Federal authorities are asking for samples of Virginia waterways in an attempt to develop a test for detecting deadly microscopic amoeba.

Health officials say two children and a young man nationwide have died this summer from a fatal infection known as primary amoebic meningoencephalitis stemming from a brain-eating amoeba that lives in water.

This month, a 9-year-old Virginia boy died a week after he went to a fishing day camp. Christian Alexander Strickland had visited several bodies of water during the Richmond camp.

The Richmond Times-Dispatch reports that The Centers for Disease Control and Prevention is asking Virginia for help to sample waters for Naegleria fowleri.

The free-living amoeba gets up the nose, burrows up into the skull and destroys brain tissue. It's found in warm lakes and rivers during the hot summer months, mostly in the South.

"It's a terrible disease that we would like to know more about and be able to tell the public more about from a prevention standpoint," said Michael Beach, the federal agency's associate director for healthy water. "We are trying to learn more, but it's a tough one because it's such a rare occurrence."

It's a medical mystery why some people who swim in amoeba-containing water get the fatal nervous system condition while many others don't, experts say.

"That's the million-dollar question," he said. "We have no idea."

The illness is extremely rare. About 120 U.S. cases -- almost all of them deaths -- have been reported since the amoeba was identified in the early 1960s, according to the CDC.

About three deaths are reported each year, on average. Last year, there were four.

But the cases that do occur tend to be tragic, and there's only been one report of successful treatment.

Earlier this month, officials say a central Florida girl who became ill after swimming in a small tributary of the St. John's River in southern Volusia County died from a brain infection caused by amoeba in the water.