A person in California recently tested positive for plague, according to El Dorado County health officials. The individual has been treated and is recovering at home.
About seven people get infected by the bacterium responsible for plague, Yersinia pestis, each year, says the U.S. Centers for Disease Control and Prevention (CDC). Most U.S. cases occur in western states including Arizona, California, Colorado, New Mexico, and Nevada; in July, an Arizona man died from plague.
Here’s what to know about plague in the U.S.
How do people get plague?
People can contract plague after being bitten by infected fleas or touching infected animals like rats, mice, squirrels, chipmunks, prairie dogs, rabbits, mountain lions, ferrets, and even dogs and cats.
El Dorado County health officials said in a statement that the person was likely infected by a flea while camping. “Plague is naturally present in many parts of California, including higher elevation areas of El Dorado County,” said the county’s acting director of public health, Kyle Fliflet, in the statement.
What are the symptoms of plague?
There are three types of plague: bubonic, which caused widespread death throughout the world in the 14th century; septicemic, which occurs when the infection spreads to the blood; and pneumonic, when the infection burrows into the lungs. All forms cause fever and weakness, and more than 80% of plague cases in the U.S. have been the bubonic form.
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Dr. Scott Roberts, medical director of infection prevention at Yale New Haven Health System and assistant professor of infectious diseases at Yale School of Medicine, says that bubonic plague is centered in the lymph nodes; the bacteria travel to the closest lymph nodes in the body from where an infection-trigging bite occurs, which leads to an inflammatory reaction including swelling of the nodes. Plague can then progress into the blood, in which case it becomes septicemic. Finally, from the bloodstream, the bacteria can spread to the lungs, leading to pneumonic plague, which can cause shortness of breath and chest pain.
Is plague contagious?
Only pneumonic plague can be spread from one infected person to another, since the bacteria can be transmitted in droplets that are released when a person sneezes or coughs. This can cause disease in as little as a day after transmission.
Therefore, it’s “not a hard-and-fast rule” that plague progresses from bubonic to septicemic to pneumonic forms, says Roberts. For example, a health care worker in close contact with someone with pneumonic plague could inhale infectious particles from the patient; those particles could then travel directly to their lungs and result in pneumonic plague.
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He says that it’s not entirely clear why some people will recover from bubonic plague, while others continue to progress to more severe disease. Some of the usual factors—such as weaker immune systems in the very young and the elderly—are likely responsible, but the driving factors aren’t well known.
What is the treatment for plague?
Because it’s caused by a bacterial infection, plague can be treated with antibiotics. But it’s important to start treatment as early as possible; left untreated, plague can be fatal.
Do animals infected with plague get sick?
Some species do get sick from the bacterial infection, but others appear to be able to manage low-level, mild infections, which makes them reservoirs for the bacterium. Cats in particular seem to be susceptible to infection, making them potential transmitters to people.
In some regions of the world where the bacteria are more common, Yersinia pestis can cause large numbers of animals to die off, which can make people in the area even more vulnerable. “When the animals die off in an outbreak, the fleas try to find warm-blooded hosts, and those are likely human hosts,” says Roberts. “So sometimes animal die-offs in a region can precede human cases.”
How can I protect myself from plague?
Health officials urge people to avoid feeding wild animals, especially rodents and squirrels, and to never touch sick animals. Using insect repellent when outdoors, especially while camping or hiking, can also reduce the risk of being bitten by infected fleas. For dogs and cats, it’s important to protect them by using flea-control products and ensure they aren’t exploring rodent burrows.
Is there a vaccine for plague?
Older versions exist, but neither the World Health Organization nor U.S. health officials recommend them. The U.S. stopped making the vaccine available in 1999 after safety concerns and studies that questioned its effectiveness. Researchers are, however, exploring ways to develop more effective vaccines.