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A neglected aspect of the epidemiology of sleeping sickness: the propensity of the tsetse fly vector to enter houses.

Vale GA, Chamisa A, Mangwiro C, Torr SJ - PLoS Negl Trop Dis (2013)

Bottom Line: Doors and windows seemed about equally effective as entry points.Houses are attractive in themselves.Some of the tsetse attracted seem to be in a host-seeking phase of behavior and others appear to be looking for shelter from high temperatures outside.

View Article: PubMed Central - PubMed

Affiliation: Natural Resources Institute, University of Greenwich, Chatham, United Kingdom. valeglyn@gmail.com

ABSTRACT

Background: When taking a bloodmeal from humans, tsetse flies can transmit the trypanosomes responsible for sleeping sickness, or human African trypanosomiasis. While it is commonly assumed that humans must enter the normal woodland habitat of the tsetse in order to have much chance of contacting the flies, recent studies suggested that important contact can occur due to tsetse entering buildings. Hence, we need to know more about tsetse in buildings, and to understand why, when and how they enter such places.

Methodology/principal findings: Buildings studied were single storied and comprised a large house with a thatched roof and smaller houses with roofs of metal or asbestos. Each building was unoccupied except for the few minutes of its inspection every two hours, so focusing on the responses of tsetse to the house itself, rather than to humans inside. The composition, and physiological condition of catches of tsetse flies, Glossina morsitans morsitans and G. pallidipes, in the houses and the diurnal and seasonal pattern of catches, were intermediate between these aspects of the catches from artificial refuges and a host-like trap. Several times more tsetse were caught in the large house, as against the smaller structures. Doors and windows seemed about equally effective as entry points. Many of the tsetse in houses were old enough to be potential vectors of sleeping sickness, and some of the flies alighted on the humans that inspected the houses.

Conclusion/significance: Houses are attractive in themselves. Some of the tsetse attracted seem to be in a host-seeking phase of behavior and others appear to be looking for shelter from high temperatures outside. The risk of contracting sleeping sickness in houses varies according to house design.

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Related in: MedlinePlus

Diurnal pattern of catches of the trap (A), refuges (B) and House 1 (C) at various seasons.The catch at each bait at each inspection time at each season is shown as a percent of the total catch for the bait and season. The refuge data refer to the pooled catches of all three refuges. Sample sizes are shown in parentheses in the legends. Only two G. pallidipes were caught in refuges in the cool season, both at 1500 h, and these catches are not shown. Temperatures indicated for each season are the mean maximum of daily screen temperatures, with the range in parentheses.
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pntd-0002086-g004: Diurnal pattern of catches of the trap (A), refuges (B) and House 1 (C) at various seasons.The catch at each bait at each inspection time at each season is shown as a percent of the total catch for the bait and season. The refuge data refer to the pooled catches of all three refuges. Sample sizes are shown in parentheses in the legends. Only two G. pallidipes were caught in refuges in the cool season, both at 1500 h, and these catches are not shown. Temperatures indicated for each season are the mean maximum of daily screen temperatures, with the range in parentheses.

Mentions: The general patterns of the availability to traps and refuges was as usually found at Rekomitjie [6]. Thus, with both species of tsetse the catches from the traps (Fig. 4, A) were greatest in the morning and late afternoon, but there were seasonal distinctions. The mid-day trough in trap catches was most pronounced in the hottest months of Sep–Nov (Fig. 4, A1) and least marked in the coolest months of May–Aug (Fig. 4, A3). Moreover, while the morning peak of trap catches was greater than the afternoon peak in Sep–Nov, the afternoon peak became more pronounced as the weather cooled. The refuge catches (Fig. 4, B) were concentrated in the middle of the day and early afternoon, and so differed markedly from trap catches. Again there were seasonal variations in that during Sep–Nov (Fig. 4, B1) the refuge catches started to rise earlier than in the cooler conditions of Dec–Aug (Fig. 4, B2 and B3), presumably because during the hotter months the need to avoid high temperatures occurred sooner in the day.


A neglected aspect of the epidemiology of sleeping sickness: the propensity of the tsetse fly vector to enter houses.

Vale GA, Chamisa A, Mangwiro C, Torr SJ - PLoS Negl Trop Dis (2013)

Diurnal pattern of catches of the trap (A), refuges (B) and House 1 (C) at various seasons.The catch at each bait at each inspection time at each season is shown as a percent of the total catch for the bait and season. The refuge data refer to the pooled catches of all three refuges. Sample sizes are shown in parentheses in the legends. Only two G. pallidipes were caught in refuges in the cool season, both at 1500 h, and these catches are not shown. Temperatures indicated for each season are the mean maximum of daily screen temperatures, with the range in parentheses.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585122&req=5

pntd-0002086-g004: Diurnal pattern of catches of the trap (A), refuges (B) and House 1 (C) at various seasons.The catch at each bait at each inspection time at each season is shown as a percent of the total catch for the bait and season. The refuge data refer to the pooled catches of all three refuges. Sample sizes are shown in parentheses in the legends. Only two G. pallidipes were caught in refuges in the cool season, both at 1500 h, and these catches are not shown. Temperatures indicated for each season are the mean maximum of daily screen temperatures, with the range in parentheses.
Mentions: The general patterns of the availability to traps and refuges was as usually found at Rekomitjie [6]. Thus, with both species of tsetse the catches from the traps (Fig. 4, A) were greatest in the morning and late afternoon, but there were seasonal distinctions. The mid-day trough in trap catches was most pronounced in the hottest months of Sep–Nov (Fig. 4, A1) and least marked in the coolest months of May–Aug (Fig. 4, A3). Moreover, while the morning peak of trap catches was greater than the afternoon peak in Sep–Nov, the afternoon peak became more pronounced as the weather cooled. The refuge catches (Fig. 4, B) were concentrated in the middle of the day and early afternoon, and so differed markedly from trap catches. Again there were seasonal variations in that during Sep–Nov (Fig. 4, B1) the refuge catches started to rise earlier than in the cooler conditions of Dec–Aug (Fig. 4, B2 and B3), presumably because during the hotter months the need to avoid high temperatures occurred sooner in the day.

Bottom Line: Doors and windows seemed about equally effective as entry points.Houses are attractive in themselves.Some of the tsetse attracted seem to be in a host-seeking phase of behavior and others appear to be looking for shelter from high temperatures outside.

View Article: PubMed Central - PubMed

Affiliation: Natural Resources Institute, University of Greenwich, Chatham, United Kingdom. valeglyn@gmail.com

ABSTRACT

Background: When taking a bloodmeal from humans, tsetse flies can transmit the trypanosomes responsible for sleeping sickness, or human African trypanosomiasis. While it is commonly assumed that humans must enter the normal woodland habitat of the tsetse in order to have much chance of contacting the flies, recent studies suggested that important contact can occur due to tsetse entering buildings. Hence, we need to know more about tsetse in buildings, and to understand why, when and how they enter such places.

Methodology/principal findings: Buildings studied were single storied and comprised a large house with a thatched roof and smaller houses with roofs of metal or asbestos. Each building was unoccupied except for the few minutes of its inspection every two hours, so focusing on the responses of tsetse to the house itself, rather than to humans inside. The composition, and physiological condition of catches of tsetse flies, Glossina morsitans morsitans and G. pallidipes, in the houses and the diurnal and seasonal pattern of catches, were intermediate between these aspects of the catches from artificial refuges and a host-like trap. Several times more tsetse were caught in the large house, as against the smaller structures. Doors and windows seemed about equally effective as entry points. Many of the tsetse in houses were old enough to be potential vectors of sleeping sickness, and some of the flies alighted on the humans that inspected the houses.

Conclusion/significance: Houses are attractive in themselves. Some of the tsetse attracted seem to be in a host-seeking phase of behavior and others appear to be looking for shelter from high temperatures outside. The risk of contracting sleeping sickness in houses varies according to house design.

Show MeSH
Related in: MedlinePlus