Plague is a bacterial illness caused by a germ named “Yersenia pestis.” It’s been around for centuries, but doesn’t cause the deadly epidemics of times past. Cases tend to be scattered, and mainly happen in rural and semi-rural settings — with most concentrated in the Southwest and Western United States.

The “Four Corners” generally has the most cases. Worldwide, case numbers are much higher and tend to happen in Southeast Asia and Africa.

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Plague usually is caused by a bite from an infected flea. The flea then passes the germ into the body and bloodstream of whatever it bites — animal or human. When it comes to animals and fleas, the bites can cause of cycle of infection, meaning the flea can give the plague to an animal and vice versa.

There are basically three forms: bubonic, septicemic and pneumonic.

The bubonic form typically begins with flu-like symptoms and a large or cluster of large swollen lymph nodes (known as buboes) that swell near the site of the bite. If untreated with antibiotics, bubonic plague can spread to other parts of the body. About 80 percent of plague seen in America is bubonic.

Septicemic plague is the type where the bite spreads the germ into the bloodstream where it can attack the lungs and other organs of the body. This type of plague is very difficult to diagnose since the symptoms are mainly flu-like, which sometimes can be mild at first, and then worsen rapidly — causing shock and death within hours. Again, this is an easily missed diagnosis especially early on.

Pneumonic plague is when the germ gets into the lungs where it causes a rapid and severe pneumonia, often causing a bloody cough. This is the most severe type of plague, and the only form that can be spread person-to-person (by cough). This type of plague is usually fatal.

Once again, plague is usually spread by the bite of a flea. The flea first bites an infected rodent, and then bites a human, injecting the bacteria as it looks for a fresh food source.

Even the young and healthy can become sick.

The timeframe from bite to illness is typically 2-7 days.

It can be diagnosed with blood and tissue testing, and treated with antibiotics.

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Besides early diagnosis and treatment, prevention is a key when it comes to plague.

Here are some tips:

– Stay away from all sick rodents, rabbits and prairie dogs. Don’t play with or feed even those that appear healthy.

– While hiking, wear long pants and sleeves — and apply insect repellent.

– Keep in mind that your pet can carry fleas, especially a pet that roams outside.

– Be aware of “die off”. This means, say a prairie dog colony that once was well populated and vibrant, but then goes silent. Health officials would then check to see if plague rapidly killed off a colony of prairie dogs.

– Sick pets should be examined by your vet ASAP — last year four people in Colorado got sick with plague from an infected dog.

– Bites from wild rodents as well as cats and dogs can cause plague. See your doctor right away if you are bitten.

– Any unusual illnesses, especially those that are flu-like (and show up this time of year) should be checked out.

For more information:

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Dr. Dave Hnida is CBS4’s Medical Editor. He blogs about the latest studies and trends in the health world. Read his latest blog entries, check out his bio or follow him on Twitter @drdavehnida