A Missouri man who claims to have had sexual relations with as many as 300 people since being diagnosed with HIV has pleaded not guilty to infecting another man with the virus.

David Mangum entered the plea after being charged with recklessly infecting another with HIV, which in Missouri -- where sentences for such crimes are among the nation's harshest -- carries up to life in prison. His attorney didn't return messages seeking comment.

According to Fox2Now.com, Mangum, 37, of Dexter, Mo. was arrested last week after a former lover tested positive for the virus and turned Mangum in to the police. The victim, identified in court documents as D.B., met Mangum on Craigslist in October 2012. D.B. says he questioned Mangum about having any diseases and he told him ‘no.’ The Associated Press reports that Mangum admitted to a roommate that he had been HIV-positive since 2003.

Court documents allege that the 36-year-old Mangum told detectives in Dexter, a small town in southeast Missouri, that he had unprotected sex with as many as 300 partners since being diagnosed with the virus that causes AIDS. Up to 60 of those contacts allegedly occurred after he moved to Missouri two years ago from Dallas, where he has convictions for prostitution, indecent exposure and public lewdness.

Many of his trysts stemmed from Craigslist ads, he told investigators, and he would meet up with men at parks, truck stops and other remote locations. Police believe many were truckers or others passing through the region, and because Mangum had little information about many of the men, investigators are concerned about finding potential victims, Dexter police detective Cory Mills said.

"First names with no phone numbers or addresses -- that's going to be a challenge," Mills said.

So authorities turned to the media, and since then more potential victims have come forward, Stoddard County prosecutor Russell Oliver said. Oliver wouldn't say how many people, but he said more charges were expected.

Local health clinics are reporting a recent surge in people seeking HIV tests. In Stoddard County, where one or two people generally get tested each week, 15 people came in for testing in the past week, said Debbie Pleimling, director of the county's Health Department. Neighboring counties are reporting a spike.

"There has to be concern," she said. "If he's randomly meeting people for sex, we have no clue where to turn."

Local authorities said they were also working with Dallas police, who didn't return several messages from The Associated Press.

It's unclear why Mangum moved to Dexter, a conservative town of about 8,000 residents. He worked at a local grocery store, according to Mills, but little else is known about him.

"Everyone's really surprised that sort of thing is going on here," local barbershop owner Charlie Parrish said as he cut hair this week.

Mangum is jailed on $250,000 cash-only bond. A preliminary hearing is set for Sept. 26. Police say Magnum admitted that he never disclosed his HIV positive status because of ‘fear of rejection,’ Fox2Now.com reports.

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The Associated Press contributed to this report.