PARASITOLOGY
What’s new in the world of UK NEQAS Parasitology?
At the most recent IBMS Congress, Monika Manser looked at parasitology and current developments in the external quality assessment of this aspect of laboratory medicine.
What’s new in parasitology? Not much, sadly, is the honest answer. An outbreak of cryptosporidia around the Preston area which affected quite a large number of people made the national news headlines, but as there have been similar outbreaks anywhere where there is water, this was not really noteworthy. In the parasitology news headlines, it was noted that Isospora had changed its name to Cystoisospora, and microsporidia have been relegated to the world of fungi. So, on reflection, there may not be much
that is new in the world of parasitology but there are some interesting changes of note in the world of UK NEQAS Parasitology. For example, a larger range of parasites was distributed and the introduction of schemes for the non-microscopic identification of parasites.
Increased range of parasites Recent visits to the Philippines and its Schistosoma Reference Laboratory have resulted in the acquisition of some interesting parasites. The first to be distributed about three years ago as part of the faecal scheme was Capillaria philippinensis, which was correctly identified by 65% of participants. This initial distribution was regarded as a teaching specimen, and was not scored. Subsequent distributions of C. philippinensis saw correct identification by 84% and 90% of participants. The aim of UK NEQAS first and foremost is
education. The scheme aims to educate by sending out new parasites, together with a teaching sheet with the first distribution of a ‘new’ parasite. These teaching sheets are also published on the website. In addition, there are the parasitology roadshow events where UK NEQAS staff go around the country to different university establishments and larger laboratories to provide a day of hands- on practical parasitology. The next new parasite circulated was
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When first circulated, Capillaria philippinensis was correctly identified by 65% of participants.
Schistosoma japonicum. Again, because this was the first time this parasite had been distributed, it was not scored. Only 18 participants out of over 500 correctly identified the ova, which could have been due to the scanty numbers present (ie approximately eight ova per coverslip). Although, eight ova per coverslip equates to about 60 ova per deposit, which in turn equates to 60 ova per mL, a look at past history of sending out three ova in the one specimen shows that identification decreases when more parasites are included; for example, >90% of participants obtain the correct results when there is only one parasite species present in the specimen, but this decreases when two ova are present, and decreases further still when three ova are present. It is a well-known fact that when participants see one ovum species in the concentrate they stop their examination of the specimen. Another ‘new’ parasite sent out in a Faecal
Parasitology Distribution was Heterophyes heterophyes, which is a liver fluke. On initial circulation 39 participants (7.1%) reported the ovum. As the ovum is quite small in size, it could resemble a type of spore or flower pollen. It is indistinguishable from
Metagonnimus yokogawi, which is what 12 participants believed it to be. Twenty-nine participants confused it with Opisthorchis. To be fair, there were only low numbers of ova present per coverslip. The last new parasite sent out over the
past year was Babesia microti, which resembles Plasmodiumspecies. It was correctly identified by 78% of participants. Unlike Plasmodiumspecies, this parasite is transmitted by a tick rather than a mosquito. Unsurprisingly, the remainder of the participants mistakenly identified it as Plasmodiumspecies. Although initial circulations are usually not scored, this was the exception, as there was a big hint in the clinical details. One does not get malaria in New England in America. So, one should always read the clinical details.
Non-microscopy schemes A new development for UK NEQAS is the introduction of non-microscopy schemes. A scheme for rapid diagnostic techniques (RDTs) for malaria has been available since 2010. In routine diagnosis, RDTs should not be used in isolation but in conjunction with microscopy in order to confirm or exclude the presence of malaria. However, due to lack of expertise in malaria identification from thick blood films, many participants have already started using a rapid diagnostic test instead of a thick blood film. The differences between a thick blood film and an RDT is that the former can be used to speciate the parasite, and an expert microscopist can detect less than 200 parasites per microlitre; one can
The liver fluke Heterophyes is quite small in size, and could resemble a type of spore or flower pollen.
AUGUST 2016 THE BIOMEDICAL SCIENTIST
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