Exceptionally High Prevalence of Infection of Bithynia siamensis goniomphalos with Opisthorchis viverrini Cercariae in Different Wetlands in Thailand and Lao PDR

Abstract

Abstract. The carcinogenic liver fluke, Opisthorchis viverrini, requires Bithynia snail intermediate hosts in its life cycle. However, the prevalence of O. viverrini in snail intermediate hosts is typically low ( 1%). Here, we examined B. siamensis goniomphalos from 48 localities in Thailand and The Lao People's Democratic Republic (Lao PDR) and reported highprevalence levels of O. viverrini. The highest-prevalence levels per locality were 6.93% (mean = 3.04%) in Thailand and 8.37% (mean = 2.01%) in Lao PDR; 4 of 13 localities examined showed prevalence higher than any prevalence previously recorded. The number of cercariae infecting snails and their prevalence were positively correlated with the size of the snails. High prevalence occurred in the Songkram River wetland (Thailand) and the Nam Ngum River wetland (Lao PDR). Our results show that transmission of O. viverrini from humans as well as animal reservoir hosts to snail intermediate hosts is ongoing and potentially increasing in endemic areas across Thailand and Lao PDR.

An ecological study of Bithynia snails, the first intermediate host of Opisthorchis viverrini in northeast Thailand

“…goniomphalos snail length above 8 mm was considered as mature snails. The cercariae shedding procedures in Kiatsopit et al (2012) were followed to determine the O. viverrini infection rate in B.s. goniomphalos snails, and if mature snails were more susceptible to infection.…”

Seasonal Transmission of Opisthorchis viverrini sensu lato and a Lecithodendriid Trematode Species in Bithynia siamensis goniomphalos Snails in Northeast Thailand

“…Trematode infection in B. s. goniomphalos was examined by cercarial shedding, 11 where individual snails were placed in small plastic containers (3 cm in diameter and 2.5 cm high) half filled with dechlorinated water (5 mL) and exposed to a 60 W light for 5 hours. The emerged cercariae were identified by morphology according to the keys published by Schell.…”

“…in Bithynia snails, particularly in B. s. goniomphalos, is typically low, although it is also variable (0.03-8.37% in infected populations), in contrast to the high prevalence found in fish and human hosts. [6][7][8][9][10][11] In addition to O. viverrini s.l., several groups of trematodes can be found concurrently in B. s. goniomphalos. These often have several fold higher prevalences of infection than for O. viverrini s.l.…”

Experimental and modelling investigations of Opisthorchis viverrini miracidia transmission over time and across temperatures: implications for control

“…This low probability of infection success is counteracted by the large numbers of O. viverrini eggs released into the environment by a single infected host. This finding also sheds some light on the extremely low snail prevalence observed, generally ranging between 0.2% and 1.2% in Thailand (reviewed in Petney et al, 2012, but see Kiatsopit et al, 2012). Understanding why snail prevalence is so low, by means of characterizing the encounter and compatibility filters (Combes, 2005) between snails and eggs will be essential for improving our understanding of transmission dynamics, improving current modeling investigations and further informing environmental control strategies.…”

“…Higher average abundances are generally observed between August and December (reviewed in Petney et al, 2012), suggesting the dominant influence of snail abundance in determining the patterns of seasonal transmission risk in our model output. In contrast, a recent study found snail infection prevalence to be highest during the cool dry season (Kiatsopit et al, 2014), although cercariae release can be high throughout the year (Kiatsopit et al, 2012). Human activity in the environment is usually high during the rainy season, as rain-fed rice farming peaks and coincides with increased fecal bacterial contamination and potentially O. viverrini egg presence in natural water reservoirs (Kaewkes et al, 2012).…”