Chrysomya putoria, a Putative Vector of Diarrheal Diseases

Abstract

Background Chrysomya spp are common blowflies in Africa, Asia and parts of South America and some species can reproduce in prodigious numbers in pit latrines. Because of their strong association with human feces and their synanthropic nature, we examined whether these flies are likely to be vectors of diarrheal pathogens.Methodology/Principal FindingsFlies were sampled using exit traps placed over the drop holes of latrines in Gambian villages. Odor-baited fly traps were used to determine the relative attractiveness of different breeding and feeding media. The presence of bacteria on flies was confirmed by culture and bacterial DNA identified using PCR. A median of 7.00 flies/latrine/day (IQR = 0.0–25.25) was collected, of which 95% were Chrysomya spp, and of these nearly all were Chrysomya putoria (99%). More flies were collected from traps with feces from young children (median = 3.0, IQR = 1.75–10.75) and dogs (median = 1.50, IQR = 0.0–13.25) than from herbivores (median = 0.0, IQR = 0.0–0.0; goat, horse, cow and calf; p<0.001). Flies were strongly attracted to raw meat (median = 44.5, IQR = 26.25–143.00) compared with fish (median = 0.0, IQR = 0.0–19.75, ns), cooked and uncooked rice, and mangoes (median = 0.0, IQR = 0.0–0.0; p<0.001). Escherichia coli were cultured from the surface of 21% (15/72 agar plates) of Chrysomya spp and 10% of these were enterotoxigenic. Enteroaggregative E. coli were identified by PCR in 2% of homogenized Chrysomya spp, Shigella spp in 1.4% and Salmonella spp in 0.6% of samples.Conclusions/SignificanceThe large numbers of C. putoria that can emerge from pit latrines, the presence of enteric pathogens on flies, and their strong attraction to raw meat and fish suggests these flies may be common vectors of diarrheal diseases in Africa.

Characteristics of Latrines in Central Tanzania and Their Relation to Fly Catches

“… Musca domestica has been found to breed in high numbers in latrines in some studies in the United States [25,26] but not in others [27]. In several studies on African latrines, as in the present study, Musca domestica does not seem to be a primary species collected in exit traps over drop holes [7,8,28,29]. …”

“…Calliphoridae (particularly Chrysomya putoria ) and Culicidae (primarily Culex quinquefasciatus ) have been noted by several studies on African latrine fauna [7,8,19]. Culex quinquefasciatus is an important vector of Wuchereria bancrofti on the east coast of Africa, and an important nuisance biting mosquito throughout the world [20].…”

“…Latrine characteristics (see Table 1), including the village sampled and chemical characteristics of pit latrine contents, were investigated for associations with the outcome variables (total fly count, Calliphoridae count, or number of larvae per gram) by tabulation. The Calliphoridae family (blowflies) was analyzed as an outcome variable because certain members of this family, particularly Chryosmyaputoria , may be of medical importance [8]. The fly counts were analysed for normality using the Shapiro-Wilk test.…”

“…Flies transmit enteric pathogens by landing on, or consuming faecal waste, and then transport this waste on body parts, regurgitate, or defecate on human food and fomites, and so complete the diarrhoea transmission cycle [6]. Despite the widespread availability of latrines and fairly standard contents, not all latrines produce equal numbers of flies [7,8]. Little is known about the reasons for these differences.…”

Public health risks associated with Enteroaggregative Escherichia coli (EAEC) as a food‐borne pathogen

“…The large numbers of Chrysomya putoria that can emerge from pit latrines, the presence of enteric pathogens on flies, and their strong attraction to raw meat and fish suggests these flies may be common vectors of diarrhoeal diseases in Africa (Lindsay et al, 2012).…”