1. Department of Internal Medicine; Chiang Mai University; Chiang Mai 50200 Thailand
2. Department of Parasitology; Chiang Mai University; Chiang Mai 50200 Thailand
3. Division of Biomedical and Life Sciences; Faculty of Health and Medicine; Lancaster University; Lancaster LA1 4YG U.K
4. Department of Pathology; Chiang Mai University; Chiang Mai 50200 Thailand