Bird flu has returned to the Midwest, with the announcement Friday that a highly pathogenic H7N8 was found in an Indiana turkey farm, forcing the killing of 60,000 birds. Since then, the USDA reported that another nine cases of avian flu have been detected near the same area, although eight of those are low pathogenic and the ninth is still being tested.

Here's what you should know:

1.) Is this a big deal?

Although this outbreak is so far relatively small – about 400,000 birds will be destroyed – it is a concern because of last year's devastating avian flu outbreak in the upper Midwest. That crisis, the worst outbreak of bird flu ever reported in North America, ultimately claimed 48 million birds and sent egg prices soaring. But it was a different strain of the virus, named H5N8.

2.) Why has it returned to Indiana?

No one yet knows or has made any announcements, but USDA and other scientists are researching the virus and may know more this week. Last year, it was blamed on wild birds during spring migration after an initial outbreak in Washington state.

Since July of last year, some 25,000 wild birds, either caught through hunting or capture, have been tested, said T.J. Myers, associate deputy administrator at the U.S. Department of Agriculture's Animal and Plant Health Inspection Service, or APHIS. The virus found in Indiana appears to be of "North American lineage," not "Asian lineage," Myers said.

So wild birds could again be blamed for the outbreak, Jürgen Richt, director of the Department of Homeland Security Center of Excellence for Emerging and Zoonotic Animal Diseases at Kansas State University wrote for the Genetic Expert News Service.

"Since low pathogenic H7N8 influenza viruses were found in poultry flocks in the area of the initial outbreak, it is possible that a low pathogenic H7N8 was introduced from wild birds into poultry flocks which subsequently mutated into a highly pathogenic avian influenza virus (HPAIV) during replication in turkeys. The limited information from USDA supports this possibility."

3.) What is the difference between H5 and H7? Low pathogenic and high pathogenic?

H5 and H7 have been common influenza virus subtypes found in wild birds through USDA-APHIS surveillance, according to Kyoung-Jin Yoon, a professor at Iowa State University College of Veterinary Medicine. Most of the time they are low pathogenic, which means the virus will sicken the bird but not kill it.

Occasionally the virus turns into highly pathogenic form, which kills the bird, because of a genetic change or mutation, Yoon said.

That appears to be what's at work in Indiana. Myers told Bloomberg Business News that the latest strain probably began as low pathogenic, then infected one or two farms before mutating into a highly pathogenic version.

All that said, both the H5 and the H7 strains post the same threat to the U.S. poultry industry, Yoon said.

"Historically both H5 and H7 strains has been implicated in HPAI (highly pathogenic avian influenza) outbreaks worldwide, so I would say this (highly pathogenic) H7 virus can be as bad as (highly pathogenic) H5 we had last year," Yoon said.

4.) You say the outbreak is so far relatively small, yet 400,000 dead birds seems like a lot. Why that many?

To put it into a little perspective, 237.5 million turkeys were produced in the U.S. in 2014, according to the National Turkey Federation. As the AP reported, the 400,000 birds affected by this flu must be euthanized according to "USDA protocols dictated by international trade treaties." As for how they are killed:

"The birds typically are killed using a type of suffocating foam, though due to cold weather, officials in Indiana also have had to use carbon dioxide gas and a device that delivers a fatal head injury. Some of the birds have also been suffocated by turning off poultry barns' ventilation systems."

5.) Has highly pathogenic H7N8 ever spread to humans?

The USDA says no, but cook with care.

"No human infections associated with avian influenza A viruses of this particular subtype (i.e., H7N8) have ever been reported. As a reminder, the proper handling and cooking of poultry and eggs to an internal temperature of 165 ËšF kills bacteria and viruses, including HPAI."