Seven US counties under plague warning as experts say prairie dogs are good indicator of outbreak

Health experts say a decline in prairie dog populations during the summer suggests plague has returned

Fleas transmit plague bacteria to humans (Rocky Mountain Laboratories)

Health authorities in Colorado are warning residents in seven counties to be on guard against the re-emergence of plague in the region.

Though not nearly as fatal as it was in medieval times – when it killed an estimated 50 million people – the disease can still be deadly in the modern era. This year's bout of plague has already killed a 10-year-old girl in the state.

The plague returns to Colorado every summer, generally carried by fleas before being passed along to small animals and in some generally rare cases, humans. This year, San Miguel County, El Paso County, Boulder County, Huerfano County, Adams County and La Plate County have all reported cases of the plague.

The girl who died reportedly raised hogs, according to The Durango Herald. It is not known definitively whether fleas leapt from her hogs to her and passed along the infection.

Health authorities began scrambling to collect and test fleas after a group of Coloradans reported that a local prairie dog colony had disappeared, according to The Colorado Sun.

The Colorado Department of Public Health & Environment notes that prairie dogs are especially susceptible to plague. Whenever a population of the animals goes silent during the summer, it is a warning to Colorado health authorities that plague has potentially returned.

The CDPHE has asked Coloradans not to kill the rodents, as it could increase the risk of transmitting the plague.

“If you notice decreased rodent activity in an area where you normally see active rodents, contact your local public health agency,” the CDPHE said.

Plague can be transmitted to a human through the bite of an infected flea or through direct contact with infected animals.

Plague can be difficult to pinpoint initially, as its symptoms are similar to other illnesses, like the flu or the coronavirus. The infected may develop a cough, fever and swollen lymph nodes.

Thankfully, if the plague is caught early, it can be treated with available medicine. If left untreated, however, it can cause further illnesses and death.

On average, seven humans become infected with the plague each year, and the infections are generally located in New Mexico and Colorado.

Plague – sometimes called the “Black Death” – is believed to have arrived in the Americas by way of rats that had infested steam ships travelling between Asia and North America.

Once the ships moored in American harbours, the rats would sneak off and begin to spread the disease.

Today, the plague is almost entirely contained within a rural region of northern New Mexico and southern Colorado.