Fleas in Arizona have tested positive for the plague and could spread the deadly disease to humans , according to officials . The plague , which famously killed millions of Europeans during the Black Death , is most commonly carried by fleas and rodents . Prairie dog deaths at Picture Canyon in Arizona alerted officials to the possibility of an outbreak . Parasitic insects from the preserve near a water treatment plant in Flagstaff were found to carry the illness . Scroll down for video . Authorities near Flagstaff , Arizona , have found fleas infected with plague after prairie dogs in Picture Canyon began dying ( file photos ) The plague , which killed millions of Europeans in the 1300s , causes pustules on the skin and is still contracted by 2,000 people a year ( file photo ) Human cases have developed from close contact with cats who have preyed on infected vermin and residents in the Southwest have been warned about dangers of the disease while camping . The Southwestern US is similar to the plains of Central Asia where plague began , Professor David Wagner of Northern Arizona University told the Arizona Daily Sun . Plague is still contracted by as many as 2,000 people a year , according to the World Health Organization , though the vast majority of cases are in sub-Saharan Africa and Madagascar . Prairie dogs are particularly susceptible to illness because they live in social burrows , and 90 per cent of the furry creatures ' colony can eventually be wiped out if plague infects one member . The disease 's rodent host dies , when fleas will look for more blood to drink , including from people . The vast majority of human plague cases reported in the US are in the arid climate of the Southwest , which scientists say is similar to the disease 's homeland of Central Asia . The discovery of the disease at Picture Canyon ( pictured ) has prompted a warning from authorities about the dangers posed by dead rodents . Insecticide has been sprayed in prairie dog burrows in Picture Canyon to halt the plague 's spread . Symptoms of pain in humans include fever , chills and muscle pain . At later stages it causes gangrene and a large amount of pustules , or buboes , on the skin . The incubation period could be up to seven days . Modern medications are effective in fighting the plague , also known by its bacterial name Yersinia pestis , though it can be deadly if left untreated . The last plague epidemic in the United States was in Los Angeles between 1924 and 1925 , according to the Centers for Disease Control . Plague originally came to North America via rodents on steamships from Asia . The bacteria Yersinia pestis originally came to North America on steamship rodents from Asia , and the last outbreak was in Los Angeles in 1924 .
Prairie dog deaths at Picture Canyon led to positive tests on fleas . Residents warned about dangers to pets , especially cats . Disease can wipe out 90 per cent of prairie dogs in a colony .