The 45-year-old Chiacchia is also a Florida Horse Park board member, a 2003 Pan American gold medalist, and a prominent activist for the county's equestrian community. He also has a farm in the area and teaches students to ride.
The charge is a third-degree felony degree; it could be upgraded to a first-degree felony if Chiacchia is found to have committed multiple violations of the crime.
According to a Marion County Sheriff's Office arrest report, the victim told investigators that between February and June 2009 he and Chiacchia carried on a sexual relationship and had unprotected intercourse several times.
The victim told deputies that, while he and Chiacchia were vacationing in New York, the victim saw some of Chiacchia's medical documents.
The report redacts what those documents said, but the law Chiacchia is accused of breaking -- Florida Statute 384.24(2) -- makes it unlawful for any person who knowingly has "human immunodeficiency virus (HIV) infection" to have sex with another person and not tell them prior to the act.
The victim told investigators that he asked Chiacchia at the beginning of their relationship about his medical "status" and that Chiacchia told him he was negative for any infection.
The State Attorney's Office issued a subpoena for Chiacchia's medical records and obtained them. However, Circuit Judge Edward Scott ordered that the medical records be used only as part of the Sheriff's Office investigation.
Chiacchia's bail was set at $2,000. He posted bond and was released from the Marion County Jail on Thursday.
According to arrest documents, the victim showed investigators an e-mail he said was from Chiacchia in which Chiacchia admitted to knowing he was infected with the disease in 2008.
The victim then gave investigators a tape recording of a conversation he had with Chiacchia in which Chiacchia said he didn't tell the victim of his medical status "because he did not think the victim was trustworthy," according to the arrest report.
In the recording, Chiacchia also berates the victim and tells him that he was naive if he thought he (the victim) had never had sex with anyone who wasn't infected.
Investigators said in the arrest report that they also made several attempts to contact Chiacchia and record the conversations between Chicchia and the victim, but failed.
When contacted by the Star-Banner, Chiacchia would not comment about the arrest, saying he wanted to get permission from his lawyer first.
He said only that the arrest situation was "pretty surprising and outrageous."
Longtime equestrian colleague and fellow Florida Horse Park board member Chester Weber said he was saddened to hear of the arrest.
"It certainly is personal in nature," he said.
As for Chiacchia's position on the Florida Horse Park board and whether he should remain at his post, Weber said the issue of Chiacchia's arrest was separate from that of Horse Park.
"This is a personal matter that he's going through unfortunately for he and the rest of his family," Weber said.
Fred Hiers can be reached at email@example.com and 352-867-4157.
A former U.S. Olympic equestrian rider and part-time Ocala resident, Darren Chiacchia, was arrested Wednesday and charged with violating a state law that required him to declare he was HIV positive to his one-time sexual partner.