Comparative Evaluation of Methods Used for Sampling Malaria Vectors in the Kilombero Valley, South Eastern Tanzania

Okumu, Fredros O.; Kotas, Maya E.; Kihonda, Japheth; Mathenge, Evan; Killeen, Gerry F.; Moore, Sarah

doi:10.2174/1874315300801010051

Cited by 36 publications

(24 citation statements)

References 24 publications

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“…Several species of Culex , Anopheles , and Mansonia mosquitoes including several known vectors of not only malaria [6,19,20,21], but also filariasis, and five different arboviruses [22] have been reported in this locality. Since scale up of LLINs in 2008, Anopheles gambiae sensu stricto population densities have declined, leaving exophagic An .…”

Section: Methodsmentioning

confidence: 99%

A low technology emanator treated with the volatile pyrethroid transfluthrin confers long term protection against outdoor biting vectors of lymphatic filariasis, arboviruses and malaria

et al. 2017

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BackgroundThe vapor phase of the volatile pyrethroid transfluthrin incapacitates mosquitoes and prevents them from feeding. Although existing emanator products for delivering volatile pyrethroids protect against outdoor mosquito bites, they are too short-lived to be practical or affordable for routine use in low-income settings. New transfluthrin emanators, comprised simply of treated hessian fabric strips, have recently proven highly protective against outdoor-biting vectors of lymphatic filariasis, arboviruses and malaria, but their full protective lifespan, minimum dose requirements, and range of protection have not previously been assessed.MethodologyThe effects of transfluthrin-treated hessian strips upon mosquito biting exposure of users and nearby non-users, as well as dependence of protection upon treatment dose, were measured outdoors in rural Tanzania using human landing catches (HLC).Principal findingsStrips treated with 10ml of transfluthrin prevented at least three quarters (p < 0.001) of outdoor bites by Anopheles arabiensis, Culex spp. and Mansonia spp. mosquitoes, and >90% protection against bites on warmer nights with higher evaporation rates, for at least one year. Strips treated with this high dose also reduced biting exposure of non-users at a distance of up to 5m from the strips for An. arabiensis (p < 0.001) and up to 2m for Mansonia spp. (p = 0.008), but provided no protection to non-users against Culex spp. No evidence of increased risk for non-users, caused by diversion of mosquitoes to unprotected individuals, was found at any distance within an 80m radius. A dose of only 1ml provided equivalent protection to the 10ml dose against An. arabiensis, Culex spp. and Mansonia spp. mosquitoes over 6 months (p < 0.001).Conclusions/SignificanceTransfluthrin-treated hessian emanators provide safe, affordable, long-term protection against several different pathogen-transmitting mosquito taxa that attack humans outdoors, where they are usually active and cannot be protected by bed nets or residual sprays with conventional, solid-phase insecticides.

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Section: Methodsmentioning

confidence: 99%

A low technology emanator treated with the volatile pyrethroid transfluthrin confers long term protection against outdoor biting vectors of lymphatic filariasis, arboviruses and malaria

et al. 2017

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“…Pyrethrum spray catch (PSC) is also widely used but this method only samples indoor-resting mosquitoes [11] and underestimates mosquito biting densities in houses where use of irritant or repellent insecticides deter resting indoors after feeding [12] and also in places where mosquitoes are endophagic but exophilic [2]. The Mbita bednet trap seemed to exhibit high sensitivity for catching human-seeking mosquitoes indoors in rural Kenya [13-15] but this could not be replicated in the highlands of Madagascar, with a highly zoophilic mosquito population [16], and in Northern and South Eastern Tanzania [17,18]. Resting boxes [19,20] or claypots [21] are sometimes used outdoors to collect outdoor resting mosquitoes.…”

Section: Introductionmentioning

confidence: 99%

Advantages and limitations of commercially available electrocuting grids for studying mosquito behaviour

et al. 2013

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Background: Mosquito feeding behaviour plays a major role in determining malaria transmission intensity and the impact of specific prevention measures. Human Landing Catch (HLC) is currently the only method that can directly and consistently measure the biting rates of anthropophagic mosquitoes, both indoors and outdoors. However, this method exposes the participant to mosquito-borne pathogens, therefore new exposure-free methods are needed to replace it. Methods: Commercially available electrocuting grids (EGs) were evaluated as an alternative to HLC using a Latin Square experimental design in Dar es Salaam, Tanzania. Both HLC and EGs were used to estimate the proportion of human exposure to mosquitoes occurring indoors (π i ), as well as its two underlying parameters: the proportion of mosquitoes caught indoors (P i ) and the proportion of mosquitoes caught between the first and last hour when most people are indoors (P fl ).Results: HLC and EGs methods accounted for 69% and 31% of the total number of female mosquitoes caught respectively and both methods caught more mosquitoes outdoors than indoors. Results from the gold standard HLC suggest that An. gambiae s.s. in Dar es Salaam is neither exophagic nor endophagic (P i ≈ 0.5), whereas An. arabiensis is exophagic (P i < < 0.5). Both species prefer to feed after 10pm when most people are indoors (P fl > > 0.5). EGs yielded estimates of P i for An. gambiae s.s., An. arabiensis and An. coustani, that were approximately equivalent to those with HLC but significantly underestimated P fl for An. gambiae s.s. and An. coustani. The relative sampling sensitivity of EGs declined over the course of the night (p ≤ 0.001) for all mosquito taxa except An. arabiensis.Conclusions: Commercial EGs sample human-seeking mosquitoes with high sensitivity both indoors and outdoors and accurately measure the propensity of Anopheles malaria vectors to bite indoors rather than outdoors. However, further modifications are needed to stabilize sampling sensitivity over a full nocturnal cycle so that they can be used to survey patterns of human exposure to mosquitoes.

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“…The large difference between the two Kenyan studies was explained by the use of bed nets that repelled the mainly zoophilic Anopheles arabiensis to seek alternative hosts outdoors and differences due to the presence/absence of cattle between sites [11,12]. The reason for the even larger differences between the Tanzanian studies [17,18], conducted in the same village just a few years apart, were suggested to be effects of minor, uncontrollable factors, such as location, vector control interventions, season, weather and house type, all of which may vary through space and time.…”

Section: Introductionmentioning

confidence: 99%

Light traps fail to estimate reliable malaria mosquito biting rates on Bioko Island, Equatorial Guinea

Overgaard

Sæbø

Reddy

et al. 2012

Malar J

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Light trap collections in combination with bed nets are not recommended as a reliable method to assess human biting rates on Bioko Island. Different statistical analyses methods give variable and inconsistent results. Substantial variation in collection methods prevents the determination of reliable and operationally feasible conversion factors for both indoor and outdoor data. Until improved mosquito collection methods are developed that can provide reliable and unbiased HBR estimates, HLCs should continue to serve as the reference method for HBR estimation.

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Comparative Evaluation of Methods Used for Sampling Malaria Vectors in the Kilombero Valley, South Eastern Tanzania

Cited by 36 publications

References 24 publications

A low technology emanator treated with the volatile pyrethroid transfluthrin confers long term protection against outdoor biting vectors of lymphatic filariasis, arboviruses and malaria

A low technology emanator treated with the volatile pyrethroid transfluthrin confers long term protection against outdoor biting vectors of lymphatic filariasis, arboviruses and malaria

Advantages and limitations of commercially available electrocuting grids for studying mosquito behaviour

Light traps fail to estimate reliable malaria mosquito biting rates on Bioko Island, Equatorial Guinea

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