Nobody knows what it is or where it's come from. Most of the sources are Norwegian, but it's spread all over Norway.

This is a timeline of the news since Sept 5 (click "Vis flere"):

https://www.nrk.no/nyheter/mystisk-hundesykdom-1.14689833

Here are more sources:

https://www.vg.no/nyheter/innenriks/i/0nkmk6/bianca-7-fikk-s...

https://www.nrk.no/ostlandssendingen/atte-nye-tilfeller-av-s...

https://www.aftenposten.no/norge/i/dOPwpo/Dette-er-de-12-for...

https://www.aftenposten.no/norge/i/kJX3ov/Vet-ikke-om-vi-vil...

https://www.vg.no/nyheter/innenriks/i/K31n1y/spania-advarer-...

https://www.vg.no/nyheter/innenriks/i/P9moz7/skrev-oppgave-o...