Highly pathogenic avian influenza has been detected in dairy herds in three more counties - Ionia, Isabella, and Ottawa - bringing the total number in Michigan to four.
The first herd to test positive was in Montcalm County on March 29.
The virus is highly contagious and fatal among poultry.
It is now spreading to dairy herds after being found in Texas, although veterinarians say it doesn’t affect cows the same as poultry: with care, they can recover.
The risk to humans remains low.
The department’s director says the virus does not stop at county or state lines and asks all producers and farm owners to be on high alert.
They are urged to tighten up biosecurity measures to avoid spreading the virus between groups of farm animals, or from wild birds which can carry it.
The virus can be spread directly between animals, or indirectly through items such as feed, equipment, and the clothing and shoes of caretakers.
Officials say the commercial milk and egg supplies remain safe, and there is no increased risk to consumer health.
