Rabies/Animal Bite Case File

Rabies/Animal Bite Case File

Eugene C. Toy, MD, Barry C. Simon, MD, Terrence H. Liu, MD, MHP, Katrin Y. Takenaka, MD, Adam J. Rosh, MD, MS

Case 13

A 15-year-old adolescent boy was cleaning some items in the shed in his backyard, when he saw a bat in middle of the shed. The bat bit the boy on his dominant hand, after which the teenager ran into the house. His parents brought the boy to the emergency department. His vital signs on arrival were a blood pressure of 115/70 mm Hg, heart rate of 105 beats per minute, respiratory rate of 14 breaths per minute, pulse oximetry of 99% on room air, and a temperature of 37.1°C (98.9°F). Inspection of the wound shows deep bite marks with a laceration close to the proximal interphalyngeal joint. The bat escaped after the boy was bitten and was not found.

⯈ What is the most likely diagnosis?

⯈ What is the next step in treatment?

ANSWER TO CASE 13:

Rabies/Animal Bite

Summary: A teenager complains of a deep bite to his dominant hand by a bat acting strangely. The bite is fresh and the bat cannot be located.

• Most likely diagnosis: Unprovoked attack by a rabies-infected bat.
• Best initial treatment: Notify animal control to locate the animal, then clean the wound and administer both passive and active rabies immunization to the patient. Administer tetanus toxoid if not received within the last 5 years.

ANALYSIS

Objectives

1. Recognize that bat bites are a common vector for rabies.
2. Know the treatment of common bite injuries.
3. Know the clinical presentation of rabies.
4. Know the treatments for rabies and when treatment should be given.
5. Understand the basic principles of snakebite management.

Considerations

This 15-year-old teenager encountered a bat exhibiting abnormal behavior. The bat, normally a nocturnal animal, is active in the afternoon. This is suspicious for a rabies-infected bat. Other important considerations in this case are that the patient was bit near a joint space, the patient’s tetanus status, and the possibility of retained teeth.

In this patient’s case, postexposure prophylaxis for rabies and delayed primary closure to observe for infection are reasonable. Postexposure prophylaxis for rabies should include a combination of immediate, passive (rabies immunoglobulin) immunization and active immunization (human diploid cell vaccine). Tetanus vaccine should be administered if the patient has not received it within the last 5 years.

Approach To:

Animal Bites

DEFINITIONS

HYDROPHOBIA: The violent contraction of respiratory, diaphragmatic, laryngeal, and pharyngeal muscles initiated by consumption of liquids.

VENOM: A specialized form of saliva that is rich in proteins, polypeptides, peptidases, and nucleases. Its effects can range from paralysis, digestion, or incapacitation to death.

CLINICAL APPROACH

General Bite Management

Good wound care is the mainstay of bite management. A detailed history of the bite including type of animal, whether provocation occurred, location of bite, and time since the bite, should be followed by a careful physical examination. Physical examination should focus on the patient’s neurovascular status, the potential for tendon involvement, any evidence of cellulitis, and the potential for joint space violation. The wound should be irrigated, tetanus booster updated if more than 5 years has elapsed since the last administration (see Case 12), and antibiotics administered if the bite is high risk for infection or already infected. A radiograph should also be obtained to evaluate for a fracture and retained teeth. For bites with potential tendon injury, the involved extremity should be splinted. Simple bites of the trunk and extremities (except for hands and feet) less than 6 hours old can generally be closed primarily. Simple bites of the head and neck area less than 12 hours old also can be repaired primarily. However, puncture wounds, bites of the hand or foot, wounds more than 12 hours old, and infected tissues, are usually left open.

With any bite injury, the appropriate authorities should be notified to find the animal and observe it for abnormal behavior. Prior to arriving to the ED, any open wound or bite should be thoroughly washed with soap and water. In the ED, irrigation of the wound with saline removes debris and lowers bacterial counts. There is no added benefit to the addition of hydrogen peroxide or povidone iodine to the irrigant. Any foreign body or devitalized tissue should be removed. Administering prophylactic antibiotics in the case of simple bites is left to physician preference, as there is no conclusive evidence that it reduces infection rates.

