The study of trypanosome species circulating in domestic animals in two human African trypanosomiasis foci of Côte d'Ivoire identifies pigs and cattle as potential reservoirs of Trypanosoma brucei gambiense

Abstract

Background: Important control efforts have led to a significant reduction of the prevalence of human African trypanosomiasis (HAT) in Côte d'Ivoire, but the disease is still present in several foci. The existence of an animal reservoir of Trypanosoma brucei gambiense may explain disease persistence in these foci where animal breeding is an important source of income but where the prevalence of animal African trypanosomiasis (AAT) is unknown. The aim of this study was to identify the trypanosome species circulating in domestic animals in both Bonon and Sinfra HAT endemic foci.

Methodology/principal findings: 552 domestic animals (goats, pigs, cattle and sheep) were included. Blood samples were tested for trypanosomes by microscopic observation, species-specific PCR for T. brucei sl, T. congolense, T. vivax and subspecies-specific PCR for T. b. gambiense and T. b. gambiense immune trypanolysis (TL). Infection rates varied significantly between animal species and were by far the highest in pigs (30%). T. brucei s.l was the most prevalent trypanosome species (13.7%) followed by T. congolense. No T. b. gambiense was identified by PCR while high TL positivity rates were observed using T. b. gambiense specific variants (up to 27.6% for pigs in the Bonon focus).

Conclusion: This study shows that domestic animals are highly infected by trypanosomes in the studied foci. This was particularly true for pigs, possibly due to a higher exposure of these animals to tsetse flies. Whereas T. brucei s.l. was the most prevalent species, discordant results were obtained between PCR and TL regarding T. b. gambiense identification. It is therefore crucial to develop better tools to study the epidemiological role of potential animal reservoir for T. b. gambiense. Our study illustrates the importance of "one health" approaches to reach HAT elimination and contribute to AAT control in the studied foci.

Fig 1. The study areas and sites of animal sampling.

A. Localization of the Bonon and Sinfra foci which reported the highest number of HAT cases diagnosed from 2000 to 2010 in Côte d’Ivoire. B. Localization of the last HAT cases diagnosed from 2011 to 2013 and the sites of domestic animals sampling in the Bonon and Sinfra foci. This figure was created by the mapping service of our team based at Institut Pierre Richet (Bouaké, Côte d’Ivoire) specifically for this manuscript.

Fig 2. Parasitological and PCR results.

Proportion of BCT (2A), T. brucei s.l. TBR-PCR (2B), T. congolense forest type TCF-PCR (2C) and T. vivax TVW-PCR (2D) positive results on the total sample collection for each host in the two foci. A significant difference between Bonon and Sinfra is indicated by a star.

Fig 3. Microsatellite genotyping results.

Neighbor-joining tree (NJTree), based on Cavalli-Sforza and Ewards Chord distance, of the amplified microsatellite genotypes. Reference stocks are in bold. The unique monophyletic lineage corresponds to Trypanosoma brucei gambiense and is indicated above the corresponding branch. The presence of several missing genotypes prohibited the use of bootstraps. Bo = Bonon, Si = Sinfra, Tbg = Trypanosoma brucei gambiense, Tbg2 = Trypanosoma brucei gambiense group 2, Tbb = Trypanosoma brucei brucei, Tbrh = Trypanosoma brucei rhodesiense.

Fig 4. Immune trypanolysis (TL) results.

Proportion of the LiTat 1.6 (4A), LiTat 1.3 (4B) and LiTat 1.5 (4C) TL positive results on the total sample collection for each host in the two foci. A significant difference between Bonon and Sinfra is indicated with a star.

Fig 5. Reactivity to the Litat 1.3, 1.5 and 1.6 VAT according to the different PCR profiles.

PCR profiles are given as follow: PCR TBR result/PCR TCF result/PCR TVW result. n = number of animals with the corresponding profile. Numbers on the top are the numbers of animal positives with Litat 1.3 and/or 1.5 TL or with LiTat 1.6 only.