Abstract
The prevalence of infection by the liver fluke, Opisthorchis viverrini (O. viverrini), has remained high in Northeast Thailand where it is a major risk factor for the eventual development of cholangiocarcinoma (CCA). The infection is acquired by the consumption of dishes containing unsafely prepared freshwater fish, a dietary tradition which has proved resistant to change. Since many people are aware that dosing with praziquantel (PZQ) is a successful treatment for an episode of the infection, there is a risk that, to avoid the long term consequences, they will engage in a cycle of infection, dosing and reinfection. There is a dearth of studies of reinfection by O. viverrini, and the aims of this study were to assess re-infection rates in a typical province of Northeastern Thailand where O. viverrini infection is likely and to investigate factors associated with reinfection. A total of infected 607 villagers were treated with PZQ, and those found to be no longer infected were followed up at six-monthly intervals over 12 months. At the end of this period data on 457 subjects were available for analysis using descriptive statistics and logistic regression, and 50 were found to have become reinfected, giving a cumulative reinfection rate of 10.9%. The results of a multiple logistic regression analysis showed that the only factor found to be associated with reinfection was past use of PZQ. Recommendations are made for future larger scale and better designed reinfection studies in the light of limitations of the current study. Further efforts are needed to discourage people from eating fish dishes likely to contain viable metacariae.
Highlights
Infection by the liver fluke, Opisthorchis viverrini (O. viverrini), continues to be a serious public problem in Thailand, especially in the northeast region where according to the most recent data the prevalence in 2009 was 16.6%, a rate which had apparently slightly increased over the previous decade (Sithithaworn et al, 2012)
There is a dearth of studies of reinfection by O. viverrini, and the aims of this study were to assess re-infection rates in a typical province of Northeastern Thailand where O. viverrini infection is likely and to investigate factors associated with reinfection
The 12-month cumulative reinfection rate found in the present study is lower than the corresponding rates reported in the two studies previously conducted in Northeastern Thailand
Summary
Infection by the liver fluke, Opisthorchis viverrini (O. viverrini), continues to be a serious public problem in Thailand, especially in the northeast region where according to the most recent data the prevalence in 2009 was 16.6%, a rate which had apparently slightly increased over the previous decade (Sithithaworn et al, 2012). The primary source of infection by O. viverrini is the tradition of eating dishes, such as koi pla (raw fish salad), which are made with raw, undercooked or improperly fermented freshwater cyprinid fish containing viable metacercariae, an intermediary form of the parasite (Sripa and Pairojkul, 2008; Sripa et al, 2011; Sithithaworn et al, 2012; Prasongwatana et al, 2013) The consumption of these dishes in Northeastern Thailand, throughout the many communities living in the lower Mekong region where freshwater fish are a plentiful source of food, is a well-established cultural practice (Grundy-Warr et al, 2012) which is difficult to break. Further efforts are needed to discourage people from eating fish dishes likely to contain viable metacariae
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