Singer Justin Bieber has told his followers on social media that he has been diagnosed with Lyme disease - a bacterial infection spread by ticks - and glandular fever.

Following speculation about his health, and a report by celebrity website TMZ that he would discuss his Lyme disease diagnosis in an upcoming documentary, Bieber responded on Instagram on Wednesday evening. 

If Lyme disease is left untreated symptoms including fever, muscle pain, joint pain and swelling and neurological symptoms can follow.

"While a lot of people kept saying Justin Bieber looks like s***, on meth etc. they failed to realize I've been recently diagnosed with Lyme disease," the 25-year-old wrote. 

"Not only that but [I also] had a serious case of chronic mono[nucleosis or glandular fever] which affected my skin, brain function, energy, and overall health."

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"These things will be explained further in a docu series I'm putting on YouTube shortly," he continued. "You can learn all that I've been battling and OVERCOMING!! 

"It's been a rough couple [of] years, but [I'm] getting the right treatment that will help treat this so far incurable disease and I will be back and better than ever NO CAP."

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