Evaluation of Permethrin Treated Clothing for Personal Protection Against Phlebotomus papatasi (Diptera: Psaychodidae)

MATERIALS AND METHODS

Chemical
The emulsifiable concentrate (EC) of permethrin (10%) (cis/trans isomers with 25/75% ration, respectively) manufactured by Bayer Ltd. (Germany).

Study Sites and Volunteers
This study was conducted in Iran between July and August 2004. Dadin village in Fars province was selected as the test site because of the high density of sand flies population and rarity of leishmaniasis and other vector-borne diseases and being the place of health research institute in this district and availability of human local volunteers.

Eight local male subjects were selected for wearing permethrin-treated and untreated uniforms (five as cases and three as controls). In order to decrease subject caused bias, they wore the uniforms in a revolving manner (subjects in eight nights wore all treated and untreated uniforms).

Subjects were 18-28 years old, age average of 19.5 years. Eight officers were also appointed as supervisors. The subjects were trained about the test time and the needed activities. The supervisors were also trained about the method of data registration in sheets.

Fabric Treatment
The uniforms were treated at 0.125 mg active ingredient cm^-2 of cloth with aqueous suspensions of permethrin from 10% Emulsifiable Concentrate (EC) formulation (cis/trans isomers with 25/75% ration, respectively). The concentrations of treating solutions of permethrin were determined based on the quality and absorption coefficient of uniforms’ textile and also the area of uniforms. Then, treatment was done by dipping method. Sufficient liquid was used to saturate each article of clothing without runoff. Saturated fabrics were placed in plastic bags for 24 h to enhance liquid penetration. The uniforms were then removed from the bags, placed horizontally on aluminum foil and turned periodically to air dry without loss of permethrin from dripping. Before testing, the clothing was labeled and stored in fresh plastic bags (Schreck and Klin, 1989). The control uniforms were treated with water. The uniforms were kept in laboratory condition (temperature: 23-26°C, humidity: 30-40%).

Test Procedure
The subjects were selected among local people of the study village and trained about the test and obtained their consent in writing to be a volunteer in the study. They were asked not to use insect repellent or attractive materials like perfumes, alcohol, smoke, garlic, mint and other odorous materials. Subjects received the uniforms, half an hour before sunset. Five of the selected subjects wore the treated uniforms and three others wore the control untreated uniforms. Subjects sat in appropriate distance of each other (5-10 m). The control subjects sat in the same manner, in 50-100 m distance of case subjects. Field test was started at sun set. One supervisor was considered for each subject. The supervisors entered the night biting data in the record sheets provided. They did the task by direct watching of the biting point. Then they captured the sand flies using aspirators and transferred them into the cups. Meanwhile, subjects changed there place every half an hour to face new mosquitoes and prevent a fatigue or knockdown effect on mosquitoes because of repeated contacts with treated uniforms in the same areas (Schreck and Klin, 1989; EPA, 1999).

Night biting test was started at 19:30 h and ended at 01:00 h every night, when number of bitings decreased. The subjects ate their dinner before starting the test and did not have any activity during the test.

This night biting test was repeated for eight times in consecutive nights.

Statistical Analysis
For statistical analysis data were first transformed by formula (y: number of bitings per min) and then Poisson distribution was used for statistical analysis of biting number in case and control groups. For comparing the means of biting on skin in treated and untreated groups, t-test was used. After statistical analysis, the means were retransformed to original units and converted to mosquito bites per min. Protection percent of treated uniforms was calculated using the following formula:

RESULTS AND DISCUSSION

The mean of air temperature and relative humidity during study was 27.4°C (20-33�C°) and 60.1% (42-75%), respectively. The supervisors recorded all of bitings on subjects besides capturing the sand flies using hand aspirators. All sand flies captured in this study were identified P. papatasi (Scopoli). The mean of biting per person for treated and untreated uniforms was 31.2 h^-1 (31.2±1.82) and 105.0 h^-1 (105±5.65), respectively (Table 1). The mean of biting in untreated uniforms was significantly higher than treated uniforms (p<0.01). Comparison of treated and untreated uniforms showed that the protection percent of treated uniforms against P. papatasi biting was 70.3% (Table 1).

In this study, the percent protection of permethrin- impregnated uniforms against natural population of P. papatasi was observed to be around 70%. In others studies, with the same condition (in rural area), permethrin-treated uniforms provided 83 and 78.7% protection against several species of the Culex mosquitoes and An. stephensi (the main malaria vector in south of Iran), respectively (Khoobdel et al., 2006). In another study permethrin-treated uniforms provided more than 89% protection against Cx. pipines in urban area in Tehran (capital of Iran) (Khoobdel et al., 2005). Also in France soldiers, wearing impregnated uniforms, had more than 90% protection against ticks (Deparis et al., 2001). Present study has showed the protection of permethrin-treated uniforms against Ph. papatasi was less than that of mosquitoes. Other study also demonstrated that sand flies are less sensitive than mosquitoes to knockdown during contact with permethrin treated fabric; however, 24 h mortality rates for sand flies were higher when compared with mosquitoes (Fryauff et al., 1996).

Table 1:	Mean of percent protection of permethrin impregnated closing against P. papatasi

Also studies in African countries showed that using permethrin-impregnated curtains in Burkina Faso lead to complete elimination of endophilic sandfly species (Maroli et al., 1991). The studies in Colombian soldiers showed wearing permethrin-impregnated uniforms decreased incidence of leishmaniasis (Soto et al., 1995). In a study in Iran, wearing permethrin-impregnated uniforms could not significantly reduce of cutaneous leishmaniasis among soldiers in endemic area (Asillian et al., 2002). It is to be noted that decrease in biting does not mean decrease in Leishmaniasis might have occurred just by one or few infected bites (Hepburn, 2003). Therefore, using permethrin-treated uniforms in endemic area may not be alone effective in preventing leishmaniasis (Deparis et al., 2004).

The results of this study has indicated that permethrin-treated uniforms provided considerable protection against sand flies biting, but this protection is not complete (100%). Therefore, for complete protection the impregnated uniforms and repellents should simultaneously be used. It may be noted that in Alaska concurrent use of impregnated uniforms and DEET 35% in skin exposed, had 99% protection against Culiseta impatiens in the place which had the density of 1188 bites for man hour (Lillie et al., 1988).

P. papatasi is widely spread in different geographical regions of Iran. Present study has been accomplished in a restricted rural area, south of Iran. Therefore this survey can be considered as a pilot study. For exact determination of protection percent of permethrin-treated fabrics against P. papatasi, complementary study in other regions of Iran is needed.

Although, the technique of permethrin-impregnated clothes are provided considerably protection against P. papatasi biting, but it may be not acceptably decreased leishmaniasis, especially in endemic and hyper endemic area. Therefore for completed of permethrin-impregnated clothes protection, concurrently using of repellents on exposed skin is suggested.

ACKNOWLEDGMENTS

The authors would like to thank residents of Dadin villages, especially local volunteers; in fact, this study could not be done appropriately, without their kind cooperation. Also we thank the staff of Health Research Center of the Kazeroon.