Epidemiology and morbidity of food-borne trematodiasis in Lao People's Democratic Republic with particular consideration to opisthorchiasis

Food-borne trematodes, parasitizing the liver, lung and intestinal tract of
humans, are an emerging public health problem in countries of tropical regions. Today,
an estimated 40 million people are infected worldwide. More than half of those occur
in Asia, particularly in Southeast Asian countries. Infection with food-borne trematode
is associated with divers and severe morbidity, i.e. a long-lasting infection with
Opisthorchis viverrini gives rise to liver fibrosis, cholecystitis and cholangitis and may
induce a malignant cholangiocarcinoma (CCA).
In Lao People’s Democratic Republic (Lao PDR), particularly in the rural
settings the habit of consumption of undercooked or insufficiently cooked food is
frequent and deeply culturally rooted. In addition access to clean water is low and
adequate sanitary facilities are virtually absent, which reflects a socio-economically
disadvantaged situation. These areas are at high risk for the transmission of food-borne
trematodiasis (FBT) and intestinal helminhiasis. The prevalence of these parasites has
an extensive geographical overlap; thus leading in a single person to an infection with
several different species of parasites. The concurrent infection of multiple species, in
turn, might aggravate the morbidity of the host. Five specific objectives were pursued in this Ph.D. thesis: (i) to investigate
the epidemiology of O. viverrini and assess the extent of co-infection with other intestinal
parasites in a highly endemic setting, (ii) to describe the diversity of FBT with intestinal
and hepato-biliar tropism in different eco-epidemiological settings and assess their
contribution to the overall morbidity, (iii) to assess the relationship between socioeconomic
status and food-borne trematode infection, in particular O. viverrini in the
distinct eco-epidemiological settings, and (iv) to assess the concomitant infections of
intestinal parasites in the distinct eco-epidemiological settings and their inter-linking to
the environmental, socio-economic and behavioural risk factors. The data presented in this Ph.D. thesis was obtained from a
series of epidemiological studies. The data pertaining to the epidemiology of O. viverrini
and other intestinal parasites were first obtained from a cross-sectional study carried out
in February and March 2004 in the Saravane district, province of Saravane. Eligible
persons were randomly selected from the district in two steps, i.e. study villages and
households, based on the village register and household register available at the district
health office (DHO) and at village. Two questionnaires were administrated to collect the
data at the individual level (demographic, behavioural and personal hygienic data) and at
the household level (food preparing method with fish, characteristics of household head).
One single stool sample was obtained from each study participant and analysed by using
Kato-Katz technique (KK-technique). Fish species from different local rivers were
collected and examined for the infection with metacercariae. A second cross-sectional study was carried out in March and May 2006 in three
distinct eco-epidemiological settings in Champasack province, i.e. islands in Mekong
River (Khong district), plain area bordering Mekong River (Mounlapamok district) and
highlands (Paksong district). A pre-tested individual questionnaire was used. All enrolled
household members were interviewed for demographic data (e.g. age, sex, educational
attainment and professional activity) and behavioural risks (e.g. food consumption habits
and personal hygiene), whereas a household questionnaire was administered to the heads
of household to collect the socio-economic characteristics (e.g. building type and water
supply), asset ownership (e.g. farm engine and bicycle) and ownership of animals (e.g.
buffalo cow and pig). From each participant three stool samples were collected on
consecutive days. Stool analysis was performed with KK-technique on each sample and
supplemented with formalin-ethyl-acetate concentration technique (FECT) on one of the
samples. The geographical coordinates of each household were registered, using a handheld
global positioning system receiver (Garmin Ltd., Olathe, USA).
