When we think about animals that can kill us, we tend to think of fast-moving predators with teeth: sharks, tigers, wolves, snakes, and so on. But our deadliest enemy is probably the humble mosquito, which inadvertently spreads deadly diseases like malaria, dengue, yellow fever, and West Nile while going about its business. These diseases can be survived in theory, but they kill millions in practice.
Media attention has more recently turned to the chikungunya virus, which infected more than a quarter-million people in Haiti and the Dominican Republic, has recently appeared in the United States and has been present in Australia for more than a decade. Although chikungunya has a relatively low mortality rate, most mosquito-borne illnesses have a relatively low mortality rate; what makes them (and most epidemic diseases) deadly is widespread infection, not high lethality. Surviving mosquito-borne illness is a numbers game: if enough people get sick, a large number of people will die from a theoretically non-fatal illness.
U.S. scientists have recently developed a three-stage chikungunya vaccine that appears to be successful, but (as has been true with respect to the malaria vaccine) the vaccine is likely to be too expensive to be of much help to people in developing nations who are most at risk of dying from the virus. A vaccine won’t stop chikungunya from joining mosquitos’ considerable arsenal of epidemic, hard-to-treat illnesses that are theoretically survivable on an average individual scale, and still manage to kill millions of us anyway.