Why we should vaccinate wild animals - Works in Progress Magazine

Vaccinating wild animals can protect human health, and spare animals from extinction and suffering.

The Coyote Getter, invented in the 1930s, was a hunting device that spewed cyanide into the mouth of any coyote that bit its scented wool bait. Thirty years later, researchers revisited the device. But rather than revamping it to kill more efficiently, they wanted to replace the cyanide payload with something wholly different: a coyote vaccine.

Wild animal vaccines are remarkable for many reasons, but the most remarkable might be that they exist at all. Vaccines are usually tools civilization reserves to defend the humans and domesticated animals within its bounds. The wild, by contrast, is a place from which we extract resources or defend ourselves, or where we simply leave things untouched.

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But defense doesn’t have to be adversarial. Around 60 percent of infectious diseases are zoonotic in origin, meaning they are transmitted from animals to humans, and the majority of them originate from wildlife rather than livestock or pets. Ebola came from fruit bats; HIV from chimpanzees; SARS from horseshoe bats and civets; Lyme disease lurks in deer and mice. In theory, preventing disease at its source in wild populations could protect people better than simply reacting to spillovers when they occur.<br>Preventing human illness is not the only reason to vaccinate wild animals. Many recent programs have been motivated by conservation, such as efforts to protect bats from white-nose syndrome or koalas from chlamydia. There is also budding recognition that these programs are valuable on welfare grounds, sparing animals from pain and suffering.<br>Nevertheless, wild animal vaccination first emerged as a form of defense. In the mid-twentieth century, laws mandating the vaccination of dogs pushed down the number of rabies cases in the United States, from 74 reported human deaths across the country in 1921 to single digits per year by the 1960s. The remaining cases occurred overwhelmingly through contact with wildlife: bats, foxes, skunks, and raccoons. But worryingly, the prevalence of rabies in wild animals seemed to be growing, both in the United States and in Europe. To keep rabies contained, researchers had to figure out how to immunize these animals, too.<br>Sick as a dog<br>Rabies is a terrifying disease. It is transmitted to humans through bites or scratches from an infected animal, such as a dog, bat, or coyote. The virus travels silently through the peripheral nervous system, taking a month or two to creep up into the brain and spinal cord. Once it infects the central nervous system, an array of alarming symptoms emerge. The ancient Greek physician Hippocrates is thought to have been describing rabies when he wrote of ‘persons in a frenzy [who] drink very little, are disturbed and frightened, tremble at the least noise, or are seized by convulsions’. And when these appear, death is virtually guaranteed within days.

Fearful descriptions of rabies date back to antiquity. This page from a 13th-century Arabic text shows an outdoor scene with a mad dog biting a man.

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Freer Gallery of Art and Arthur M. Sackler Gallery, Smithsonian Institution, Washington, D.C.

Since rabies doesn’t spread between humans, infecting us only incidentally, it’s far more cost-effective to wipe out the disease reservoir in animals than to vaccinate humans. So developed countries have long implemented public health programs to control its spread from animals to humans: vaccinating pets and regulating their movement across borders, neutering or euthanizing strays, surveilling and investigating cases, and rapidly administering treatment after potential exposure. These early efforts worked. By the 1960s, the US had largely brought dog-mediated rabies under control, reducing the number of cases affecting humans almost twentyfold. In 2007, the canine variant of the rabies virus was officially declared eradicated from the United States, with the last recorded case occurring in 2004. Many European countries had achieved this milestone earlier. The United Kingdom had been free of canine rabies since 1922; France, 1960; and Italy, 1973. Human deaths from rabies are now almost unheard of in rich countries, though it continues to kill tens of thousands of people per year in the developing world.<br>But as canine rabies subsided in the West, another problem arose: wildlife rabies. Between 1938 and 1958, the annual number of rabies cases reported in wild animals grew from 44 to 2,075. Part of the reason for this was increased detection, but there also seemed to be a genuine rise in the number of cases. Rabies was spreading in raccoons, skunks, and foxes across the Americas; in Europe, too, a growing number of rabies cases were identified in red foxes, beginning in Eastern Europe in the 1940s and...