Clinical Pearls
In 2011 in Massachusetts, 110 animals with rabies were identified.Bats accounted for 20 (18%) of the animals that tested positive. Mostof the bats with rabies were identified in the summer and early fall.- What is the principal means of rabies transmission in the UnitedStates?Although a dog bite is responsible for most rabies infections inhumans in the developing world, bats are responsible for mostinfections in humans in the United States. Transmission is usuallythrough a bite, which is often unrecognized. Rabies can also betransmitted by aerosolized exposure, which could occur in a cave witha very large density of bats, and there have also been reports of thetransmission of rabies in association with organ or tissuetransplantation.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). Thereare two varieties of rabies: encephalitic (or "furious," accountingfor 80% of cases) and paralytic (or "dumb," accounting for 20% ofcases). The prodrome may last a few days to weeks. Signs and symptomsthat commonly occur in the encephalitic phase of rabies includehyperexcitability, agitation, and hydrophobia, which is a fear ofswallowing liquids. Hydrophobia is unique to rabies, and conditioningcan occur, in which the sight of liquids can trigger laryngeal,pharyngeal, or diaphragmatic spasms. Aerophobia, or fear of air, mayalso be observed, in which the force of air on the face or airway cantrigger spasms. In addition, hallucinations and excessive salivationmay occur in this phase of infection. Death typically occurs within 5days after infection. Autonomic dysfunction is common, withhypertension, cardiac dysrhythmias, priapism, sweating, and fever.
Q: What treatment strategies for rabies exist?A: Postexposure prophylaxis is highly efficacious, but once rabiesencephalitis has begun, there is, unfortunately, no proven treatment,and the mortality rate approaches 100%. Therefore, for most patientswith symptomatic rabies, the standard of care is palliation. TheMilwaukee protocol is a strategy developed to minimize brain injurywhile allowing the patient's immune response to eradicate the virus.Key features of the protocol are sedation and other supportivemeasures designed to suppress brain activity and minimize injury fromcatecholamine storm and cerebral vasospasm. In addition, it isimportant to avoid the administration of glucocorticoids, rabies IgG,and the rabies vaccine in patients. There is no good evidence tosupport the use of the protocol, although there are no otherreasonable alternatives outside of palliative care. This protocolshould be considered only for persons early in the course ofsymptomatic disease who are otherwise in good health. It iscritically important that patients and family members understand thatthis approach is unlikely to be successful and that there is a highrisk of neurologic sequelae if the patient survives.
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