Epidemiology of Trypanosoma Infections in Cattle and Glossina Flies at the Human-wildlife-livestock Interface of Akagera National Park, Rwanda
Abstract
African Trypanosomosis is a major neglected tropical disease of animals and humans in low
resource settings in Africa. The disease is cyclically transmitted by Glossina (tsetse flies) spp.
and mechanically by biting flies such as Tabanus spp. and Stomoxys spp. and has enormous
negative effects on the health and life of both humans and animals. The socio-economic and
health impact of the disease is often felt at the edge of protected, tsetse-infested wildlife areas.
In Rwanda, tsetse flies and trypanosomosis are reported in areas around the Akagera National
Park but the situation has previously not been well documented. This study aimed at
determining (i) the distribution of species of Glossina (ii) the Trypanosoma species circulating
in tsetse flies, their infection rate, and the endosymbionts, (iii) the hosts’ preference for the
tsetse flies, and (iv) the Trypanosoma species circulating in cattle, at the wildlife-livestock
interface of Akagera National Park in Rwanda.
To determine the distribution of Glossina, a longitudinal stratified sampling entomological
survey was carried out inside the park and its surroundings. Biconical traps were deployed in
55 sites for six consecutive days of each study month from May 2018 to June 2019 and emptied
every 48hours. Flies caught in the traps were identified using FAO keys for entomological
taxonomy. The number of flies per trap per day (FTD) was used to determine the apparent
density (AD) of the flies. Pearson chi-square (χ2) and parametrical tests (t-test and ANOVA)
were used to determine the variability between the variables. Logistic regression was used to
determine the association between predictors of tsetse flies occurrence. A selected sample of
1101 tsetse flies, recovered from the traps, was analysed for trypanosome species and
endosymbionts using PCR, and 2-gene High Resolution Melting analysis for blood meal
source. A total of 1037 blood samples collected between March and July 2019 from randomly
selected cattle (local and local x Friesian breeds) in four districts neighboring the National Park,
and were examined for species of Trypanosoma. Four districts viz. Kayonza, Gatsibo,
Nyagatare and Kirehe were selected for their proximity to the park and for being adjacent to
protected game reserves in Tanzania. The presence of trypanosomes in the blood samples was
determined by microscopy, immunological rapid test, and PCR coupled with High-Resolution
Melt (HRM) analysis. Sanger sequencing was done on the amplicons to complement the
analysis. The Cohen Kappa test was used to compare the level of agreement between the
diagnostic methods.
Thirty-nine thousands and five hundreds sixteen (39,516) tsetse flies were collected using the
traps, of which 73.4% (29,019) and 26.6% (10,497) were from inside the park and the interface
area, respectively. Female flies accounted for 61.3% (24,223) while 38.7% (15,293) were
males. Two species of Glossina, i.e. G. pallidipes [n=29,121, 7.4 flies/trap/day (FTD)] and G.
morsitans centralis (n=10,395; 2.6 FTD) were identified. The statistical difference was
significant between the two species (p=0.000). The flies were more abundant during the wet
season (15.8 FTD) than the dry season (4.2 FTD) [p=0.000]. Large numbers of flies were
trapped around the swamp areas (69.1 FTD) inside the park and in Nyagatare District (11.2
FTD) at the interface [p=0.000]. One thousand and one hundred and one (1101) tsetse flies
(771 Glossina pallidipes and 330 Glossina morsitans centralis) were analysed for trypanosome
infections. The overall infection rate was 13.9% (153/1101) in the head and proboscis (HP) and
24.3% (268/1101) in thorax and abdomen (TA) of the flies. Eight species of trypanosomes were
identified. For each species, head +proboscis and thorax+ abdomen were analyzed in parallel
and are presented as HP/TA. Of these species, Trypanosoma (T.) brucei brucei accounted for
4.1/7.1%, T.congolense Kilifi (2.2/2.1%), T.congolense savannah (1.6/1.2%), T. evansi
(0/0.9%), T.godefreyi (1.2/3.1%), T. grayi (0/1.08%), T.simiae (2.08/3.7%), T.theileri (0/2.08%)
and T.vivax (5.2/3.7%). Mixed infections were 2.2/0.8% (25/9). No T.brucei rhodesiense was
found in tsetse flies analyzed.
The endosymbionts found in tsetse flies were the bacteria Sodalis (2.8%; 31/1101) and
Wolbachia (4.8%; 53/1101). No Spiroplasma and SGH Virus were found in all samples
analyzed. The preferred hosts for blood meal by the tsetse flies were buffalo (36.5%), warthog
(14.1%), cattle (10.6%), savannah elephant (8.7%), bushbuck (7.3%), and human (5.7%).
The overall prevalence of trypanosome infections in cattle was 5.6%, 7.1%, and 18.7% by thin
blood smear, Buffy coat technique, and PCR/HRM, respectively. Microscopy showed a low
sensitivity (28.9%) while the rapid test (VerY Diag) showed a low specificity (32.5%).
Trypanosomes were detected in cattle blood, including species that are pathogenic to cattle (i.e.
T. brucei brucei, T. congolense savannah, T. evansi and T. vivax) and T. theileri which is nonpathogenic.
T. congolense was the most prevalent (10.7%), followed by T. vivax 5.2%, T. brucei brucei
2%, and T. evansi 0.7% by PCR/HRM analysis. Lower trypanosome infections were observed
in Ankole Friesian cross-breeds than indigenous Ankole. No human-infective T. brucei
rhodesiense was detected. There was no significant difference between the mean PCV of
infected and non-infected animals (p>0.162).
The study results on tsetse distribution, endosymbionts, hosts preference, and trypanosomes
infections, corroborate other similar regional findings. Glossina pallidipes were found in
higher numbers and therefore conceivably the most important vectors of trypanosomes. This
study confirms that the cattle reared around the Akagera NP are infected by Trypanosoma
species causing African Animal Trypanosomiasis (AAT), and the area should, therefore, be
targeted in control activities. Future studies should focus on the AAT impact assessment on
cattle production and information on the use of trypanocides to help policymakers prioritize
target areas and optimize intervention strategies.
Publisher
University of Nairobi
Rights
Attribution-NonCommercial-NoDerivs 3.0 United StatesUsage Rights
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