Acta Trop. 2010 Sep;115(3):248-56.
An exploratory survey of malaria prevalence and people’s knowledge, attitudes and practices of mosquito larval source management for malaria control in western Kenya.
Imbahale SS, Fillinger U, Githeko A, Mukabana WR, Takken W.
Wageningen University and Research Centre, EH Wageningen, The Netherlands. email@example.com
A large proportion of mosquito larval habitats in urban and rural communities in sub-Saharan Africa are man-made. Therefore, community-based larval source management (LSM) could make a significant contribution to malaria control in an integrated vector management approach. Here we implemented an exploratory study
to assess malaria prevalence and people’s knowledge, attitudes and practices on malaria transmission, its control and the importance of man-made aquatic habitats for the development of disease vectors in one peri-urban lowland and two rural highland communities in western Kenya.
We implemented monthly cross-sectional malaria surveys and administered a semi-structured questionnaire in 90 households, i.e. 30 households in each locality. Malaria prevalence was moderate (3.2-6.5%) in all sites. Nevertheless, residents perceived malaria as their major health risk. Thirty-two percent (29/90) of all respondents did not know that mosquitoes are responsible for the transmission of malaria. Over two-thirds
(69/90) of the respondents said that mosquito breeding site could be found close to their homes but correct knowledge of habitat characteristics was poor. Over one-third (26/67) believed that immature mosquitoes develop in vegetation. Man-made pools, drainage channels and burrow pits were rarely mentioned. After
explaining where mosquito larvae develop, 56% (50/90) felt that these sites were important for their livelihood.
Peri-urban residents knew more about mosquitoes’ role in malaria transmission, could more frequently describe the larval stages and their breeding habitats, and were more likely to use bed nets even though malaria prevalence was only half of what was found in the rural highland sites (p<0.05). This was independent of their education level or socio-economic status. Hence rural communities are more vulnerable to malaria infection, thus calling for additional methods to complement personal protection measures for vector
control. Larval source management was the most frequently mentioned (30%) tool for malaria control but was only practiced by 2 out of 90 respondents.
Targeting the larval stages of malaria vectors is an underutilized malaria prevention measure. Sustainable elimination or rendering of such habitats unsuitable for larval development needs horizontally organized, community-based programs that take people's needs into account. Innovative, community-based training programs need to be developed to increase people's awareness of man-made vector breeding sites and acceptable control methods need to be designed in collaboration with the communities.
Scientists have developed an improved method for controlling container-inhabiting mosquitoes responsible for the transmission of chikungunya and dengue viruses.
New pellet formulations of a chemical that kills mosquito larvae and pupae — Agnique — were used for the first time in combination with another insecticide — Altosid — in laboratory and field tests. Combined, the two insecticides had a longer-lasting effect than using either one alone.
They were used in a spray to coat water-filled containers where mosquitoes deposit their eggs.
In the laboratory, this provided 80 per cent mosquito control for 60 days, and 95 per cent control for at least 32 days in the field trials, according to the study published in this month’s (May) issue of The American Journal of Tropical Medicine and Hygiene.
The spray’s dual action interfered with mosquitoes’ development as well as the surface tension of the water — preventing larvae and pupae from remaining on the surface to breathe.
Altosid also remained effective after 107 days of a drought simulated in the laboratory, suggesting that it could prevent mosquitoes breeding even when dried-out water containers are refilled after periods of drought.
Co-author of the study Banugopan Kesavaraju, entomologist at US-based Salt Lake City Mosquito Abatement District, told SciDev.Net that “the container mosquitoes like Asian tiger mosquitoes, Aedes albopictus, colonise containers that can hold small quantities of water such as trash cans, cemetery vases and toys, which are more common in urban and suburban areas”.
He said that this makes the use of pesticides difficult in urban areas. Since the combined spray targets all mosquito life stages in the containers, this would permit better long-term mosquito control, he added.
Nuananong Jirakanjanakit, biomedical researcher at Mahidol University, Thailand, said this new method could be a realistic way of tackling mosquitoes and capping the transmission of diseases such as chikungunya and dengue fever.
Chikungunya virus is spread by mosquitoes found in standing water in urban areas. It re-emerged on several islands in the Indian Ocean in 2005, caused an outbreak in India in 2006–07, and was reported in Europe in 2007.
Dengue is now the most rapidly spreading mosquito-borne viral disease in the world (see also Dengue fever surges in Americas). In the absence of an effective drug or vaccine, vector control is the only way to reduce disease transmission.
Theeraphap Chareonviriyaphap, entomologist at Thailand-based Kasetsart University, welcomed the new development as “a major breakthrough in the battle against dengue and chikungunya viruses”. He told Scidev.Net that this is “a very simple combination but with a powerful effect on the ground leading to the killing of most vectors hidden in the containers”.
But Michael Turell, medical entomologist at USArmy Medical Research Institute of Infectious Diseases told SciDev.Net that educating people about how discarded trash provides breeding ground for disease-carrying mosquitoes could be as important as improving insecticides. “If these [trash cans] were turned upside down so that they would not hold water, I think it would have an even greater effect than a more efficient formulation of insecticides.”
Achieving high coverage of larval-stage mosquito surveillance: challenges for a community-based mosquito control programme in urban Dar es Salaam, Tanzania
Source: BioMed Central, 30 Dec 2009
Background – Preventing malaria by controlling mosquitoes in their larval stages requires regular sensitive monitoring of vector populations and intervention coverage. The study assessed the effectiveness of operational, community-based larval habitat surveillance systems within the Urban Malaria Control Programme (UMCP) in urban Dar es Salaam, Tanzania.
Methods – Cross-sectional surveys were carried out to assess the ability of community-owned resource persons (CORPs) to detect mosquito breeding sites and larvae in areas with and without larviciding. Potential environmental and programmatic determinants of habitat detection coverage and detection sensitivity of mosquito larvae were recorded during guided walks with 64 different CORPs to assess the accuracy of data each had collected the previous day.
Results – CORPs reported the presence of 66.2% of all aquatic habitats (1,963/2,965), but only detected Anopheles larvae in 12.6% (29/230) of habitats that contained them. Detection sensitivity was particularly low for late-stage Anopheles (2.7%, 3/111), the most direct programmatic indicator of malaria vector productivity. Whether a CORP found a wet habitat or not was associated with his/her unfamiliarity with the area (Odds Ratio (OR) [95% confidence interval (CI)] = 0.16 [0.130, 0.203], P<0.001), the habitat type (P<0.001) or a fence around the compound (OR [95%CI] = 0.50 [0.386, 0.646], P<0.001). The majority of mosquito larvae (Anophelines 57.8 % (133/230) and Culicines 55.9% (461/825) were not reported because their habitats were not found. The only factor affecting detection of Anopheline larvae in habitats that were reported by CORPs was larviciding, which reduced sensitivity (OR [95%CI] = 0.37 [0.142, 0.965], P=0.042).
Conclusions – Accessibility of habitats in urban settings presents a major challenge because the majority of compounds are fenced for security reasons. Furthermore, CORPs under-reported larvae especially where larvicides were applied. This UMCP system for larval surveillance in cities must be urgently revised to improve access to enclosed compounds and the sensitivity with which habitats are searched for larvae.