Riverside County health officials issued a warning on Tuesday urging residents to take precautions when swimming in lakes, ponds, and hot springs.

The warning comes after a 9-year-old boy died on Saturday from a brain infection triggered by an amoeba, Naegleria fowleri. The boy had gone swimming in Lake Elsinore several times this summer, but there is no clear evidence so far on the place where the boy got infected with the parasite.

According to the US Centers for Disease Control and Prevention, the parasite is known to inhabit bodies of freshwater, geothermal water or hot springs, but also warm water discharged from industrial plants and poorly chlorinated swimming pools. It is not found in salt-water locations like the ocean. It is most common during the summer and typically infects a person when it is ingested through a nasal passage. The amoeba kills its host by destroying brain tissue.

Symptoms of the disease tend to resemble those experienced in bacterial or viral meningitis, such as fever, headache, nausea, vomiting and neck stiffness, Riverside County Public Health Director Eric Frykman said. Later symptoms include a state of confusion, lack of attention to people and surroundings, loss of balance, seizures, and hallucinations. The disease progresses rapidly and causes death within three to seven days. What is even worse than that, it’s the fact that, currently, there is no vaccine or effective medication to stop the infection.

The amoeba has caused fatal infections in 15 southern states. About 33 fatalities were reported from 1998 through 2007 in the United States.

However low the risk of getting infected with the parasite is , Frykman urged people to avoid warm fresh water, hot springs and water around power plants; to avoid the water when temperatures are high and water levels are low; to hold their nose shut while in the water or use a nose clip and to avoid digging or stirring up sediment while in shallow freshwater areas.

“The risk of infection is extremely low and is no different in Lake Elsinore than in any other warm-water lake. This is not a new risk, but because of the unique nature of it and because it is fatal, we wanted to get this information out to the public. There are probably tens of millions, if not hundreds of millions, of exposures of people going into any particular lake in this country. And only three people get this on average (per year), so you can see that the risk (of infection) is exceptionally low,” said Dr. Frykman.

He also added that many people may have been exposed but only a very small percentage of people haven’t developed the antibodies to fight the bug.

For their safety, the CDC recommended that “people should seek medical care immediately whenever they develop a sudden onset of fever, headache, stiff neck, and vomiting particularly if they have been in warm fresh water within the previous 2 weeks.”