The U.S. is seeing an uptick in West Nile virus cases, and some people living among a remote Amazonian tribe survived exposure to the rabies virus without having received medical treatment, the Centers for Disease Control and Prevention reported this week.

WNV uptick

For the first six months of the year, the CDC has learned of 241 cases of the mosquito-borne West Nile virus, the highest reported for the time period since July 2004. Almost half of all cases occurred in Texas.

"It is not clear why we are seeing more activity than in recent years," Dr. Marc Fischer, a CDC epidemiologist, said in a statement.

West Nile virus, a seasonal disease that generally is at its worst in the summer months and early fall, was first isolated from a patient in the 1930s in Uganda. It was first reported in North America in 1999.

Only 20 percent of people infected by the West Nile virus experience the disease's mostly flu-like symptoms. But 1 percent will be afflicted by a more serious form of the infection, neuroinvasive disease, characterized by inflammation of the brain or spinal cord. About 10 percent of these people will die, according to the CDC.

Four deaths have been reported so far this year, one in Arizona, one in Mississippi and two in Texas.

Some 60 percent of cases reported to the CDC had neuroinvasive disease, but this is due to surveillance bias, as milder cases are less likely to be reported, according to the agency.

Rabies immunity?

From WNV we turn to another deadly virus that's also sometimes transmitted by winged creatures: rabies.

The virus is almost invariably fatal for those who fail to get a vaccine and develop a clinical infection after exposure. But some people from two small Peruvian communities, who live amongst rabies-carrying vampire bats that nibble on human flesh from time to time, appear to have survived bouts with the disease without treatment.

"Our results support the idea that under very unique circumstances there may be some type of enhanced immune response in certain populations regularly exposed to the virus, which could prevent onset of clinical illness," Amy Gilbert, who led the CDC and Peruvian Ministry of Health study, said in a statement.

The study, published in the August issue of the American Journal of Tropical Medicine and Hygiene, looked at blood samples of 63 people, many of whom were known to have been bitten by bats in the past. Seven of the people tested positive for rabies antibodies, suggesting prior exposure to the disease. Only one person was known to have had any sort of follow-up medical treatment, the researchers said.

About two people die a year in the U.S. from rabies, the CDC said.

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