Medical Hydrology

This body of work critically examines the role of hydrology and water resources in contributing to public health-related issues in developing countries.  An initial area of concern is the wide-spread occurrence of the tremotode parasite Opisthorchis vivirrini, the cause of opsishorchiasis, which may lead to fatal cholangiocarcinoma. Opisthorchiasis is a neglected tropical disease in the Mekong region of SE Asia. Another project is looking at the occurence of giardia and cryptosporidium in drinking water supplies in rural areas of northern Thailand.  Some initial findings are listed below.

Cryptosporidium and Giardia (oo)cysts in rural water sources in Northern Thailand

Conducted by Joon Chuah, Alan Ziegler, Yvonne Lim (University of Malaya)

In 2014 a total of 120 samples were collected from 60 different sites in rural areas of the provinces of Chiang Mai and Lamphun, northern Thailand. Two samples were collected from each site – one during the dry season (collected between March and April 2014) and another during the wet season (collected between July and August 2014). Samples were collected from various water bodies including rivers, streams and canals – all of which are potential drinking water sources for nearby villages.

          Almost half of the sites were tested positive for the presence of Cryptosporidium and/or Giardia, disregarding the seasonal factor. From these sampling sites, 22% tested positive for Cryptosporidium while 42% tested positive for Giardia. This result highlights the ubiquitous nature of these health hazards in the water resources in the rural areas of Chiang Mai and Lamphun. Equipped with only very basic water treatment systems, the general population of the rural communities in Northern Thailand are at risk and highly susceptible to cryptosporidiosis or giardiasis.

          The seasonal effects of the region seem to play an important role in the distribution and prevalence of Cryptosporidium/Giardia in the surface waters of the study sites. From this study, we found that the likelihood of Cryptosporidium/Giardia detection increased by almost a hundred percent during the rainy season. More than a third (35%) of the samples were tested positive for Cryptosporidium and/or Giardia during the wet season, compared with 18% during the dry season. The maximum number of (oo)cysts recorded for Cryptosporidium and Giardia for both the dry and wet seasons were the following: 

Dry season        Wet season        

Cryptosporidium: 6.50 oocysts/10L Cryptosporidium: 4.00 oocysts/10L                               Giardia:         2.94 cysts/10L Giardia:         13.89 cysts/10L

It can be inferred that the increase of surface runoff during the rainy season have also increase the transport of faecal matter from infected hosts (e.g. manure from cattle in pasture lands) via overland flow to the water sources. Additionally, we also propose the idea of the re-suspension of Cryptosporidium/Giardia (oo)cysts which may have settled in the sediments of the river bed. These hardy and environmentally resistant (oo)cysts may have been deposited and stored within the stream sediments over time. During storm events, the volumetric discharge and the velocity of river flow are increased, causing a disturbance to the river bed and thereby re-suspending the (oo)cysts from the sediment to the water column.

          Alarmingly, we also noted that all of the samples collected from Lai River were tested positive for these waterborne parasites. Not only does this pose an immediate threat to the local water consumers in the villages dotted along the river, but also the urban dwellers further downstream. Lai River is an important tributary to the Mae Kuang reservoir which supplies water to the many urban areas including the high density, populous town and city centres such Chiang Mai city, Lamphun town, Doi Saket town etc. 

Graphical representation of study site showing distribution and concentration of Cryptosporidium and Giardia (oo)cysts at sampling points.
Graphical representation of study site showing distribution and concentration of Cryptosporidium and Giardia (oo)cysts at sampling points.

Prevalence of cryptosporidiosis and giardiasis in beef and dairy cattle in northern Thailand

Nabila Mukhaidin, Alan Ziegler, Yvonne Lim Yvonne Lim (University of Malaya), Ian Mendanhall (DUKE-NUS)

