Targeting the semi-wild dogs that roam city streets and rural hamlets all over the world can break the chain of rabies transmission and eliminate cases in humans
Photo courtesy of Wikimedia Commons
In comparison to other looming global problems, most people might not see rabies as rating particularly high on the list of health-related issues in need of address. It’s a disease that feels relegated to some distant backwater or far off past. But rabies is still a massive problem, with 50 individuals bitten by a rabid animal every minute and someone dying of the disease every 10 minutes. And, in the United States, thanks to our complacency (and the flagging success of traditional containment measures) rabies is actually on the rise, with some areas reporting 100 to 800 percent spikes in cases in 2014 alone. Yet despite this disheartening and resurgent prevalence, some scientists now believe that we might be able to eradicate rabies worldwide by 2020—and do it on the cheap—by simply vaccinating feral dogs.
The focus on dogs might seem odd, considering that they’re far from the only vector for rabies infection. The rabies virus can also survive in the saliva of bats, foxes, raccoons, and skunks. Once bitten, the virus makes its way to the victim’s brain, causing drooling, convulsions, numbness, loss of muscle function, fever, muscle spasms, pain, restlessness, and difficulty swallowing. But it can take anywhere from 10 days to seven years to develop from infection into illness, meaning that animals or humans usually carry the virus for a good one to three months before becoming visibly rabid. The difficulty of detecting bites from animals like bats, the long latency period and narrow window in which to seek treatment (which can be difficult to find in rural areas), and the lack of a cure (save one case in 2004, which used a chemically-induced coma to stop the virus’ spread) all add up to a widespread, daunting illness that goes way beyond a wild dog problem.
Accordingly, governments have attempted to target as many potential carriers as possible for vaccination in the past. (Exterminating the animals through mass culls has proven too expensive and ineffective.) For decades, health authorities have laid millions of packets of food laced with rabies vaccinations in strategic bottlenecks or in wide bands of woods, creating barriers of immunized wild animals to break chains of infection. In some countries—Switzerland, for example—these techniques have virtually eradicated rabies, but within a decade, as the immunized animals died off and new infected animals reemerged, rabies inevitably returned, promoting further costly rounds of scattering doctored food. Even this short-lived success was limited as the dispersed vaccinations never worked very well in vast, open frontiers, and were never able to entice bats.
Rabies vaccine in bait. Photo courtesy of Hannu/Wikimedia Commons
Yet it turns out that wild animals aren’t the main agents of rabies transmission to humans. Of all human rabies infections, 99 percent are caused by bites from the semi-domesticated, semi-feral dogs that roam much of the world. Wild animals that live further off from humans infect the dogs, which in turn infect other dogs and humans. Armed with this knowledge, scientists attempted a mass vaccination of dogs in nearly 200 rural Tanzanian villages and discovered that once 70 percent had been immunized against the disease, the chain of transmission could be broken and human rabies cases wholly eliminated, regardless of how many bats or raccoons continued to carry the disease. Published in 2009, this research led to calls for mass dog vaccinations worldwide.
That sounds like a daunting task, considering that even one nation can have upwards of one million wild or semi-wild dogs. But in further tests of the mass vaccination process in Latin America, rural residents knew exactly where the local dogs lived and, understanding the threat of rabies and the project at hand, willingly brought in thousands of dogs for treatment. And, as it turns out, it only costs $3 per dog to administer a vaccination (including veterinarians’ travel expenses and supplies), whereas treating infected humans costs at least $50 per person. In total, a global mass dog vaccination could cost as little as six billion dollars, versus the $124 billion spent annually on human treatment, scattered vaccinations, and other such programs.
These mass vaccinations have, over the past couple of years, caught on in selective nations like the Philippines and Tanzania. The success in these nations has been heartening. But borders remain porous, flimsy things, and so long as these drives remain piecemeal there is always the risk of reintroducing rabies from non-vaccinating countries. All signs indicate that we have a real shot at wholly eliminating this dreaded disease in humans within our lifetime. But to get there we need a piddling amount of funding, and the trickier bit will be achieving a modicum of ever-illusive global cooperation and dedication to the project.