Merlin D. Tuttle
A recent wave of scientific literature on viral diseases finds some virologists – and the mass media – suggesting that bats pose a serious health risk to people. Reality, however, rarely matches sensational headlines like this one: “Scientists have discovered an unexpected but potent threat to global health: bats.”
When this issue is carefully examined, we find some surprising leaps from initial facts to sweeping suppositions. And those suppositions too often are presented as “facts” in newspapers and on television news.
While antibodies to several disease-related viruses have been found in bats, the critical question remains: what does it really mean? The answer is far from clear. Antibodies for the Hendra virus, for example, were isolated from captive flying foxes that had been maintained in very close contact with their human caretakers for many years. Yet there have been no cases of disease transmission from these bats.
Relevant statistics are often lost in such discussions. How common are Ebola antibodies in bats? Ninety-six percent of the 679 African bats tested did not harbor the antibodies or related nucleotide sequences, but 27% of domestic dogs tested in one outbreak region did.
What about the highly publicized SARS-like virus found in some species of horseshoe bats in Asia? That virus is Bat CoV – not the SARS virus that infects humans. In fact, researchers have been unable to grow the Bat CoV virus in cultures that support the growth of the human SARS virus.
In general, virologists concede that it is unlikely these diseases are transmitted from bats to humans. In the case of the Nipah and Hendra viruses, they speculate that viruses present at relatively low levels in bats may be transmitted to intermediate hosts, such as pigs or horses, where the virus is amplified (concentrated) until it is capable of transmission to people.
Obviously, it is important for researchers to study relationships between animals and human diseases. But it is imperative that preliminary results do not lead to unsupported speculation that bats pose a serious health risk to people.
Contrary to common misconceptions, bats have an above-average record when it comes to living safely with humans. Just ask the people of Austin, Texas, who have benefited greatly from sharing their downtown area with 1.5 million bats for nearly 25 years without a single case of bat-related illness – despite initial public health warnings.
Bat Conservation International members can read the complete story of bats and viruses in the Spring issue of BATS magazine.