As spring turns into summer we turn our flu attention away from seasonal flu (at least, in the Northern Hemisphere) to another influenza threat which has emerged in recent years; human infection with swine-variant flu viruses.
Over the past 15 years we've seen more than 460 confirmed human infections with these swine-origin viruses, mostly associated with pig exposure at county and state animal exhibits.
|Swine Variant Human Cases : 2010-2018 - Credit CDC|
While the number of cases vary greatly from year-to-year, with our county and state fair season beginning in June, it would not be unexpected to see outbreaks - in swine, and humans - in the coming months.
Although most of the reported swine variant infections over the past decade have been mild-to-moderate in severity, some people have required hospitalization, and deaths - while rare - have occurred (see J. Virology: Analysis Of A Swine Variant H1N1 Virus Associated With A Fatal Outcome).The CDC's general risk assessment of these swine variant (H1N1v, H1N2v, H3N2v) 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 websiteLast week the CDC released updated interim guidance for clinicians who may see suspected swine-variant influenza cases in the coming months. In addition, a CDC Expert commentary has been published by Medscape (link).
Due to its length I've only posted the first two sections, follow the link to read it in its entirety. I'll have a bit more when you return.
Influenza A viruses circulating in swine that have infected humans are referred to as “variant” viruses and denoted with a letter “v”. Human infections with H1N1v, H3N2v and H1N2v viruses have been detected in the United States.
Most commonly, human infections with variant viruses occur in people with exposure to infected swine (e.g., children near swine at a fair or workers in the swine industry). There have been documented cases of multiple people becoming sick after exposure to one or more infected swine and rare cases of limited spread of variant influenza viruses from person-to-person. The vast majority of human infections with variant influenza viruses do not result in person-to-person spread. However, each human infection with a swine influenza virus should be fully investigated to be sure that such viruses are not spreading in an efficient and ongoing way in humans and, if infected animals are identified, to limit further exposure of humans to these animals.
Clinical characteristics of human infections with variant viruses generally have been similar to signs and symptoms of uncomplicated seasonal influenza, including fever, cough, pharyngitis, rhinorrhea, myalgia, and headache. Vomiting and diarrhea also have been reported in some infections in children. Milder clinical illness is possible, including lack of fever. The duration of illness appears to be similar to uncomplicated seasonal influenza, approximately 3 to 5 days. While assumed to be similar to seasonal influenza virus infection, the duration of viral replication and possible infectiousness of variant virus infection has not been studied.(Continue . . . )
Exacerbation of underlying conditions (e.g., asthma) has occurred. The same people at increased risk for complications of seasonal influenza are likely at high risk for serious complications from variant virus infection, including children younger than 5 years, pregnant women, people 65 years and older, those who are immunosuppressed, and persons with chronic pulmonary, cardiac, metabolic, hematologic, renal, hepatic, neurological or neurodevelopmental conditions, as well as those with other co-morbidities, including extreme obesity.
We regularly cover swine and swine variant influenza in this blog, both in North America and around the world. A few studies over the past year include:
BMC Vet.: Novel Reassortant H1N2 & H3N2 Swine Influenza A Viruses - Chile
J. Virology: Pathogenesis & Transmission of H3N2v Viruses Isolated in the United States, 2011-2016
JVI: Divergent Human Origin influenza Viruses Detected In Australian Swine Populations