AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Background

Animal bites are common, with more than 4.7 million people (almost 2% of the population) in the United States affected each year, according to the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia. Typically, these are dog or cat bites, with the patient's age most commonly being 7-9 years, but persons of any age can be affected. Typically, the aggressor is a dog, such as a collie, a boxer, or a German shepherd. Other animal bites include bites caused by small animals, such as rabbits, ferrets, monkeys, and farm animals.

Certain breeds of animals tend to be more dangerous, and, based on a recent study by the CDC, Allstate Insurance Company comprised a list of 8 dogs they won't insure against bites. On the list are Akitas, boxers, chow chows, Doberman pinschers, pit bulls, American Staffordshire bull terriers, rottweilers, and wolf hybrids.¹

In the United States, snakes account for 8000 bites per year. These snakes are typically pit viper types, including rattlesnakes, copperheads, cottonmouth water moccasins, and coral snakes. Many of these snake bites occur after hurricanes and floods (eg, Hurricane Katrina) and may be avoided or mitigated with sensible precautions.²

Interestingly, a recent retrospective study by Bhattacharjee et al³ showed that animal bites increase significantly during a full moon. This study, performed in England, tabulated animal bites in the emergency department (ED) on all days of the month, showing this surprising result.

Pathophysiology

The body site on which dog bites occur varies with age; however, the hand is most frequently involved in cat bites.

Snakebites can cause a variety of symptoms, including diarrhea, a burning sensation and pain at the wound site, convulsions, fainting, dizziness, weakness, blurred vision, fever, increased thirst, nausea and vomiting, numbness and tingling, and tachycardia.

Dog bites may cause infections by Staphylococcus, Streptococcus, Eikenella, Pasteurella, Proteus, Klebsiella, Haemophilus, Enterobacter, Capnocytophaga (formerly CDC group DF-2), and Bacteroides species. Cat bites may cause infections by Pasteurella, Actinomyces, Propionibacterium, Bacteroides, Fusobacterium, Clostridium, Wolinella, Peptostreptococcus, Staphylococcus, and Streptococcus species.

Frequency

United States

The incidence of dog bites is 4.7 million people per year in the United States, and the incidence of snake bites is 8000 cases per year. Data collected by the University of Pittsburgh show the median age of persons who sustain dog bites is 15 years, with a significant increase in boys aged 5-9 years.⁴ While the overall incidence for dog bites is 12.9 cases per 10,000 individuals, the incidence in boys aged 5-9 years is 60 cases per 10,000 individuals.⁴

Mortality/Morbidity

Annually, in the United States, 10-20 people receive bites that are fatal. Elderly people are more susceptible to animal bites because their ability to fend off attacks is compromised.

Although mortality is rare with most animal bites in the United States, morbidity is common, especially with cat bites infected by Pasteurella species. Dog bites may become infected by Pasteurella species as well.

From 1979 to 1996, 304 people in the United States died from dog bites, according to data from the CDC.

• In bites by rabid animals, morbidity can result in significant illness. Although bites by rabid dogs comprise 16% of cases, bites by rabid skunks, foxes, and bats comprise most cases. Squirrel bites and hamster bites rarely cause rabies.


• According to the Humane Society of the United States⁵, from January 1997 to December 1998, 27 people died from dog bites, 19 of whom were children younger than 12 years and 8 of whom were adults (mostly elderly persons). Most bites are nonfatal, with 230,000 nonfatal bites for every fatal bite.


• Sepsis can occur in immunocompromised persons with infections caused by Capnocytophaga organisms.

Sex

Males are typically bitten by dogs; usually, young males are most frequently affected. Conversely, women are more frequently bitten by cats than are men.

Age

As a result of their vulnerability and increased possibility of exposure to the animals, individuals who are bitten are usually younger or older persons.

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

History

Usually, patients with animal bites present to the ED. Occasionally, patients may present to the dermatology office. In either case, inquire about the following:

• Circumstances leading to the animal bite and disruption of skin integrity


• Immunization status of the aggressing animal and whether the patient has reason to believe that the animal has rabies


• Treatment administered up to the time of admission to the ED (Patients may have used folk remedies or performed treatments that may lead to other infections.)


• Immunization status for tetanus (Immunize patients if their immunizations are not up-to-date.)

Physical

• Observe the patient with an animal bite for disruption of the skin's integrity. Prescribe antibiotics if disruption of the skin is noted.
• In patients with snakebites, look for signs of toxicity, including pain, diarrhea, a burning sensation, seizures, syncope, dizziness, blurred vision, hyperhidrosis, fever, increased thirst, loss of coordination, nausea, vomiting, dysesthesias, and tachycardia.
• If the bite is deep, neurovascular events may have occurred, and injury to tendons and bones must be excluded.
• Foreign bodies may be observed in the wound.

Causes

Usually, causes of animal bites are related to the possibility of exposure to the animals.

