The second case of the influenza H1N2 virus ever recorded in humans was identified early this week in Minnesota.
The infant fell ill in October and has since recovered. The Minnesota Department of Health believes that the recovery and lack of transmission (no family members were sick) suggest that this virus is not a danger to the public.
H1N2 is a strain of flu that is typically found in swine – not humans. Interestingly, the infant had no reported contact with pigs. The CDC hypothesizes that “limited human-to-human transmission may have occurred.”
In addition to the new H1N2 case, ten cases of H3N2 have been reported in humans this year. Seven of the cases had contact with swine, while three cases from Iowa had no contact with swine, but contact with each other, suggesting transmission from person to person. The Iowa Department of Health has since increased surveillance for other cases but has found nothing.
What does this mean for the public? As health officials have affirmed, no new cases have been reported and these viruses do not seem to be extremely dangerous. The cases are, however, a reminder of the complexity of the influenza virus.
One might describe the virus, as Helen Branswell does in The Scientific American, as mercurial; or maybe fickle, devious and simply frustrating. Health effects can be mild to life-threatening. Epidemics can last for a few days or months. Some strains affect the immunocompromised more severely whereas with other strains, the impact is felt more heavily by healthy twenty-somethings. Influenza doesn’t discriminate. Further, unlike other viruses (for example, polio or the now eradicated smallpox), influenza cannot be prevented by one simple vaccine. As explained earlier on The Disease Daily by David Scales, this virus is constantly changing, forcing our policies to change with it. The influenza virus demands the attention of the health and vaccine community every season.
This new case of H1N2, while mild, serves as a reminder of the virus’s capricious nature; reminding the public health community to remain vigilant.
A Quick Tutorial on Influenza Virology
There are three types of influenza viruses, A, B and C. Influenza A and B are of more concern as they cause the seasonal epidemics in humans, whereas influenza C causes mild respiratory illness. Influenza A is the virus that you hear about in the news. It can be broken down into different subtypes based on the proteins on the virus’s outer layer. These antigenic (meaning that they cause our immune system to produce antibodies to attack) proteins, hemagglutinin and neuraminidase, are the “Hs” and “Ns” you see in flu names like H1N1. There are 16 different hemagglutinin subtypes and nine different neuraminidase subtypes.
Influenza viruses also change through two processes referred to as antigenic shift and antigenic drift. Antigenic drift is the change, which could be minute or drastic, in the proteins on the virus’s outer wall. It helps to think of drift as changes within existing flu viruses. These minor changes are why we need to get a new flu vaccine every year.
Antigenic shift is the genetic change that occurs enabling a flu virus to jump from one species to another. For example, one influenza virus type could be transmitted from a human to a pig. The virus could then change within that pig and produce a new strain of influenza, which could spread to another species.
To learn more about flu activity in your area, as well as where the nearest flu vaccination site may be, check out the Flu Near You Challenge. This innovative challenge is the result of collaboration between the American Public Health Association, Skoll Global Threats Fund and HealthMap. Take part in flu surveillance by reporting to this open and available tool once a week. For more on Flu Near You, check out this video.
For more information on the influenza virus, visit:
http://www.virology.ws/2009/09/22/the-a-b-and-c-of-influenza-virus/
