BILLINGS (AP) -- Anthrax has killed four cattle in northeast Montana in the state's second case of the disease this month, the state veterinarian said Thursday.

The cattle were from a ranch near Culbertson, in the same general area as the earlier anthrax cases, the Department of Livestock said. The agency initially put the number of dead cattle in the first case at 37, but spokeswoman Karen Cooper said Thursday two additional animals had also died.

Prior to that case, anthrax had not been confirmed in Montana since 1999, the agency said.

State Veterinarian Tom Linfield said the site of Montana's more recent case is under quarantine and will remain so for about 40 days. Remaining cattle in the herd have been moved to an alternate pasture and given antiobitics and vaccinations, he said.

Last week, when Linfield announced the first case, he said he wouldn't be surprised if there were more.

Anthrax is caused by a spore-forming bacterium found naturally in some soil types, the department said. Spores can live in soil for decades, and livestock -- such as cattle, sheep and goats -- can get infected after inhaling or ingesting spores during grazing, it said.

Anthrax often occur follows changes in climate, though land disturbances, such as road work, can also turn up spores, the department said.

Linfield encouraged ranchers to have their cattle vaccinated, saying that conditions are right for naturally occuring anthrax not only in northeast Montana but also, potentially, other parts of the state.