Molecular identification of Trypanosoma brucei gambiense in naturally infected pigs, dogs and small ruminants confirms domestic animals as potential reservoirs for sleeping sickness in Chad

Abstract

Human African trypanosomiasis (HAT) has been targeted for zero transmission to humans by 2030. Animal reservoirs of gambiense-HAT could jeopardize these elimination goals. This study was undertaken to identify potential host reservoirs for Trypanosoma brucei gambiense by detecting its natural infections in domestic animals of Chadian HAT foci. Blood samples were collected from 267 goats, 181 sheep, 154 dogs, and 67 pigs. Rapid diagnostic test (RDT) and capillary tube centrifugation (CTC) were performed to search for trypanosomes. DNA was extracted from the buffy coat, and trypanosomes of the subgenus Trypanozoon as well as T. b. gambiense were identified by PCR. Of 669 blood samples, 19.4% were positive by RDT and 9.0% by CTC. PCR revealed 150 animals (22.4%) with trypanosomes belonging to Trypanozoon, including 18 (12%) T. b. gambiense. This trypanosome was found in all investigated animal species and all HAT foci. Between animal species or villages, no significant differences were observed in the number of animals harboring T. b. gambiense DNA. Pigs, dogs, sheep and goats appeared to be potential reservoir hosts for T. b. gambiense in Chad. The identification of T. b. gambiense in all animal species of all HAT foci suggests that these animals should be considered when designing new control strategies for sustainable elimination of HAT. Investigations aiming to decrypt their specific role in each epidemiological setting are important to achieve zero transmission of HAT.

Free-ranging pigs identified as a multi-reservoir of Trypanosoma brucei and Trypanosoma congolense in the Vavoua area, a historical sleeping sickness focus of Côte d’Ivoire

“…The global results obtained with BCT, TL and PCR confirmed high trypanosome infection rates in pigs as already observed in previous studies conducted on the neighboring Bonon and Sinfra HAT endemic foci [11,39] or in other study areas in West and Central Africa as in Nigeria [40], Chad [41] or Cameroon [42][43][44]. Such high infection rates in pigs may be linked to their tolerance to trypanosomes as already observed in the field [20] or during experimental infections with T. b. gambiense [45], and certainly illustrate that the pig is a preferential host for tsetse flies [46,47].…”

“…These results confirm that the CATT is not specific of T. b. gambiense due to cross-reactions with other trypanosomes as already observed [51][52][53][54]. The SD Bioline HAT rapid diagnostic tests (RDT) [55], another serological test initially developed for HAT diagnosis, also showed a lack of T. b. gambiense specificity when used in animals [41,56,57]. In absence of serological tests adapted for field diagnosis of African trypanosomiases in animal surveys, we propose the use of CATT as screening methods, despite their lack of T. b. gambiense-specificity.…”

“…In a recent study targeting TgsGP to detect T. b. gambiense in tsetse flies in a very low HAT prevalence area in Uganda, the TgsGP primers were suspected to crossreact with DNA from an "unidentified source" after sequencing the DNA products [64]. Nonspecific TgsGP PCR products could explain the reported presence of T. b. gambiense in domestic and wild animals in foci where no or very few HAT cases were reported [41,65,66]. This might also explain the TgsGP positive results recently observed on animals in the Mandoul focus in Chad [57], an area where tsetse densities were significantly reduced by a vector control campaign [67].…”

Diversity of trypanosomes in humans and cattle in the HAT foci Mandoul and Maro, Southern Chad—A matter of concern for zoonotic potential?

“…gambiense in two human samples from the Maro area. It was detected in one child and one older man confirming the presence of the parasite in the area and the ongoing risk of HAT infections, as it was also identified in animal reservoirs reported by Vourchakbé et al ., 2020 [ 44 ]. These two participants have had no previous infection with this parasite.…”

Modelling to infer the role of animals in gambiense human African trypanosomiasis transmission and elimination in DRC

“…There are a considerable number of reports of Trypanosoma brucei gambiense parasites in both wildlife and domestic livestock -Büscher et al [7] provide a concise recent summary and, in addition, a recent study reported T. b. gambiense infections in domestic animals in Chad with 1.2-4.5% of those sampled testing positive in the three main foci [8]. Furthermore, experimental evidence of transmission of T. b. gambiense from animals back to humans, through the tsetse vector, has been documented [9], demonstrating that it is possible for animal-tsetse-human transmission cycles to exist.…”