152. Rabies

General

Dogs account for < 5% cases where controlled, whereas they account for >90% causes in other parts of the world. Other animals: foxes, skunks, mongooses, bats. For US, most cases (not human infection, just diagnosed rabies in the wildlife) were with raccoons (36.6%), bats (27.2%), skunks (20.4%), foxes (6.7%), and other animals including coyotes, opossums, otters, bobcats, rodents and lagomorphs (rabbits, hares, picas).

Animal bites not causing rabies: squirrels, hamsters, guinea pigs, gerbils, chipmunks, rats, mice, domesticated rabbits, other small rodents. Nonbite exposures very rarely cause rabies. Dogs/cats with two vaccines will never get rabies from exposure. Have been cases with aerosolized virus in bat caves.

Most human infections are associated with bats (80%, specifically the silver-haired bat) with most other cases related to dog bites from other countries. Highest risk for transmission with multiple bites around the face.

Features

No great test for confirmation. Negri bodies on autopsy. Most reliable test: nuchal skin biopsy with immunofluorescent rabies antibody staining. If did not receive vaccine or IG, serum rabies antibodies confirms diagnosis.

Tetanus does not have altered mental status. Rabies does.

Basically is an encephalitis. Incubation period 20-90 days (though some documented much earlier and much later).

Prodromal period: fever, sore throat, chills, malaise, anorexia, headache, nausea. Sometimes get early limp pain, limb weakness, paresthesia at exposure site.

Acute neurologic phase: Two forms: furious and paralytic. Furious: 80% of patients, hyperactivity, disorientation, hallucinations, bizarre behavior. Sympathetic surge. 50% have hydrophobia in which they get pharynx/larynx/diaphragm spasm with drinking fluid.  Aerophobia occurs with pharyngeal spasm triggered by feeling draft of wind. Paralytic: paralysis primarily in the bitten extremity, though can have diffuse or symmetric paralysis as well.

Coma usually occurs within 10 days of onset of symptoms. Death occurs due to seizures/respiratory dysfunction. Only 6 people have survived with all but one receiving pre or post exposure prophylaxis.

Treatment

Clean (soap/water) the wound immediately. Found in animal experiments that simple cleaning reduced risk of rabies.

Patients suspected of having rabies should have contact isolation and healthcare workers wear masks/eye protection (though no healthcare associated transmission documented).

No treatment for patient with rabies. One case report of ketamine, versed, ribavirin, and amantadine (‘Milwaukee protocol’) saved patient’s life (NEJM, 2005).

Prophylaxis

Pre-Exposure: For people at risk for possible rabies exposure. Primary vaccinations given IM HDCV (Human diploid cell vaccine) or PCECV (purified chick embryo cell vaccine) 1.0mL on days 0, 7, 21 and 28. Still will need treatment after possible rabies exposure, though much less treatment. Wont need immune globulin. Vaccine given to people who work in rabies labs, vets, animal-control, wildlife, spelunkers. Serology testing in the higher risk individuals and booster given if antibody titer below normal range. If exposed after this, only need vaccine on day 0 and day 3 with no HRIG.

Post-Exposure: If animal exposure with bite/salivary exposure, if cat/dog and can be captured, then it will be quarantined for 10 days and released if normal behavior at that time. No prophylaxis at all. If the cat/dog can not be captured, check epidemiological data for area and if low risk, no prophylaxis. If unavailable or higher risk, give vaccine + HRIG. If animal is other carnivore or bat/raccoon, bobcat, fox, cow, if can be captured and quarantined, it will be sacrificed and sent to lab and patient given vaccine. If results negative for rabies, no HRIG. If animal can not be captured, patient receives HRIG and vaccine. It states consider post-exposure prophylaxis for persons who were in the same room as a bat and who might be unaware that a bite or direct contact had occurred. Contact public heath officials if unsure of therapy. Treatment: 1 dose of HRIG 20 IU/kg (as much can be injected in wound and then distal site) and 4 doses (0,3,7,14) of rabies vaccine over 14 days. Give first doses within 24 hrs. Vaccine must be injected IM into the deltoid.

Clinical Cases

Hydrophobia in Rabies Video

Rabies Patient, Aerophobia with acute hydrophobia Video

Extraordinary People, The Girl Who Survived Rabies Video

EM:RAP, January 2010, Al Sacchetti, A Bizarre Rabies Case Audio

References / Resources

Tintinalli, Seventh Edition, Chapter 152: Rabies

Crashing Patient, Scott Weingart, Rabies

CDC, Rabies, Reviewed 3/8/14

Clinical Infectious Diseases, A. Jackson, 2003, Management of Rabies in Humans

UptoDate, Clinical Manifestations and Diagnosis of Rabies, Reviewed on 3/8/14

EM:RAP, July 2004, Richard Harrigan, Rabies Audio

152. Rabies

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