Control approaches for Opisthorchis viverrini and co-infections in Lao PDR

Background: In Lao People’s Democratic Republic (Lao PDR) helminth infections are highly prevalent. All groups of helminths, including nematodes, trematode and cestodes can be found throughout the country. Besides high rates and intensity of infections, most individuals are infected with several different species of intestinal parasitic infections. As in many other countries, a main underlying factor for high worm infestations is the scarce economic resources which lead to a lack of appropriate sanitary facilities, and hygiene related education and adequate behaviour. Therefore, the parasite infection is common among the rural population. However in Laos, there is an additional, particular risk factor responsible for the populations, high worm-load; namely the consumption of raw or insufficiently cooked foodstuff such as raw meat, fish and vegetables. This habit is deeply culturally rooted, and widespread in the Lao population. In this PhD thesis, we tested and determined the appropriate control approaches for Opisthorchis viverrini (O. viverrini) and other important helminth infections such as Strongyloides stercoralis (S. stercoralis) and Schistosoma mekongi (S. mekongi). The tested approaches compose of latrine promotion programme, eco-health intervention study and novel urine test for S. mekongi diagnosis in Khong District, Champasack Province, Lao PDR.
Goal and specific objectives: The present PhD study aimed to develop the appropriate control approaches for O. viverrini infection and co-infections in Lao PDR. Four specific objectives were pursued: i). To assess S. stercoralis infection and the risk of infection among the populations on three islands in Khong district, Champasack province, Southern Laos; ii). To define O. viverrini, S. mekongi and STH infections in humans in the ecological environment of Khong district, Champasack province where their potential animal reservoir, and intermediate hosts are living in close connectivity; iii).To compare the diagnostic tools for detection of S. mekongi infection in Lao People’s Democratic Republic and neighbouring country Cambodia; and iv). To assess the impact of improved sanitation and its use on the transmission of intestinal helminth infections in highly endemic areas, three islands in Khong district, Champasack province, Southern Laos.
Methodology: Both cross-sectional and cohort studies were used in this PhD thesis’s research. All data of this PhD thesis were obtained from community-based studies.
First study of this PhD research was latrine intervention which was called as latrine study, conducted in March 2011 to January 2013 on three islands, i.e. Donlong, Donthan and Donlieng island located in the Mekong River in Khong district, Champasack province, southern Laos. Given an experimental pre-test and post-test with one control group was used to assess the effects of latrine in the study villages on preventing of helminth infections particularly O. viverrini and S. mekongi. Household-based promoting latrine construction was conducted. Two stool samples were collected per study participants within a five day period. Each sample was examined by using Kato-Katz (KK) thick smears and Baermann technique. There were three different phases of the study which described elsewhere in material and methods section of Chapter 7.
A baseline study of ecohealth intervention for O. viverrini, S. mekongi and STH was conducted in October 2011 and August 2012 on Done Khon and Done Som islands. Household members aged two years and older and potential animal reservoir hosts, i.e., dogs, cats, pigs and buffaloes, from selected households were enrolled and examined for helminth infections. For O. viverrini, snails of the genus Bithynia spp. were collected with a scoop from water bodies near the study villages (e.g., ponds, canals, and rice fields). Cyprinoid freshwater fish were captured from the same selected water bodies as well as from the Mekong using fishing net. For S. mekongi, N. aperta snails were hand-picked from the rocky area of the Mekong River. Two KK thick smears, formalin ether concentration technique (FECT), the shedding test and the pepsin enzyme digestion technique were performed for human, animal reservoir hosts, Bithynia spp. and N. aperta snail hosts and Cyprinoid fish, respectively to assess their infections.
The evaluation of the new diagnostic techniques for S. mekongi was conducted between February and April 2016 in S. mekongi-endemic villages in Lao PDR and Cambodia. Urine and serum samples were obtained from each study participant to be tested for Schistosoma infection by POC-CCA, UCP-LF CAA and ELISA assays. We collected three stool samples from each participant during five consecutive days. Stool samples were subjected to examination by duplicate KK thick smears examined under a light microscope.
Principle findings/results: Our first report was from the first phase of latrine study which emphasized on epidemiology of S. stercoralis infection on Mekong islands, showed 41.0% overall prevalence rate. The infection rate did not differ between the islands (Donlong 44.1% vs. Donthan/Donlieng 38.2%, p=0.107). The highest infection rate was observed with O. viverrini (72.2%), followed by hookworm (56.1%) and S. mekongi (12.8%). Trichuris trichiura (3.3%), Ascaris lumbricoides (0.3%) and Taenia spp. (0.3%). The most important risk factor was sex. Male study participants had a significantly higher risk for a S. stercoralis infection than female participants taking into account the age of the study participants (adjusted OR 1.97, 95% CI 1.45–2.67).
