Chapter 157: Rabies

INTRODUCTION AND EPIDEMIOLOGY

This chapter reviews the 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/).

More than 3 billion people are at risk of rabies in over 100 countries.¹ The World Health Organization estimates that more than 15 million people receive a postexposure preventive regimen with more than 55,000 people dying of rabies annually, despite the availability of effective postexposure prophylaxis.

Rabies is primarily a disease of animals.^2,3,4 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 157-1.

In the United States, rabies is endemic in many wild animal populations, with more than 6000 rabid animals reported in 2010.⁵ Although human rabies is rare in the United States, postexposure rabies prophylaxis is provided to about 40,000 persons each year.⁶ From 2001 to 2011, 29 cases of human rabies were reported in the United States, with eight cases contracted in other countries. About 90% of these cases were associated with bats. Most cases contracted outside the United States and Canada were from dog bites.^5,7,8

PATHOPHYSIOLOGY

Rabies virus is the prototype member of the genus Lyssavirus.^9,10 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.

Viral infection of the salivary glands of the biting animal is responsible for the infectivity of saliva.^2,3,,4,11 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, the spinal cord, and the CNS. Following CNS replication in the gray matter, the virus spreads outward by peripheral nerves to virtually all tissues and organ systems.

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