For Spanish-speaking
Blastocystis geeks, this summer must have been a real treat: Londoño-Franco and colleagues published a paper in Biomédica on
Blastocystis in children and Colombia. But not only did they look for
Blastocystis in faecal samples, they also sampled from finger nails, house floors, toys, tap water, vegetables, other food items, etc... It is extremely rare to see studies aiming to identify sources of potential transmission, and I thought that this study would merit a blog post (unfortunately, I will have to rely on the Google translated version with all its potential limitations; I excuse for any misunderstandings).
Of course one of the big questions still remaining in
Blastocystis research is: From where do we get this parasite? With more than one billion people colonised on the globe, the transmission pressure must be massive, and it's tempting to expect infectious cysts (or other stages) being more or less ubiquitous. There is some evidence accumulating that the parasite can be water-borne, and we also know that zoonotic transmission can occur (although relatively rarely, supposedly). However, this study takes things way further:
The authors carried out their study in Calarcá where they identified a prevalence of
Blastocystis (based on microscopy of stool concentrates) of 57.5% in 275 children less than 5 years old; children aged 48 months or more were more prone to be positive than those who were younger. This is something we see a lot, and it either suggests a cumulative effect of colonisation (once established, colonisation is chronic), or that the behaviour (~exposure) or intestinal microbiota of older children favours colonisation.
Blastocystis was also found in dogs (63.3%), cats (56.3%), and poultry (35.7%). Moreover, it was found in tap water (38.5%), on toys (29.9%), baby bottles (18.5%), and under the nails of infected children (42.2%), their siblings (44.8%), and their mothers (34.2%).
Among the vegetables that are typically consumed raw, it was found most frequently in lettuce (66.7%), and, in descending order, in tomato (44.4%), carrots (37.5%), cabbage (28.6%) and onion (25%). A high occurrence was seen in containers used to store 'aqua de panela', which is allegedly some kind of sugar water (haven't had the opportunity to sample it myself), with 47.7% of the samples positive. I believe that this drink is used as a sweetener and possibly also as a refreshment/energy drink, and maybe served with for instance cheese (image). Taken into account that Blastocystis is not exactly fussy about growth medium requirements, it may not be surprising at all to learn that this type of drink serves as a perfect stronghold for Blastocystis.
The authors also explored a number of other things, among them i) the relative occurrence of cysts and vacuolar stages in the different types of samples and ii) whether any symptoms experienced over the past month could be attributed to
Blastocystis, and iii) risk factors for colonisation. However, Google translate plays tricks on me on some of these bits, so I won't try to go more into detail with these findings. Suffice to say that the approach of distinguishing between different stages should help researchers find out more about which stage(s) that is/are responsible for transmission. Also, if for instance vacuolar stages are found in agua de panela and not cysts, then this might indicate that
Blastocystis is actually
growing in the drink? Which again is interesting because this would mean that
Blastocystis capable of infecting humans can grow at temperatures lower than 37 degrees C.
Now, I could only have great confidence in the diagnostic work carried out by this team; however, I would have absolutely loved molecular confirmation of all of these
findings. Also, maybe it would have been an idea to
try and culture some of the
Blastocystis found on fomites and in
food/water to test for viability, or, as mentioned by the authors
themselves, to test for viability using trypan blue. However, the
authors should be praised for their perseverance and ingenuity, and I
hope that this study will inspire other colleagues to pursue and expand
on these initiatives and ideas.
This month saw a number of different
Blastocystis-related papers, among them a paper from Klimes et al. on issues with
Blastocystis genome annotation and polyadenylation-mediated termination codon creation in nuclear mRNA transcripts. Moreover, there's a paper on population structure analysis of seven eukaryotic microbial lineages, including
Blastocystis, that apparently makes it possible to infer variable impacts of genetic exchange in populations of predominantly clonal micro-pathogens
(in fact the authors used our MLST data for ST3 in their analyses!). Finally, our colleagues in České Budějovice have produced an interesting review on self-infections with parasites; in the paper they point to the traditional focus on sussing out the pathogenic potential of parasites instead of trying to identify the potentially positive effects of parasite colonisation. Definitely worth a read!
Reference:
Londoño-Franco AL, Loaiza-Herrera J, Lora-Suárez FM, & Gómez-Marín JE (2014). [Blastocystis sp. frequency and sources among children from 0 to 5 years of age attending public day care centers in Calarcá, Colombia]. Biomedica : Revista del Instituto Nacional de Salud, 34 (2), 218-27 PMID: 24967927
Klimeš
V, Gentekaki E, Roger AJ, & Eliáš M (2014). A large number of
nuclear genes in the human parasite Blastocystis require mRNA
polyadenylation to create functional termination codons. Genome Biology and Evolution PMID: 25015079
