Limits...
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.

Show MeSH

Related in: MedlinePlus

Temperature in a refuge and Houses 1–3 at various times of day.Temperature is expressed as the mean difference between the temperature in the refuge or house and the temperature in a Stevenson screen, so that if the difference is negative the temperature in the refuge or house was lower than in the screen. Vertical bars through the plots indicate the 95% confidence limits of the mean. Some plots are slightly displaced horizontally to ensure that the bars are not confused. Houses 1, 2 and 3 had roofs of thatch, asbestos and tin, respectively.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3585122&req=5

pntd-0002086-g002: Temperature in a refuge and Houses 1–3 at various times of day.Temperature is expressed as the mean difference between the temperature in the refuge or house and the temperature in a Stevenson screen, so that if the difference is negative the temperature in the refuge or house was lower than in the screen. Vertical bars through the plots indicate the 95% confidence limits of the mean. Some plots are slightly displaced horizontally to ensure that the bars are not confused. Houses 1, 2 and 3 had roofs of thatch, asbestos and tin, respectively.

Mentions: The elements in the attractiveness of the house are suggested by considering the percent of G. pallidipes in catches from the various baits. The proportion in the trap was very high, at 91%, and significantly different (P<0.001) from the 36% evident at the refuges. With the house treatments the percents were intermediate, at 61–81% (average 76%). This suggested the hypothesis, henceforth termed the “mixed sample” hypothesis, that the catches from House 1 consisted of two segments, one comparable to refuge catches and the other comparable to trap catches. The implication is that House 1 functioned as both a trap and a refuge, attracting some flies that were host-seeking and others looking for shelter. It seemed that House 1 did indeed offer a good refuge since in the middle of the day, when screen temperatures were greatest, the temperatures in the house were about two degrees lower than screen temperatures – much like the Box refuges but in sharp contrast to the asbestos-roofed House 2 and particularly the tin-roofed House 3 (Fig. 2).


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)

Temperature in a refuge and Houses 1–3 at various times of day.Temperature is expressed as the mean difference between the temperature in the refuge or house and the temperature in a Stevenson screen, so that if the difference is negative the temperature in the refuge or house was lower than in the screen. Vertical bars through the plots indicate the 95% confidence limits of the mean. Some plots are slightly displaced horizontally to ensure that the bars are not confused. Houses 1, 2 and 3 had roofs of thatch, asbestos and tin, respectively.
© Copyright Policy
Related In: Results  -  Collection

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

pntd-0002086-g002: Temperature in a refuge and Houses 1–3 at various times of day.Temperature is expressed as the mean difference between the temperature in the refuge or house and the temperature in a Stevenson screen, so that if the difference is negative the temperature in the refuge or house was lower than in the screen. Vertical bars through the plots indicate the 95% confidence limits of the mean. Some plots are slightly displaced horizontally to ensure that the bars are not confused. Houses 1, 2 and 3 had roofs of thatch, asbestos and tin, respectively.
Mentions: The elements in the attractiveness of the house are suggested by considering the percent of G. pallidipes in catches from the various baits. The proportion in the trap was very high, at 91%, and significantly different (P<0.001) from the 36% evident at the refuges. With the house treatments the percents were intermediate, at 61–81% (average 76%). This suggested the hypothesis, henceforth termed the “mixed sample” hypothesis, that the catches from House 1 consisted of two segments, one comparable to refuge catches and the other comparable to trap catches. The implication is that House 1 functioned as both a trap and a refuge, attracting some flies that were host-seeking and others looking for shelter. It seemed that House 1 did indeed offer a good refuge since in the middle of the day, when screen temperatures were greatest, the temperatures in the house were about two degrees lower than screen temperatures – much like the Box refuges but in sharp contrast to the asbestos-roofed House 2 and particularly the tin-roofed House 3 (Fig. 2).

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