What you need to know about the biggest confirmed killers in the US

Top line

Colorado health officials on Tuesday confirmed a rare human case of bubonic plague, urging people to be on alert for the deadly bacterial infection that fueled some of the deadliest pandemics in history and still sickens a handful of people in the U.S. each year.

Key facts

The plague is caused by the Yersinia pestis bacteria that can infect humans and a wide range of animals, particularly small mammals such as rats, woodchucks, prairie dogs, rabbits, mice, squirrels, and chipmunks.

Plague is most commonly spread through the bites of infected fleas, although humans can also become infected through direct contact with contaminated body fluids or tissues, such as by handling an infected animal or caring for someone without protective equipment, or by inhaling infectious airborne droplets, which could come from the cough of infected people or animals, such as cats.

The disease manifests itself in three main ways depending on how the person is infected, the most common being bubonic plague, caused when the bacteria enters the body and multiplies in the lymph nodes, and septicemic plague occurring if the bacteria enters the bloodstream, which can happen directly or through an untreated case of bubonic plague.

Pneumonic plague is by far the most severe form of the disease and the only form of plague that can spread directly between humans, occurring when plague bacteria reach the lungs, emerging as quickly as a day after inhalation of infectious droplets, and killing within as little as 18 hours of onset.

Plague is an incredibly serious disease that can cause fever, chills, fatigue, and headache, as well as painful pus-filled swellings known as buboes for the bubonic form, death and blackening of skin and tissue for the septicemic form, and severe pneumonia symptoms such as difficulty breathing, chest pain, and cough for the pneumonic forms.

While plague can be easily treated with antibiotics, the rapid progression of the disease means that it must be diagnosed and treated very quickly (if treated early and within 24 hours of the onset of symptoms, recovery rates from plague are high) and, if left untreated, bubonic plague kills up to 60% of people, while pneumonic and septicemic plague are invariably fatal.

How can you protect yourself against pests?

Plague is distributed worldwide, circulating naturally among animals and their fleas on every continent except Oceania, according to the World Health Organization, and Antarctica. In the U.S., plague is most common in rural areas of the West, Southwest, and Rocky Mountains, including Arizona, Colorado, and particularly New Mexico. There are about seven cases in the U.S. each year, according to the Centers for Disease Control and Prevention. To reduce your risk of contracting plague, the CDC recommends taking steps to reduce the number of rodents around you and protect yourself against potential flea bites. This includes using flea repellent on your skin during activities like camping or hiking that might expose you to fleas, applying flea control products to pets and clothing, and taking steps to “reduce rodent habitat” around homes, workplaces, and recreational areas by removing trash and weeds and securing pet and animal food, as well as “rodent-proofing” buildings. While plague vaccines have been used since the late 1800s, they have not been evaluated to modern clinical standards and do not appear to be very effective. There is no commercial plague vaccine in the United States, and vaccines are only rarely used in some countries for people with high exposure to plague through their work. New plague vaccines are in development but “are not expected to be commercially available in the immediate future,” the CDC said.

Peg News

The Colorado case is one of several plague cases reported in the United States this year. It comes several months after a man in New Mexico died after contracting the plague in March and another case in Oregon in February, which was the first reported in the state in nearly 10 years.

Worldwide, cases are much higher, and according to the CDC, between 2010 and 2015, 3,248 people were infected with plague, mostly in Madagascar, the Democratic Republic of the Congo and Peru. Of those infected, 584 people died.

Key Background

While modern plague outbreaks are relatively small and infections can be treated with antibiotics, this has not always been the case. Plague is known as one of the biggest killers in history and has terrorized humanity for centuries. The microbe Yersinia pestis It is believed to be responsible for several of humanity’s deadliest pandemics, including the Black Death, which wiped out a third of Europe’s population in the 14th century — some 25 million people — and the Plague of Justinian, which ravaged Asia, Europe, and parts of Africa some 800 years earlier, killing around half the world’s population at the time — between 30 and 50 million people. In total, researchers believe the plague has killed more than 200 million people over time.


Despite the availability of antibiotics, health safety experts are concerned Yersinia pestis In the future, the virus could be used as a bioterrorist weapon, and health authorities in the United States and other countries are prepared for possible attacks using this agent. In the United States, it is considered a “high priority” agent due to its “potential threat to national security.” Although experts stress that it is unlikely that a terrorist would use a biological weapon against the plague, there are multiple examples of its use as a biological weapon throughout history.

Can your cat or dog give you the plague?

The infected Oregon native is believed to have contracted the disease from a domestic cat, officials said. Animals are considered vulnerable to exposure because of their propensity to catch and eat rodents, which may be infected or harbor infected fleas. The CDC advises people who live in areas where the disease is known to circulate not to allow dogs or cats to sleep in their beds.

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