Disease can drive a mammal species to extinction: this doesn't seem surprising, but until today it hadn't been proven. And now that it has, members of our own mammalian species might understandably feel uneasy.

The extinction in question took place a century ago on Christmas Island, an uninhabited Indian Ocean atoll to which a merchant ship inadvertently carried flea-ridden black rats. Within a decade, both of the island's native rat species were extinct.

Scientists have argued whether the native rats were outcompeted by the newcomers, or fell victim to diseases carried by the fleas. According to DNA analysis of remaining native rat specimens, infection was widespread within the population after contact, and nonexistent before — suggesting that disease caused the die-off.

Resolving this argument has implications for another debate, over the hypothesis that disease can be so lethal and contagious as to drive a mammal species extinct. This had been observed in snails and amphibians, but not in mammals.

The authors of the study, published today in Public Library of Science ONE, hope conservationists will take heed: accidentally-introduced pathogens could wipe out endangered species. But to me, the findings also have human implications. Some would say that the rats were vulnerable because they lived on an island; but the Earth is an island, too.

Historical Mammal Extinction on Christmas Island (Indian Ocean) Correlates with Introduced Infectious Disease [PLoS ONE]

*Image: PLoS ONE

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