title: Experimental and modelling investigations of Opisthorchis viverrini miracidia transmission over time and across temperatures: implications for control.
abstract: Transmissibility is a significant factor in parasite fitness. The rate and magnitude of parasite transmission affect prevalence and infection intensity in individual hosts and are influenced by environmental factors. In this context, the objectives of this study were: (i) to experimentally assess Opisthorchis viverrini miracidia survival and infectivity over time and across temperatures; and (ii) to combine these experimental results with environmental data to build a key component of a transmission model, identifying seasonal windows of transmission risk in hyper-endemic northeastern Thailand. Five replicates of 50 O. viverrini eggs were randomly distributed and maintained under four temperature conditions (25°C, 30°C, 35°C, 40°C). Microscopic observations were performed on all experimental units over a period of 3months to record miracidia motility and mortality trends. Six infection trials were also conducted to assess infectivity of miracidia over time and across temperatures, using observations of egg hatching success and infection rates. Upon completion of experiments, data were integrated into a transmission model to create a transmission risk index and to simulate seasonal transmission risk. Miracidia survival rate and motility decreased steadily with 50% mortality observed after 2weeks. Hatching and infection success also decreased significantly after 3weeks. Temperatures over 30°C were associated with increased mortality and decreased infectivity. When incorporating local environmental parameters into our model, we observed low transmission risk during the dry season and increasing transmission risk at the onset of the rainy season, culminating with the highest risk in September. We believe that our results provide the first estimates of O. viverrini miracidia survival and transmission potential under variable temperature conditions and suggest that high temperature treatment (>40°C) of fecal waste could be an efficient control strategy.
authors.affiliation: Global Health Asia, Integrative Education and Research Programme, Faculty of Public Health, Mahidol University, Bangkok, Thailand; WHO Collaborative Center for Research and Control of Opisthorchiasis, Tropical Disease Research Laboratory, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand; Department of Biology, Laurentian University, Sudbury, Ontario P3E 2C6, Canada. Electronic address: pn_echaubard@laurentian.ca.
authors.forename: Pierre
authors.initials: P
authors.lastname: Echaubard
authors.affiliation: WHO Collaborative Center for Research and Control of Opisthorchiasis, Tropical Disease Research Laboratory, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand; School of Public Health, University of California, Berkeley, CA 94720, USA.
authors.forename: Tomas
authors.initials: T
authors.lastname: León
authors.affiliation: Department of Parasitology, Khon Kaen University, Khon Kaen 40002, Thailand.
authors.forename: Kulwadee
authors.initials: K
authors.lastname: Suwanatrai
authors.affiliation: Department of Parasitology, Khon Kaen University, Khon Kaen 40002, Thailand.
authors.forename: Jukkrid
authors.initials: J
authors.lastname: Chaiyos
authors.affiliation: WHO Collaborative Center for Research and Control of Opisthorchiasis, Tropical Disease Research Laboratory, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand.
authors.forename: Christina S
authors.initials: CS
authors.lastname: Kim
authors.affiliation: Department of Biology, Laurentian University, Sudbury, Ontario P3E 2C6, Canada.
authors.forename: Frank F
authors.initials: FF
authors.lastname: Mallory
authors.affiliation: Department of Parasitology, Khon Kaen University, Khon Kaen 40002, Thailand.
authors.forename: Sasithorn
authors.initials: S
authors.lastname: Kaewkes
authors.affiliation: School of Public Health, University of California, Berkeley, CA 94720, USA.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Spear
authors.affiliation: WHO Collaborative Center for Research and Control of Opisthorchiasis, Tropical Disease Research Laboratory, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand; Liver Fluke and Cholangiocarcinoma Research Center, Department of Parasitology, Khon Kaen University, Khon Kaen 40002, Thailand. Electronic address: banchob@kku.ac.th.
authors.forename: Banchob
authors.initials: B
authors.lastname: Sripa
mesh_terms: D000818:Animals; D002980:Climate; D003198:Computer Simulation; D006224:Cricetinae; D005393:Fish Diseases / Q000469:parasitology / Q000517:prevention & control; D005399:Fishes / Q000469:parasitology; D006790:Host-Parasite Interactions; D008297:Male; D008647:Mesocricetus; D008954:Models, Biological; D009889:Opisthorchiasis / Q000453:epidemiology / Q000469:parasitology / Q000635:transmission / Q000662:veterinary*; D009891:Opisthorchis / Q000166:cytology / Q000472:pathogenicity*; D015995:Prevalence; D012621:Seasons; D012908:Snails / Q000469:parasitology*; D013785:Thailand / Q000453:epidemiology
keywords: Bithynia siamensis goniomphalos; Host–parasite; Liver fluke; Temperature-dependent; Thailand; Transmission dynamics