The clenched-fist injury, also called a “fight bite,” is especially important to assess because a small bite injury may deeply embed bacteria into the joint spaces or tendon sheaths of the hand. This can lead to a serious infection. A radiograph to assess for fracture or foreign body should be performed. The wound should be irrigated, the tendons examined, and antibiotics administered. In cases of delayed evaluation, look for signs of infection including cellulitis, abscess formation, or tenosynovitis. Due to the high risk of infection, these cases typically require admission to the hospital for IV antibiotics or surgery.

Bacterial Infections

Dogs, cats, and humans account for almost all mammalian bite injuries. Oral flora in dogs and cats include Staphylococcus aureus, Pasteurella spp, Capnocytophaga canimorsus, Streptococcus, and oral anaerobes. Humans usually have mixed flora, including S aureus, Haemophilus influenzae, Eikenella corrodens and beta-lactamase–positive oral anaerobes. In cat bite wound infections, P multocida is the most commonly isolated bacteria. Human bite infections are typically polymicrobial. Good initialchoice antibiotics include amoxicillin–clavulanic acid, ticarcillin–clavulanic acid, ampicillin–sulbactam, or a second-generation cephalosporin. Duration of administration for established infections is 10 to 14 days and 3 to 5 days for prophylaxis. Failed outpatient treatment of wound infections is an indication for admission and IV antibiotics.

Rabies

Rabies is a single-stranded ribonucleic acid (RNA) rhabdovirus that attacks the central nervous system causing an encephalomyelitis that is almost always fatal. It has a variable incubation period, averaging 1 to 2 months, but may be as short as 7 days or as long as 1 year. Clinical presentation begins with a 1- to 4-day prodrome with fever, headache, malaise, nausea, emesis, and a productive cough. An encephalic stage follows with hyperactivity, excitation, agitation, and confusion. Brain stem dysfunction follows with cranial nerve involvement, excessive salivation, followed by coma and respiratory failure. Hydrophobia (the violent contraction of respiratory, diaphragmatic, laryngeal, and pharyngeal muscles initiated by consumption of liquids) is a late sign of infection.

A bite is the most common means of transmission of rabies. Although, animal vaccination programs have decreased the incidence of rabies, they have not completely eliminated it. Risk factors for transmission include unprovoked attacks, unknown or unobserved animals, or animals displaying unusual behavior. Animals with increased lacrimation, salivation, dilated irregular pupils, unusual

behavior, or hydrophobia are particularly suspected. Bites to the face or hands confer the highest risk of rabies transmission, but any breakage of the skin can transmit the virus. Worldwide, in locations with incomplete animal vaccination, dogs are the most frequent vector for rabies transmission to humans. In the United States, dogs are largely rabies free. No cases have been recorded in animals having received two injections, but animals only receiving one vaccine have been infected. Healthy dogs, cats, or ferrets that bite humans should be confined and observed for at least 10 days for signs of illness; with any sign of illness, the animal should be euthanized and its head shipped refrigerated to a laboratory qualified to assess for rabies.

Rabies Prophylaxis

A thorough history and physical examination in the context of the geographical location will give important clues for treatment. Identification of the animal and observation will help guide treatment as described above. Preexposure prophylaxis with active vaccination may be given to individuals at risk (animal trainers, animal control field workers, etc). This does not obviate the need for postexposure prophylaxis. Postexposure prophylaxis is indicated for any person possibly exposed to a rabid animal. Postexposure prophylaxis is a medical urgency, not an emergency, but time is essential. Rabies immunoglobulin can give a rapid, passive immunity that will last for 2 to 3 weeks. Passive immunization with human rabies immunoglobulin 20 IU/kg should be injected around the wound site as soon as possible. Active immunization should then be given intramuscularly with a different syringe at a different site. The active vaccines include human diploid cell vaccine (HDCV), purified chick embryo cell vaccine (PCEC), and rabies vaccine adsorbed (RVA), and should be administered on days 0, 3, 7, and 14. Active immunization will lead to antibody formation in about 1 week and should last for several years.

