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INTRODUCTION AND EPIDEMIOLOGY
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This chapter reviews the pathophysiology and epidemiology of rabies, pre- and postexposure rabies prophylaxis, and clinical presentation and treatment of rabies. Current information is available from the Centers for Disease Control and Prevention (http://www.cdc.gov/rabies/).
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More than 3 billion people are at risk of rabies in over 100 countries.1 Rabies is responsible for approximately 60,000 fatalities annually worldwide, with India accounting for approximately one third of cases.2,3 The World Health Organization estimates that more than 15 million people receive a postexposure preventive regimen annually.4
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Rabies is primarily a disease of animals.5-7 The epidemiology of human rabies reflects both the distribution of the disease in animals and the degree of human contact with these animals. A summary of major rabies vectors is provided in Table 158-1.
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In the United States, rabies is endemic in many wild animal populations, with more than 5500 rabid animals reported in 2015.8 Although human rabies is rare in the United States, postexposure rabies prophylaxis is provided to between 40,000 and 50,000 persons each year.9 The cost of rabies prevention in the United States is greater than $300 million, most of which is spent on dog vaccinations.10 From January 2003 to September 2016, 38 cases of human rabies were reported in the United States, of which 12 cases were contracted in other countries. Bats represent the most common exposure for human rabies cases in the United States.8 Worldwide, greater than 99% of human rabies cases are acquired by dog bite.2
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Rabies virus is the prototype member of the genus Lyssavirus.11,12 All lyssaviruses are adapted to replicate in the mammalian CNS, are transmitted by direct contact, and are not associated with transmission by or natural replication in insects.
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Viral infection of the salivary glands of the biting animal is responsible for the infectivity of saliva.5-7,13 After a bite, saliva containing infectious rabies virus is deposited in muscle and subcutaneous tissues. The virus remains close to the site of exposure for the majority of the long incubation period (typically 20 to 90 days). Rabies virus binds to the nicotinic acetylcholine receptor in muscle, which is expressed on the postsynaptic membrane of the neuromuscular junction. Subsequently, the virus spreads across the motor end plate and ascends and replicates along the peripheral nervous axoplasm to the dorsal root ganglia, ...