In a famous scene in To Kill a Mockingbird, Atticus Finch shoots a rabid dog. For many Americans, these pages will be their only exposure to the disease. In the industrialized world, it is tempting to think of rabies as more of a boogeyman than a disease. Frightening, certainly, but frightening the way ghosts are frightening: a spooky force that may or may not be lurking in the shadows, waiting to get you if you’re not careful. But the reach of rabies is not limited to fiction; it is very real, and remains extremely deadly.
Rabies has spread worldwide; it is on all continents except Antarctica, and is endemic in more than 150 countries and territories. Despite its global reach, its impact is heavily concentrated; 95% of human cases occur in Asia and Africa2, resulting in tens of thousands of deaths each year1,2. The exact figure is impossible to measure, because rabies- like so many other diseases- disproportionately affects the poor and the vulnerable. It is most common in rural communities where the average daily income is about US$1-2, and there is limited medical care; post-exposure treatment costs about US$40 in Africa and US$49 in Asia, putting it well out of reach for those most affected by the disease2. Because of this isolation and the high likelihood of misdiagnosis, rabies is likely massively underreported. This feeds a cycle of neglect: because the impact of the disease is hard to measure, it is difficult to justify aid and education efforts, and that negligence allows the disease to persist1,2.
How does all this tie in with July’s theme of wildlife? Rabies is a perfect illustration of the fact that, for better or worse, humanity tends to measure the importance of wildlife diseases by how much they affect humans. And with rabies, the numbers are formidable. There are a number of animal hosts, but nearly all human rabies cases come from dogs; canine rabies potentially threatens more than 3 billion people in Asia and Africa2. Rabies also demonstrates that humans are willing to sacrifice animals, even those they love, if there is a chance it will provide them greater safety from disease: there have been several mass dog culls attempting to stop the spread of rabies.
But it’s not all bad news! Rabies also demonstrates that sometimes the best way to combat a disease is also the kindest. Culling failed. Research has shown that rabies is not density dependent, meaning that the number of dogs isn’t important. In turns out that what matters is what proportion of dogs are resistant to the virus. What matters is how many dogs have been vaccinated. Mass canine vaccination, when more than 70% of the dog population is vaccinated, is the best defense against rabies. Not only is mass canine vaccination more effective than culling at reducing disease, it is more cost effective than relying human post-exposure treatment alone to prevent human cases1. Vaccination: good for man and beast.
Cause: Rabies is caused by the aptly named rabies virus, which infects humans, as well as domestic and wild animals. Typically, the virus is transmitted when infectious material (usually saliva) from a sick individual comes in contact with mucous membranes (i.e. eyes, mouth or nose) or open wounds, like bites or scratches, on a healthy individual. Although the overwhelming majority of human cases come from dog bites, bats are the biggest source of the disease in the Americas. Despite being theoretically possible, a case of human-human transmission via biting has never been confirmed2.
Consequence: Disease symptoms usually emerge after an incubation period of 1-3 months, but this varies widely; it can range from less than a week to more than a year. The first symptoms typically include fever and pain or an unexplained tingling, pricking or burning sensation around the wound. As the virus spreads throughout the body, the brain and spinal cord become inflamed and one of two forms of the disease develops. Furious rabies is more common (about 70% of cases) and is the popular image of the disease, with symptoms including hyperactivity, exited behavior, hydrophobia, and sometimes aerophobia. After a few days, it causes cardio-respiratory arrest and death. The remaining 30% of cases are paralytic rabies, which is less dramatic and takes longer to develop than the furious form; starting at the wound site, the muscles gradually become paralyzed, and a coma slowly develops. Rabies is a bit of a catch-22; there are no diagnostic tests for the disease (meaning you can only be diagnosed by symptoms), but once symptoms develop, the disease is almost always fatal2.
Cure: Rabies is very treatable, if it’s caught early enough. While there is a preventative vaccine, it is usually only administered to people with high risk of contact with infected animals. More commonly, the disease is treated after exposure. Post-exposure prophylaxis (PEP, aka treatment after exposure) includes treating the wound directly by flushing it with water and washing it with soap or antiseptics. This is followed by a post-exposure vaccine. Every year, more than 15 million people (yes, that’s MILLLION) worldwide get a post-exposure vaccine, saving hundreds of thousands of lives annually2.
- Cleaveland, S., H. Beyer, K. Hampson, D. Haydon, F. Lankester, T. Lembo, F.X. Meslin, M. Morters, Z. Mtema, M. Sambo, & S. Townsend. 2014. The changing landscape of rabies epidemiology and control. Journal of Veterinary Research, 81. doi: 10.4102/ojvr.v81i2.731
- Rabies. World Health Organization. Web. 10 July 2015.
Image source: Creative Commons, https://commons.wikimedia.org/wiki/File:Smiling_Dog_Face.jpg