First death by vampire bat in US

The 19-year-old man was a migrant farm worker who had been bitten on the heel by a vampire bat in his native Michoacan on July 15, 2010, 10 days before he left for the United States to pick sugar cane at a plantation in Louisiana.

"This case represents the first reported human death from a vampire bat rabies virus variant in the United States," said the Centers for Disease Control and Prevention in its Morbidity and Mortality weekly report.

The unusually aggressive form of rabies had an incubation period of just 15 days, compared to the median 85 days seen in other cases of human rabies in the United States, the CDC said.

Although vampire bat populations are currently confined to Latin America, climate change could be forcing their populations northward, leading to more cases of human infection in the southern United States, the CDC warned.

The patient had never received a rabies vaccine and fell ill about two weeks after he was bitten by the blood-sucking creature.

At the end of July, after one day of working in the fields, the man sought medical help for fatigue, shoulder pain, numbness in his left hand and a drooping left eye. He soon developed respiratory distress and a 101.1-degree fever (38.4 Celsius).

"During the next several days, the patient became gradually less responsive to external stimuli, developed fixed and dilated pupils, and began having episodes of bradycardia (slow heartbeat) and hypothermia," the CDC said.

Tests showed he had developed encephalitis, or swelling of the brain. On August 20, samples of his spinal fluid confirmed a diagnosis of rabies.

A subsequent brain scan revealed severe impairment. His family decided to take him off life support and the man died shortly after.

Postmortem tests on his brain tissue "determined the variant to be a vampire bat rabies virus variant," the CDC said.

The case "highlights the growing importance of bats in public health," added the CDC, urging the public to avoid contact with vampire bats and get vaccinated if possible.

"Research suggests that the range of these bats might be expanding as a result of changes in climate," it said.

"Expansion of vampire bats into the United States likely would lead to increased bat exposures to both humans and animals (including domestic livestock and wildlife species) and substantially alter rabies virus dynamics and ecology in the southern United States."

The United States has documented a total of 32 cases of human rabies, mostly from a canine rabies variant, since the year 2000, eight of which were acquired abroad. Two of the cases originated in Mexico.

Vampire bats are bloodsucking nocturnal mammals that are typically found in Mexico, Brazil, Chile and Argentina. They usually feed on sleeping wildlife and livestock, but sometimes bite people, too.

(c) 2011 AFP