Effectiveness and durability of Interceptor® long-lasting insecticidal nets in a malaria endemic area of central India

Bhatt, Sharma, Uragayala Sreehari, Dash, Kamaraju, Kamaraju Raghavendra

Description

In the present study, Interceptor®, long-lasting polyester net, 75 denier and bursting strength of minimum 250 kPa coated with alpha-cypermethrin @ 200 mg/m 2 was evaluated for its efficacy in reducing the mosquito density, blood feeding inhibition and malaria incidence in a tribal dominated malaria endemic area in Chhattisgarh state, central India. Its durability, washing practices and usage pattern by the community was also assessed up to a period of three years. Methods The study was carried out in two phases. In the first phase (September 2006 to August 2007), 16 malaria endemic villages in district Kanker were randomized into three groups, viz. Interceptor net (LN), untreated polyester net (100 denier) and without net. Malaria cases were detected by undertaking fortnightly surveillance by home visits and treated as per the national drug policy. Mosquito collections were made by hand catch and pyrethrum space spray methods from human dwellings once every month. Slide positivity rate (SPR) and malaria incidence per 1000 population (PI) were compared between the three study arms to assess the impact of use of Interceptor nets. Simultaneously, wash resistance studies were carried out in the laboratory by doing cone bioassays on Interceptor LNs washed up to 20 times. Activities undertaken in second Phase (April 2008 to October 2009) after an interval of about 18 months post-net distribution included questionnaire based surveys at every six months, i.e. 18, 24, 30 and 36 months to observe durability, usage pattern of LNs and washing practices by the community. After 36 months of field use, 30 nets were retrieved and sampled destructively for chemical analysis. Results Interceptor nets were found effective in reducing the density, parity rate and blood feeding success rate of main malaria vector Anopheles culicifacies as compared to that in untreated net and no net villages. SPR in LN villages was 3.7% as compared to 6.5% in untreated and 11% in no net villages. PI in LN villages was 16.4 in comparison to 24.8 and 44.2 in untreated polyester net and no net villages respectively. In surveys carried out after three years of initial distribution, 78.7% (737/936) nets were still in possession with the households, of which 68% were used every night. An. culicifacies mortality was >80% in cone bioassays done on LNs washed up to 20 times in laboratory. Mean alpha-cypermethrin content was 43.5 ± 31.7 mg/m 2 on Interceptor LNs withdrawn after three years of household use against the baseline specification of 200 mg/m 2 . A gradual increase in the proportion of holed nets was observed with the increased period of usage. Conclusion Interceptor nets were highly effective in reducing vector densities as well as malaria incidence in the study villages. Availability of 78% nets with .

Sujets

• Anopheles culicifacies
• Bioassay
• Density
• Malaria
• Mosquitoes

Informations

• Publié par: biomed
• Publié le: 01 janvier 2012
• Nombre de lectures: 6
• Langue: English

