"Lyme disease is the fastest growing epidemic in the world," Dr. Erica Lehman, tick-borne disease specialist, tells PEOPLE

Avril Lavigne's Battle with Lyme Disease: 3 Things to Know About the Condition

Singer Avril Lavigne opens up about the devastating disease that kept her bedridden for months – and how she’s fighting to recover. Subscribe now for instant access to the exclusive interview, only in PEOPLE.

On this week’s cover of PEOPLE, Avril Lavigne opens up about the severe case of Lyme disease that left her bedridden for months. The singer, 30, joins others like Real Housewives of Beverly Hills star Yolanda Foster, who have suffered from the illness and experienced the difficulty of getting properly diagnosed.

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Here is what you should know about Lyme disease:

1. Lyme disease is contracted when the bacteria Borrelia burgdorferi is spread to humans through a bite by an infected tick.

“When a tick bites you, it has an anesthetic in its saliva that actually numbs the surface of your skin so you don’t feel the bite, and that’s why people don’t know that a tick is latched onto them and is biting them,” says Dr. Erica Lehman, a tick-borne disease specialist.

2. “If bitten, early symptoms include headaches, nausea, numbness, muscle aches, extreme fatigue and Bell’s palsy,” Lehman says of the manifestations on the more minor side of the spectrum. Severe symptoms include dementia and arthritis.

“It can affect people physically, cognitively and psychologically,” she continues.

3. It is “the fastest growing epidemic in the world,” says Lehman.

According to the Centers for Disease Control and Prevention, over 25,000 Americans were diagnosed with Lyme disease in 2013, but Lehman says this number is “significantly underestimated” due to factors such as imperfect testing and symptoms that mimic those of Parkinson’s, multiple sclerosis and lupus.

For more information on Lyme disease, visit the CDC’s website.