The baseline result of our ecohealth intervention revealed that human infection rates with O. viverrini, hookworm, S. mekongi, T. trichiura, A. lumbricoides and Taenia spp. were 60.7%, 44.1%, 22.2%, 4.1%, 0.6% and 0.1%, respectively. Heavy intensity infections were 4.2%, 3.6% and 1.8% for O. viverrini, S. mekongi and hookworm, respectively. . O. viverrini infection rate among dogs and cats were 25.0% and 53.1%, respectively. S. mekongi infection rates among dogs were 14.7%.. Prevalence of O. viverrini and S. mekongi in snails was 0.3% and 0.01%, respectively. Overall prevalence of O. viverrini infection in fresh water fish was 26.9%, with the highest infection rates occurring in Hampala dispa (87.1%), Cyclocheilichthys apogon (85.7%) and Puntius brevis (40.0%). Illiteracy and lower socioeconomic status increased the risk of O. viverrini infection, while those aged 10–16 years and possessing latrines at home were less likely to be infected. Household dogs and cats that consumed raw fish were significantly and positively associated with O. viverrini infection of the household members. For S. mekongi, children under 9 years old were exposed significantly to this infection, compared to older age groups.
Study on comparison of novel and standard diagnostic tools for the detection of S. mekongi infection in Lao PDR and Cambodia which was carried out between February and April 2016. Stool microscopy by KK thick smear revealed an overall prevalence of S. mekongi of 6.4% (one case in Cambodia and 23 cases in Lao PDR), while that of O. viverrini, hookworm, T. trichiura, A. lumbricoides and Taenia spp. were 50.4%, 28.1%, 3.5%, 0.3% and 1.9%, respectively. In total, 377 urine and serum samples were tested for S. mekongi infection. In the urine samples, the tests for CCA and CAA detected S. mekongi infections in 21.0% and 38.7% of the study participants, respectively. In the serum samples, the CAA assay revealed a prevalence of 32.4%, while a combination of the CAA assay in serum and in urine revealed a prevalence of 43.2%. There was a difference between the two study locations with a higher prevalence reached in the samples from Lao PDR.
Study on assessment the effects of latrine in the study villages on preventing of helminth infections particularly O. viverrini and S. mekongi which was performed by using an experimental pre-test and post-test with one control group. In the intervention villages, the helminth infection rates at baseline for S. mekongi, O. viverrini, hookworm, A. lumbricoides, T. trichiura, Enterobius vermicularis, S. stercoralis and Taenia spp. were 28.6%, 79.5%, 48.8%, 0.3%, 3.5%, 0%, 43.1% and 0%, respectively. At follow-up they were reduced to 22.6%, 68.2%, 26.2%, 2.5%, 1.1%, 0.4%, 31.1% and 0.4%, respectively. Reduction in prevalence of four important helminthiasis were significantly observed (baseline vs follow-up, P-value), S. mekongi (28.6% vs 22.6%, P-value <0.001), O. viverrini (79.5% vs 68.2%, P-value <0.001), Hookworm (48.8% vs 26.2%, P-value <0.001) and S. stercoralis (43.1% vs 31.1%, P-value <0.001) in the intervention villages. While S. mekongi infection in the control villages was increased (1.8% vs 2.6%, P-value =0.74) and other helminths were decreased O. viverrini (71.8% vs 59.9%, P-value =0.027), Hookworm (65.6% vs 38.3%, P-value <0.001) and S. stercoralis (38.3% vs 34.8%, P-value =0.001).
Conclusion/Significance: O. viverrini, S. mekongi, and STH particularly S. stercoralis were still high prevalence in Mekong islands as well as the multiparasitism was observed in all studies of this PhD thesis works. There is a pressing need to design and implement an integrated helminth control intervention on the Mekong Islands in southern Lao PDR. An appropriate integrated control approach involving interventions targeting human behaviour, animal reservoirs, and environmental modification, health education and improved access to clean water and adequate sanitation might improve the effectiveness of interventions and lead to the elimination of infections. Furthermore, the new diagnostic tool CCA, CAA and ELISA were evaluated and showed a substantially higher prevalence estimates for S. mekongi compared to Kato-Katz thick smears. Active schistosomiasis mekongi in Lao PDR and Cambodia might thus have been considerably underestimated previously. Hence, sustained control efforts are still needed to break transmission of S. mekongi. The pivotal role of highly sensitive diagnostic assays in areas targeting elimination cannot be overemphasised.