A deadly form of a common childhood illness called hand, foot and mouth disease is thought to be behind a mysterious spate of child deaths in Cambodia, health officials said Monday.

Lab tests have confirmed that EV-71, one of several viruses known to cause the disease, is to blame for a good portion of the 59 cases that have been reviewed since April, according to a joint statement from the World Health Organization and Cambodian Health Ministry.

Those illnesses have resulted in 52 deaths. (Lab testing done in recent days has allowed the numbers to be lowered from the initial report of 62 cases.)

"Based on the latest laboratory results, a significant proportion of the samples tested positive for Enterovirus 71 (EV-71), which causes hand, foot and mouth disease (HFMD)," the statement published late on Sunday said.

“The EV-71 has been known to generally cause severe complications among some patients.”

Dr. Nima Asgari, who is leading the WHO investigation, says of 24 samples tested so far, 15 came back positive for EV-71. He said that based on the information available, it's likely that the majority of untested patients were infected with it.

"We are a bit more confident. We are hoping that we can come up with something a bit more conclusive in the next day or so," he said.

Hand, foot, and mouth disease is a common viral illness that affects children younger than 5 years old all around the world. It causes fever, blister-like sores in the mouth, and a skin rash and is spread by sneezing, coughing and contact with fluid from blisters or infected feces.

(It should not be confused with foot-and-mouth disease -- also called hoof-and-mouth disease – which affects cattle, sheep, and swine. The two diseases are caused by different viruses and are not related.)

Hand, foot, and mouth disease is caused by viruses that belong to the Enterovirus group, which includes polioviruses and coxsackieviruses.

In North America, coxsackievirus A16 is the most common cause of the illness. Here, the illness is typically mild and most children develop a rash and fever and then recover quickly without problems.

In this Cambodian outbreak, EV-71 is the cause, a virus that can result in brain swelling and death. Most of the Cambodian cases involved children younger than 3 who experienced fever, respiratory problems that led to rapid shutdown and sometimes neurological symptoms.

No vaccine or specific treatment exists for hand foot and mouth disease.

Hand, foot, and mouth disease has been raging across Asia for many years.

In neighbouring Vietnam, hand, foot and mouth disease sickened more than 110,000 people in recent years and killed 166, mostly children. China is also experiencing an outbreak, and more than 240 people have died of the disease there this year, according to China's Health Ministry.

Asgari said as far as she’s aware, EV-71 was not identified as a virus in Cambodia. That means the children would have had no natural immunity to it.

As for those children who have not tested positive for EV-71, lab results have also identified other diseases in some of those cases, including dengue fever and Streptococcus suis, a germ commonly seen in pigs that sometimes infects people, often causing meningitis.