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

Abstract

Background The existence of an animal reservoir of Trypanosoma brucei gambiense (T. b. gambiense), the agent of human African trypanosomiasis (HAT), may compromise the interruption of transmission targeted by World Health Organization. The aim of this study was to investigate the presence of trypanosomes in pigs and people in the Vavoua HAT historical focus where cases were still diagnosed in the early 2010’s. Methods For the human survey, we used the CATT, mini-anion exchange centrifugation technique and immune trypanolysis tests. For the animal survey, the buffy coat technique was also used as well as the PCR using Trypanosoma species specific, including the T. b. gambiense TgsGP detection using single round and nested PCRs, performed from animal blood samples and from strains isolated from subjects positive for parasitological investigations. Results No HAT cases were detected among 345 people tested. A total of 167 pigs were investigated. Free-ranging pigs appeared significantly more infected than pigs in pen. Over 70% of free-ranging pigs were positive for CATT and parasitological investigations and 27–43% were positive to trypanolysis depending on the antigen used. T. brucei was the most prevalent species (57%) followed by T. congolense (24%). Blood sample extracted DNA of T. brucei positive subjects were negative to single round TgsGP PCR. However, 1/22 and 6/22 isolated strains were positive with single round and nested TgsGP PCRs, respectively. Discussion Free-ranging pigs were identified as a multi-reservoir of T. brucei and/or T. congolense with mixed infections of different strains. This trypanosome diversity hinders the easy and direct detection of T. b. gambiense. We highlight the lack of tools to prove or exclude with certainty the presence of T. b. gambiense. This study once more highlights the need of technical improvements to explore the role of animals in the epidemiology of HAT.

Experimental evidence that immune trypanolysis using the LiTat 1.3 and LiTat 1.5 variant antigen types is not specific to Trypanosoma brucei gambiense in pigs

“…Thanks to its performance in terms of specificity and sensitivity described in humans, TL has become the reference immunological diagnostic tool for the surveillance of g-HAT [3,7,23]. However, its reliability as a diagnostic tool of T. b. gambiense infection in animals has been questioned and further experimental studies proposed to confirm or reject the T. b. gambiense specificity of this method [39]. This was the main objective of this experimental infection conducted in pigs.…”

“…The immune trypanolysis (TL) based on the detection of antibodies against predominant or specific variant antigen types (VAT) [41] is increasingly used for the epidemiological surveillance of g-HAT [7,8,21,23] and it was also recently applied to animal surveys conducted in Côte d'Ivoire. With positivity rates of up to 50% that were inconsistent with HAT prevalence in the studied hypo-endemic or historical foci, the T. b. gambiense specificity of VAT LiTat 1.3 and LiTat 1.5 was questioned [30,39]. This specificity was also questioned with positive TL results observed with these two VAT in cattle in a rhodesiense HAT and AAT endemic region in Uganda [27].…”

“…As mentioned in the WHO road map for neglected tropical diseases 2021-2030, the scientific community has been requested to elucidate this crucial question [43]. Recent studies conducted in Côte d'Ivoire showed that pigs often carry multiple trypanosome infections and highlighted the lack of tools to prove or exclude with certainty the presence of T. b. gambiense [30,39]. The challenge is to distinguish between the subspecies T. b. brucei and T. b. gambiense that may be found in sympatry.…”

Diagnosis of animal trypanosomoses: proper use of current tools and future prospects

“…An additional difficulty can appear in a “One Health” context: it may be necessary to treat animals infected by zoonotic trypanosomes, not because they are sick, but because they may be a threat to humans as a reservoir. This latter question is increasingly relevant in the context of eliminating transmission of T. b. gambiense (HAT) [ 94 ]. Finally, the treatment’s fully curative effect should be demonstrated in such a context.…”

Enhancing research integration to improve One Health actions: learning lessons from neglected tropical diseases experiences

“…For, instance, it has been recently demonstrated that the emergence of animal reservoirs of Dracunculus medinensis , particularly in fish-consuming domestic dogs (93% of all Guinea worms detected worldwide in 2020 were in dogs in Chad), has become the major impediment to eradication of this human disease 3 4. For human African trypanosomiasis, the importance of latent infections in seropositive asymptomatic individuals,5 the identification of domestic pigs as reservoirs of Trypanosoma brucei gambiense 6 and the probable role of skin-dwelling trypanosomes in transmission maintenance7 8 are active research areas that may be crucial for reaching the elimination goal 9. Actually, the lack of fundamental scientific knowledge about the natural reservoirs and even the transmission of Mycobacterium ulcerans, that still remain elusive in most endemic areas,10 is also pointing to the crucial need for more fundamental knowledge on NTDs.…”