Could raw milk — or a cat — help explain how a person who had no contact with animals caught the virus?

News that a person in Missouri contracted H5 bird flu despite having no known contact with infected animals or birds — in other words, no evident route of infection — raises pressing questions public health officials are surely scurrying to answer.

The rationale for that urgency is this: An unexplained H5 infection raises the possibility of person-to-person spread of a flu virus that has never before circulated in humans, and to which people would not have immunity. And this with a dangerous flu virus that scientists have long feared could someday trigger a pandemic.

To be clear, it is far too soon to conclude this infection can’t be linked to some direct or indirect exposure to infected animals or birds, or to some farm product contaminated with the virus.

But there are, as we noted, questions that need to be answered, and the sooner the better. Here are five.