Little known parasite may be culprit behind diseases
"After assimilating the data from our recent studies and after critical analysis of many papers in the field, I conclude that Blastocystis can cause a variety of diseases and clinicians should be more aware of infections caused by this organism."
Dr Kevin Tan, Department of Microbiology
WHILE the word Blastocystis may not ring a bell to most of us, Dr Kevin SW Tan of the Department of Microbiology at the Yong Loo Lin School of Medicine has devoted much of his time to the study of this little known microorganism. Dr Tan's research provided an understanding of the parasite's disease-causing molecules which may be responsible for causing common bowel disorders, such as diarrhoea and irritable bowel syndrome. More intriguingly, the parasite may also be associated with urticaria, a form of allergy involving the skin.
"After assimilating the data from our recent studies and after critical analysis of many papers in the field, I conclude that Blastocystis can cause a variety of diseases and clinicians should be more aware of infections caused by this organism," said Dr Tan.
His research challenges what is commonly believed in the scientific field, that the parasite does not cause disease. The last extensive review on Blastocystis published in 1996 concluded that current knowledge of Blastocystis and the supposed disease it causes was insufficient to determine the significance of the parasite in humans.
TEAMWORK: Members of the Tan Laboratory at their 2008 Lab Retreat. The team is led by Dr Kevin Tan (front, in orange).
Dr Tan explained that Blastocystis infections in humans can be caused by one of many subtypes, each with a very different genetic background. It is possible that some subtypes possess greater disease causing ability than others, and this may explain why some studies support a disease-causing role for the parasite while others do not. A survey among individuals in Singapore showed that about 3 per cent harbour the parasite and two out of the seven commonly described subtypes are found in our local population.
Explaining the nature of Blastocystis, Dr Tan said that it is an unusual intestinal protozoan parasite of humans and many animals, with a worldwide distribution. The parasite can take up various distinct forms within a single culture, is fragile and only grows in the absence of oxygen. This has proved to be challenging when conducting studies on the parasite. Recent studies from his laboratory has shown that the parasite can compromise the normal functioning of intestinal cells and also activate or inhibit components of the immune system (Puthia et al, 2006, Infection and Immunity; Puthia et al, 2008, Eukaryotic Cell).
His findings were included in a review paper he recently authored, and published in the October 2008 issue of Clinical Microbiology Reviews, the top microbiology journal published by the American Society of Microbiology.
Dr Tan, a member of the Life Science Institute's Infectious Diseases Programme and the NUS Graduate School for Integrative Sciences and Engineering, is currently working with Dr Paul Macary of the Immunology Programme to better understand early immune responses to Blastocystis infections. Preliminary studies from their groups have revealed that the parasite possesses an exquisite ability to modulate the host immune response.
BLASTOCYSTIS PARASITES: Fluorescence, light, and merged micrographs show activity and localisation of cysteine proteases in live Blastocystis parasites. Figure adapted from Puthia et al, 2008, Eukaryotic Cell.
