By Steve Bittenbender

(Reuters) - At least eight people in the Cincinnati area who died of heroin drug overdoses since mid-July had traces of a drug used to tranquilize elephants in their bodies, a coroner said Tuesday.

At least five other overdose deaths since mid-July are suspected to be connected to heroin laced with carfentanil, Hamilton County Coroner Lakshmi Sammarco told a news conference.

The coroner's office is awaiting the test results on those cases, she said.

Authorities expect that tally to rise as they test blood and urine samples from older cases, Sammarco added.

Drug users might not know they are taking the drug. Dealers may be adding it to heroin to boost their supply or the effects, authorities said.

Carfentanil is roughly 10,000 times more potent than morphine, according to the National Center for Biotechnology Information.

Throughout Ohio, the number of overdose deaths rose from 2,531 in 2014 to 3,050 last year, and the number of fentanyl-related overdose fatalities surged from just 84 in 2013 to 1,155 in 2015.

The Ohio deaths come as authorities in several parts of the United States are grappling with opioid and heroin crises. For example, in Scott County, Indiana, a rural county 75 miles southwest of Cincinnati, a state of emergency was declared last year after the number of HIV cases skyrocketed due to the use of intravenous pain killers. 

Sammarco, the county coroner, said the strength of the powerful sedative renders "conventional treatment methods for overdoses not as effective."

Last week, officials in Kentucky, one state to the south of Ohio, issued a public health advisory urging hospitals to stock up on antidotes to drug overdoses after law enforcement agencies reported illicit drugs mixed with other, legal substances were coming into the state.

According to a press release, officials in Kentucky said they anticipated heroin and other drugs were being laced with fentanyl, an addictive and powerful opioid, and being distributed within the state.

Hiram Polk, the Kentucky Department for Public Health Commissioner, likened the drug scourge to a tornado and said it was "tied to a number of overdoses, hospitalizations and deaths across the county and needs public attention now."

Sammarco said some of the batches her offices has tested included traces of carfentanil and fentanyl.

(Reporting by Steve Bittenbender in Louisville, Kentucky; Editing by Eric M. Johnson)