Snakebites

Venomous snakes are found throughout the United States except in Maine, Alaska, and Hawaii. There are two main families of venomous species; the Crotalinae and the Elapidae. The Crotalinae, also called pit vipers because of the presence of a pitlike depression on their face, include rattlesnakes, copperheads, and water moccasins. The Elapidae includes the coral snakes.

Not every snakebite results in the release of venom into the victim; “dry bites” occur up to 20% of the time. When venom is injected, it usually occurs in subcutaneous tissue and is absorbed via the lymphatic and venous system. Clinical manifestations of envenomation will vary depending on the toxin, depth of envenomation, location of the bite, and size and underlying health of the victim. Pit viper envenomation ranges from minor local swelling and discomfort at the injection site to marked swelling, pain, blisters, bruising, and necrosis at the incision site; and systemic symptoms such as fasiculations, hypotension, and severe coagulopathy. In contrast, Elapid envenomation usually begins as minor pain at the incision with a delayed serious systemic reaction that may lead to respiratory distress secondary to neuromuscular weakness.

The primary objectives in snakebite management are to determine if envenomation occurred, to provide supportive therapy, to treat the local and systemic effects of envenomation, and to limit tissue loss and disability. If the species can be identified, the appropriate antivenin can be administered if required. Treatment of envenomations is also varied. If it is a “dry bite,” general wound care is usually sufficient. Radiographs should be performed to evaluate for retained teeth. Signs of envenomation can be broadly classified into either hematologic or neurologic. Hematologic effects of envenomation include disseminated intravascular coagulopathy, ecchymosis, and bleeding disorders. If there are signs of envenomation, then laboratory studies including, but not limited to, clotting studies, liver enzymes, and complete blood counts with platelets are necessary. Giving blood products to an envenomated patient with a coagulopathy will not correct the problem. The circulating venom responsible for the coagulopathy is still present and will likely inactivate the blood products. Therefore, the mainstay in treatment in venom-induced coagulopathy is antivenin, preferably type specific, not blood products. Nonetheless, if the patient is bleeding, it is prudent to administer both antivenom and blood products. The most commonly available antivenom for treatment of North American Crotalid envenomations is Crotalidae polyvalent immune Fab CroFab. Surgical debridement or fasciotomy in the setting of envenomation should not be done as this may lead to further bleeding. Neurologic effects include weakness, paresthesia, paralysis, confusion, and respiratory depression. Asymptomatic patients who were bit by a pit viper should be observed for 8 to 12 hours after the bite. This should be extended to 24 hours for coral snakebites because of the absence of early symptoms. The local poison control center should be contacted early in all symptomatic snakebites and will be able to help with management and location of antivenin. The national phone number for the poison control center is 1-800-222-1222. While the American Heart Association has recommended the use of pressure dressings in the treatment of snakebites, correct application of these is extremely difficult and incorrect application may result in harm. Their position is still being debated at this time.

COMPREHENSION QUESTIONS

Match the single best therapy (A to E) to the clinical scenarios in Questions 13.1 to 13.4.

    A. Identify the species, clean and immobilize the site, and administer antivenin.

    B. Clean bite site and treat with prophylactic antibiotics.

    C. Clean site, observe animal, and watch for signs of secondary infection.

    D. Clean the site and begin rabies prophylaxis with active and passive immunization.

    E. Admit for radical surgical debridement in the operating room.

13.1 Your dog, who was immunized against rabies within the last year, bites your neighbor.

13.2 A woman arrives in your ED with a human bite to her breast that occurred earlier in the day. There is a small puncture wound and no signs of cellulitis.

13.3 A scoutmaster brings a boy scout to the ED with a snakebite to his left foot. He says he heard the snake’s rattle just before it bit him. His entire foot is purple, swollen to his mid-calf, and very painful to the touch.

13.4 While raking leaves under his fruit tree at dusk, a man says a bird flew into his face. When he checked his face in the mirror he saw a bite mark under blood streaks.