• Most animal bites involve young children who may play with or inadvertently tease a dog or an animal that attacks the child.
• Less often, cat bites are associated with severe trauma, but they can result in infection with Pasteurella multocida, thereby causing a significant medical problem.
• Snakebites occur frequently in campers or hikers in wilderness areas.

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Other Problems to be Considered

Hand infections
Osteomyelitis
Rabies

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Lab Studies

• If infection by P multocida is suspected, perform a Gram stain for the organism, which is a small, gram-negative, ovoid bacillus. Typically, treatment is instituted based on the history of a cat or dog bite.
• Test for rabies by using the fluorescence antibody method, which assays the viral antigen. Alternatively, analyze a biopsy specimen from the brain of the affected animal.
• Cultures may be necessary in older wounds and when infection is clinically suggested. Sepsis, although rare, can occur in certain patients.

Imaging Studies

• If deep wounds occur, radiographs may be necessary to exclude fractures or osteomyelitis in patients presenting after a few days.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical Care

• Treat both dog bites and cat bites with amoxicillin and clavulanate (Augmentin) for 7-10 days, with close follow-up observation of the patient. Alternative treatments include ampicillin and tetracycline; cephalosporins provide lesser benefit than amoxicillin and clavulanate (Augmentin), ampicillin, and tetracycline.


• If rabies is suspected, typically, the health department is called in to ascertain the status of the animal in question. The local health department can be a significant help in finding out trends in the community and protocols that may be in place for treatment and/or nontreatment of rabies. Updated Infectious Disease Society of America guidelines should be consulted for the most recent recommendations. Until 2004, rabies was considered fatal in unvaccinated individuals. In this year, one individual, Jeana Giese, was treated with a combination of amantadine and ribavirin while in an induced coma. Since this time, other individuals have been treated with this modality, but without success.
• • Postexposure treatment includes administration of rabies immune globulin (RIG) or human diploid cell vaccine (HDCV).
  
  
  • HDCV can be administered prior to exposure if people are traveling to endemic areas or working with rabid animals.
  
  
  • Animal bites with little or no risk for rabies include bites by squirrels, hamsters, guinea pigs, gerbils, chipmunks, rats, mice, and rabbits.


• Good wound care is essential for all animal bites. In the ED, irrigate the wound and, if possible, leave it open for healing.


• Snakebites may require treatment with antivenin if they are serious.
  
  
  • Until recently, antivenin was solely derived from horse serum and therefore unable to be administered to patients who are sensitive to horse serum. Now, a newer form called CroFab (Crotalidae Polyvalent Immune Fab), which is an antigen-binding-fragment that is derived from sheep, is available. CroFab is the result of sheep immunized with venom from the Western Diamondback rattlesnake, the Eastern Diamondback rattlesnake, the Mojave rattlesnake, and the cottonmouth water moccasin. It is more effective in studies than the previous equine version.
• • The initial treatment of snakebites involves washing the area of the bite with soap and water, immobilizing the area, keeping the area of the bite below the level of the heart, and monitoring vital signs.


• Various authorities disagree on whether to suction the area, although all authorities agree that surgical alteration of the area is not appropriate because of the risk of increasing the infection.

Surgical Care

Hand injuries pose a special concern for infection, which may spread into the metacarpophalangeal space; therefore, arrange surgical consultation when appropriate.

Consultations

• Whether to close the wounds and to what degree surgical cosmesis outweighs the risk of infection are difficult to decide. The questions may be approached best by a multispecialty team, which includes an infectious disease specialist.
• If the wound has occurred on the hand, advise consultation with a hand surgeon prior to discharge.

Activity

Activity is limited based on the injury. If edema occurs after a dog bite, elevation of the affected area is best; however, in patients with snakebites, do not elevate the affected area to prevent the venom from traveling to the heart.

MEDICATION

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Amoxicillin and clavulanate (Augmentin) is the drug of choice for the treatment of both dog bites and cat bites. Tetracycline and ampicillin are second-choice drugs. Cephalosporins provide lesser benefit than amoxicillin and clavulanate (Augmentin), ampicillin, and tetracycline. If rabies is diagnosed, administer RIG and HDCV. Serious snakebites are typically treated with antivenin.

Drug Category: Antibiotics

Therapy must be comprehensive, covering all likely pathogens in the context of the clinical setting.

Drug Category: Immune globulins

These agents are used with rabies vaccine in individuals previously unvaccinated to provide maximum coverage before immune response to the vaccine occurs.

Drug Category: Inactivated viruses

These agents are used for active immunization against rabies.

Drug Category: Antivenom agents

These agents are used to neutralize toxins from snakebites. The physician must be prepared to support the victim's cardiovascular and respiratory systems.

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Further Inpatient Care

• Inpatient care is reserved for patients with the most severe cases of animal bites, especially severe injuries caused by large animals. Fortunately, it is rarely required for most patients with animal bites.
• Individuals with rabies pose a significant difference and obviously require care if unvaccinated.

