PARASITOLOGY
participants take individual action and seek to remedy any discrepant results, and ask for help and advice. Returning to the lyophilised blood,
it proved to be a stable matrix when shipped at ambient temperatures, which means a cold chain is not needed during distribution. This helps to keep costs down and opens distribution up to a much wider range of participants.
An expert microscopist can distinguish between parasite stages in a thick blood film.
distinguish between parasite stages in a thick film, detect non-P. falciparumspecies and can estimate the parasitaemia. This is not possible using an RDT. Some rapid RDTs distinguish between P. falciparumand non-P. falciparum. A five-year analysis of the RDT scheme
shows that participants are performing very well, better than in the examination of thick blood films. It was noted that there were more false-negative results reported with non- P. falciparumspecies than P. falciparum when using RDTs, although both false positives and false negatives were reported. Fewer false-positive results were reported
when using RDTs than when examining a thick blood film. The reasons for this could be due to the fact that less expertise is required to perform RDTs, or that participants could be afraid to declare UK NEQAS blood films negative, thus reporting artefacts as parasites. Discrepant RDT results could be kit-related because some kits have higher parasite detection scores than others (kit performance is published on the World Health Organization [WHO] website). It could also be operator-related; some add too much blood, others do not add enough; then there is the amount of buffer (variation in the number of drops) and incorrect run time. Participants are always advised to follow the manufacturer’s instructions.
Going molecular Last year UK NEQAS Parasitology established a pre-pilot molecular study for the diagnosis of malaria. Two pre-pilot distributions were available and 35 participants in 24 countries applied to take part. The specimens consisted of lyophilised blood, which was a matrix that had not been used before in UK NEQAS Parasitology distributions, and the results proved very encouraging. In these two pre-pilot distributions, all four malaria species were included with different concentrations of parasites of each Plasmodiumspecies. False positives and false negatives were seen and some participants only used a pan- Plasmodiumpolymerase chain reaction (PCR) method, but the results were encouraging. The majority of participants were in
good agreement with the UK NEQAS pre- distribution results, and it satisfied the scheme’s criteria that include helping
THE BIOMEDICAL SCIENTIST AUGUST 2016
Faecal parasites A recent advance has been the introduction of a scheme for the non-microscopic detection of faecal parasites. Initially, a questionnaire was circulated to 580 participants and 105 responded. From the responses it was noted that 10 out of 53 participants used PCR and the other 43 used various antigen and antibody tests to detect Cryptosporidiumand Giardia. In the most recent distribution that contained Cryptosporidiumspecies, 24 participants comment that they no longer used microscopic tests. In response to this demand, UK NEQAS
investigated preservatives because, at present, UK NEQAS Parasitology tends to preserve faecal parasites in formalin, which has an adverse effect on many non- microscopic kits (eg enzyme-linked immunosorbent assay [ELISA] and PCR). Following the success of the malaria molecular scheme, it was decided to assess the effect of freeze-drying faecal specimens. Initially, two clinical samples, one containing Cryptosporidiumsp. and the other containing Giardia lamblia (both confirmed by microscopy), were sent to six volunteers. All participants saw the Cryptosporidium and Giardia in each specimen using various tests, including Meri-fluor, PCR, Quik-Check, IVD, ELISA, Techlab and Alere. A pre-pilot with more participants is now
anticipated and around 75 participants have already expressed interest in participating.
Definitive diagnosis A definitive diagnosis of parasitic disease requires the parasite to be seen in the specimen so microscopy is still needed, and RDTs, serology and PCR are unlikely to replace it completely. Molecular methods can provide greater sensitivity and specificity for some organisms such as microsporidia and leishmaniasis, and RDTs can help to provide reassurance to experienced and inexperienced microscopists.
Endnote The world of parasitology changes only very slowly but the diagnosis of parasites is evolving and thus UK NEQAS Parasitology must evolve, too, and the scheme aims to keep up with the times.
Monika Manser recently retired from UK NEQAS Parasitology, Hospital for Tropical Diseases, London.
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