Plague has apparently now spread to eastern Fall River County where it has decimated prairie dog populations and made that area much less attractive for the reintroduction of endangered black-footed ferrets, wildlife officials say.

However, plague still has not been found in Conata Basin near Badlands National Park, site of the most successful black-footed ferret reintroduction in the country so far.

Plague first was confirmed in western South Dakota almost three years ago, when a rancher found a sick prairie dog in extreme southwestern Custer County and took it in for testing. Before that case, plague had not been confirmed in South Dakota for decades, although plague had wiped out prairie dog towns in eastern Wyoming.

Plague in prairie dogs and other animals (known as sylvatic plague) generally does not pose a widespread threat to humans, although people can get the disease (see related story).

However, the appearance of plague has wildlife officials worried about the already established ferret population in Conata Basin.

After the Custer County case, plague killed thousands of prairie dogs in a huge complex north of Oglala on the Pine Ridge Indian Reservation two years ago.

Since then, plague has spread on the reservation, with smaller outbreaks east of Oglala, to the Wolf Creek community northeast of Pine Ridge, west near the Prairie Wind Casino, and about 15 miles north just below Cuny Table and Red Shirt Table, according to Trudy Ecoffey, senior biologist with the Oglala Sioux Tribe Parks and Recreation Department.

Ecoffey said she thought last fall the plague would spread faster. But it hasn't moved far this summer, she said.

Although plague showed up northeast of Pine Ridge, it skipped other prairie dog towns between Oglala and Pine Ridge, she said.

Ecoffey said she estimates plague has affected 30,000 acres of prairie dogs. She said pockets of prairie dogs have begun showing up again at the huge complex just north of Oglala.

Now, plague is suspected of spreading west where it has killed sizeable numbers of prairie dogs in eastern Fall River County on the Buffalo Gap National Grassland, east of Smithwick, according to Fall River District Ranger Mike McNeill.

The die-offs are in the heart of an area targeted for a ferret reintroduction, he said.

Although no prairie dogs have been tested and confirmed with plague, they have disappeared from large colonies in the area. McNeill said plague is the most reasonable explanation.

Of 900-1,200 acres in the area occupied by prairie dogs a year or two ago east of Smithwick, only about 450-500 acres have prairie dogs now, according to U.S. Fish & Wildlife Service biologist Scott Larson of Pierre.

The die-off makes the area much less attractive as a site to reintroduce black-footed ferrets, Larson said. "It becomes a lower priority at this time."

But Larson wouldn't rule out the Smithwick area for a future ferret reintroduction. "We probably have better sites now than Smithwick. It might look entirely different in five years."

Ferrets can get plague by eating prairie dogs that have died of the disease or may get it from fleas that carry the organism, as prairie dogs do. Prairie dogs make up about 90 percent of the ferrets' diet.

Ferrets reintroduced elsewhere in the country have died from eating plague-infected prairie dogs, Larson said.

FWS officials have said plague in prairie dog towns has hampered black-footed ferret reintroductions in Wyoming, Montana, Colorado and Utah.

Officials also said ferrets can get plague from one flea bite.

Wildlife officials continue to worry about plague harming the estimated 250 black-footed ferrets now roaming Conata Basin just south of Badlands National Park's North Unit.

Conata Basin is about 40 miles northeast of the big Oglala complex hit hard by plague in 2005. With plague now approaching Cuny Table, it is about 25 miles from Conata Basin.

At Conata Basin, the government has spent years and millions of dollars to establish a population of black-footed ferrets, which were once thought to be extinct.

To protect the project, FWS crews have been dusting prairie dog burrows in Conata Basin with an insecticide that kills fleas, the primary carriers of plague.

This year, they will dust about 1,600 acres of at least 26,000 acres occupied by prairie dogs, Larson said. But the dusting is being done in an area known to be occupied by ferrets.

The dusting by itself won't keep the plague out of Conata Basin, Larson said. "We're hoping to hang onto a few ferret-occupied areas in case it comes in."

Now in its third year, the dusting appears to be reducing the number of fleas, according to David Jachowski, an FWS biologist with the national Black-footed Ferret Conservation Center in Colorado who is helping with the dusting. "We see fewer fleas on prairie dogs," Jachowski said.

Crews dusted 7,000 acres two years ago.

They spray an insecticide powder into the prairie dog burrows, where it gets onto the prairie dogs' hides and kills fleas.

Crews sprayed more than 300,000 burrows in 2005, according to Micah Reuber, a biologist with FWS, based in Wall.

Ironically, the FWS crews dusting for plague to prevent prairie dogs and ferrets from getting plague are working in areas not far from places where state crews have poisoned prairie dogs in recent years to keep them from spreading onto nearby private rangeland.

Ranchers have complained prairie dogs damaged vegetation on their private ground and on parts of the national grassland they lease for grazing.

The Nebraska National Forest, which administers the Buffalo Gap National Grassland, is considering expanding the poisoning to kill prairie dogs in the interior of Conata Basin beyond the public-private boundaries.

Most of the poisoning alternatives being considered are aimed at capping prairie dog acres on the national grasslands.

Environmental groups say the poisoning, particularly if expanded into the grasslands interior, poses a threat to the ferrets and other species, such as the burrowing owl, that depend on prairie dogs.

They argue that ferrets, one of the rarest mammals in the world, occupy just six-tenths of 1 percent of the national grasslands and some of the poisoning alternatives would reduce that percentage even lower. Livestock are allowed to graze on approximately 99 percent of the national grasslands.

Art Smith, wildlife-damage-management program administrator for the South Dakota Game, Fish & Parks Department, said none of the areas being dusted for fleas, in order to protect prairie dogs, are areas being poisoned to kill prairie dogs.

"In some areas, (the prairie dog) needs to be controlled," Smith said. "In other areas, it needs to be protected."

Meanwhile, Larson said, the annual ferret population survey in Conata Basin has just begun.

"They're finding decent numbers," he said. Last year's survey counted about 245 ferrets, he said.

But if plague gets into Conata Basin and threatens the ferrets, federal officials might move the ferrets elsewhere.

So far, it appears the plague has been confined to the Pine Ridge Reservation and a little way into Fall River County.

Ecoffey, who is monitoring the plague's spread on the Pine Ridge Reservation, said the disease eventually may reach Conata Basin, home of the endangered ferrets. "If it's here to stay, there's no reason to say it won't," she said.

Contact Steve Miller at 394-8417 or steve.miller@rapidcityjournal.com