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Commentary
ProMED Confusion On Qatar MERS Camel Tests
Recombinomics Commentary
19:15
November 29, 2013
As apparent from item 2 above, the discovery of the 3 camel "cases" in Qatar is based upon serological tests; more specifically, "3 different tests" applied by the Dutch investigators. Further details of the techniques applied and on their respective validation status will be helpful.
On 12 Nov 2013, Saudi Arabia's Ministry of Health notified the 1st time that a camel related to a human case had tested positive for MERS-CoV by PCR (see ProMED-mail 20131112.2051424). Reportedly, further testing was ongoing to sequence the patient's and the camel's viruses and compare genetic similarity levels to conclude causality. The results of these tests are not yet available. - Mod.AS\
The above comments in a ProMED RFI on the detection of MERS-CoV in the 3 camels in Qatar represents a gross misrepresentation of the facts presented yesterday by Qatar and a large number of media reports.
The detection of MERS-CoV was based on a MERS PCR test, which is one of the three tests cited in the quoted media report. Other reports made it clear that both antibody tests and sequencing were done in addition to the PCR testing. The assumption that the MERS-CoV was solely based on antibody testing is curious. The limitations of such testing are well known and the official announcement, as well as associated media reports, made it clear that the camel testing went well beyond antibody assays.
The media reports were followed by reports by WHO, OIE, and ECDC that confirm the significance of the PCR result. There was no doubt that the camels were infected with MERS-CoV and there was interspecies transmission between the two MERS confirmed cases and the camels, but the direction of the transmission was still under investigation.
The MERS PCR test, in contrast to the universal PCR conoravirus, is designed to limit a positive result to MERS-CoV because confirmation requires positive results for two or more regions, which target MERS-CoV. Thus, the positive result in Qatar camels was similar to the positive result for the Jeddah camel, which also supported interspecies transmission since the owner of that camel was also MERS confirmed.
The universal PCR test, in contrast, requires follow-up sequence data to determine the type and sub-clade of coronavirus. This test was used to find SARS-related sequences in bats in China. It was then used to find additional coronavirus sequences, including beta2c sub-clades in Europe and Africa, which were more closely related to MERS sequences. However, only the BIsha bat sequence is close enough to MERS to resent a candidate for recent jumps to humans.
However, the recent MERS PCR data in camels signals MERS CoV which will be very closely related to the Jeddah and Qatar human sequences in the owners of these camels.
The Qatar camel data should offer additional insight into MERS in camels, since the Jedda and Qatar camels were tested during active infection, and sequences from their owners should also be generated and released soon.
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