Factors Affecting the Propensity of Tsetse Flies to Enter Houses and Attack Humans Inside: Increased Risk of Sleeping Sickness in Warmer Climates

Abstract

BackgroundSleeping sickness, or human African trypanosomiasis, is caused by two species of Trypanosoma brucei that are transmitted to humans by tsetse flies (Glossina spp.) when these insects take a bloodmeal. It is commonly assumed that humans must enter the normal woodland habitat of the flies to become infected, but recent studies found that tsetse frequently attack humans inside buildings. Factors affecting human/tsetse contact in buildings need identification.Methodology/Principal FindingsIn Zimbabwe, tsetse were allowed access to a house via an open door. Those in the house at sunset, and those alighting on humans in the house during the day, were caught using hand-nets. Total catches were unaffected by: (i) the presence of humans in the house and at the door, (ii) wood smoke from a fire inside the house or just outside, (iii) open windows, and (iv) chemicals simulating the odor of cattle or of humans. Catches increased about 10-fold with rising ambient temperatures, and during the hottest months the proportion of the total catch that was taken from the humans increased from 5% to 13%. Of the tsetse caught from humans, 62% consisted of female G. morsitans morstans and both sexes of G. pallidipes, i.e., the group of tsetse that normally alight little on humans. Some of the tsetse caught were old enough to be effective vectors.Conclusion/SignificancePresent results confirm previous suggestions that buildings provide a distinctive and important venue for transmission of sleeping sickness, especially since the normal repellence of humans and smoke seems poorly effective in such places. The importance of the venue would be increased in warmer climates.

Knowledge, attitude, and practices about tsetse control among communities neighbouring Serengeti National Park, Tanzania

“…Tsetse flies are vectors of blood parasite of the genus Trypanosoma, which causes African trypanosomiasis. It is a debilitating and often fatal disease unique to Sub-Saharan Africa that affects both man [Human African Trypanosomiasis (HAT)] and livestock [African Animal Trypanosomosis (AAT)] or nagana ( Vale et al, 2013 ; Vale et al, 2015 ; Wamwiri and Changasi, 2016). In Tanzania tsetse infestation rate was about 33% against 60% documented earlier ( Daffa et al, 2013 ).…”

Host-seeking efficiency can explain population dynamics of the tsetse fly Glossina morsitans morsitans in response to host density decline

“…In addition to the effects of host density on vector density, and mortality rates, the existence of hungrier flies in regions where wild hosts are scarce can have implications for trypanosome transmission. First, hungrier flies may be more inclined to bite less-favoured hosts, including humans, thereby increasing the risk of transmission of the zoonotic Rhodesian human African trypanosomiasis [ 42 ]. Second, laboratory experiments suggest that starved flies are more susceptible to acquiring a trypanosome infection [ 43 ], which may influence transmission dynamics.…”