When most people hear the word “plague,” they think back to the medieval epidemic that killed a third of Europe’s population, but was the plague really just an issue for the middle ages?

As it turns out, the plague is not just a symbol of times past – it is still in circulation.

Considered one of the the most deadly infectious diseases by the World Health Organization, there are three forms of the plague: bubonic, in which the host’s skin becomes infected, creating painful, swollen lymph nodes called buboes, as portrayed in medieval paintings; septicemic, in which the bacterium are in the host’s bloodstream; and pneumonic, in which the bacterium have found their way into the lungs are capable of traveling through cough residue.

Just this past July, four cases were reported in Colorado and another surfaced in China.

The Colorado cases were all believed to have surfaced after the four came into contact with the same infected, flea-bitten prairie dog.

The bubonic case in Yumen, China, resulted in the death of a 38-year-old man, who may have contracted the plague through interaction with a squirrel-like marmot.

Yumen was sealed off, putting 30,000 residents in lockdown and more than 150 who had been in contact with the diseased man in quarantine. Even after nine days, no one else showed symptoms of the plague.

Symptoms typically take two to seven days to appear, but only one day in cases of pneumonic plague. These symptoms include swelling of the lymph nodes, fever, headache, blackened skin and possibly coughing and trouble breathing.

The United States Centers for Disease Control & Prevention (CDC) says present-day antibiotics are capable of fighting the plague, but must be treated early.

Plague rises from the bacteria Yersinia Pestis, which use fleas as hosts. It spreads into the gut and stomach of the flea and tampers with the digestive route so the flea discharges the bacteria into the bloodstream of any other animal it bites (commonly a rodent), thus spreading the disease.

American cases tend to occur more often in the western area of Colorado, chiefly because there are more rodent species present to spread the disease.

Ken Gage of the CDC said in an npr.org interview that once rodent densities rise above a certain level, the risk of the plague surfacing and spreading greatly increases.

As of recent years, the United States has been seeing between one to 17 cases of plague per year, averaging seven.

However, the worldwide count of reported cases tallied to 1000 to 2000 per year, according to the World Health Organization.

In late 2013, the Huffington Post reported 20 villagers at once who died of the bubonic plague on the island of Madagascar.

Similarly, the CDC says that Madagascar and sub-Saharan Africa have accounted for 95 percent of worldwide plagues cases in recent years. This is suspected to be due to unsanitary conditions, particularly in Madagascan prisons.

To avoid contracting plague, it is wise to avoid contact with dead animals.

The Mayo Clinic recommends seeking immediate medical attention at any signs of becoming ill.