Assessing the risk of rabies entering Japan

Dogs and veterinary epidemiology

Assessing the risk of rabies entering Japan

Katsuaki Sugiura

Project Professor, Graduate School of Agricultural and Life Sciences

There are fears that rabies could be brought into Japan via an infected animal accidentally arriving in a freight container.
Project Professor Sugiura has calculated the risk of such an event. What did he find?

There is a once-in-360,000-years probability that an animal accidentally transported in a container causes rabies to enter Japan

Japan is one of the few countries that is completely free of rabies, with the last case being reported in a cat in 1957. Rabies is a zoonotic disease affecting not only dogs and cats, but also other mammals, including humans. The Rabies Prevention Act of 1950, which introduced the compulsory rabies vaccination of dogs, as well as intensive measures to capture stray dogs, contributed to the eradication of the disease. With annual vaccinations still practiced in Japan, what is the probability that rabies could enter the country? I quantitatively estimated the probability based on various scenarios, and for all of them the calculated probabilities were low.

For example, if a wild animal is accidentally placed inside an international freight container and transported to Japan, it might be able to survive without food for about five days. Lots of containers coming to Japan originate from Southeast Asia or other nearby regions, so an animal trapped in a container sent from those areas could conceivably make it to Japan alive. Based on the probabilities of the animal being infected with rabies, of still being alive when the container arrives in Japan, and of escaping when the container is opened, I have calculated that the rabies virus could enter Japan by this route once every 360,000 years. Even if all animals accidentally transported in containers managed to escape when the container was opened, it would be once in 70,000 years. Every year, about 8,000 dogs and cats are imported into Japan. As long as the strict quarantine rules are followed for these animals, including two vaccination shots, antibody testing and microchipping for identification, the probability of the rabies virus getting into Japan via these animals is a once-in-50,000-years event. The probability will substantially increase if accompanying documents are forged, however, so it is critical that animal quarantine officers are trained to detect such forgeries.

As a reference for thinking about the appropriateness of requiring yearly rabies vaccinations in Japan, a country with such a low entry risk, I have also estimated the antibody levels of vaccinated dogs. The results indicate that the immunity of vaccinated dogs lasts for two to three years, with a high probability. The main carriers of the rabies virus are dogs and wild animals. Due to the “species barrier,” it would take multiple generations of infection for the disease to be established in the species in which the disease is newly introduced. On the other hand, the fatality rate of those infected with rabies is almost 100%, with the World Health Organization (WHO) estimating that 59,000 people in the world die from the disease each year. It is also worth knowing that if you did get bitten by a rabid dog, you could protect yourself from the disease with post exposure prophylaxis (multiple vaccination shots within a month of the incident).

Countries/regions free from rabies and animals that carry rabies virus