Evaluation for the larval and pupal growth conditions for Chrysomya bezziana under clinical microbiology laboratory setting in Hong Kong

River C.W. Wong, D.C. Lung, K.M. Chan and T.L. Que

Department of Clinical Pathology, Tuen Mun Hospital, Hospital Authority, Hong Kong Special Administrative Region, China.

The Old World screwworm fly (OWS), Chrysomya bezziana (Diptera: Calliphoridae) is an obligatory parasite that serves as the major causative agent for traumatic human myiasis in the tropics and sub-tropics of the Old World. This study was conducted to evaluate the larval and pupal growth conditions for OWS from Hong Kong under a typical clinical microbiology laboratory setting without application of extra resources. Thirty-two live larvae were collected from a single patient who suffered from OWS myiasis. The larvae and subsequent pupae were allowed to develop under controlled laboratory conditions at temperatures of 25⁰C, 30⁰C & 37⁰C with a food supply of horse blood agar block or cooked meat medium. This study evaluated for the first time growth conditions for larvae and pupae of a Hong Kong strain of OWS and demonstrated that it is possible to rear larvae through to adult flies by using simple equipments available in a microbiology laboratory. It is possibly best to use 30⁰C because least mortality rate for larvae was found at that temperature (10% over all foods, 1 out of 10 larvae) compared to 25⁰C (20% over all foods, 2 out of 10 larvae) and 37⁰C (42% over all foods, 5 out of 12 larvae) and both horse blood agar block and cooked meat medium could be applied for the feeding of larvae. Pupae were developed into adulthood earlier at 30⁰C than 25⁰C and the average time duration for pupae completed development was 6.6 days at 30⁰C compared to 9.4 days at 25⁰C. The findings provide useful information for the rearing of OWS removed from wounds, from larvae to adulthood under laboratory conditions. They facilitate the study of OWS biology and enhance the ability to accurately identify OWS as a causative agent of human myiasis, because identification can be based on larvae as well as adults.

Keywords: Old World screwworm, Chrysomya bezziana, larvae, pupae, human myiasis, temperature, Hong Kong.

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