[A shorter version of this article first appeared on SciDev.Net]
Scientists working to reduce dengue among school children in Thailand are testing something new: insecticide-treated school uniforms. A recent model published in PLoS One suggests that this intervention can be economically attractive in the context of Thailand.
Using data from dengue studies in Thailand, the study examines the cost-effectiveness—as defined by WHO guidelines—of insecticide-treated uniforms under various conditions, including hypothetical efficacies and costs. Results show that the cost-effectiveness of insecticide-treated uniforms depends on its ability to reduce dengue infection and the cost per uniform. The model assumes that each student changes a set of uniform each year.
“Going by the 50% effectiveness,” says Yesim Tozan, assistant professor of New York University and lead author of this study—referring to the minimum reduction in dengue infection rates required for a public health intervention to be considered—“the intervention would be cost-effective only if treating each uniform costs $5.30 or less.” More expensive treatments must better reduce dengue infection rates to stay cost-effective.
In 2011, Annelies Wilder-Smith, professor at Lee Kong Chian School of Medicine, Singapore, hypothesized that treating school uniforms with insecticides can reduce dengue infection rates among school children. Wilder-Smith leads research within the global consortium DengueTools (funded by European Union) for innovative strategies to reduce dengue among children. In Thailand, children aged 5-14 make up about 65% of dengue hemorrhagic fever patients. Aedes aegypti, the vector of the dengue virus, bites during the day when most children and adolescents are in schools. Given that most Thai students wear uniforms, applying insecticides to the uniforms may protect the students during that vulnerable period.
“For now, the study is only of hypothetical value for policy makers,” says Olaf Horstick, public health expert at the University of Heidelberg, Germany “because we do not know the effectiveness of impregnating uniforms with insecticides in protecting people from dengue.” Horstick was a colleague of Tozan but was not involved in this study. He notes that “the crucial element of intervention effectiveness is needed.”
That crucial element may soon be available. According to Wilder-Smith who is a co-author of this study, a trial of the insecticide-treated school uniforms in ten schools in Thailand will end in 2015. Meanwhile, laboratory tests at the London School of Hygiene and Tropical Medicine shows that the treated uniforms achieve 80% efficacy against mosquitoes.
Although scientists have just begun to test insecticide-treated school uniforms against dengue, clothes treated with the insecticide permethrin have been used for decades by the military and various outdoor groups to protect their personnel from ticks and mosquito bites. Permethrin is a synthetic chemical widely used to kill and repel insects in agriculture and residences. According to the US Environmental Protection Agency (EPA), permethrin poses low toxicity to mammals but is highly toxic to aquatic fish and invertebrates. Studies show that exposure to permethrin-treated clothes stay well within the safety thresholds set by the US Environmental Protection Agency (EPA).
The approval by EPA may help ease safety concerns of the treated uniforms, but thorough studies are still needed to assess Thai parents’ attitudes towards the uniforms. A 2012 survey of over three hundred Thai parents in one province revealed that most parents (87%) would accept insecticide-treated clothes for their children . “In this specific community, people would be happy to use the clothes,” says Horstick “but the important thing is [for acceptability studies] to be repeated in different communities.”
Another factor determines if insecticide-treated uniforms would be implemented: costs. The 2012 survey shows that two-fifths of parents would not pay extra to get treated uniforms. Furthermore, Tozan estimates that each insecticide-treated uniform would need to cost $1 or less to be considered for Thailand’s universal health benefit package, as the Thai government uses very strict criteria for cost-effectiveness. “An intervention that I find cost-effective in my analysis doesn’t mean it will be implemented by any government,” says Tozan “because there is the question of affordability.”
The treated uniforms will be cheaper if they are mass-produced in Thailand. Wilder-Smith says that the Thai Ministry of Science is keen on producing the treated uniforms locally. Members of the DengueTools consortium, particularly Pattamaporn Kittayapong, professor at Mahidol University in Thailand, are working with the Ministry to develop insecticide-treated uniforms.
Noting that the public has no functioning dengue vaccine (a vaccine that can reduce dengue incidence by half will be released in 2015), Horstick welcomes any ideas that contribute to dengue vector control. Still, Peter Hotez, President of the Sabin Vaccine Institute, says that “until we get a safe and effective vaccine, these [interventions] are ultimately stop-gap measures.”
It seems then that Thai school children would have to wait till 2015, when the effectiveness of the insecticide-treated school uniforms to reduce dengue incidence among students is reported, to know if they will be wearing uniforms that kill mosquitoes.
Tozan Y, Ratanawong P, Louis VR, Kittayapong P, & Wilder-Smith A (2014). Use of insecticide-treated school uniforms for prevention of dengue in schoolchildren: a cost-effectiveness analysis. PloS one, 9 (9) PMID: 25247556
- Wilder-Smith, A., Lover, A., Kittayapong, P., and Burnham, G. (2011). Hypothesis: Impregnated school uniforms reduce the incidence of dengue infections in school children. Medical Hypotheses 76, 861–862.
- Banks, S.D., Murray, N., WILDER-SMITH, A., and Logan, J.G. (2014). Insecticide-treated clothes for the control of vector-borne diseases: a review on effectiveness and safety. Medical and Veterinary Entomology.
- Murray, N., Jansarikij, S., Olanratmanee, P., Maskhao, P., Souares, A., Wilder-Smith, A., Kittayapong, P., and Louis, V.R. (2014). Acceptability of impregnated school uniforms for dengue control in Thailand: a mixed methods approach. Global Health Action 7.