Further Outpatient Care

• During the healing phase of either a dog bite or a cat bite, a simple infection can easily spread to become a widespread infection. For this reason, monitor the patient for 2-3 days to observe the wound. If the wound continues to heal appropriately, the patient needs little, if any, follow-up care after the antibiotic course is finished.

In/Out Patient Meds

• Medications are used as detailed in Medication.

Transfer

• If the facility does not have specialists for the treatment of facial or neurovascular wounds, transfer the patient to a facility that has specialists in the treatment of these injuries.

Deterrence/Prevention

• Children should be taught to be cautious around any unknown (and even known) animal. Certain breeds of dog have a higher incidence of biting (eg, collie, boxer, German shepherd), and observation of these breeds is especially needed if young children are playing near or with them.


• The Web site for The Humane Society of the United States⁵ has an excellent section on the prevention of animal bites.


• Administer prophylactic rabies vaccination to spelunkers prior to trips.


• HDCV can be administered prior to exposure if people are traveling to endemic areas or working with rabid animals.

Complications

• Most complications involve hand infections, although occasionally, serious infections of other parts of the body affected by animal bites have been reported.


• Fractures of the skull may be seen in small children if the bite is deep.


• Rabies is a significant concern if the animal has rabies.

Prognosis

• In minor bites, the prognosis is excellent.
• In major bites, the prognosis solely rests on the extent of trauma to the affected organ system.

Patient Education

• Education plays an important role after the initial visit to the ED because many patients tend to underestimate the need for constant vigilance for infection. Follow-up care is recommended if signs of infection occur despite treatment.


• For excellent patient education resources, see eMedicine's patient education article Rabies.


• An excellent website is Dog Bite Law.

MISCELLANEOUS

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical/Legal Pitfalls

• Failure to seek a surgical consultation or an infectious disease consultation in patients with extensive trauma and in patients with hand involvement is a pitfall.

Special Concerns

• Children are particularly susceptible to bites and trauma, which occur more extensively than in adults.

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

1. Leech M. Insuring Is Hard With Dog - Firms Won't Write Policies For Some Pooch Owners. Los Angeles Daily News. August 2, 2002.
2. North Carolina A&T State University, US Department of Agriculture. Dealing with Snakes After a Storm or Flood. Adapted by P. Bromley from Alabama Cooperative Extension Service. North Carolina State University. Available at http://www.ces.ncsu.edu/disaster/factsheets/pdf/snakes.pdf. Accessed 2002.
3. Bhattacharjee C, Bradley P, Smith M, Scally AJ, Wilson BJ. Do animals bite more during a full moon? Retrospective observational analysis. BMJ. Dec 23-30 2000;321(7276):1559-61. [Medline].
4. Weiss HB, Friedman DI, Coben JH. Incidence of dog bite injuries treated in emergency departments. JAMA. Jan 7 1998;279(1):51-3. [Medline].
5. The Humane Society of the United States. Preventing and Avoiding Dog Bites. 2001. Humane Society. Available at http://www.hsus.org. Accessed July 5, 2001.
6. Arndt KA, LeBoit PE, Robinson JK. Skin infections caused by unusual bacterial pathogens. In: Cutaneous Medicine and Surgery. Vol 2. Philadelphia, Pa: WB Saunders; 1996:939-48.
7. Bruce S, Schroeder TL, Ellner K, Rubin H, Williams T, Wolf JE Jr. Armadillo exposure and Hansen's disease: an epidemiologic survey in southern Texas. J Am Acad Dermatol. Aug 2000;43(2 Pt 1):223-8. [Medline].
8. Cunningham BB, Paller AS, Katz BZ. Rat bite fever in a pet lover. J Am Acad Dermatol. Feb 1998;38(2 Pt 2):330-2. [Medline].
9. Doud Galli SK, Miller JP. Animal Bites. eMedicine from WebMD [serial online]. August 1, 2006;Available at http://www.emedicine.com/ent/topic725.htm.
10. Epstein ME, Amodio-Groton M, Sadick NS. Antimicrobial agents for the dermatologist. II. Macrolides, fluoroquinolones, rifamycins, tetracyclines, trimethoprim-sulfamethoxazole, and clindamycin. J Am Acad Dermatol. Sep 1997;37(3 Pt 1):365-81; quiz 382-4. [Medline].
11. Fitzpatrick TB, Eisen AZ, Wolff K. Animal bites, infestations, and insect bites and stings. In: Baker AS, ed. Fitzpatricks Dermatology in General Medicine. Vol 1. New York, NY: McGraw-Hill; 1987:2468-76.
12. Mayo Foundation for Medical Education and Research. Bites and Stings. December 20, 2000. Mayo Clinic. Available at http://www.mayohealth.org. Accessed July 5, 2001.
13. Spanierman C. Animal Bites. eMedicine from WebMD [serial online]. March 30, 2006;Available at http://www.emedicine.com/ped/topic107.htm.
14. Stump J. Bites, Animal. eMedicine from WebMD [serial online]. Februrary 2, 2006;Available at http://www.emedicine.com/emerg/topic60.htm.

Article Last Updated: May 25, 2007