Italian authorities have opened a double murder investigation following the deaths of a mother and her teenage daughter following a Christmas Eve meal last year, after prosecutors said preliminary blood tests showed the pair had the poison ricin in their systems.

Antonella Di Ielsi, 50, and Sara Di Vita, 15, were treated in the Cardarelli Hospital, in southern Italy, on December 24 with suspected food poisoning, but died two days later.

Blood tests later found the lethal substance ricin in the victims’ blood, prosecutors say.

Symptoms of ricin poisoning vary depending on how the person came into contact with the substance – whether ingested, inhaled or injected.

If eaten, it can cause vomiting, diarrhea, seizures, bleeding in the gut and organ damage, according to the US Centers for Disease Control and Prevention. A small amount of ricin can be deadly, and it can kill a person within three days.

While supportive medical care can be given to lessen the effects, there is currently no cure for ricin poisoning, according to the CDC.

Originally, five doctors at the Cardarelli Hospital were accused of medical negligence and placed under investigation for manslaughter after the mother and daughter were sent away from the emergency room on Christmas Eve. Staff had suspected food poisoning, possibly from seafood traditionally served for the holiday, according to the prosecutor’s office.

Toxicology testing was carried out on the two victims, with blood samples showing traces of the potent poison ricin, according to lawyers for the doctors.

Analysis of the blood from the father and husband of the victims, and their 19-year-old daughter and sister, who did not fall ill, found no traces of ricin, prosecutor Elvira Antonelli, who is leading the new investigation, told La Repubblica newspaper.

But Antonelli also questioned reports the two had been deliberately poisoned.

“They are risky, to say the least, and in fact I have never confirmed them. Nor will I be able to do so until I receive the autopsy results complete with the conclusions of the Pavia experts.”

“We still have no certainty how the mother and daughter were poisoned with ricin but the Pavia poison control center preliminary report shows that they tested positive for that substance,” Antonelli said in the newspaper.

CNN has contacted Antonelli’s office.

The father, an accountant and a former local mayor, and the surviving sibling have not been charged or named in the investigation, prosecutors said.

The investigation into the doctors has not been dropped, but lawyers for two of the doctors say they filed a request with the local court for dismissal.

Fabio Albino, a lawyer for one of the doctors – whose names have not been made public – said he hoped the new double homicide investigation would exonerate his client.

“If the latest news is confirmed, and I have no reason to doubt it, the doctors’ position will change radically,” he told CNN by phone Friday.

“It’s a given that by following the guidelines for food poisoning, a doctor would be unaware of this type of poisoning,” Albino added.

Another lawyer for one of the other doctors, Domenico Fiorda, told CNN affiliate Sky24 : “This is something that occurred before they arrived at the hospital and perhaps couldn’t even be addressed in the emergency room.”

“Therefore, the doctors certainly aren’t responsible, especially since, as we’ve always said, they followed the protocol for the symptoms with which the two women presented to the Cardarelli Hospital,” Fiorda said.

The hospital said it would not be commenting when contacted by CNN Friday, citing privacy concerns.

The family home has been sequestered and investigators are now searching the premises for traces of the powerful poison, according to Marco Graziano, vice police commissioner at Campobasso police. He told local media that they are also searching for anyone who might have obtained ricin on the dark web in the months leading up to the poison.

The caster bean plant from which ricin can be extracted is found in the region of Molise in southern Italy, but it is difficult to extract the toxin without specialized equipment, Graziano told local media.

Authorities say they are also looking into family acquaintances and people who might have had access to the home or food, Graziano said.

Local coroner Pia Benedetta De Luca has ordered further autopsy tests on the victims now that ricin has been found, according to an interview she gave to a local newspaper.

Those results will be made available to the prosecutor’s office by the end of April, when charges could be filed, according to local news reports. (CNN)

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