Blastocystis in water - Need for screening?

Infectious diseases caused by parasites continue to cause disease burdens which influence the quality of life, retards economic progress and dampens overall development especially in developing countries. The emerging group of protozoan parasites namely Blastocystis, Cryptosporidium, Isospora and Cyclospora causes generally diarrhea, bloating stomach, abdominal cramps and other gastrointestinal disturbances. Prevalence of these parasites varies from community to community and from country to country but they possess the same fecal-oral route of transmission. Contaminated water and food are the main causes of transmission with sporadic reports providing evidence for zoonotic transmission. High risk groups are the HIV-infected population, children and pet lovers. The presentation highlights the biology, prevalence, transmission, diagnosis and treatment on Blastocystis which is one of the most enigmatic protozoan. Blastocystis infection occurs worldwide but generally developing countries have higher prevalence of B. hominis (approximately 30 to 50%) than developed countries (approximately 1.5 to 10%). The parasite has been incriminated to be waterborne and our findings of cysts in the lakes and rivers screened around Klang Valley, Malaysia provides further evidence of the potential of the organism to be transmitted to humans. Moreover, river isolates of Blastocystis were found to be either subtype 1, 3 or 5 which could be of human origin and may potentially result in transmission. Detection of Blastocystis cysts has been challenging using light microscopy. The presentation will highlight the technical challenges involved in enumerating the cyst collected from water sources, the density gradient centrifugation used with both Ficoll-paque and Lymphoprep and the usage of DAPI staining and in vitro culture for detecting the parasite. Results using 0.5 L water samples from rivers showed that 28% and 72% of samples were positive for Blastocystis using in vitro culture and DAPI staining respectively. Standardization protocols involving large amount of water to be screened, the processes and steps involved especially in the centrifugation, the influence of timing of collection as well as the frequency of collection etc will be discussed.