There’s yet another pig flu virus to watch out for.

Federal health officials say this one has made three people in Minnesota sick. Like the other unusual flu strains reported this year, this strain, called H1N2v, has only been found in people who had close contact with pigs at a state fair, the Centers for Disease Control and Prevention reported on Friday.

It’s becoming clear that pigs and people can pass influenza viruses back and forth. Health experts are watching the new strains closely because they can mutate and mix with one another to create even newer strains. The worry is the new strains will spread and cause flu pandemics, similar to the global outbreak of H1N1 swine flu virus in 2009. 

So far, the three new variants identified this year --  H3n2v (the little v stands for “variant”), H1N1v and now H1N2v – don’t spread easily from person to person. Almost everyone infected has been close to pigs. One person has died from the new H3N2v virus, but everyone else has recovered. H1N2v was reported twice  before in humans, in one person in 2007 in Michigan and in one person in Minnesota in 2011.

“This virus is different from the H3N2v virus that, as of today, is reported to have caused 296 human infections across 10 U.S. states since July 2012. These additional human infections underscore the fact that swine influenza viruses can spread to people after close contact with infected pigs, and support the importance of ongoing surveillance for both human and swine influenza viruses,” the CDC says in a statement on its website.

All three people who got sick in Minnesota with the new H1N2v virus have recovered but two had to be treated in the hospital. All three had close contact with a pig.

The new H1N2v virus appears to have already mixed with the H1N1 swine flu virus that caused the 2009 pandemic and that is now circulating as seasonal flu. CDC says the genetic sequence of the new virus shows it has a gene from the older H1N1 strain. Health experts are afraid that one of these new viruses will mutate or mix in a way that both makes it deadly and that gives it the ability to spread from person to person.

The good news is that the virus has at least one other gene that resembles circulating seasonal flu, meaning many people will have immune resistance to it, either from vaccination or from having had the flu.

These new variants of flu are very rare. “As of September 7, 2012, 335 cases of infection with variant influenza viruses have been reported in the United States since 2005. Of these 335 cases, 13 have been H1N1v viruses, 317 have been H3N2v viruses and 5 have been H1N2v viruses,” CDC says.

“With the exception of one death, the remaining 334 people infected with variant viruses recovered from their illness.”

The CDC estimates that anywhere between 3,000 to 49,000 people a year die from flu in the United States. A lot depends on the strains circulating. CDC recommends that everyone get vaccinated against influenza every year. The vaccine formula usually changes a little bit each year to match the most common flu strains, although this year's flu vaccine is not formulated to protect against the newly discovered pig flu viruses H1N1v, H1N2v or H3N2v.

Related links:

Ohio woman dies from new pig flu

New pig flu spreads to more people

CDC cautions about swine flu

(Updated Aug 11: CDC has raised the number of people confirmed infected to 153)

As many as 153 people have been infected this summer with a new pig flu virus, the U.S. Centers for Disease Control and Prevention said this week, although the disease does not appear to be any more serious than normal seasonal flu. Nine out of 10 of them are children, CDC says.

Most cases appear to be among people who were showing pigs, or people visiting fairs and other places where these pigs are, CDC says. This suggests they are catching the flu directly from infected pigs. So far everyone has gotten better on their own, Dr. Joseph Bresee, from the CDC's influenza division, told reporters on a telephone briefing Thursday.

“At this point there is no evidence of sustained, efficient human to human spread,” Bresee said. “This is not a pandemic situation.”

But Bresee cautioned that even seasonal flu can kill people and this is likely the case with the new form of flu, which is designated H3N2v.

The new strain of H3N2 was first seen last year, and three people were confirmed to have caught the bug from other people. So far it has not been any more serious than regular, seasonal flu, causing fever, a sore throat and achy muscles. Last year no one ended up in the hospital with the new flu. This year, two people have but they are fine now, Bresee said.

While the current flu vaccine does not protect against this new virus coming straight from pigs to people, patients can be treated with the two drugs that work against seasonal flu – Tamiflu and Relenza.

Most of the cases have been in Indiana, where 120 have been reported, the CDC said. There have also been 31 cases in Ohio, one case in Hawaii and one case in Illinois.

Flu viruses have eight genes, and this one is seven-eighths pig virus -- a virus designated H3N2 that’s been circulating among swine for years. But one single gene comes from the H1N1 swine flu virus that caused a new pandemic of influenza  among people in 2009 and which is now part of the human seasonal flu mix.

The names can be confusing because there's also an H3N2 virus that causes seasonal flu in people, and it's one of the three strains of flu virus that is included in the vaccine that's just arriving in doctor's offices and clinics now. "Get your flu vaccine," Bresee advised. "Everybody should get a flu vaccine this year in the U.S. because regular, seasonal flu will be here soon."

CDC stressed that only people who have contact with pigs are at any real risk of catching this flu. "This time of year is the time when you have state and county fairs…there’s thousands of them," Bresee said. CDC has some simple advice to prevent infection:

• Wash your hands after you've been near any live pigs
• Don't bring any food or drink into areas where live pigs are
• Stay away from swine if you are at high risk from flu, for instance if you are elderly or have a weakened immune system.

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