Migratory Pattern of Opisthorchis Viverrini in Hamsters

The migratory pattern of Opisthorchis viverrini was studied by feeding each of 55 hamsters orally with 50 metacercariae collected from cyprinoid fish. The route of migration was followed from the gastrointestinal (GI) to biliary tracts for 3 months after infection at 11 durations: 1, 3, 6, and 12 hours, 1, 3, 7, and 14 days, 1, 2, and 3 months. After sacrifice, the stomach, small intestine, common bile duct, gallbladder, and 3 equal portions of each lobe (right, left, median, and caudal) of the liver were examined and counted for worm burden. The newly excysted worms of O. viverrini migrated from the duodenum into the common bile duct, gallbladder and proximal bile duct of the right lobe as early as 1 hour after infection. The farthest migratory distance, the distal bile ducts of all lobes, occurred with worms aged 14 days. After reaching maturity, the number of worms remaining in the extrahepatic bile ducts was lower than the intrahepatic bile ducts. The worm recovery rates in the right and left lobes were not significantly different, while those in the median and caudal lobes were significantly lower. Less than 5% of juvenile worms could migrate far to the distal part of the bile ducts, but these decreased when the worms became adult. This finding revealed the migratory pattern of O. viverrini in hamsters from the GI to the biliary system in detail, which should be useful for better understanding the host-parasite relationships along these routes of migration. detailed information about the relationship between the route of migration and the duration of infection. The objective of this study was to investigate the migratory pattern of O. viverrini from the gastrointestinal to the biliary tracts of experimentallyinfected hamsters during 3 months of infection. MATERIALS AND METHODS Opisthorchis viverrini metacercariae were obtained from naturally-infected cyprinoid fish from an endemic area in Khon Kaen Province, northeast Thailand, by pepsin-HCl digestion and infiltration. They were identified and collected under a stereomicroscope. Each of 55 male golden Syrian hamsters, aged 6-8 weeks, were infected with 50 metacercariae by intragastric intubation. Five animals were sacrificed at each period of 1, 3, 6 and 12 hours, 1, 3, 7 and 14 days, and 1, 2 and 3 months post-infection. After sacrifice, the position of ampulla of Vater and the terminal part of the common bile duct connecting to the cystic and intrahepatic bile ducts were tied to prevent the movement of worms from the normal position. The stomach, small intestine, common bile duct, gallbladder and 4 lobes (right, left, median, and caudal) of the liver were removed from the host. The cavity structures were opened and sedimented in normal saline, and the number of worms in each part was counted. Each lobe of the liver was divided into 3 portions; proximal, median, and distal, then each was separated into small pieces by 2 forceps, sedimented in normal saline and counted for worm burden per portion. Correspondence : Sasithorn Kaewkes, Department of Parasitology, Khon Kaen University, Khon Kaen 40200, Thailand. INTRODUCTION Opisthorchis viverrini is a human liver fluke endemic in Thailand, Lao PDR, and Cambodia. It has been estimated that 6 million Thai people are infected with this parasite (calculated from overall 9.4% prevalence within the population in the year 2001) (Jongsuksuntigul and Imsomboon, 2003). The infection is associated with hepatobiliary diseases, including cholangitis, obstructive jaundice, hepatomegaly, cholecystitis, cholelithiasis and cholangiocarcinoma (Thamavit et al, 1978; Harinasuta et al, 1984; IARC, 1994; Vatanasapt et al, 1999). These pathologies occur mainly in the liver, extrahepatic bile duct and gallbladder in both infected humans and experimental animals (Bhamarapravati et al, 1978; Harinasuta et al, 1984; Riganti et al, 1989; Sripa and Kaewkes, 2000, 2002). Hosts become infected by ingestion of raw or inadequately cooked cyprinoid fish. After excystation in the duodenum, newly-excysted worms migrate up through the ampulla of Vater and common bile duct into the intrahepatic bile ducts and the gallbladder. Slightly higher numbers of worms were recovered in the right than the left lobes of human livers examined post-mortem, but the difference was not statistically significant (Sithithaworn et al, 1991). However, a few data show a relationship between the site of the host’s organs and worm location, but no