Showing posts with label Field Work. Show all posts
Showing posts with label Field Work. Show all posts

Friday, April 26, 2013

This Month in Blastocystis Research (APR 2013)

I've been extremely bored all day writing up my evaluation of a (not so interesting) PhD thesis, and I thought I'd spice up my day by introducing a new series of posts on this blog inspired by so many other blogs, namely: This Month in Blastocystis Research! A place for me to go through some of the most recent papers on Blastocystis.

There is paper out by Gould and Boorom who look at the stability of Blastocystis surface antigen over time. They show that detection of Blastocystis by an immunofluorescense assay (IFA) is not hampered after1 year of storage of faecal material in formalin compared to results immediately after the sampling point. Detection of Blastocystis by IFA is something that is not often used (that's my impression, anyway), but makes sense in cases where laboratory analyses can be performed only weeks-months after sample collection (e.g. during field work), in which case samples need to be preserved. We usually, however, recommend storing faecal material in (70%) ethanol (in the relationship 1 part faecal sample to 4 parts of ethanol), where the sample is mixed with the ethanol initially by vortexing the tube (typically a 2 mL Eppendorf tube) for 5-10 min, and subsequently keeping the tubes away from light until further processing. Importantly, in contrast to formalin-fixed stool, ethanol-fixed stool can be made highly suitable for PCR by just washing the samples x3 in PBS prior to DNA extraction. An example of this methodology can be seen in our study of Blastocystis in members of the Tapirapé tribe in Mato Grosso, Brazil (go here for a free download).

I'd wish that Gould and Boorom had validated their findings by running a PCR on the samples too (specificity and sensitivity testing). The IFA assay was also used in a publication from 2010 by Dogruman-Al et al., who found a diagnostic sensitivity of the IFA assay of 86.7% compared to culture; also here, adding PCR would have been relevant to better determine the diagnostic qualities of the IFA assay.

I was lucky to be involved in field work in the Lao PDR in 2003 conducted by regional WHO authorities; preserving and analysing faecal samples for parasites by microscopy (Kato Katz) and - later - PCR was what we did!

Adding to the endless row of cross-sectional prevalence papers, there is an article out just now by Abdulsalam et al. (2013) on Prevalence, predictors and clinical significance of Blastocystis sp. in Sebha, Libya (free for download here). The study used culture (Jones' medium) as diagnostic modality and confirmed the existence of frequent asymptomatic carriage. The authors used questionnaire info and multivariate statistical analysis to identify risk factors for Blastocystis carriage among 380 individuals aged 1-75, and what I find really interesting is that they found that participants aged > 18 years were much more prone to having Blastocystis than participants < 18 years (P < 0.001). This is something that we see in Denmark too, and I'm currently trying to collect "sufficient proof"! Whether this is an age accumulation effect due to the chronicity of colonisation remains to be investigated. The authors also found that carriers were more likely to experience symptoms than those who were not carriers (P < 0.001), mainly abdominal pain (P < 0.001), but notably not diarrhoea (P = 0.117).
It's a pity that molecular data was not included the study from Libya. Incidentally, our group recently published subtype data from Sebha, Libya, and it appears that Blastocystis found in humans in Libya mainly belongs to ST1, whereas ST3 is often the most common subtype in most other countries, and what is more: ST4 appears virtually absent in Libya and the rest of Africa... But let's see: The investigators might have more data up their sleeve waiting to be published...

May I also again draw your attention to our recent paper on Blastocystis in non-human primates, in which we find that despite the fact that there is a great overlap of subtypes in human and non-human primates, it appears that ST1 and ST3 strains found in non-human primates differ genetically from those found in humans, indicating cryptic host specificity. We have additional data supporting the theory that Blastocystis in humans is a result of human-to-human transmission (anthroponotic) rather than animal-to-human (zoonotic) transmission. Which is really interesting, since the theory of zoonotic transmission of Blastocystis has been heavily (I dare not say purported, so I'll say) propagated. Having said that, I think we still need to look much deeper into barcoding of Blastocystis from pets and other synanthropic animals before we can make more poignant conclusions.

And, finally, yet another add for our recent review on Recent Development in Blastocystis Research!

Please note that I'm happy to take suggestions for future posts, and I'd also like to encourage guest blogging!

Suggested reading:

Abdulsalam AM, Ithoi I, Al-Mekhlafi HM, Khan AH, Ahmed A, Surin J, & Mak JW (2013). Prevalence, predictors and clinical significance of Blastocystis sp. in Sebha, Libya. Parasites & Vectors, 6 PMID: 23566585

Alfellani MA, Jacob AS, Perea NO, Krecek RC, Taner-Mulla D, Verweij JJ, Levecke B, Tannich E, Clark CG, & Stensvold CR (2013). Diversity and distribution of Blastocystis sp. subtypes in non-human primates. Parasitology, 1-6 PMID: 23561720

Alfellani MA, Stensvold CR, Vidal-Lapiedra A, Onuoha ES, Fagbenro-Beyioku AF, & Clark CG (2013). Variable geographic distribution of Blastocystis subtypes and its potential implications. Acta Tropica, 126 (1), 11-8 PMID: 23290980

Clark CG, van der Giezen M, Alfellani MA, & Stensvold CR (2013). Recent developments in Blastocystis research. Advances in Parasitology, 82, 1-32 PMID: 23548084

Dogruman-Al F, Simsek Z, Boorom K, Ekici E, Sahin M, Tuncer C, Kustimur S, & Altinbas A (2010). Comparison of methods for detection of Blastocystis infection in routinely submitted stool samples, and also in IBS/IBD Patients in Ankara, Turkey. PloS One, 5 (11) PMID: 21124983 

Gould R, & Boorom K (2013). Blastocystis surface antigen is stable in chemically preserved stool samples for at least 1 year. Parasitology research PMID: 23609598

Malheiros AF, Stensvold CR, Clark CG, Braga GB, & Shaw JJ (2011). Short report: Molecular characterization of Blastocystis obtained from members of the indigenous Tapirapé ethnic group from the Brazilian Amazon region, Brazil. The American Journal of Tropical Medicine and Hygiene, 85 (6), 1050-3 PMID: 22144442