The blow fly, Chrysomya megacephala, and the house fly, Musca domestica, as mechanical vectors of pathogenic bacteria in Northeast Thailand

摘要

The Oriental latrine fly, Chrysomya megacephala (Fabricius) (Diptera: Calliphoridae)and the house fly, Musca domestica L., (Diptera: Muscidae) are synanthropic flies which areadapted to live in close association with human habitations, thereby making them likelymechanical vectors of several pathogens to humans. There were two main aims of this study.The first aim was to determine the prevalence of these two fly species from five types ofhuman habitations including: fresh-food markets, garbage piles, restaurants, school cafeteriasand paddy fields, in the Muang Ubon Ratchathani and Warinchamrap districts of UbonRatchathani province of Northeast Thailand. Flies collection were conducted monthly fromSeptember 2010-October 2011 using a reconstructable funnel trap, containing 1 day-taintedbeef offal as bait. A total of 7 750 flies (6 401 C. megacephala and 1 349 M.domestica) werecollected. The second aim was to examine the potential of these flies to carry pathogenicbacteria. Bacteria were isolated from 994 individual flies collected using a sweep net (555 C.megacephala and 439 M. domestica). A total of 15 bacterial genera were isolated from theexternal surfaces, comprising ten genera of gram-negative bacteria and five gram-positivebacteria. The most common bacteria isolated from both species were coagulase-negativestaphylococci, followed by Streptococcus group D non-enterococci. Human pathogenic entericbacteria isolated were Salmonella sp., Shigella sp., Escherichia coli O157:H7, Salmonellatyphi, Bacillus sp., and Enterococcus sp., of which S. typhi is the first report of isolation fromthese fly species. Other human pathogens included Staphylococcus aureus and Pseudomonasaeruginosa. Not only were the number of C. megacephala positive for bacteria significantlyhigher than for M. domestica, but they were also carrying ~11-12 times greater bacterial loadthan M. domestica. These data suggest that both fly species should be considered potentialmechanical vectors of bacterial pathogens associated with human habitations year-round inthis region of Northeast Thailand.