Endangered Species Now Need Vaccines, Too

(Photo: Julie Larsen Maher ©WCS)

One reason some modern parents persist in their delusional fear of vaccines is that they’ve forgotten the appalling reality of measles and other childhood diseases. But I remember, because measles was the closest I came to dying as a child, in the last gasp of the disease before widespread availability of a vaccine. It has left me with a feverish memory of feeling as if a suffocating pink graft of skin had been stretched across my face (probably because I couldn’t open my eyes) and of being unable to do much more than lie on my back struggling to breathe. Measles killed about 500 American children a year then. I got away cheap.

But this is a column about wildlife, and about a different virus—essentially measles for carnivores—that is causing an equally miserable sickness, often leading to death, in some of the world’s rarest species. Scientists are now proposing to use vaccines to save these animals from the brink of extinction. But figuring out how to vaccinate a scarce, shy, wide-ranging predator can be even more frustrating than trying to talk sense into recklessly misinformed human parents.

As the name suggests, canine distemper virus generally spreads among domestic dogs. In the United States, anybody who takes little Maggie or Jack to the vet for mandatory rabies shots typically gets the canine distemper vaccine too. But in parts of the world with feral dog problems or poor vaccine coverage of domestic dogs, the virus can readily jump to wildlife, and the victims aren’t just members of the canine family. In the mid-1990s, for example, canine distemper roared through the Serengeti, killing more than 1,000 lions over a period of just a few months.

Vaccination may be the single critical step needed to avoid extinction from such epidemics. For instance, fewer than 500 Amur tigers—commonly known as Siberian tigers—are left in eastern Russia and the northeastern corner of China. They face poaching and habitat loss, of course. But scientists recently identified distemper as a factor in the deaths of several of these magnificent animals. The disease causes neurological symptoms, such as loss of orientation, before it kills. It can also make these normally shy cats unafraid of humans. In one case, in 2010, a tiger attacked and killed a fisherman, then relaxed by the side of a road until police shot it. “As populations continue to decline and fragment,” said Martin Gilbert, a carnivore health specialist with the Wildlife Conservation Society, “we are going to see more situations where disease becomes an immediate threat.”

One of the main problems with vaccinating tigers, said Gilbert, is finding them in the first place. The most effective distemper vaccine isn’t available in oral form, so scientists can’t simply leave vaccine-laced bait for tigers to eat. A tiger wandering a 500-square-mile home range could easily miss the bait, in any case. One possible alternative would be to set up a vaccine delivery system at a tree where a tiger periodically scent marks to tell other tigers to keep off its turf. A trigger system not yet devised could then deliver a spray vaccine into the tiger’s nose. More immediately, wildlife managers could routinely administer a vaccine when they trap a tiger to put on a radio collar or when relocating an animal to minimize conflict with humans.

Safety and effectiveness are still critical issues, especially for endangered species. The live vaccine used for pet dogs is already known to be deadly for African wild dogs and red pandas. But vaccine types using a different method to generate distemper antibodies have so far proved less effective than the live vaccine.

Ethiopian wolf

Canine distemper also threatens to wipe out Ethiopian wolves, which have the dubious distinction of being among the world’s rarest canids. These reddish, fox-like wolves persist in Ethiopia’s mountainous highlands. As with wildlife species almost everywhere, the biggest long-term threat to Ethiopian wolves is habitat loss, because of the rapidly expanding human population. But feral dogs are the forerunners of human development, and they are already making distemper and rabies a more immediate threat to the continued existence of this species. In the Bale Mountains, where more than half of the total population of Ethiopian wolves lives, researchers estimated in 2010 that fewer than 300 individuals survive. Since then, 23 carcasses have turned up, and 56 individuals have gone missing, probably due to a distemper outbreak.

“You could very realistically see local extinctions” caused by the distemper virus, especially for some of the smaller populations of wolves, according to Christopher Gordon, a researcher for the Zoological Society of London, who will soon publish research on a distemper vaccine for these wolves. The hazard of local extinctions also applies to tigers. A recent study led by Gilbert noted that more than half the world’s tigers now live in populations of 25 individuals or fewer—and that even a conservative distemper infection scenario increased by 65 percent the likelihood that such a population would go extinct. Most tigers, moreover, live in India, which has a huge feral dog population.

What can people do? Obviously, you should keep any pet on a proper vaccination schedule. You should also support programs to remove—that is, euthanize—feral dog populations, because they are a threat to both wildlife and humans.

This is an emotional subject, so here’s a quick story about the emotions on the other side of the issue.

At about the same time distemper was wiping out lions in the Serengeti, I visited with a researcher in Botswana on a long-term study of African wild dogs, a beautiful but beleaguered species, then down to about 5,000 animals. The researcher had named all the dogs in one study pack after different beers—something he wasn’t getting to drink much during field work. One day, a young male named Newkie (for Newcastle) wandered off in search of a female.

By the time he eventually returned home, his entire family had been killed off by distemper or rabies picked up from domestic dogs. Newkie spent the next few months wandering in the old Beer Pack home range, taking solace in the scent marks of his kin, which lingered like ghosts for months afterwards.

That’s a terrible fate to inflict on any animal—much worse than what happened to me with measles. But keep both experiences in mind—the loss of love ones and the trauma of disease. Then run out and get your kids vaccinated. Also bear in mind that what happens to wildlife affects their well-being, too. With “the falloff in vaccination of children,” said Gilbert, “there’s a niche there for another morbillivirus,” such as measles or distemper. Theoretically, he said, canine distemper, or another related virus, could start showing up in people.

By Richard Conniff, with reporting by Geoffrey Giller.