Thursday, November 05, 2020

Alberta Canada Reports Rare Case of H1N2v `Swine' Flu



For the past decade, mostly during the summer and fall, we have been on watch for reports of novel swine flu infections in humans, which are usually associated with swine exposure at county or state fair exhibits, or the raising of pigs.

Since 2005, over 465 human `swine variant' infections (H1N1v, H1N2v or H3N2v) have been documented in the United States, with over 300 of those reported in 2012.  H3N2v viruses have been, by far, the most common - followed by H1N2v and then H1N1v. 

The CDC's Risk Assessment for these viruses reads:

Sporadic infections and even localized outbreaks among people with variant influenza viruses may occur. All influenza viruses have the capacity to change and it’s possible that variant viruses may change such that they infect people easily and spread easily from person-to-person. The Centers for Disease Control and Prevention (CDC) continues to monitor closely for variant influenza virus infections and will report cases of H3N2v and other variant influenza viruses weekly in FluView and on the case count tables on this website 
While most swine variant infections don't appear to transmit well in humans, the CDC's IRAT (Influenza Risk Assessment Tool) lists 3 North American swine viruses as having at least some pandemic potential (2 added in 2019).
H1N2 variant [A/California/62/2018]  Jul   2019   5.8  5.7 Moderate
H3N2 variant [A/Ohio/13/2017]          Jul   2019   6.6  5.8 Moderate
H3N2 variant [A/Indiana/08/2011]      Dec 2012   6.0  4.5 Moderate 

This year, likely due to the shuttering of county and state fairs around the United States and the world, we've only seen 1 U.S. case (H3N2v in Hawaii)

Global surveillance for these types of viruses, however, is quite limited.
It is likely that far more cases occur than are reported. Earlier this year, in WHO: Influenza A(H1N2) variant virus – Brazil we looked at a recent case reported from South America, and in mid July the WHO reported on a case in Germany. 

Over the summer we also saw renewed concerns over the evolution and spread of an EA H1N1 `G4' virus in China (see PNAS: Eurasian Avian-like H1N1 Swine Influenza Virus With Pandemic Potential In China), prompting the CDC, ECDC, and WHO to issue statements and risk assessments.

While most swine variant detections end up being a brief flash in the pan, every once in awhile - as we saw in the spring of 2009 - it can herald something bigger.  So we take note whenever a case is detected by surveillance. 

Yesterday Alberta Health officials announced the discovery of Canada's first known H1N2v infection in a resident living in central Alberta. An investigation is ongoing into the source of this novel virus (no known exposures are listed), and increased testing in the region is underway.

First this statement from the CMO of Alberta, then I'll return with a brief postscript.

Influenza A (H1N2)v: Chief medical officer of health and chief provincial veterinarian

Dr. Deena Hinshaw, chief medical officer of health, and Dr. Keith Lehman, chief provincial veterinarian, issued the following statement on Influenza A (H1N2)v in Alberta:

“A confirmed case of variant Influenza A (H1N2)v has been detected in central Alberta. This currently appears to be one isolated case and there is no increased risk to Albertans at this time. This is the only influenza case reported in Alberta so far this flu season.
“The virus was detected in mid-October after an Alberta patient sought medical care with influenza-like symptoms. The patient experienced mild symptoms, was tested and then quickly recovered. There is no evidence at this time that the virus has spread further.
“Health officials, in conjunction with Alberta Agriculture and Forestry, have launched a public health investigation to determine the source of the virus and to verify that no spread occurred. The Government of Alberta will continue working closely with Alberta Health Services, the Public Health Agency of Canada and other partners across Canada.
“AHS will proactively offer influenza testing to residents in parts of central Alberta if they are presenting for COVID-19 testing at an AHS assessment centre. This testing will be optional and supports our ongoing influenza surveillance in the region.
“We are taking this seriously, but Albertans should know that sporadic cases of variant influenza have been reported over the past decade in North America. Variant Influenza A (H1N2) is rare with only 27 cases reported globally since 2005, and no cases in Canada prior to this one.
“H1N2 is not a food-related illness. It is not transmissible to people through pork meat or other products that come from pigs and there is no risk associated with eating pork.
“We will keep Albertans informed of the outcomes of the public health investigation.”

While this Albert case will likely end up being a self-limiting event, swine flu viruses - like avian and seasonal flu - continue to evolve and occasionally jump species. Making it only a matter of time before a new novel virus manages to adapt well enough to human physiology to spark another pandemic. 

As we explored in Are Influenza Pandemic Viruses Members Of An Exclusive Club? - swine influenza viruses are typically either H1, H2, or H3 - giving them a distinct advantage, as those are the only influenza subtypes known to have sparked a human pandemic in the last 130 years. 

A few other recent studies on swine-origin influenza include: