"A seemingly benign lick from a pet dog, devoid of any bite or scratch, can unexpectedly lead to a persistent, tumor-like skin lesion caused by a rare bacterial infection, highlighting the importance of considering animal contact even in the absence of typical trauma."
In a striking medical case that underscores the complex and sometimes surprising ways animal-human interactions can lead to health issues, a 44-year-old man in Turkey endured a year-long battle with a debilitating sore on his leg. Initially presenting as a small, inflamed bump, the lesion evolved into a significant, wart-like growth measuring approximately 3 centimeters across. Its crusted appearance and foul odor raised immediate concerns for malignancy, prompting dermatologists to investigate. However, subsequent diagnostic procedures revealed an unexpected culprit: a bacterium commonly found in the mouths of domestic animals. This case, detailed in the International Journal of Infectious Diseases, serves as a compelling illustration of zoonotic transmission—the spread of disease from animals to humans—through a route far less direct than the commonly understood bites or scratches.
A Persistent Lesion Mimics Malignancy
The man’s ordeal began subtly, with a small bump that he inadvertently scratched open. Despite its initial innocuous appearance, the lesion failed to heal, persisting for nearly a year. Crucially, the man reported no systemic symptoms such as fever, nor did he exhibit elevated markers of inflammation like a high white blood cell count or C-reactive protein levels, which often accompany significant infections. This lack of generalized illness, coupled with the lesion’s localized nature, contributed to the diagnostic challenge.
When dermatologists finally examined the growth, its size, texture, and odor strongly suggested the possibility of skin cancer, a concern amplified by its resemblance to a wart-like lump. However, a biopsy performed to investigate this possibility conclusively ruled out malignancy. The tissue analysis revealed ulcerated and inflamed healing tissue, indicating a chronic inflammatory process rather than cancerous cell proliferation.
Further investigation delved into the nature of the infection. A wound culture, designed to identify microbial agents, yielded a surprising result: Pasteurella stomatis. This bacterium is a known inhabitant of the oral cavities and upper respiratory tracts of cats and dogs. The man recalled that his household dog had intermittently licked the affected area of his leg. This observation provided a crucial link between the persistent wound and potential animal transmission.
An MRI scan confirmed a lesion measuring 21 millimeters, characterized by inflammatory changes but importantly, it did not infiltrate the underlying muscle tissue. Additional tests to rule out other potential causes of chronic lesions, such as tuberculosis and related mycobacteria, returned negative. Blood cultures, an echocardiogram, and other imaging studies were also performed to assess for any systemic spread of infection, specifically to the brain lining, heart valves, or bone, all of which were ruled out.
The Challenge of Treating a Rare Infection
The identification of Pasteurella stomatis as the causative agent presented a unique treatment challenge. While laboratory testing indicated that the bacterium was susceptible to amoxicillin-clavulanate, a common antibiotic combination, initial treatment proved ineffective. The man was prescribed oral amoxicillin-clavulanate, along with ciprofloxacin and a topical antibiotic ointment. Despite this regimen, the lesion showed no signs of improvement.
Recognizing the lack of response, clinicians escalated the treatment approach. Surgical drainage of the lesion was performed while antibiotic therapy continued. However, a persistent lump remained, necessitating a more aggressive course of intravenous antibiotics. The man was admitted to the hospital for 21 days of intravenous ampicillin therapy. While this significantly reduced the drainage from the wound, the stubborn, tumor-like tissue persisted. Ultimately, complete surgical excision of the remaining tissue was required to achieve a full cure.
The decision to opt for inpatient intravenous treatment was driven by the understanding of the potential severity of Pasteurella infections. While often localized, depending on the specific bacterial species and the individual’s immune status, these infections can disseminate to cause serious complications, including bone and heart valve infections, meningitis, sepsis, and in severe cases, can be fatal. The authors referenced a concerning 2014 report describing catastrophic bleeding in an elderly woman who developed sepsis and meningitis caused by P. stomatis. This prior experience underscored the need for a robust treatment strategy in the present case.
Beyond Bites and Scratches: The Role of Licking
Pasteurella species are well-known pathogens, with Pasteurella multocida being the most frequently identified bacterium associated with soft tissue infections following animal bites or scratches. However, the case of P. stomatis in this Turkish patient presented several atypical features. P. stomatis is less commonly reported in human infections and is generally more associated with cats than dogs. Furthermore, the infection occurred in the absence of any reported bite or scratch, with the only identified animal contact being the dog’s licking of the affected area.
This case highlights that animal saliva, not just direct trauma like bites or scratches, can serve as a conduit for bacterial transmission. When there is broken skin, even a minor abrasion or a pre-existing wound, the bacteria present in an animal’s mouth can gain access to the human body. The authors noted that infection can occur when broken skin comes into contact with animal secretions.
The role of licking in transmitting Pasteurella infections has been documented in other instances. A 2024 report from West Virginia University described a woman in her 90s who developed septic shock from Pasteurella multocida traced to her dog licking her chronic leg wounds. This further supports the notion that licking can be a significant, albeit less recognized, route of infection.
The American Academy of Pediatrics acknowledges that Pasteurella bacteria are common in the mouths of most cats and a substantial percentage of dogs. While bites and scratches are the primary modes of transmission, saliva and nasal mucus can also play a role. Typically, symptoms of skin infection following a bite or scratch appear within 24 hours and include swelling, redness, warmth, and tenderness. More severe complications can involve infections of joints, bones, and tendons, and less frequently, pneumonia, meningitis, or bloodstream infections. The slow, year-long progression of the lesion in the Turkish patient stood in stark contrast to this typical rapid onset, further complicating the initial diagnosis.
Implications for Clinicians and Pet Owners
The findings from this case carry significant implications for both healthcare professionals and pet owners. The authors of the study urge clinicians to broaden their differential diagnoses when encountering unusual nodular skin lesions, particularly in individuals with pet contact, even in the absence of characteristic signs of infection like fever, elevated white blood cell counts, or pronounced inflammatory markers. They emphasize the critical importance of both bacterial culture and tissue analysis for accurate diagnosis, noting that P. stomatis can be the sole pathogen responsible for an infection, though it may also co-occur with other Pasteurella species.
The choice of antibiotic therapy is also a crucial consideration. Guidelines from the Infectious Diseases Society of America suggest penicillins as first-line treatments, with tetracyclines and fluoroquinolones as potential alternatives for resistant strains. Certain antibiotics, such as cephalexin, erythromycin, and dicloxacillin, have been reported as ineffective against Pasteurella infections. For persistent or complex cases, the authors recommended a comprehensive approach involving hospitalization, intravenous antibiotics, and surgical intervention.
It is important to contextualize this case within the broader picture of pet ownership. The vast majority of interactions between pets and humans do not result in infection. However, pet owners can take proactive steps to minimize the risk of zoonotic transmission. The American Academy of Pediatrics advises preventing pets from licking any cuts, scrapes, or other forms of broken skin. Prompt and thorough cleaning of any bite or scratch wounds with soap and water is also essential.
Individuals experiencing a sore that fails to heal, or a lesion that exhibits growth, drainage, or changes in appearance, should seek prompt medical attention. Crucially, they should inform their clinician about the presence of pets in their household. This seemingly simple piece of information can significantly guide diagnostic testing and lead to a more timely and accurate diagnosis, as demonstrated by this unusual case in Turkey. The interplay between animal health and human well-being is a continuous area of medical research and public health awareness, and this case serves as a potent reminder of the diverse pathways through which it can manifest.
