In North America and Western Europe rabies is no longer much of a threat to people because of vast and effective rabies vaccination protocols in pet dogs. But in other areas, such as Africa and Asia, many people still die every year after they’ve been bitten by rabid dogs. Is there a way to eliminate the threat of rabies in these areas as well? A group of researchers investigated just this question. They chose two rural areas in Tanzania, one of which had a high domestic dog population—the Serengeti district—and one of which had a lower population—the Ngorongoro district. From 2002 to 2006, the researchers investigated case-to-case transmission of rabies in domestic dogs in these areas. They concentrated on domestic dogs instead of the numerous other wildlife in the region because more than 90% of the rabid animals identified were domestic dogs and all of the rabies isolates were consistent with the Africa 1b canid strain.
The researchers were trying to determine the basic reproductive number, or R0, for rabies, which is the average number of secondary infections an infected individual will cause in a susceptible population. They arrived at an R0 of about 1.2 for both areas, which is extremely low. This R0 was close to previously established basic reproductive numbers in other parts of the world, which averaged to less than 2. No difference in R0 was apparent between the Serengeti district, which had a high domestic dog population, and the less populated Ngorongoro district. During the five-year study period, villages in the region occasionally attempted vaccination programs in dogs, and when more than 70% were vaccinated, no outbreaks occurred. Small outbreaks were seen when lower percentages of dogs were vaccinated. The largest and longest outbreaks occurred in villages with less than 20% vaccination coverage.
Based on the low R0 of rabies and other factors, the authors arrived at a recommendation of vaccinating 60% of domestic dogs to prevent rabies outbreaks in that area. Further, they recommended pulse vaccination since the dog population overturns so quickly—after a year, there are enough young, unvaccinated dogs to again start an outbreak. The authors think annual vaccination of 60% of domestic dogs is achievable if there is a coordinated effort throughout these more susceptible areas. So, yes, with international commitment rabies could become completely eradicated worldwide, say these researchers.
Hampson K, Dushoff J, Cleaveland S, et al. Transmission dynamics and prospects for the elimination of canine rabies. PLoS Biol 2009;7(3):e53. [Epub ahead of print]