DNR: Deadly deer disease shows ‘exponential growth’ in Iowa

A fatal neurological disease that affects whitetail deer has become a statewide concern and is poised to rapidly become a bigger threat in parts of Iowa.

That’s because chronic wasting disease has been increasingly detected in central Iowa — far away from known hotbeds of infections — and because about 10 years have lapsed since its first appearance in the state.

“We know based on data and how the disease has progressed in other states that we would expect to see this kind of slow progression for the first six to 10 years, and then once the disease is established, this exponential growth,” said Tyler Harms, a wildlife research biometrician for the Iowa Department of Natural Resources. “In areas where we’ve had it the longest, like in northeast Iowa, we should expect to see some pretty rapid growth.”

The DNR’s surveillance program discovered 96 deer with the disease last year, which is nearly double what it found the year before. Nearly all of them were in far northeast or southern Iowa where the disease has lingered for years.

But two infected deer were also found in central Iowa, in Grundy and Jasper counties. And the DNR recently announced it had confirmed the disease in a deer in Marshall County. Another infected deer was discovered in Greene County in 2021.

“What it tells us is we need to start being concerned about this disease, kind of at a statewide scale,” Harms said. “We’ve always done statewide surveillance, but picking up these detections in central Iowa — far outside of where we have these established zones — just lends more evidence to the fact that this disease can pop up almost anywhere.”

The state tests thousands of tissue samples each year from road kill carcasses and hunted deer. The DNR has also created targeted hunts in areas where the disease has been found, which aids its testing and helps control population growth.

It’s unclear how the disease migrated to central Iowa. Deer tend to live relatively close to where they are born but can travel long distances. Carcasses of infected deer that are transported away from where they were hunted also have the potential to spread the abnormal protein that causes the disease.

That protein — known as a prion — damages the brains of infected deer and eventually kills them, but the process takes months or years. Many infected deer appear healthy. Those in the advanced throes of an infection loose weight, become less afraid of humans, drool and move awkwardly, among other symptoms.

The prions spread among deer via bodily fluids and feces, but they also persist in the environment and can be infectious for years. Deer can become infected by ingesting contaminated water or food.

The DNR advises people to avoid putting out food for deer, which can cause the animals to congregate. It also suggests that hunters dispose of carcasses in the areas where they killed the deer.

The prion was identified in captive deer at a Colorado research facility in the 1960s and was found in wild deer in 1981, according to the U.S. Centers for Disease Control and Prevention. It has infected deer in more than 30 states, and was first discovered in Iowa in 2013 in Allamakee County — at the northeast corner of the state.

Marshall County is the 16th Iowa county known to have the disease.

More than a quarter of the infected deer discovered last year were felled during special hunts in Allamakee, Clayton and Wayne counties, Harms said. About 10% of deer killed during those hunts were infected.

In Wisconsin, where the disease was first discovered in 2002, one county’s male deer population is about 50% infected, Harms said.

“I hope that we don’t get to that point,” Harms said. “I hope that we can maintain some pressure on the population to keep that number low, but time will tell.”

The disease has not been shown to infect humans, but the CDC advises people not to eat the meat of infected deer. It has the potential to decrease the number of trophy deer in Iowa, which is a destination for hunters who spend more than $200 million annually in the state.

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