A study to establish the prevalence of cryptosporidiosis and giardiasis in beef and dairy cattle in Chiang Mai, Thailand, and to assess the zoonotic potential of these waterborne parasites, was initiated with the assistance from Dr. Yvonne Lim and her students from the Parasitology Department from the University of Malaya. A total of 126 samples were collected from dairy cattle (n=62) from four farms from Huai Hak Phattana village and Thung Khao Tok village and beef cattle (n=64) grazing along a canal flowing through San Sai district. There were no Cryptosporidium or Giardia (oo)cysts detected in dairy cattle.  Meat cattle had a prevalence of 12.5% via microscopy and 3.1% via nested polymerase chain reaction (PCR) for giardiasis. For cryptosporidiosis, beef cattle had a prevalence rate of 3.1% via PCR. Molecular characterisation revealed that beef cattle are a not a source of Cryptosporidium for human infection and a low source of G. duodenalis for human infection. Such a pattern can be attributed to the differences in farm management between meat and dairy cattle. The close proximity of the farms to the villagers meant that contaminated faeces could be washed away and could potentially enter the water systems of the villagers, infecting villagers, many of whom are still relying on these water sources for agriculture and personal use such as bathing.

SE Asian Liver fluke

AD Ziegler, YT Lee, P Echaubard, CJ Chuah, C  Grundy-Warr, BA Wilcox, L Laithevewat, P Sithithaworn, N Khuntikeo, B Sripa,  XY Ong, R Andrews, P Tungtang

Carl Grundy-Warr, Alan Ziegler and several others have been involved in transdisciplinary field learning experiences in northeast Thailand involving university students was structured around investigating the multiple factors influencing transmission and infection of Opisthorchis viverrini (O. viverrini), the Asian liver fluke. Endemic to the lower Mekong sub-region, O. viverrini is associated with hepatobiliary diseases and suspected to be involved in cholangiocarcinoma etiology. Three life stages and distinct hosts, including humans, Bithynia snails and cyprinid fish are involved in the complex ecological life cycle of the O. viverrini trematode. The approach involves assigning teams of Singaporean and Thai (Isaan-Lao) student “observers” to homestays in different villages to explore aspects of local landscape dynamics, aquatic ecology, livelihoods, food culture, and health education. Qualitative data were gathered on the multiple dimensions of vulnerability to opisthorchiasis and provide insight into how paratsite transmission is influenced by numerous, non-trivial and inter-related social, economic, cultural, health education and development factors.  The project also revealed apparent misconceptions and misunderstandings regarding the prevention and treatment of O. viverrini infection that likely contribute to its persistence in the region, despite several decades of O. viverrini eradication efforts. The observations point to the need for an integrated health promotion approach that recognizes the liver fluke issues as embedded within a complex social-ecological system. Intervention approaches should incorporate the multiple, distinct, yet complementary health models and risk perspectives held by various stakeholders. Future control efforts aimed at reducing high incidence of liver fluke infections and cholangiocarcinoma in the region should also take into consideration their impacts on other dimensions of health behavior and education.  


Publications (go to Pub Hub)

Ziegler AD, TN Petney, RH Andrews, C Grundy-Warr, Baird, RJ Wasson, P Sithithaworn. 2013. Dams and disease triggers on the Mekong River. PLoS Neglected Tropical Diseases 7(6):1-4. .


Sithithaworn, P, AD Ziegler, AD, Grundy-Warr, RH Andrews, T Petney. 2012. Alterations to the lifecycle of liverflukes: dams, roads, and ponds.  The Lancet Infectious Disease 12(8): 588.


Ziegler, AD, RH Andrews, C Grundy-Warr, P Sithithaworn, TN Petney. 2011. Fighting liverflukes with food safety education.  Science 331: 282-283.


Petney, T, P Sithithaworn, R Andrews, N Kiatsopit, S Tesana, C Grundy-Warr, AD Ziegler. 2012.  Ecology of the Bithynia first intermediate hosts of Opisthorchis viverrini: a critical review. Parasitology Internat 61: 38-45.

Grundy-Warr, C., RH Andrews, P Sithithaworn, TN Petney, B Sripa, L Lathavewat, AD Ziegler. 2012. Raw Attitudes, Wetland Cultures, Life-Cycles: Socio-cultural dynamics relating to Opisthorchis viverrini in the Mekong Basin. International Journal of Parasitology 61: 65-70.






Ziegler, AD. Identification of at-risk rural communities to protozoan diarrheal illnesses in Thailand. Faculty Research  Fund, National University of Singapore ($100,000): Thailand.