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A comparative study to evaluate Wonder and Sherman traps for the surveillance of ectoparasitic chigger vector mites of the scrub typhus

 ICMR-Vector Control Research Centre, Field Station, Madurai, Department of Health Research, No.4, Sarojini Street, Chinnachokkikulam, Tamil Nadu, India

Correspondence Address:
Philip Samuel Paulraj,
ICMR-Vector Control Research Centre, Field Station, Madurai, Department of Health Research, No.4, Sarojini Street, Chinnachokkikulam, Madurai-625002, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0972-9062.321752

Introduction: Scrub typhus is caused by Orientia tsutsugamushi and transmitted by larval trombiculid chigger mites. Rodents and shrews are hosts for chigger mites in the transmission to humans. Wonder and Sherman traps are widely used for trapping rodents and shrews for the collection of ectoparasitic chigger mites. A comparative trapping study was undertaken in different villages in Vellore district, Tamil Nadu and Thiruvananthapuram district, Kerala, India to evaluate the efficiency of traps for trapping rodents & shrews. Methods: Wonder and Sherman traps were set in outdoors and indoors to capture the rodents. Wonder Traps, large wired cage, and Sherman Traps are foldable. These traps were employed for the rodents/ shrew surveillance to gather chigger vector mites. Identification of rodents, chigger mites and Trap index were observed. Results: Z Test comparing the capture rates showed wonder trap (P<0.001) to be significantly more efficient than the Sherman traps. The number of rodents /shrews collected in a Sherman trap was always one. But the number of rodents /shrews collected in a positive wonder tap was 2.83 in both states, 2.25 and 1.24 in Tamil Nadu and Kerala, respectively. Wonder traps (77%) were found more attractive in collecting more rodents in Tamil Nadu compared to Sherman traps (23%). But the Sherman trap (60.9%) was found efficient in collecting more shrews in Kerala compared to wonder traps (39.1%). Shrew's collection was more in Sherman collections from both Tamil Nadu and Kerala. In Tamil Nadu and Kerala sex-wise collection of Male & female rodent/shrew was uniformly found in both the wonder (85% &75%) and Sherman traps (86% & 83%) with a maximum proportion of females. Interpretation & conclusion: Sherman traps can be used as single-capture live traps and on the other hand wonder traps can be used as multiple-capture live-traps. The geographical distribution pattern of various rodents trapped can be determined to identify the target areas for control of a particular species and also for the control of selected species. Mostly females were captured abundantly in both wonder and Sherman traps. In wonder traps, female rodents were trapped as family members in large numbers. Wonder traps are more attractive for trapping more rodents. This study addressed the careful choice of wonder traps for ectoparasitic chigger vector surveillance.

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