Bites from tiny bats cause almost all cases of rabies in people in the US, according to a new analysis. The infected bats can weigh just ten grams and their bite can easily be mistaken for a thorn prick or bee sting.
鈥淲orldwide, bat transmission of rabies is the tip of the iceberg. But in the US human cases of rabies are very rare now, which is why we鈥檙e interested in this route,鈥� says Robert Gibbons of the Walter Reed Army Institute of Research in Silver Spring, US.
Gibbons reviewed the 26 human deaths from rabies acquired in the US over the past decade. Blood tests revealed that 24 of these were from a subtype of the virus that infects bats. But only two of these people reported being bitten by a bat.
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鈥淧eople thought perhaps it spread through the air, or a bat bit a cat and the person caught rabies from the cat,鈥� Gibbons says. But a closer examination of the cases revealed that direct contact with a bat was probably responsible for each transmission.
For example, an engineer who visited caves in the US to evaluate their suitability for guano mining denied any bat bites after he developed symptoms of rabies. But his case history reveals that he did have a bleeding lesion on his face when leaving the cave, Gibbons says.
Swarming mites
Indigenous rabid bats have been reported in every mainland US state, except Hawaii. The most common bats in the US, the silver-haired and eastern pipistrelle bats, weigh up to about ten grams and have jaws less than one centimetre across. These bats are often found alone in trees, foliage and crevices in wood and rock.
Rabies prophylaxis is 100 per cent effective if given before symptoms appear. 鈥淏ut symptoms are generally a death sentence,鈥� Gibbins says. Only about one per cent of US bats are probably infected with rabies, but anyone bitten by a bat should seek immediate vaccine treatment, he says.
Worldwide, about 50,000 people die from rabies each year. Most of these deaths are in Africa and Asia, where canine rabies is common and the majority of deaths follow bites from infected dogs.
Gregory Moran at the Division of Infectious Diseases at the Olive View-UCLA Medical Center in California, says: 鈥淢any issues related to rabies transmission from bats need further study.鈥� But direct research in bat caves is unpleasant, he adds. 鈥淔ew researchers would be willing to brave the rain of bat urine, pools of guano and swarming mites.鈥�
Journal reference: Annals of Emergency Medicine (vol 39, p 528)