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  • Writer's pictureJennifer

Grab your popcorn: The Cyclospora methods debate is on!

It was hard to tell if the spectacle over the 18s rRNA-based molecular methods for detecting Cyclospora cayetanensis during the recent NACMCF meeting was a scientific debate or a more personal one. Either way it was a drawn out public battle that probably shouldn’t have happened. I described it to a colleague as “awkwardly exciting”. He described it as “horrible”. How controversial can methods be? To some this is a dry topic. But people get pretty defensive of their methods, and this was on full display at the meeting.


First, what is NACMCF? It stands for the National Advisory Committee on Microbiological Criteria for Foods. It is a public advisory committee of the US Department of Agriculture, but FDA is also very involved. Committee members are selected by the Secretary of Agriculture and represent food microbiology experts from all backgrounds- academia, the public sector, trade associations, etc. This group of scientific experts are charged with evaluating and making recommendations on scientific issues. The agencies (USDA and FDA) develop charges (topics and questions) for the committee to tackle, generally over the course of years. The resulting NACMCF reports often carry a lot of weight.


So in this round, the committee was charged with addressing Cyclospora. This vexing parasite continues to cause illness, peaking each summer. This year multiple outbreaks are being investigated, with many more sporadic illnesses. Compared to our understanding of bacterial pathogens (e.g., Salmonella, Listeria monocytogenes, etc.) our understanding of the parasite Cyclospora cayetanensis is limited. The fact that it doesn’t grow in a lab means it’s really difficult to do research—because the supply is very limited!


I’m no parasitologist. I like the simplicity of bacteria- their methods of reproduction and their genetics are relatively straightforward. Parasites are complicated. Their genetic relationship with other parasites is proving to be quite complex. Since they don’t grow in a lab (no possibility for enrichment), detection relies largely on molecular methods. This is the root of the NACMCF debate. How do you know if the little bit of DNA you detected is really from Cyclospora cayetanensis or one of its cousins?


Because different labs around the world have used different approaches and different molecular targets in their methods, the NACMCF committee asserted, in the draft report, that as they reviewed the literature, even if the author said they found the parasite, the committee viewed it as a ‘presumptive’ finding unless additional confirmation was done. This seems pretty fair to me. The report further notes that when researchers went to confirm molecular detection (based on detecting portions of the 18s rRNA), there was a 90% false positive rate (!!!!). FDA, the agency who tasked the committee with evaluating methods, took issue with this. It was not said this way, but my interpretation of the *lengthy* exchange, was that FDA viewed this as an attack on their method (referred to as BAM 19b—which is a molecular detection method that targets part of the 18s rRNA gene). In actuality, I believe the report was making a more general comment about the diversity of targets- it appears that some are not unique to C. cayetanensis and also detect related parasites. I didn’t interpret the report language to call into question the validity of BAM 19b; FDA is arguably a leader in developing C. cayetanensis detection methods, and continues to pursue improved methods, most recently one using mitochondrial primers.


I was the only person who registered to make a public comment and had intended to voice support for the committees recommendation that older research studies on “Cyclospora” be viewed with some skepticism. Upon hearing the debate (which bled into a discussion over secondary confirmation methods), I had to make some quick edits to my prepared remarks! The scientific bottom line is this: Scientists use the best available methods. Methods improve. Our knowledge and understanding increase. For C. cayetanensis, this means some of the things we thought we knew may no longer be valid, or might warrant reinterpretation. Such is the nature of science. That’s progress. It’s not personal.

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