This digitally-colorized scanning electron micrograph (SEM) depicts a number of purple-colored Yersinia pestis bacteria, the pathogen that causes bubonic plague. National Institute of Allergy and Infectious Diseases (NIAID) A child who got the plague while camping in Yosemite National Park in July is now recovering, the LA Times reported.

After a family visit to the park's Crane Flat National Campground, the child fell ill and was hospitalized. State officials are now working with public health, park, and forest officials to find out how he or she got sick.

The child's infection was caused by the same bacterium (Yersinia pestis) that was the culprit in the Black Death, which decimated Europe's population in the 14th century. People can become infected by a flea bite, or by contact with an infected animal, such as a squirrel, chipmunk, or other rodent.

Plague has a 3-to-7 day incubation period, and causes flu-like symptoms including high fever, chills, nausea, weakness and swollen lymph nodes in the neck, armpit, or groin.

There are 3 different kinds of plague, depending on the type of infection: bubonic, septicaemic, and pneumonic. Bubonic plague is the most common form in humans, causing swollen lymph nodes called "buboes." Septicaemic plague infects the bloodstream, and pneumonic plague infects the lungs.

Plague is treatable with antibiotics. But untreated bubonic plague is fatal in 50% to 60% of cases, and untreated pneumonic or septicaemic plague is always fatal, according to the World Health Organization.

The California case is the third one in recent months. Last week, a woman died of plague in a rural part of Colorado's Pueblo County. And a Colorado teen died of the disease in June. But cases of plague in the United States are still rare — the last one in California occurred in 2006, and only about 7 cases are reported across the country each year.

When plague does crop up in the US, it usually occurs in rural parts of western states, including southern Colorado, northern New Mexico, northern Arizona, California, southern Oregon, and western Nevada. These areas are home to rodents that carry the disease, especially prairie dogs.

Globally, between 1,000 and 2,000 cases of plague are reported each year to the WHO, but the number of unreported cases is likely much higher. Plague is endemic to many countries in Africa, the former Soviet Union, the Americas and Asia. In recent years, it has been most endemic to Madagascar, the Democratic Republic of Congo and Peru. The mortality rate from plague in developing countries is hard to pin down, though, because few cases are correctly diagnosed and reported.