But here, literally in my back yard?
This should be no surprise, according to the tale David Quammen tells in “Spillover,” his highly engaging exploration of animal infections and the perils they pose for people. This year’s West Nile outbreak, the deadliest in the United States since the virus was first spotted in New York in 1999, represents the local front in a perpetual global struggle with what are called zoonotic diseases. These are diseases that cross from animals to humans, and they are the subject of Quammen’s inquiry and his many adventures. An intrepid author, he tracks the killers — some with storied names such as ebola, SARS and HIV, others lesser known such as Hendra and Q fever — across jungles and farms to identify the animals on which the germs hide and to chronicle how they make the leap to people.
These diseases merit our urgent concern. For one, they constitute the majority of all illnesses that strike humans. More than 1,400 human pathogens have been catalogued, and about 60 percent of them cross from nonhuman species to humans. An even higher proportion of human diseases that have emerged in recent decades, such as SARS and Lyme disease, have their origins in animals. And since the 1970s, the emergence of new zoonotic diseases has been accelerating. If we’re watching for the source of the next big epidemic, look to the animals.
As Quammen writes, such zoonotic diseases are particularly confounding because they are so hard to eradicate. Over the generations, mankind has notched only a few victories over microbes. The elimination of smallpox was one. For years, armed with a range of vaccines, global public health officials have been closing in on polio as well, with the virus continuing to circulate only in a few Asian and African countries. Neither virus infects animals. So when global vaccination campaigns finally eliminate polio in humans, it’s finished.
But diseases such as influenza and HIV live on in animals — in water birds in the former case, chimpanzees in the latter — and as long as they do, the bug can again cross to humans and ignite a new epidemic.
Identifying the species that act as reservoirs, silently sheltering the pathogens with few outward signs or symptoms, can be a challenge. Quammen accompanies researchers on their hunts time and again. In pursuit of the Nipah virus, which frequently causes fatal inflammation of the brain, he journeys to the Ganges Delta of southern Bangladesh and recounts the efforts on a moonless night to catch flying fox bats in vast mist nets for testing. In northern Bangladesh, he joins a team of researchers at a Hindu shrine atop a hillock overrun by macaques possibly infected with the herpes B virus, which can devastate the human neurological system. The team courageously corners several of the frenzied monkeys in a makeshift trap and injects them with a tranquilizer before stuffing them into a duffel bag.