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The elimination of Trypanosoma brucei gambiense? Challenges of reservoir hosts and transmission cycles: Expect the unexpected.
Parasite Epidemiol Control. 2019 Aug; 6:e00113.PE

Abstract

The World Health Organisation has set the goal for elimination of Human African Trypanosomiasis (HAT), caused by Trypanosoma brucei gambiense (gHAT), as a public health problem for 2020 and for the total interruption of transmission to humans for 2030. Targeting human carriers and potential animal reservoir infections will be critical to achieving this ambitious goal. However, there is continuing debate regarding the significance of reservoir host animals, wild and domestic, in different epidemiological contexts, whilst the extent and duration of the asymptomatic human carrier state is similarly undefined. This paper reviews the status of the knowledge of latent infections in wild and domestic animal reservoir hosts towards the goal of better understanding their role in the transmission dynamic of the disease. Focus areas include the transmission cycles in non-human hosts, the infectivity of animal reservoirs to Glossina palpalis s.l., the longevity of infection and the stability of T. b. gambiense biological characteristics in antelopes and domestic animals. There is compelling evidence that T. b. gambiense can establish and persist in experimentally infected antelopes, pigs and dogs for a period of at least two years. In particular, metacyclic transmission of T. b. gambiense has been reported in antelope-G.p.palpalis-antelope and pig-G.p.gambiensis-pig cycles. Experimental studies demonstrate that the infectiveness of latent animal reservoir infections with T. b. gambiense is retained in animal-Glossina-animal cycles (antelopes and pigs) for periods of three years and human infectivity markers (human serum resistance, zymodeme, DNA) are stable in non-human hosts for the same period. These observations shed light on the epidemiological significance of animal reservoir hosts in specific ecosystems characterized by presently active, as well as known "old" HAT foci whilst challenging the concept of total elimination of all transmission by 2030. This target is also compromised by the existence of human asymptomatic carriers of T. b. gambiense often detected outside Africa after having lived outside tsetse infested areas for many years - sometimes decades. Non-tsetse modes of transmission may also play a significant but underestimated role in the maintenance of foci and also preclude the total elimination of transmission - these include mother to child transmission and sexual transmission. Both these modes of transmission have been the subject of case reports yet their frequency in African settings remains to be ascertained when the context of residual foci are discussed yet both challenge the concept of the possibility of the total elimination of transmission.

Authors+Show Affiliations

Institute for Parasitology and Tropical Veterinary Medicine, Department of Veterinary Medicine, Freie Universität Berlin, Germany.Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, UK.

Pub Type(s)

Journal Article
Review

Language

eng

PubMed ID

31528738

Citation

Mehlitz, D, and D H. Molyneux. "The Elimination of Trypanosoma Brucei Gambiense? Challenges of Reservoir Hosts and Transmission Cycles: Expect the Unexpected." Parasite Epidemiology and Control, vol. 6, 2019, pp. e00113.
Mehlitz D, Molyneux DH. The elimination of Trypanosoma brucei gambiense? Challenges of reservoir hosts and transmission cycles: Expect the unexpected. Parasite Epidemiol Control. 2019;6:e00113.
Mehlitz, D., & Molyneux, D. H. (2019). The elimination of Trypanosoma brucei gambiense? Challenges of reservoir hosts and transmission cycles: Expect the unexpected. Parasite Epidemiology and Control, 6, e00113. https://doi.org/10.1016/j.parepi.2019.e00113
Mehlitz D, Molyneux DH. The Elimination of Trypanosoma Brucei Gambiense? Challenges of Reservoir Hosts and Transmission Cycles: Expect the Unexpected. Parasite Epidemiol Control. 2019;6:e00113. PubMed PMID: 31528738.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - The elimination of Trypanosoma brucei gambiense? Challenges of reservoir hosts and transmission cycles: Expect the unexpected. AU - Mehlitz,D, AU - Molyneux,D H, Y1 - 2019/08/04/ PY - 2019/05/23/received PY - 2019/07/03/revised PY - 2019/07/11/accepted PY - 2019/9/19/entrez PY - 2019/9/19/pubmed PY - 2019/9/19/medline KW - Elimination KW - Glossina KW - Human African Trypanosomiasis (HAT) KW - Infectivity to tsetse KW - Longevity of parasitaemia KW - Non-tsetse transmission KW - T. b. gambiense KW - Transmission cycles KW - Wild and domestic animal reservoirs SP - e00113 EP - e00113 JF - Parasite epidemiology and control JO - Parasite Epidemiol Control VL - 6 N2 - The World Health Organisation has set the goal for elimination of Human African Trypanosomiasis (HAT), caused by Trypanosoma brucei gambiense (gHAT), as a public health problem for 2020 and for the total interruption of transmission to humans for 2030. Targeting human carriers and potential animal reservoir infections will be critical to achieving this ambitious goal. However, there is continuing debate regarding the significance of reservoir host animals, wild and domestic, in different epidemiological contexts, whilst the extent and duration of the asymptomatic human carrier state is similarly undefined. This paper reviews the status of the knowledge of latent infections in wild and domestic animal reservoir hosts towards the goal of better understanding their role in the transmission dynamic of the disease. Focus areas include the transmission cycles in non-human hosts, the infectivity of animal reservoirs to Glossina palpalis s.l., the longevity of infection and the stability of T. b. gambiense biological characteristics in antelopes and domestic animals. There is compelling evidence that T. b. gambiense can establish and persist in experimentally infected antelopes, pigs and dogs for a period of at least two years. In particular, metacyclic transmission of T. b. gambiense has been reported in antelope-G.p.palpalis-antelope and pig-G.p.gambiensis-pig cycles. Experimental studies demonstrate that the infectiveness of latent animal reservoir infections with T. b. gambiense is retained in animal-Glossina-animal cycles (antelopes and pigs) for periods of three years and human infectivity markers (human serum resistance, zymodeme, DNA) are stable in non-human hosts for the same period. These observations shed light on the epidemiological significance of animal reservoir hosts in specific ecosystems characterized by presently active, as well as known "old" HAT foci whilst challenging the concept of total elimination of all transmission by 2030. This target is also compromised by the existence of human asymptomatic carriers of T. b. gambiense often detected outside Africa after having lived outside tsetse infested areas for many years - sometimes decades. Non-tsetse modes of transmission may also play a significant but underestimated role in the maintenance of foci and also preclude the total elimination of transmission - these include mother to child transmission and sexual transmission. Both these modes of transmission have been the subject of case reports yet their frequency in African settings remains to be ascertained when the context of residual foci are discussed yet both challenge the concept of the possibility of the total elimination of transmission. SN - 2405-6731 UR - https://www.unboundmedicine.com/medline/citation/31528738/The_elimination_of_Trypanosoma_brucei_gambiense_Challenges_of_reservoir_hosts_and_transmission_cycles:_Expect_the_unexpected_ L2 - https://linkinghub.elsevier.com/retrieve/pii/S2405-6731(19)30076-5 DB - PRIME DP - Unbound Medicine ER -
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