At least 38 tribespeople in Venezuela, including several children, are thought to have died after being attacked by vampire bats.

Although the precise cause of the deaths has not been confirmed, experts say that it was almost certainly rabies carried by the blood-sucking creatures. It is thought that the bats were probably disturbed by nearby mining, logging or damming projects, and were forced to find new prey — in this case, members of the Warao tribe.

Vampire bats hunt only when it is fully dark and can survive on a purely liquid diet. Their hearing is highly sensitive to the sound of animals sleeping and they typically approach on foot, biting their victim then lapping up the blood at the site of the haemorrhage. Their saliva contains a substance known as draculin, which prevents their prey's blood from clotting.

The experts who brought the highly unusual case to the world's attention include two researchers from the University of California at Berkeley — the husband-and-wife team of anthropologist Charles Briggs and public health specialist Clara Mantini-Briggs. They said that victims' symptoms included fever, body pains and tingling in the feet followed by progressive paralysis and an extreme fear of water. The victims also suffered convulsions and grew rigid before death.

Charles Rupprecht, the chief of the rabies programme at the Centres for Disease Control and Prevention in Atlanta, agrees with the preliminary diagnosis. “The history and clinical signs are compatible with rabies,” he said. “Prevention is straightforward: prevent bites and vaccinate those at risk.” Health officials in Venezuela have responded to the deaths with plans to send a medical boat to the remote villages in the Orinoco River delta. Outbreaks of rabies spread by vampire bats are rare but not unheard of in tropical areas of South America. “Vampire bats are very adaptable,” Dr Rupprecht said. “Homo sapiens are a pretty easy meal”.

The 38 deaths have occurred since June 2007, with 16 in the past two months. One village, Mukuboina, with a population of about eighty, lost eight inhabitants, all children.

During their study trip, Mr Briggs and Dr Mantini-Briggs travelled through 30 villages in the delta. The couple have worked among the Warao for years, and had been personally invited by indigenous leaders to investigate the outbreak.

Dr Mantini-Briggs said she was surprised to find that many Warao villages now had cats. “They told us it was because there were too many bats that were biting the children,” she said. The couple have been forced to take precautions themselves. Dr Mantini-Briggs said she woke up one morning in a Warao village to find blood on her sheets. She dismissed it as an insect bite but felt a pain in her finger and noticed two red dots. “I'm sure a bat bit me,” she said. “I said, 'I'm going to get vaccinated'.”

Tirso Gómez, a Warao traditional healer, said that his people, who number 35,000, had never experienced anything like it. “It's a monster illness,” he said.

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