What is the primary cause of infection resulting from dog and cat bites, specifically due to Pasteurella (Pasteurella) species, Mycobacterium, Staphylococcus aureus, Actinomyces, or Candida?

From the Guidelines

The correct answer is (a) Pasteurella species. Dog and cat bites commonly lead to infections caused by Pasteurella species, particularly Pasteurella multocida, which is found in the oral flora of approximately 50-90% of cats and 50-70% of dogs 1. These infections typically develop rapidly, often within 24 hours of the bite, and present with intense pain, erythema, swelling, and sometimes purulent discharge. For treatment, amoxicillin-clavulanate is the first-line antibiotic, typically prescribed at 875/125 mg twice daily for 5-7 days for uncomplicated infections 1. Alternative options for penicillin-allergic patients include doxycycline, trimethoprim-sulfamethoxazole, or fluoroquinolones combined with clindamycin 1. While other organisms like Staphylococcus aureus can be present in bite infections, Pasteurella species are the predominant pathogens specifically associated with dog and cat bites due to their prevalence in the oral microbiome of these animals 1. Some key points to consider in the management of dog and cat bites include:

• The risk of infection depends on the type of bite, the site of injury, the time elapsed from the bite until presentation, host factors, and the management of the wound 1
• The bacteriology of these wounds can differentiate the number of isolates per wound and whether additional coverage for anaerobes is required 1
• Cultures are often not done on wounds, and empirical therapy might miss pathogens 1
• Broader empirical coverage for abscesses might yield better therapeutic results 1
• A more focused therapy for nonpurulent infected wounds could allow narrower therapy 1

From the FDA Drug Label

Doxycycline is also indicated for the treatment of infections caused by the following gram-negative microorganisms: ... Plague due to Yersinia pestis (formerly Pasteurella pestis). Tularemia due to Francisella tularensis (formerly Pasteurella tularensis).

The correct answer is (a) Pasteurella species, as the drug label mentions that doxycycline is indicated for the treatment of plague due to Yersinia pestis (formerly Pasteurella pestis) and tularemia due to Francisella tularensis (formerly Pasteurella tularensis), suggesting that Pasteurella species can cause infections that may be treated with doxycycline, which could be relevant to dog and cat bites 2.

From the Research

Infection Causes

• The most common cause of infection from dog and cat bites is Pasteurella species, particularly Pasteurella multocida 3, 4, 5, 6, 7.

Pathogens Involved

• Pasteurella multocida is a common pathogen found in dog and cat bites, and can cause a range of infections from localized cellulitis to more severe conditions like osteomyelitis 3, 4, 5, 6, 7.
• Other pathogens like Staphylococcus aureus, Streptococcus pyogenes, and Pseudomonas aeruginosa may also be present in polymicrobial infections 7.

Infection Characteristics

• Cat bites have a higher risk of infection than dog bites, with Pasteurella multocida being the most frequent and important pathogen 3, 4.
• Infections can range from superficial to deep and invasive, with more severe infections being more common in older adults and those with underlying comorbidities 7.

Treatment

• Penicillin is considered the drug of choice for treating Pasteurella infections, although other antibiotics like amoxicillin/clavulanate and cefuroxime may also be effective 5, 6.