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In April of this year (see Manitoba Public Health reported on two unrelated swine variant flu infections) and again in July (see Canada: Manitoba Public Health Announces 3rd Swine Variant Case (H3N2v)), Manitoba province announced rare novel swine variant flu infections (H1N1, H1N2 & H3N2).
While reports out of Canada have been relatively rare, the United States has reported 483 cases over the past dozen years, including 14 during the 2020-2021 flu season, and two more since the start of the 2021-2022 flu season in October (see CDC FluView Week 46: Another Novel Flu (H1) Variant (Oklahoma) While Seasonal Flu Slowly Climbs).
These spillover infections are thought to be more common than we know, but most mild flu cases go untested, and are unlikely to be picked up by surveillance. Human-to-human transmission has been reported, but only rarely.
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
Yesterday Manitoba announced their 4th case of 2021, this time involving H1N2. While this appears to be an isolated case, with the patient reporting direct contact with swine prior to falling ill, the incidence of novel flu detections in Canada has increased this year.
Health officials offer two plausible explanations:
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.
While we watch the more exotic (and often deadlier) spillovers of H5 & H7 avian flu closely, over the past 130 years all influenza pandemics have sprung from the H1, H2, or H3 subtype (see Are Influenza Pandemic Viruses Members Of An Exclusive Club?) - and as we saw with the H1N1 pandemic in 2009 - some of those have come from swine.
As a result, we follow swine variant infections closely.
The full report from Manitoba Public Health follows:
Media Bulletin - Manitoba
December 2, 2021
CASE OF VARIANT INFLUENZA VIRUS IDENTIFIED IN MANITOBA
Manitoba Agriculture and Resource Development advises a new case of a variant H1N2 (influenza A) flu virus has been identified. The case has been reported to the Public Health Agency of Canada in accordance with international health regulations.
This flu virus is 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’.
This human influenza A(H1N2)v appears to be an isolated case. The current assessment is that there is no increased risk to Manitobans, Canadians or the food supply chain at this time.
The virus was detected in October after the individual independently sought testing after developing an influenza-like illness. The individual experienced mild symptoms, was tested and then recovered. The test came back negative for COVID-19, but was later identified as a case of human influenza A(H1N2)v through regular influenza surveillance processes.
The individual had direct exposure to pigs. Based on available evidence, the current assessment is that there is no increased risk to people, with no evidence of human-to-human transmission at this time.
The virus 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.
Health officials, in conjunction with Manitoba Agriculture and Resource Development, have performed a public health investigation to determine the source of the virus and have not identified any further spread. The province will also continue working closely with the Public Health Agency of Canada and other partners across Canada to share information about this case.
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. One case was reported in Alberta in October 2020 and one in Manitoba in April 2021.
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.
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. Additional tips to help reduce the risk of spreading influenza viruses include:The same influenza antiviral drugs used to treat seasonal flu can be used to treat variant virus infection.
- 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; and
- 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.
In April, Manitoba reported two separate cases of variant influenza viruses found in two unrelated individuals in different communities in southern Manitoba. One was a case of human influenza A(H1N2)v and one was a case of human influenza A(H1N1)v. In June, Manitoba reported an unrelated case of H3N2 variant influenza.
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.
