32-03: Other Neurotropic Viruses

General Considerations

Rabies is a viral (rhabdovirus) encephalitis transmitted by infected saliva that enters the body by an animal bite or an open wound. Worldwide, over 17 million cases of animal bites are reported every year, and it is estimated that about 59,000 deaths annually are attributable to rabies. Rabies is endemic in over 150 countries; on the basis of interviews, it is estimated that over 40% of the world’s population lives in areas without rabies surveillance. Most cases of rabies occur in rural areas of Africa and Asia. India has the highest incidence, accounting for 36% of global deaths (http://www.who.int/rabies/epidemiology/en/). In developing countries, more than 90% of human cases and 99% of human deaths from rabies are secondary to bites from infected dogs. Rabies among travelers to rabies-endemic areas is usually associated with animal injuries (including dogs in North Africa and India, cats in the Middle East, and nonhuman primates in sub-Saharan Africa and Asia), with most travel-associated cases occurring within 10 days of arrival. Rare but related viruses are the Australian lyssavirus, transmitted by bats including one referred to as the black flying fox, and which has caused three deaths over the last 20 years, and the European lyssavirus, with cases from Germany and the United Kingdom. Rabies-free areas include much of Western Europe, Australia, New Zealand, Japan, and the state of Hawaii in the United States. A map outlining these areas is available with Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Rabies_Free_Countries_and_Territories.svg).

In the United States, domestically acquired rabies cases are rare (approximately 92% of cases are associated with wildlife) but probably underreported. Reports largely from the East Coast show an increase in rabies among cats, with about 1% of tested cats showing rabies seropositivity. The annual caseload in the United States is 1–3 cases (https://www.cdc.gov/rabies/location/usa/surveillance/human_rabies.html). Between 1960 and 2018, a total of 125 human rabies cases were reported in the United States. These included 36 cases (28%) with a history of dog bites during international travel. The remaining 89 cases (72%) were acquired in the United States, most often by bats.

Surveillance for animal rabies in 2017 showed 4454 animal and 2 human cases occurring in 49 states and Puerto Rico. Wild animals accounted for 91% of cases, and among wild animals, bats were the most common animal (31.2%). Wildlife reservoirs, with each species having its own rabies variant(s), follow a unique geographic distribution in the United States: raccoons on the East Coast; skunks in the Midwest, Southwest, and California; and foxes in the Southwest and in Alaska (eFigure 32–2). However, some areas have all three wildlife reservoirs (eg, the hill country of Texas) https://www.cdc.gov/rabies/location/usa/surveillance/wild_animals.html.