The data on morbidity induced by O. viverrini infection and multiparasitism,
especially morbidity related to a single infection with O. viverrini versus species and
double infection with O. viverrini and S. mekongi were obtained from an in-depth
hospital- and community-based study carried out in the year of 2005 and 2006 in the two
referral hospitals (Mahosot and Savannakhet provincial hospital) and communities of three provinces in central and southern Lao PDR (Savannakhet, Saravane and
Champasack). A purgative was added after praziquantel treatment (single oral dose: 40
mg/kg). All diarrhoeal stools produced were collected and repeatedly washed until the
supernatant became clear. The sediment was examined for the presence of adult worms as
follows. First, adult Taenia spp., Echinostoma spp., and O. viverrini worms were visually
searched. Second, the remaining sediment was examined with a stereo-microscope for the
presence of minute intestinal flukes (MIF). The number of each species of parasites was
recorded. Species identification was confirmed under light microscope after specimens
were colored. The detailed clinical data (physical examination, ultrasound examination,
liver function test and whole blood count) were obtained and were additionally associated
to the infection status. Our first study on the epidemiology of O. viverrini infection carried out in
Saravane province showed a high O. viverrini prevalence rate of 58.5% among 814 study
participants. Infection occurred in all age-groups including pre-school children of less
than 6 years (20.0%). The highest prevalence (> 80.0%) and infection intensity (mean
200 epg) was observed among the adult people aged between 45 and 55 years, indicating
an accumulation of this food-borne trematode infection over time. Soil-transmitted
helminths were found at lower rates, e.g. hookworm at 46.1%, A. lumbricoides at 15.7%,
and T. trichiura at 11.1%. Almost two-third of study participants harboured with two or
more parasite species. Examination of cyprinoid fish species in the local rivers showed
the high rates of infection with metacercariae. From 98 fish samples out of 23 cyprinoid
species, almost two-third; the metacercariae were found.
Our investigation in Champasack province revealed an overall prevalence of
O. viverrini infection of 64.3%. There were remarkable differences found between the
settings. High prevalence rates were observed in the low-lands of the Mekong plain (e.g.
Khong district 92.0% and Mounlapamok district 90.9%). In Paksong district the
prevalence was only 5.7%. The occurrence of soil-transmitted helminth infections was
distinctly different. All three major soil-transmitted helminths were higher in the
mountainous Paksong district compared to the settings in the plain (e.g. hookworm
94.8%, A. lumbricoides 85.9% and T. trichiura 55.7%). S. mekongi was highly prevalent
in Kong district (68.0%: 153/225), while only 3.9% (9/232) was observed among study participants living in Mounlapamok. There was no S. mekongi infection in Paksong
district. Regarding multiparasitism, 4 out of 5 study participants harboured two or more
parasite species. Habit of raw food consumption, unavailability of sanitary facilities and
socio-economic disadvantages were identified as being the key underlying risk factors for
O. viverrini infection and multiparasitism.
The results from our in-depth study on morbidity showed that 83% of the
examined person harboured at least 2 parasite species. Six different species of small
intestinal trematodes and one of Echinostomatidae were identified in the purging process.
The intensity of infection with O. viverrini worms varied in our patients. The worm
burden was significantly associated with observed hepato-biliary pathologies, i.e. study
participants diagnosed with common bile duct dilatation, liver fibrosis and intrahepatic
bile duct dilatation had 2.4 times, 3.1 times and 7.7 times higher worm burden than those
without such pathologies. Co-infections of O. viverrini and S. mekongi increased
consistently the risk for liver pathologies. Study participants infected with later coinfections
were at 2 and 6 times and 30 and 75 times higher risk of having the observed
liver fibrosis and hepatomegaly compared to infection with O. viverrini alone and noninfected
individuals, respectively in the ultrasound examination. The prevalence rates and intensity of infection with O. viverrini, and
associated multiparasitism with soil-transmitted helmints, food-borne trematodes and
S. mekongi, and the hepto-biliar morbidity related to these infections call for concerted
actions for control. Long-term and integrated efforts must improved access to preventive
and curative treatment courses in health facilities and the communities coupled with
health education and improved access to clean water and adequate sanitation.