Zoonoses: How real is the threat? (Proceedings)
Legal/Liability Considerations of Zoonotic Diseases
In the language of law (at least in the US), the term "zoonoses" has not been defined. In medical terms, it refers to "infectious diseases shared by animals and humans." Of particular importance in both human and veterinary medicine are those zoonoses known to be transmitted directly from animals (vertebrates) to humans. To date, there are about 250 zoonotic infections known to be transmitted from animals to humans, with about 20 to 30 resulting from contact with cats and/or dogs. Transmission can occur through inhalation, ingestion, bites, or scratches. Arthropod vectors, while certainly capable of transmitting infectious organisms from animals to humans, pose a threat to humans and animals alike, but these infections are likely to occur simultaneously and independently of each other.
The question at hand, therefore, becomes, "How real is the threat of an individual acquiring a pet-associated infection?" From the perspective of the legal profession, the categories of concern for the veterinary profession, arising from the risk of exposure to a known or suspected zoonotic infection, include:
Although over 1 million people are reportedly bitten by dogs every year, it has been estimated that this represents only half of the dog bites that actually occur. Accounting for approximately 1% of all emergency room admissions, dog bite wounds cost over $30 million in annual health care costs.
In the last 10 years, a number of significant facts have been learned about animal bites to humans. For example, dog bites to humans are more likely to occur in males (especially young boys) than in females. From one-half to two-thirds of dog bite victims are less than 20 years old and many of these are less than 10 years old. About half of all bites are from dogs owned by neighbors and are inflicted by medium or large-sized dogs. Arms and hands are the most likely part of the body to sustain injury from bite wounds. About 65% of all facial bites occur in children less than 10 years old.
Although dogs appear to inflict more bite wounds than cats, the likelihood of infection developing subsequent to a bite wound is greater in cats than in dogs. Wound infection is most common in those victims who are more than 50 years of age, when wounds are not properly nor adequately cleansed, when there is more than a 24 hour delay in seeking treatment, and when wounds occur on the hands.
While an animal bite to a human is not, per se, a zoonotic disease, the potential for significant injury or infection does exist. Recently, renewed concern has developed over the ability of the dog to cause severe, even fatal, sepsis in humans following the inoculation of resident oral bacteria via bite into human tissue. It is interesting to note that, although infections from dog bites are a major concern, cat bites and human bites are much more likely to become infected. The likelihood of infection following a dog bite is only 3 to 5% (gram negative, aerobes) while infection rates following human or cat bites can be as high as 50% (esp. Pasteurella multocida).
The DF-2 organism, now recognized as Capnocytophaga canimorsus , has surfaced as one of the resident organisms in dog saliva that, following bite-wound contamination, can cause sepsis in humans leading to severe morbidity or death. At particular risk are individuals who have experience splenectomy or are otherwise immune compromised. This group of gram-negative rods has a propensity to cause disseminated intravascular coagulation (DIC) and symmetric peripheral gangrene in asplenic patients. True incidence of bacteremia after dog bite is considered to be underestimated. Penicillin is the treatment of choice in affected patients.