 since farmers were more interested in sampling cattle in 2017. However, these were the same village in most instances.