Why Bats Are So Prone to Pathogens
Posted by Richard Conniff on January 13, 2015
I’ve written here before about why bats are the source of so many deadly diseases–including MERS, SARS, Nipah virus, Hendra virus, Lassa and Marburg hemorrhagic fevers, and of course Ebola.
Why bats? It’s partly because they are such a diverse group, with 1,250 species, comprising about 20 percent of all mammals, says Jon Epstein, a veterinary disease ecologist with EcoHealth Alliance in New York. Some researchers theorize that immune systems or other physiological differences might make bats more likely to carry viruses. But so far that’s only a theory. The bat lifestyle of roosting together in dense colonies may also encourage viruses. These colonies often occur in and around human habitations, and the ability of bats to fly means any virus can get dispersed across a wide geographic area.
But when you see an emerging disease come from wildlife, says Epstein, “it’s generally triggered by something people have done to manipulate the environment,” meaning agricultural expansion or intensification, or urbanization, coupled with the modern tendency to move plants, animals, and people all over the world. “It’s really human activities that are driving spillover.”
In today’s New York Times, Natalie Angier suggests that the proneness to pathogens is all about the immune system:
Yet bats appear largely immune to the many viruses they carry and rarely show signs of the diseases that will rapidly overwhelm any human, monkey, horse, pig or other mammalian host the microbes manage to infiltrate.
Scientists have also learned thatbats live a seriously long time for creatures of their small size. The insectivorous Brandt’s bat of Eurasia, for example, weighs an average of just six grams, compared with 20 grams for a mouse. But while a mouse is lucky to live for a year, the Brandt’s bat can survive well into its 40s — a disparity between life span and body mass that a report in Nature Communications called “the most extreme” of all mammals.
Bats may be girded against cancer, too. “At this stage, the evidence is anecdotal,” said Lin-Fa Wang, a bat virologist at the Duke-NUS Graduate School in Singapore and the Australian Animal Health Laboratory in Geelong. “But of all the bat biologists I’ve spoken with, I’ve only heard of one or two cases of bat tumors.”
Researchers are scrutinizing bat DNA and the details of the bat vocation for clues to what sets the flying mammals apart from other members of the lactating clade. Preliminary findings indicate that bats’ apparent indifference to the viral throngs they harbor, together with their Methuselah-grade longevity, probably arose from the adaptations needed to grant them the power of flight.
Read the rest of Natalie’s story here. (And reflect on that little Angier-esque gem that we are all members of “the lactating clade,” defined by a trait exclusive to the female gender. I guess if we wanted to bring the male side into it, in the interest of gender balance, we would have to put a little more emphasis on fur-bearing.)