Infectious Disease Compendium

Rabies virus

Microbiology

A virus.

Epidemiologic Risks

Bites from a rabid animal: dogs, bats lead the list, other animals include raccoons, skunks, cats, foxes, and coyotes. Occasional cases from cave explorers and rare cases from corneal and other transplants.

Syndromes

An encephalitis. Incubation is a days to years, usually 1-3 months is the average.

The first symptoms are flu-like malaise, fever, or headache. There may be discomfort or paresthesias at the site of exposure (bite), progressing within days to symptoms of cerebral dysfunction, anxiety, confusion, agitation, progressing to delirium, abnormal behavior, hallucinations, and insomnia. Then death.

Treatment

Post exposure prophylaxis (from http: //www.cdc.gov/mmwr/preview/mmwrhtml/00056176.htm). To quote the CDC site:

Treatment of Wounds "Immediate and thorough washing of all bite wounds and scratches with soap and water and a virucidal agent such as a povidone-iodine solution irrigation are important measures for preventing rabies. In studies of animals, thorough wound cleansing alone without other post exposure prophylaxis has been shown to reduce markedly the likelihood of rabies. Tetanus prophylaxis and measures to control bacterial infection also should be administered as indicated. The decision to suture large wounds should take into account cosmetic factors and the potential for bacterial infections.

Post exposure antirabies vaccination should always include administration of both passive antibody and vaccine, with the exception of persons who have previously received complete vaccination regimens (pre exposure or post exposure) with a cell culture vaccine or persons who have been vaccinated with other types of vaccines and have had documented rabies antibody titers. These persons should receive only vaccine. The combination of RIG and vaccine is recommended for both bite and nonbite exposures, regardless of the interval between exposure and initiation of treatment.

Rabies Immune Globulin Use. RIG is administered only once (i.e., at the beginning of antirabies prophylaxis) to previously unvaccinated persons to provide immediate antibodies until the patient responds to HDCV, RVA, or PCEC by actively producing antibodies. If RIG was not administered when vaccination was begun, it can be administered through the seventh day after the administration of the first dose of vaccine. Beyond the seventh day, RIG is not indicated since an antibody response to cell culture vaccine is presumed to have occurred. Because RIG can partially suppress active production of antibody, no more than the recommended dose should be administered. The recommended dose of human RIG is 20 IU/kg body weight. This formula is applicable to all age groups, including children. If anatomically feasible, the full dose of RIG should be thoroughly infiltrated in the area around and into the wounds. Any remaining volume should be injected intramuscularly at a site distant from vaccine administration.

This change in the recommendations for RIG administration is based on reports of rare failures of post exposure prophylaxis when smaller amounts of RIG were infiltrated at the exposure sites . RIG should never be administered in the same syringe or in the same anatomical site as vaccine.

Vaccine Use. Three rabies vaccines are currently available in the United States; any one of the three can be administered in conjunction with RIG at the beginning of post exposure therapy. A regimen of five 1-mL doses of HDCV, RVA, or PCEC should be administered intramuscularly. The first dose of the five-dose course should be administered as soon as possible after exposure. Additional doses should be administered on days 3, 7, 14, and 28 after the first vaccination. For adults, the vaccination should always be administered IM in the deltoid area. For children, the anterolateral aspect of the thigh is also acceptable.

The gluteal area should never be used for HDCV, RVA, or PCEC injections because administration of HDCV in this area results in lower neutralizing antibody titers." So there.

Notes

Several cases who have survived (MMWR):

"With a presumptive diagnosis of rabies, the patient was sedated with ketamine and midazolam and started on amantadine and nimodipine to prevent cerebral artery vasospasm, and fludrocortisone and hypertonic saline to maintain her sodium at a level >140 mmol/L. Neither human rabies immunoglobulin nor rabies vaccine was administered.

During the first week of hospitalization, the patient developed autonomic instability manifested as significant hypertension. She required esmolol and nicardipine infusions as well as intermittent hydralazine and scheduled amlodipine. She also had frequent episodes of supraventricular tachycardia requiring adenosine. These resolved with repositioning of her central venous catheter. Cerebral artery spasm was not demonstrated by repeated transcranial Doppler ultrasound examinations and CT angiography of the head.

On May 8, the patient moved her head spontaneously. Over the next few days, she moved her head more, then began moving her arms and then her legs. With progressive improvement in her strength, she tolerated extubation on May 16 and was transferred to the pediatric wards 1 week later. On May 31, she was transferred to the rehabilitation service with residual left foot drop. At discharge on June 22, she showed no signs of cognitive impairment and was able to walk and perform activities of daily living."

Intersesting analysis suggests that treating bats without bites is not rational, not that I am suggesting it, but it is food for thought (PubMed).

ICD9 Codes (Soon to be supplanted by ICD10)

Rabies 071; contact V01.5.