Via CIDRAP, a useful report from Robert Roos: Genomic study finds no ominous changes in MERS-CoV. Excerpt:
A genomic analysis of 32 Middle East respiratory syndrome coronavirus (MERS-CoV) isolates from Saudi Arabia has revealed little evidence that the virus is evolving to become more contagious in humans, according to a new report by Saudi, British, and US researchers.
The team analyzed isolates from MERS cases that were confirmed in Sauda Arabia from May through September of 2013. They identified four different MERS-CoV clades or families, but three of those no longer seem to be contributing to cases, says the report, published in mBio.
The findings also suggest that the pace of human MERS cases gradually increased until April 2013 but has declined since then, the researchers say.
The number of publicly reported MERS cases has ebbed in recent months. A World Health Organization (WHO) chart shows that the monthly tally of cases peaked last year at about 35 in August and then hovered around 10 to 12 the rest of the year. A case list maintained by the FluTrackers infectious disease message board shows six cases so far this year.
In-depth genetic analysis
The research team sequenced the genomes of all 32 isolates and completed at least 99% of the sequence for 20 of those, with partial sequencing of the rest. They compared these 32 viruses with 33 previously sequenced isolates to map their phylogenetic relationships.
The researchers identified four clades with at least four cases each (Hafr-Al-Batin_1, Buraidah_1, Al-Hasa, and Riyadh_3) and six sporadic cases that didn't fit in any of the clades.
In mapping the clades, the team found that the Al-Hasa clade was confined to that region of eastern Saudi Arabia, but each of the other three included cases in several locations. "The geographical dispersion of MERS-CoV lineages suggests a mobile infection source, either as human-to-human or nonhuman-to-human infection or via transported animal product," they wrote.
The persistence of each clade was assessed by checking the dates of the first and last recognized isolates belonging to it. This revealed that the durations ranged from 62 to 147 days, with an average of 98 days. Three of the clades appeared to have faded out of circulation by the end of the observation period, the team said.