ANSWERS

13.1 C. This is a low-risk bite. The dog is your housedog with a low risk of ever contracting rabies. You have it immunized every year and can observe it for 10 days. As always, clean the bite thoroughly and consider radiographs to be sure no broken teeth are in the wound or that the bone has been penetrated. Administer tetanus if indicated and watch for secondary bacterial infection. Prophylactic antibiotics are indicated.

13.2 B. Human bites have high rates of infectivity. This wound does not appear to be infected. Nonetheless, the wound should be cleaned and 3- to 5-day course of prophylactic antibiotics should be initiated. Human bites rarely lead to retained teeth so a radiograph is not indicated. If this bite occurred on the hand or across a joint space, a radiograph should be performed. Tetanus toxoid should be given if indicated. TDaP has now been approved for use in patients over 65 years old.

13.3 A. This is a high-risk snakebite. The authorities should immediately be notified to search for the snake. Although some percent of venomous snakebites fail to inject venom, this bite is clearly envenomed. The rapid swelling, pain, and discoloration demands immediate attention. First responders should immobilize the site and place constriction bands that do not obstruct arterial flow. The swelling is not a compartment syndrome unless elevated pressures are measured. Avoid incisions and fasciotomies or packing in ice. Immediate antivenin injection in and around the site should be a priority. Remember that species-specific antivenin is important and that administration time is critical. Best results are obtained within 4 hours. Mark the swelling every 15 minutes, evaluate coagulation profiles, electrocardiogram (ECG ), renal function, and liver function, and consider ICU admission to

ensure adequate perfusion and to avoid disseminated intravascular coagulation (DIC). An index of antivenin can be obtained from the American Zoo and Aquarium Association (301-562-0777) as well as your local poison control center (800-222-1222).

13.4 D. This injury is at high risk for rabies transmission. Dusk is the usual time for bat activity, and although this man did not feel a bite, he discovered bite marks under his injury site. Bats carry high rates of rabies and this man was bitten on the face. Because the animal cannot be examined, immediate passive and active immunization should be initiated and tetanus administered, if indicated. As always, watch for secondary bacterial infection and update his tetanus status if it has been more than 5 years since his last immunization.

CLINICAL PEARLS

⯈ In the United States, rabies transmission by dogs is nearly zero whereas transmission by bats is more often seen. Worldwide, dog transmission is still common.

⯈ Rabies prophylaxis is indicated for uncaught wild animals and animals that start behaving abnormally.

⯈ Bites that are more than 6 hours old are, in general, left open, because of the risk of infection.

⯈ Snakebites should be treated like other bites with special attention paid to species identification and rapid administration of antivenin if required.

References

Ball V, Younggren BN. Emergency management of difficult wounds: part I. Emerg Med Clin North Am. 2007;25:101-121. 

Campbell BT, Corsi JM, Boneti C, et al. Pediatric snakebites: lessons learned from 114 cases. J Pediatr Surg. 2008;43(7):1338-1341. 

Gold BS, Dart RC, Barish RA. Bites of venomous snakes. N Engl J Med. 2002;347(5):347-356. 

Leung AK, Davies HD, Hon KL. Rabies: epidemiology, pathogenesis, and prophylaxis. Adv Ther. 2007;24(6):1340-1347. 

Markenson D, Ferguson JD, Chameides L, et al. Part 13: First aid: 2010 American Heart Association and American Red Cross International consensus on first aid science with treatment recommendations. Circulation. 2010;122(16 Suppl 2):S582-S605. 

Riley BD, Pizon AF, Ruha A. Snakes and other reptiles. In: Goldfrank’s Toxicologic Emergencies. 9th ed. New York, NY: McGraw-Hill; 2010. 

Rupprecht CE, Briggs D, Brown CM , et al. Use of a reduced (4-dose) vaccine schedule for postexposure prophylaxis to prevent human rabies. MMWR Recomm Rep. 2010; 59(RR-2):1-9. 

Schalamon J, Ainoedhofer H, Singer G, et al. Analysis of dog bites in children who are younger than 17 years. Pediatrics. 2006;117(3):e374-e379.

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