Detection of enteric parasite DNA in household and bed dust samples: potential for infection transmission

Abstract

Background: Enteric parasites are transmitted in households but few studies have sampled inside households for parasites and none have used sensitive molecular methods.

Methods: We collected bed and living room dust samples from households of children participating in a clinical trial of anthelmintic treatment in rural coastal Ecuador. Dust was examined for presence of DNA specific for 11 enteric parasites (Ascaris lumbricoides, Trichuris trichiura, Ancylostoma duodenale, Necator americanus, Strongyloides stercoralis, Toxocara canis and T. cati, Giardia lamblia, Blastocystis hominis, Cryptosporidium spp., and Entamoeba histolytica) by quantitative PCR (qPCR).

Results: Of the 38 households sampled, 37 had positive dust for at least one parasite and up to 8 parasites were detected in single samples. Positivity was greatest for B. hominis (79% of household samples) indicating a high level of environmental fecal contamination. Dust positivity rates for individual pathogens were: S. stercoralis (52%), A. lumbricoides (39%), G. lamblia (39%), Toxocara spp. (42%), hookworm (18%) and T. trichiura (8%). DNA for Cryptosporidium spp. and E. histolytica was not detected. Bed dust was more frequently positive than floor samples for all parasites detected. Positivity for A. lumbricoides DNA in bed (adjusted OR: 10.0, 95% CI: 2.0-50.1) but not floor dust (adjusted OR: 3.6, 95% CI: 0.3-37.9) was significantly associated with active infections in children.

Conclusions: To our knowledge, this is the first use of qPCR on environmental samples to detect a wide range of enteric pathogen DNA. Our results indicate widespread contamination of households with parasite DNA and raise the possibility that beds, under conditions of overcrowding in a humid tropical setting, may be a source of transmission.

Keywords: Beds; Dust; Ecuador; Enteric parasites; Environment; Floors; Protozoa; Soil-transmitted helminths; Transmission.

Fig. 1

a Percentage of dust samples positive for each parasite from living room floors (grey bars) and mattresses (black bars). b Percentage of dust samples positive for one or more parasites from living room floors (grey) and mattresses (black). Abbreviations: Bh, B. hominis; Ss, S. stercolaris; Al, A. lumbricoides; Gl, G. lamblia; Tcn, T. canis; Ad, A. duodenale; Tt, T. trichiura; Tct, T. cati; Na, N. americanus

Fig. 2

Bar graph showing the percentage of household (all) (a), bed (b), and living room floor (c) dust samples that were positive for A. lumbricoides DNA stratified by A. lumbricoides infection intensity in children’s fecal samples. Sample numbers for each group are shown (n). Intensity groups are those of the WHO (1987) [11]: light, < 5000 eggs per gram (epg); moderate. 5000–50,000 epg; and heavy, > 50,000 epg. Percent positivity for each infection intensity group is shown at the head of each bar