Laboratory investigations have yet to confirm the cause, but the symptoms point to rabies, according to two researchers from the University of California at Berkeley and other medical experts.
The two UC Berkeley researchers - the husband-and-wife team of anthropologist Charles Briggs and public health specialist Dr. Clara Mantini-Briggs - said the symptoms include fever, body pains, tingling in the feet followed by progressive paralysis, and an extreme fear of water. Victims tend to have convulsions and grow rigid before death.
Dr. Charles Rupprecht, chief of the rabies program at the U.S. Centers for Disease Control and Prevention in Atlanta, agreed with their preliminary diagnosis.
"The history and clinical signs are compatible with rabies," Rupprecht told The Associated Press on Friday. "Prevention is straightforward: Prevent bites and vaccinate those at risk of bites."
Venezuelan health officials are investigating the outbreak and plan to distribute mosquito nets to prevent bat bites and send a medical boat to provide treatment in remote villages on the Orinoco River delta, Indigenous Peoples Minister Nicia Maldonado told the state-run Bolivarian News Agency on Thursday.
Outbreaks of rabies spread by vampire bats are a problem in various tropical areas of South America, including Brazil and Peru, Rupprecht said.
He said researchers suspect that in some cases environmental degradation - including mining, logging or dam construction projects - may also be contributing to rabies outbreaks.
"Vampire bats are very adaptable," Rupprecht said. And when their roosts are disrupted or their normal prey grow scarce, "Homo sapiens is a pretty easy meal."
More study is needed to confirm through blood or other samples from victims that it is the rabies virus in Venezuela, researchers say.
At least 38 Warao Indians have died since June 2007, and at least 16 have died since the start of June 2008, according to a report the Berkeley researchers and indigenous leaders provided to Venezuelan officials this week.
All victims died within two to seven days from the onset of symptoms, Briggs said.
One village, Mukuboina, lost eight of its roughly 80 inhabitants
all of them children, he said.
During a study trip Briggs and Mantini-Briggs made through 30 villages in the river delta, relatives said the victims had been bitten by bats. The couple have worked among the Warao in Delta Amacuro state for years and were invited by indigenous leaders to study the outbreak.
"It's a monster illness," said Tirso Gomez, a Warao traditional healer who said the indigenous group of more than 35,000 people has never experienced anything similar.
Another tropical medicine expert, Dr. Daniel Bausch of Tulane University in New Orleans, agreed the symptoms and accounts suggest rabies transmitted by bats, and if confirmed, "probably a vaccination campaign would be in order."
The common vampire bat, which feeds on mammals' blood, swoops down and generally approaches its sleeping prey on the ground. The bat then makes a small incision with its teeth, and an anticoagulant in its saliva keeps the blood flowing while it laps up its meal with its tongue.
The researchers in Venezuela have begun taking precautions. Mantini-Briggs, a Venezuelan former health official, said she started to wonder about her own health Friday while talking with biologist Omar Linares, a bat expert at Caracas' Simon Bolivar University.
She remembered there was blood on her sheet after sleeping in a hammock in a village two weeks ago. Initially she dismissed it as nothing important, but she also remembered her finger hurt that morning and that she saw two small red dots there.
Linares suggested she get rabies shots immediately.
"They're vaccinating me," Mantini-Briggs said. "I'm sure a bat bit me."