Clinical Pearls

In 2011 in Massachusetts, 110 animals with rabies were identified.
Bats accounted for 20 (18%) of the animals that tested positive. Most
of the bats with rabies were identified in the summer and early fall.

- What is the principal means of rabies transmission in the United
States?

Although a dog bite is responsible for most rabies infections in
humans in the developing world, bats are responsible for most
infections in humans in the United States. Transmission is usually
through a bite, which is often unrecognized. Rabies can also be
transmitted by aerosolized exposure, which could occur in a cave with
a very large density of bats, and there have also been reports of the
transmission of rabies in association with organ or tissue
transplantation.


Q: What are the clinical manifestations of rabies?

A: Disease progression occurs in five stages: incubation, prodrome,
acute neurologic phase, coma, and death (or, rarely, survival). There
are two varieties of rabies: encephalitic (or "furious," accounting
for 80% of cases) and paralytic (or "dumb," accounting for 20% of
cases). The prodrome may last a few days to weeks. Signs and symptoms
that commonly occur in the encephalitic phase of rabies include
hyperexcitability, agitation, and hydrophobia, which is a fear of
swallowing liquids. Hydrophobia is unique to rabies, and conditioning
can occur, in which the sight of liquids can trigger laryngeal,
pharyngeal, or diaphragmatic spasms. Aerophobia, or fear of air, may
also be observed, in which the force of air on the face or airway can
trigger spasms. In addition, hallucinations and excessive salivation
may occur in this phase of infection. Death typically occurs within 5
days after infection. Autonomic dysfunction is common, with
hypertension, cardiac dysrhythmias, priapism, sweating, and fever.

Q: What treatment strategies for rabies exist?

A: Postexposure prophylaxis is highly efficacious, but once rabies
encephalitis has begun, there is, unfortunately, no proven treatment,
and the mortality rate approaches 100%. Therefore, for most patients
with symptomatic rabies, the standard of care is palliation. The
Milwaukee protocol is a strategy developed to minimize brain injury
while allowing the patient's immune response to eradicate the virus.
Key features of the protocol are sedation and other supportive
measures designed to suppress brain activity and minimize injury from
catecholamine storm and cerebral vasospasm. In addition, it is
important to avoid the administration of glucocorticoids, rabies IgG,
and the rabies vaccine in patients. There is no good evidence to
support the use of the protocol, although there are no other
reasonable alternatives outside of palliative care. This protocol
should be considered only for persons early in the course of
symptomatic disease who are otherwise in good health. It is
critically important that patients and family members understand that
this approach is unlikely to be successful and that there is a high
risk of neurologic sequelae if the patient survives.

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