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Two weeks ago, in CDC FluView Week 14: Novel H1N1v Reported In Wisconsin, we looked at the second reported case of novel swine variant flu (H1N1v) in a human reported in the United States in 2021. In late January, we looked at the first case of the year - also from Wisconsin - but of subtype H3N2v.
While the United States has reported just over 470 cases since 2005, these spillover infections are thought to be more common than we know. Most mild flu cases go untested, and swine variant virus are only rarely are transmitted from person-to-person.
Swine variant infections (H1N1v, H1N2v, and H3N2v) are reported - albeit rarely - around the world, and last November we saw Alberta Canada Report A Rare Case of H1N2v `Swine' Flu. Most, but not all cases, report some contact with swine.
Whil 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
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 ModerateH3N2 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
While the risk of one of these swine variant viruses sparking a pandemic is relatively low, it isn't zero. A swine-origin H1N1v virus jumped to humans and sparked a mild-to-moderate flu pandemic in 2009, and the CDC currently ranks a Chinese Swine-variant EA H1N1 `G4' as having the highest pandemic potential of any flu virus on their list.
Today the Canadian Province of Manitoba made the following announcement on the detection of two unrelated swine variant cases.
Media Bulletin - Manitoba
April 30, 2021
TWO SEPARATE CASES OF VARIANT INFLUENZA VIRUSES IDENTIFIED IN MANITOBA
Two separate cases of variant influenza (flu) viruses have been found in two unrelated individuals in different communities in southern Manitoba. One is a case of human influenza A(H1N2)v and one is a case of human influenza A(H1N1)v.
The cases are the result of two different viruses and based on the case investigations, they are not linked. These cases have been reported to the Public Health Agency of Canada in accordance with international health regulations.
These two flu viruses are related to influenza viruses that circulate in pigs. Influenza viruses from pigs do not normally infect humans. However, sporadic human infections with influenza viruses that normally circulate in pigs have occurred. When this happens, these viruses are called ‘variant viruses’.The human influenza A(H1N2)v case and the human influenza A(H1N1)v both appear to be isolated cases. While these investigations are ongoing, the current assessment is that there is no increased risk to Manitobans, Canadians or the food supply chain at this time.The viruses were detected in early April after the two individuals independently sought testing after developing an influenza-like illness. The individuals experienced mild symptoms, were tested and then recovered. The tests came back negative for COVID-19, but were later identified as a case of human influenza A(H1N2)v and human influenza A(H1N1)v through regular influenza surveillance processes.The investigations are ongoing to determine how transmission may have occurred for these individuals. Both had either direct or indirect exposures to pigs. Based on available evidence, the current assessment is that there is no increased risk to people, with no evidence of sustained human-to-human transmission at this time.The viruses are not a food-related illness. They are not transmissible to people through pork meat or other products that come from pigs and there is no risk associated with eating pork.Health officials, in conjunction with Manitoba Agriculture and Resource Development, have launched a public health investigation to determine the source of the viruses and to verify that no spread has occurred. The Manitoba government will also continue working closely with the Public Health Agency of Canada and other partners across Canada to share information about these cases.Anyone who works with pigs or poultry, has influenza-like symptoms and is seeking testing or treatment is reminded to identify themselves as an agricultural worker to medical officials including at COVID-19 testing sites. This will help to identify any potential additional influenza cases.Sporadic human cases of variant influenza have been reported over the past decade in North America. Human influenza A(H1N2)v is rarely seen in humans, with only 29 cases reported globally since 2005, and no cases in Canada until one was reported in Alberta in October 2020.Human influenza A(H1N1)v is rarely seen in humans. This is the second ever case reported in Canada; the first was reported in Ontario in September 2012. Two human influenza A(H1N1)v cases were detected in the U.S. during the 2020-21 season.In most cases, variant flu viruses have not shown the ability to spread easily and sustainably from person to person.Health officials advise the detection of these cases could be occurring for a number of reasons including that increased respiratory surveillance for COVID-19 and influenza has been occurring during the pandemic. It is also possible that there is a true increase in the number of these cases, possibly occurring from exposure to infected pigs or through subsequent, limited human-to-human transmission.The increased respiratory surveillance currently done for COVID-19 and influenza allows Manitoba to continue to monitor for any new cases. No influenza cases have been detected since these cases were identified in early April, despite increased surveillance.While rare, influenza can spread from pigs to people and from people to pigs. It is important for people who have contact with pigs to take measures to reduce the spread of influenza viruses between pigs and people.
• Do not take food, drink or other items into pig areas and do not put anything in your mouth in pig areas.• Avoid close contact with pigs that look or act ill or are known or suspected to be sick. This includes minimizing contact with pigs and wearing personal protective equipment like protective clothing, gloves and masks that cover your mouth and nose when contact is required. Call a veterinarian if you suspect illness in pigs.• Wash your hands often with soap and running water before and after exposure to pigs. If soap and water are not available, use an alcohol-based hand rub.• Avoid contact with pigs if you have flu symptoms.• Anyone who is at high risk of complications from influenza should avoid pigs and pig barns. If you develop flu symptoms, call a health-care provider and tell them about your exposure to pigs. The same influenza antiviral drugs used to treat seasonal flu can be used to treat variant virus infection.
For more information on human influenza A H1N2v viruses, visit www.canada.ca/en/public-health/services/diseases/human-influenza-a-h1n2-v-swine-origin.html.
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While these cases in Canada are unlikely to be the vanguard of a new flu epidemic, it is important that local public health officials ramp up testing in order to detect any additional cases.
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:
