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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

Percent distribution of uterine contents of catches at the trap (A), refuges (B) and Houses 1–3 (C).L1, L2 and L3 are first, second and third instar larvae, respectively. Sample sizes for the trap, refuges and houses were 80, 54 and 85, respectively, for G. m. morsitans and 601, 47 and 295, respectively, for G. pallidipes.
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pntd-0002086-g006: Percent distribution of uterine contents of catches at the trap (A), refuges (B) and Houses 1–3 (C).L1, L2 and L3 are first, second and third instar larvae, respectively. Sample sizes for the trap, refuges and houses were 80, 54 and 85, respectively, for G. m. morsitans and 601, 47 and 295, respectively, for G. pallidipes.

Mentions: Despite the seasonality in some aspects of the results, the pooled data for ovarian categories (Fig. 5) and uterine contents (Fig. 6) in the whole study period illustrate two matters that applied at all seasons. First, with each bait the samples of G. pallidipes were older than for G. m. morsitans and contained a lower proportion of flies with larvae as against eggs. Second, the samples of G. m. morsitans from all baits were older, and with higher proportions of larvae, than the samples taken from men during other work performed at Rekomitjie in parallel with the present investigations [4]. In that other work the catches of G. m. morsitans from the men in various situations inside and outside houses throughout the year showed only 18% (N = 257) in ovarian categories 4–7, and only 23% (189) of the flies in categories ≥1 carried larvae. These compositions are significantly different from the figures of 32% (N = 98, P<0.01) and 51% (N = 85, P<0.001), respectively, for the present catches of G. m. morsitans from houses over the year (Figs. 5 and 6).


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)

Percent distribution of uterine contents of catches at the trap (A), refuges (B) and Houses 1–3 (C).L1, L2 and L3 are first, second and third instar larvae, respectively. Sample sizes for the trap, refuges and houses were 80, 54 and 85, respectively, for G. m. morsitans and 601, 47 and 295, respectively, for G. pallidipes.
© Copyright Policy
Related In: Results  -  Collection

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

pntd-0002086-g006: Percent distribution of uterine contents of catches at the trap (A), refuges (B) and Houses 1–3 (C).L1, L2 and L3 are first, second and third instar larvae, respectively. Sample sizes for the trap, refuges and houses were 80, 54 and 85, respectively, for G. m. morsitans and 601, 47 and 295, respectively, for G. pallidipes.
Mentions: Despite the seasonality in some aspects of the results, the pooled data for ovarian categories (Fig. 5) and uterine contents (Fig. 6) in the whole study period illustrate two matters that applied at all seasons. First, with each bait the samples of G. pallidipes were older than for G. m. morsitans and contained a lower proportion of flies with larvae as against eggs. Second, the samples of G. m. morsitans from all baits were older, and with higher proportions of larvae, than the samples taken from men during other work performed at Rekomitjie in parallel with the present investigations [4]. In that other work the catches of G. m. morsitans from the men in various situations inside and outside houses throughout the year showed only 18% (N = 257) in ovarian categories 4–7, and only 23% (189) of the flies in categories ≥1 carried larvae. These compositions are significantly different from the figures of 32% (N = 98, P<0.01) and 51% (N = 85, P<0.001), respectively, for the present catches of G. m. morsitans from houses over the year (Figs. 5 and 6).

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