Extrait

Bhatt et al. Malaria Journal 2012, 11:189
http://www.malariajournal.com/content/11/1/189
RESEARCH Open Access
WEffectiveness and durability of Interceptor
long-lasting insecticidal nets in a malaria endemic
area of central India
1 1 2 3 2*Rajendra M Bhatt , Shri N Sharma , Sreehari Uragayala , Aditya P Dash and Raghavendra Kamaraju
Abstract
WBackground: In the present study, Interceptor , long-lasting polyester net, 75 denier and bursting strength of
2minimum 250 kPa coated with alpha-cypermethrin @ 200 mg/m was evaluated for its efficacy in reducing the
mosquito density, blood feeding inhibition and malaria incidence in a tribal dominated malaria endemic area in
Chhattisgarh state, central India. Its durability, washing practices and usage pattern by the community was also
assessed up to a period of three years.
Methods: The study was carried out in two phases. In the first phase (September 2006 to August 2007), 16 malaria
endemic villages in district Kanker were randomized into three groups, viz. Interceptor net (LN), untreated polyester
net (100 denier) and without net. Malaria cases were detected by undertaking fortnightly surveillance by home
visits and treated as per the national drug policy. Mosquito collections were made by hand catch and pyrethrum
space spray methods from human dwellings once every month. Slide positivity rate (SPR) and malaria incidence per
1000 population (PI) were compared between the three study arms to assess the impact of use of Interceptor nets.
Simultaneously, wash resistance studies were carried out in the laboratory by doing cone bioassays on
LNs washed up to 20 times. Activities undertaken in second Phase (April 2008 to October 2009) after an interval of
about 18 months post-net distribution included questionnaire based surveys at every six months, i.e. 18, 24, 30 and
36 months to observe durability, usage pattern of LNs and washing practices by the community. After 36 months
of field use, 30 nets were retrieved and sampled destructively for chemical analysis.
Results: Interceptor nets were found effective in reducing the density, parity rate and blood feeding success rate of
main malaria vector Anopheles culicifacies as compared to that in untreated net and no net villages. SPR in LN
villages was 3.7% as compared to 6.5% in untreated and 11% in no net villages. PI in LN villages was 16.4 in
comparison to 24.8 and 44.2 in untreated polyester net and no net villages respectively. In surveys carried out after
three years of initial distribution, 78.7% (737/936) nets were still in possession with the households, of which 68%
were used every night. An. culicifacies mortality was>80% in cone bioassays done on LNs washed up to 20 times
2in laboratory. Mean alpha-cypermethrin content was 43.5±31.7 mg/m on Interceptor LNs withdrawn after three
2years of household use against the baseline specification of 200 . A gradual increase in the proportion of
holed nets was observed with the increased period of usage.
Conclusion: Interceptor nets were highly effective in reducing vector densities as well as malaria incidence in the
study villages. Availability of 78% nets with the households in usable condition clearly indicated durability of
Interceptor LNs up to three years in the rural setting of India. The nets were found to contain an effective
concentration of alpha-cypermethrin against malaria vector after three years of household use.
Keywords: Anopheles culicifacies, Bioassay, Density, Interceptor nets, Malaria, Mosquitoes
* Correspondence: [e-mail]
2
National Institute of Malaria Research, Sector 8, Dwarka New Delhi-110 077,
India
Full list of author information is available at the end of the article
© 2012 Bhatt et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.Bhatt et al. Malaria Journal 2012, 11:189 Page 2 of 8
http://www.malariajournal.com/content/11/1/189
Background made interim recommendations for use of Interceptor
Long-lasting insecticidal nets (LNs) are being widely pro- nets for prevention and control of malaria based on a
moted for malaria vector control in malaria endemic Phase II study, and requires large-scale field studies for
countries [1]. The use of LNs is an effective intervention making full recommendations for the use of these nets
method with an efficacy lasting about three to five years. in the national malaria control programme.
The World Health Organization has given full recommen- Chhattisgarh state in India is endemic for malaria. The
W W W
dation to Olyset ,PermaNet 2.0 and Yorkool LNs, hilly forested and tribal dominated districts, 5 in the
while interim recommendation has been given to Inter- north and 3 in the south including Kanker, contribute
W
ceptor and severalother LN brands [2]. >90% of the reported malaria cases. In 2010, the state
W
The Interceptor LN is manufactured by M/s. Sunshine ranked third by reporting about 10% of the total malaria
World Net 2003 Co. Ltd. Ratchaburi, Thailand, under the cases and 14% of Plasmodium falciparum cases in the
license of M/s. BASF Agro B.V. Arnhem (NL) Wädenswil country [11]. Anopheles culicifacies is the main malaria
Branch, BP 69, CH-8820 Wädenswil, Switzerland and dis- vector. Malaria continues to be a major health problem
tributed by BASF. The specifications of Interceptor nets especially in difficult to reach areas. In view of this, an
used in the present study were 100% polyester, multifila- evaluation of Interceptor LNs was undertaken in district
ment yarn: 75 denier with a minimum 250 kPa bursting Kanker to assess the impact on vector density, malaria
2 2
strength, mesh: 24 holes/cm ; density: 30±2 g/m ; active incidence, bio-efficacy and durability over a three-year
2
ingredient: 200 mg/m alpha-cypermethrin coated on period. While plenty of scientific evidence shows effect-
polyester fibers.Thenetsusedmeasured 180cm inlength, iveness of treated nets, little is known about durability of
160 cm width and 150 cm height, and had a total surface various brands of long-lasting insecticidal nets under op-
area of 13.92 m². WHOPES supervised laboratory and erational conditions of use and therefore this element of
field trials have demonstrated wash resistance and efficacy the study makes it important and highly relevant to the
of Interceptor nets [3]. Field trials carried out with alpha- national malaria control programme.
cypermethrin treated bed nets have shown promising
results in terms of efficacy against mosquito vectors and Methods
malaria incidence in India [4,5]. Study area
Various field trials have shown further evidence that The study was undertaken during September 2006 to
Interceptor nets are effective against malaria vectors in August 2007 in 16 villages of district Kanker in Chhattis-
different countries or settings [6-10]. WHOPES has garh state central India (Figure 1). Durability surveys
Figure 1 The map showing the location of study villages.Bhatt et al. Malaria Journal 2012, 11:189 Page 3 of 8
http://www.malariajournal.com/content/11/1/189
were carried out after 18, 24, 30 and 36 months of net consideration, 16 villages with varying degree of endem-
distribution (April 2008 to October 2009). District Kan- icity were identified for the study. Baseline data on mal-
ker (pop. 763,549) is one of the malaria endemic districts aria incidence and mosquito density were generated for
2
in the state. It has an area of 5,285 km lying between three months from September to November 2006 from
latitudes 19°09’ and 20°06’ North and longitudes 80°30’ all villages before randomizing them into three arms, viz.
to 81°15’ East. About 60% of the area is hilly and Interceptor net (LN), untreated polyester net (UN) and
forested. The district has a tropical climate with an aver- no net. A population census was carried out in every vil-
age annual rainfall of 1,100 mm received between June lage during the pre-intervention period and all the
and October in 60–70 rainy days. The villages are scat- houses in the selected villages identified for net distribu-
tered and mostly inhabited by tribals belonging to Gond tion were numbered. The census also revealed that
tribe of marginal socio-economic status. The houses are about 1.13 nets/house were owned by the community.
brick built with tiled or thatched roof and mud plastered Interceptor nets, rectangular netting consisting of 75
walls and flooring. There are about 4–5 bedrooms in- denier multifilament, 100% polyester, with minimum
2
cluding 1–2 separate rooms for cattle and fodder within 250 kPa bursting strength, mesh: 24 holes/cm ; density:
2 2
the compound. Mud plastering is done generally for 30±2 g/m ; active ingredient: 200 mg/m alpha-
about six times in a year or more due to festivals and cypermethrin coated on polyester fibers, warp knitting
family occasions or celebrations. People generally sleep and untreated polyester nets (100% polyester, multifila-
in rooms during all seasons and quite often the elder ment yarn: 100 denier strength with a minimum
2
members sleep in verandah within the compound. Sub- 405 kPa bursting strength, mesh: 24 holes/cm ; density:
2
sistence agriculture is the main occupati