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Determining of the success of a parasite's infectiveness in its snail host clearly depends on environmental conditions. Temperature, one of the most influential factors impinging on metabolism of cold-blooded animals, is believed to be an important factor in parasitic infection in snails. In order to elucidate the influence of temperature, sex and size of snails on infectivity of Opisthorchis viverrini to its first intermediate host, Bithynia siamensis goniomphalos , 960 snails were divided into 2 groups by sex. Each group was subdivided by their size into small and medium sub-groups. Each snail was fed with embryonated uterine-eggs of O. viverrini at different temperatures (16–37 °C, 3 °C intervals). Dissections were carried out 1, 7, 14, 28 and 56 days thereafter and detection of O. viverrini infection was undertaken by PCR using specific primers. Infection was strongly temperature-dependent, as temperature increases of 1 °C resulted in increased odds of infection 5.4% ( P < 0.01). A temperature of 34 °C gave the highest rate of infection of 44.14%. We also found that the odds of infection in small sized snails was 39.8% higher relative to medium sized snails ( P < 0.05). Relative to day 1, the decrease in the odds of infection was detected when the day post infection was longer ( P < 0.01). Proportion of infection in female was not different to male significantly. [ABSTRACT FROM AUTHOR]

• Praziquantel treatment for opisthorchiasis alleviates parasite burden • 30.8% of participants showed no relapse of hepatobiliary abnormality over five years • 37.5% of participants showed persistent hepatobiliary abnormality Infection of the liver fluke, Opisthorchis viverrini (OV) is an important public health problem in northeast Thailand and adjacent countries, where people have a habit of eating raw or undercooked fish. A community case-control study was carried out with 8,936 participants from 89 villages, in Khon Kaen province, Thailand. There were 3,359 OV-infected participants all of whom underwent ultrasonography of upper abdomen for the evaluation of hepatobiliary morbidity. The participants with advanced periductal fibrosis (APF) by ultrasound (n = 785) were invited to undergo annual follow-up ultrasonography for five years after praziquantel treatment. The sonographer was blinded with respect to status of OV infection at each visit. The study findings revealed variability in the study population profile of the hepatobiliary morbidities before and after praziquantel treatment over the follow up interval. At the end of the study, 32 (30.8%) out of 104 participants showed no relapse of APF whereas, by contrast, 39 (37.5%) participants showed relapse or persistent APF since the outset of the study (≥ two consecutive visits). The APF in most follow-up visits was significantly associated with male sex, with intrahepatic duct stones, with the width of the gallbladder "pre" minus "post" fatty meal, and with the ratio of left lobe of the liver to aorta. Five cases of suspected cholangiocarcinoma were observed over the five years of follow-up. This long-term ultrasound follow-up study demonstrates a significant incidence of persistent APF in over one-third of opisthorchiasis cases after praziquantel treatment, findings that support the prospect of ongoing cholangiocarcinogenesis long after successful elimination of liver fluke infection among the population. [Display omitted] [ABSTRACT FROM AUTHOR]

• Recombinant chimeric form of the large extracellular loop of Ov-TSP-2 and O. viverrini leucine aminopeptidase, designated rOv-TSP-2-LAP, was produced in bacteria. • Hamsters immunized with recombinant rOv-TSP-2-LAP produced humoral and cellular immune responses. • Hamsters vaccinated with rOv-TSP-2-LAP had significantly reduced fluke burdens compared to control animals that received adjuvant alone. Opisthorchiasis is a serious public health problem in East Asia and Europe. The pathology involves hepatobiliary abnormalities such as cholangitis, choledocholithiasis and tissue fibrosis that can develop into cholangiocarcinoma. Prevention of infection is difficult as multiple social and behavioral factors are involved, thus, progress on a prophylactic vaccine against opisthorchiasis is urgently needed. Opisthorchis viverrini tetraspanin-2 (Ov -TSP-2) was previously described as a potential vaccine candidate conferring partial protection against O. viverrini infections in hamsters. In this study, we generated a recombinant chimeric form of the large extracellular loop of Ov -TSP-2 and O. viverrini leucine aminopeptidase, designated r Ov -TSP-2-LAP. Hamsters were vaccinated with 100 and 200 µg of r Ov -TSP-2-LAP formulated with alum-CpG adjuvant via intraperitoneal injection and evaluated the level of protection against O. viverrini infection. Our results demonstrated that the number of worms recovered from hamsters vaccinated with either 100 or 200 µg of r Ov -TSP-2-LAP were significantly reduced by 27% compared to the adjuvant control group. Furthermore, the average length of worms recovered from animals vaccinated with 200 μg of r Ov -TSP-2-LAP was significantly shorter than those from the control adjuvant group. Immunized hamsters showed significantly increased serum levels of anti-r Ov -TSP-2 IgG and IgG1 compared to adjuvant control group, suggesting that r Ov -TSP-2-LAP vaccination induces a mixed Th1/Th2 immune response in hamsters. Therefore, the development of a suitable vaccine against opisthorchiasis requires further work involving new vaccine technologies to improve immunogenicity and protective efficacy. Image, graphical abstract [ABSTRACT FROM AUTHOR]