We posted a couple of months ago about a novel human norovirus, a GII.17 genotype, that had taken the place of the common GII.4 Sydney in an eastern region of China last winter. It seems some GII.17’s have gotten the traveling bug, as a GII.17 like one originally found in Japan was recently identified in Italy, and a GII.17 found last winter in the U.S. has turned out to be very closely related to the Asian GII.17’s.
Norovirus genotypes are sort of like fancy ice cream flavors. There are a handful of basic flavors, like chocolate, strawberry, and vanilla (your genogroups, named GI through GVI), but then these serve as a base for more complex flavors (like how rocky road and fudge brownie are usually made with chocolate ice cream), which are your genotypes. To complete the analogy, if the GII.4 noroviruses are rocky road, the GII.17’s are chocolate with pistachio nuts…something a little new and unusual, but a relative of the GII.4’s.
The GII.4 noroviruses have been the predominant type worldwide for over a decade, and a new GII.4 has popped up every couple of years to take its place as King of the Mountain, like GII.4 Sydney is now. By contrast, GII.17’s have been quite rare, though a few have emerged over the years.
The particular GII.17 of interest in Italy was genetically very similar to one first identified in Kawasaki, Japan in 2014. This February, it was detected in samples from two hospitalized Italian children, as part of that country’s regular disease surveillance. These findings were published a few days ago in Eurosurveillance. The two cases were from different parts of Italy, and were the only GII.17’s found out of 81 norovirus-positive samples for that norovirus season.
As for the U.S., last month, scientists at the National Institutes of Health published an article detailing a case of a GII.17 norovirus in a child in Maryland last November. Now that there is more sequence data on the new Asian varieties, the researchers checked this Maryland virus and found it to be genetically similar to the Asian GII.17’s, concluding it to be part of that group of viruses.
It is a little too early to know what this all means, but empirically, the novel GII.17’s have been spreading around in a manner not unlike the GII.4’s, and the GII.17’s in China we talked about before caused a greater than expected number of cases in their regions, possibly because these populations had not encountered that flavor of norovirus before. Only time will tell, but know that there are epidemiologists around the world keeping an eye on these GII.17’s.
Original article citations:
Medici, M.C., Tummolo, F., Calderaro, A., Chironna, M., Giammanco, G.M., De Grazia, S., Arcangeletti, M.C, De Conto, F., Chezzi, C., Martella, V. 2015. Identification of the novel Kawasaki 2014 GII.17 human norovirus strain in Italy, 2015. Eurosurveillance, 20 (35).
Parra, G.I. and Green, K.Y. 2015. Genome of emerging norovirus GII.17, United States, 2014. Emerg Infect Dis, 21(8).