Showing posts with label transmission. Show all posts
Showing posts with label transmission. Show all posts

Monday, August 1, 2016

This Month in Blastocystis Research - Interactive Edition

What are your thoughts on Blastocystis carriage and age?

More and more data suggest that the prevalence of Blastocystis carriage increases by age - at least to a certain point.

Some intestinal parasites, such as Cryptosporidium, may not be that uncommon in infants/very young toddlers, while they are much less common in older children and adolescents. Other parasites appear to peak in prevalence around the age of 7, e.g., Dientamoeba fragilis.

Meanwhile, Blastocystis appear to increase in prevalence by age until mature adulthood... why is that? And what does it tell us? Please comment! I'm not having all the answers to these questions myself, and if some interesting suggestions pop up, I'll post them! You only need a Google account to be able to comment. If you don't have one, please send your comment using


For those interested in Blastocystis carriage in association with age, I have listed a couple of relevant recent studies below.


Forsell J, Granlund M, Samuelsson L, Koskiniemi S, Edebro H, & Evengård B (2016). High occurrence of Blastocystis sp. subtypes 1-3 and Giardia intestinalis assemblage B among patients in Zanzibar, Tanzania. Parasites & Vectors, 9 (1) PMID: 27356981  

Poulsen CS, Efunshile AM, Nelson JA, & Stensvold CR (2016). Epidemiological Aspects of Blastocystis Colonization in Children in Ilero, Nigeria. The American Journal of Tropical Medicine and Hygiene, 95 (1), 175-9 PMID: 27139454

Monday, July 28, 2014

This Month In Blastocystis Research (JUL 2014)

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.
Agua de panela (source).

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!


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 

Lukeš J, Kuchta R, Scholz T, & Pomajbíková K (2014). (Self-) infections with parasites: re-interpretations for the present. Trends in Parasitology PMID: 25033775

Tomasini N, Lauthier JJ, Ayala FJ, Tibayrenc M, & Diosque P (2014). How often do they have sex? A comparative analysis of the population structure of seven eukaryotic microbial pathogens. PLoS One, 9 (7) PMID: 25054834 

Monday, July 29, 2013

Birds of America

Yesterday evening, I was watching another compelling BBC production, broadcast on Danish television: Earthflight, North America. In quite a unique way, the viewers got the rare opportunity to see through the eyes of birds such as eagles, geese, and pelicans and follow birds as they were migrating, escaping, hunting for prey, etc. It made me think of the 19th century masterpiece 'Birds of America' by John James Audubon, which can be viewed in the National History Museum in London. The book features 435 stunning hand-coloured plates that show birds life-size, in natural positions and in their natural habitat.

One of the things that I find interesting - and quite unexplored - is Blastocystis in birds. By 'unexplored' I mean that relatively little sampling has been done, and so the number of observations of Blastocystis in birds is still limited compared to other types of hosts. However, there is a brand new paper out in 'Infection, Genetics and Evolution' which includes observations on Blastocystis in birds (of America!).

You see, I was invited in on a study by colleagues in Colombia who had access to DNA from quite a few faecal samples from a number of host species, including feral birds, and what we found confirms the quite unambiguous trend seen so far: Birds - no matter where on this planet - appear to be colonised mainly by ST6 and ST7. As a matter of fact, in the present study only ST6 was seen in almost 50 Colombian passerine birds of varying species, most of which I believe are limited in geographical distribution to the Americas: Passer domesticus, Thraupis episcopus, Oryzoborus maximiliani, Sicalis flaveola, and Petrochelidon pyrrhonota. Moreover, only one allele of ST6, allele 122, was identified. Notably, the prevalence of Blastocystis in the sampled bird population was 90%. I believe that this is the first official report on Blastocystis in passeriformes. Other major groups of birds previously sampled include galliformes, anseriformes, and ratites (Stensvold et al., 2009; Alfellani et al., 2013).

Other subtypes have been reported in birds (Alfellani et al., 2013), but due to the very low number of samplings these subtypes may be more or less co-incidental/abberant findings. Of note, some samples from birds have been untypable. I have a slight recollection of detecting ST3 in Icelandic rock ptarmigans (in mixed ST infection) collected by Dr Karl Skírnission, but that certainly needs confirmation.

Bird contact/bird droppings - a significant source of Blastocystis in humans? Me feeding some 'Birds of Australia'. Photo by Dr Rebecca J Traub.

ST6 is very rarely seen in humans in Europe. In other parts of the world, for instance in Egypt and some Asian countries, ST6 appears relatively common, but we do not know much about 'bird subtypes' in those particular regions. Also, the situation in the US and Canada is more or less completely unknown (Blastocystis subtyping is something that appears not to attract research groups in North America apart from the one led by Dr Ron Fayer in Beltsville, Maryland).

ST7 is occasionally seen in humans in countries such as Sweden and Denmark. But in my - still limited - experience, individuals infected by these subtypes are not necessarily prone to 'suffer more' from intestinal symptoms than those who do not have these subtypes. While human cases of ST6 (and ST7) may represent cases of zoonotic transmission, it is far to early to draw any conclusions on this. It would be important to compare ST6 and ST7 18S alleles from humans and birds. MLST typing systems for these two subtypes are not yet available, but 18S analysis in itself may prove valuable for molecular epidemiological analyses as in the case of other subtypes (Stensvold et al., 2012).

Walton Ford: "Falling Bough" (Source). You will also see the now extinct Passenger Pigeon in 'Birds of America'.


Ramírez JD, Sánchez LV, Bautista DC, Corredor AF, Flórez AC, & Stensvold CR (2013). Blastocystis subtypes detected in humans and animals from Colombia. Infection, Genetics and Evolution: Journal of Molecular Epidemiology and Evolutionary Genetics in Infectious Diseases PMID: 23886615

Alfellani MA, Taner-Mulla D, Jacob AS, Imeede CA, Yoshikawa H, Stensvold CR, & Clark CG (2013). Genetic diversity of Blastocystis in livestock and zoo animals. Protist, 164 (4), 497-509 PMID: 23770574

Stensvold CR, Alfellani M, & Clark CG (2012). Levels of genetic diversity vary dramatically between Blastocystis subtypes. Infection, Genetics and Evolution: Journal of Molecular Epidemiology and Evolutionary Genetics in Infectious Diseases, 12 (2), 263-73 PMID: 22116021

Stensvold CR, Alfellani MA, Nørskov-Lauritsen S, Prip K, Victory EL, Maddox C, Nielsen HV, & Clark CG (2009). Subtype distribution of Blastocystis isolates from synanthropic and zoo animals and identification of a new subtype. International Journal for Parasitology, 39 (4), 473-9 PMID: 18755193