Three recent deaths in Nassau County and a sharp upward swing in both heroin arrests and deaths in Northeast Florida are signs of a shift toward the street drug from harder-to-get prescription opioid drugs, law enforcement and health officials said in a briefing Friday.

A dramatic increase in cases has been seen in Duval, Clay and Nassau counties in current years, according to the three sheriff's offices.

Jacksonville Sheriff Mike Williams said the drug being purchased on the streets is coming from Mexico and that heroin-related deaths in Duval County increased 265 percent in one year, from 17 in 2014 to 45 in 2015.

"Typically it is one or two steps out of Mexico and then into Jacksonville," he said.

Nassau Sheriff Bill Leeper said the county had one heroin-related arrest last year, but that since Feb. 17, deaths due to the drug occurred in Fernandina Beach, Callahan and Hilliard.

"Prior to the last few weeks we have not seen a lot of heroin in Nassau County," he said. "But it is something that is really concerning us now."

Leeper said he believed other drugs being cut with the heroin made it particularly dangerous.

The sheriffs and Medical Director Kelli Wells of the Duval County Public Health Department warned that the trend could worsen.

"The numbers that we are seeing, without a community-based intervention and without raising concerns of those who are using, we expect these numbers to climb," Wells said.

Drug Free Duval is a community coalition working to develop a comprehensive plan to address the problem, she said.

Addicts once dependant on prescription-level narcotic opioid drugs have shifted to now easier-to-get heroin following the shutdown in prescription pill mills in recent years.

"We find now heroin is easier to obtain than the prescription drugs that many were addicted to," Wells said.

In addition, penalties have increased for dealing in prescription pills as part of that crackdown, according to an analysis from the Clay County Sheriff's Office, where there has been an increase from two cases in 2010 classified as heroin-related to 51 in 2015. Clay County had three heroin deaths last year.

In Jacksonville there were 56 heroin-related arrests in 2013 and 117 in 2015. There have been 19 so far this year.

There were 99 heroin seizures in the city in 2103 and 472 in 2015, with 72 so far this year, Williams said.

"We are on pace to eclipse last year's numbers again," he said.

The last spike in heroin cases was two decades ago, Williams said.

"It's something that we haven't seen around here in many years," he said.

It was a more prevalent drug in the 1970s and spiked again in the 1990s, he said.

"We are clearly seeing a re-emergence in the country but especially in Florida," he said.

Williams said law enforcement agencies are working street-level drug crimes as well as into the higher levels of distribution to make cases.

Heroin is synthesized from morphine which is extracted from the opium poppy plant. About 23 percent of people who use heroin become dependent on it, according to the National Institute on Drug Abuse.

It can be injected, inhaled by snorting or sniffing, or smoked, all of which contribute to its high risk of addiction.

Users report feeling a surge of euphoria accompanied by dry mouth, a warm flushing of the skin, heaviness of the extremities and clouded mental functioning, according to the institute.

Dangers include fatal overdose, spontaneous abortion and risk of infectious diseases like hepatitis and HIV.

Heroin was developed in Germany in the late 19th century and was promoted as a substitute for morphine, though it turned out to be more addictive, according to Heroininfo.org. There were attempts in the United States to control its prescription and sale then its manufacture was banned in 1924.

Possession of greater than 100 grams of heroin or even a mixture that contains heroin carries a minimum mandatory sentence of five years in federal prison.

The average cost of a single dose of heroin on the street is about $15 to $20, according to heroin.net.

Those with addiction issues should contact their medical providers, Wells said.

"Every provider in our community is aware of the steep rise that we are seeing in opioid abuse and overdose," she said.

A federal program for substance abuse and mental health referral service can be reached at (800) 662-4357 (HELP) or for the Florida Poison Information service call (800) 222-1222.

Dana Treen: (904) 359-4091