BURLINGTON, Vt. – Four planes will drop a rabies vaccine over the northern third of Vermont this week to prevent the spread of rabies in wildlife.

About 400,000 vaccine-laced baits will be dropped from the low-flying planes in an attempt to vaccinate raccoons, skunks, coyotes and foxes. The bait drop is scheduled for Friday and Saturday. Bait will be dropped in Caledonia, Chittenden, Essex, Franklin, Grand Isle, Lamoille and Orleans counties. Packets will be placed by hand in some suburban and residential areas.

Thirty-nine animals have tested positive for rabies in Vermont this year, including 23 raccoons. Sixteen animals tested positive for the disease by mid-August of last year. No human cases of rabies have been reported in Vermont, and nationally, only one or two cases are reported each year.

The bait drop is designed to keep rabies from spreading across the U.S. and Canadian border.

“Rabies vaccine has nearly wiped out the disease in the domestic animal population, and the bait drop is an effective way to target wildlife that is susceptible to the disease,” said Dr. Robert Johnson, state veterinarian for the Vermont Department of Health, in a news release.

The bait cannot cause rabies if it is touched or eaten and is not harmful to children or pets, but officials advise that the pellets should not be disturbed so that wildlife can eat them.

The Health Department has asked that pet owners in the drop zone keep their dogs and cats indoors or away from the baits, which will be coated with fish meal.

The bait drop is a precautionary measure and does not rid Vermont of rabid animals.

Raccoon rabies was first confirmed in southern Vermont in 1994. Since then, hundreds of cases of rabies have been confirmed, and the outbreak has spread northward.