A 7-Year-Old Girl With Ulcerative Lesion After a Rodent Bite

A previously healthy 7-year-old girl was bitten on the hand by a wild rat after she mistook the rat for a toy and tried to retrieve it from her dog's mouth. The bite, which occurred on the lateral aspect of the proximal interphalangeal joint of the right index finger, initially healed, but then developed a painless erythematous papule at the bite site 1-week later. The papule ulcerated and the ulcer continued to progress with time. The patient reported moderate pain with movement of the affected finger but little discomfort without movement. She denied systemic symptoms and fever. She did not have a history of travel outside the United States. The patient was treated sequentially with amoxicillin-clavulanate, trimethoprimsulfamethoxazole, and clindamycin without response. Bacterial culture of a superficial swab grew only Candida albicans. The patient was administered with topical antifungal and oral fluconazole. The ulceration continued to progress without response and the patient was referred to the pediatric infectious diseases clinic for evaluation. On physical examination, the patient appeared healthy and vital signs were normal. She had a 1 × 1 cm ulcerative lesion (Fig. 1) on the lateral aspect of the proximal interphalangeal joint of the right index finger. This was tender to palpation and with flexion of the finger. There were multiple enlarged right axillary lymph nodes that were nontender and mobile. The overlying axillary skin was nonerythematous. The rest of the physical examination was normal. Blood count and chemistry panels were both normal and radiographs did not show bone or joint involvement. A deep tissue biopsy of the lesion site was performed which led to a definitive diagnosis. Denouement Continued from p. 185. The deep tissue biopsy grew Sporothrix schenckii. Pathology demonstrated necrotizing granulomatous inflammation with no evidence of asteroid bodies and negative Periodic Acid Schiff (PAS) and Grocott's Methenamine Silver (GMS) stain for fungus. Itraconazole therapy was undertaken which lead to the healing and resolution of the ulcer. Length of therapy was 3 months. The patient remained well 3 months off therapy with minimal scarring at the site of the ulcer and lymphadenopathy completely resolved. Sporotrichosis is an infection caused by Sporothrix schenckii, a dimorphic soil-dwelling fungus initially described by Benjamin Schenck in 1898 in Baltimore. Disease typically presents as a skin and subcutaneous lesion with or without lymphatic involvement.1 Inoculation occurs via pricks from thorny plants or fomites in contact with contaminated soil. In the United States, the disease is endemic in the Mississippi Valley with 1 notable epidemic reported in seed handlers in Pennsylvania in 1988 from seeds imported from Wisconsin.2 Worldwide, infection is most common in tropical and subtropical environments, particularly in Central and South America.3 Zoonotic transmission remains rare and sporadic with the exception of a recent epidemic in Rio de Janeiro Brazil, where transmission of zoonotic sporotrichosis has been associated with contact with cats.4 Even though S. schenckii has been isolated from the skin, mouth and nose in many mammals,4 zoonotic transmission has been documented in a relatively few number of species. Cats have since been shown to harbor the organism.5 In Brazil, transmission has been associated primarily with cat contact without injury or cat scratches, and less frequently with cat bites.5 Despite the ability of the organism to infect several species, the potential for zoonotic transmission from animals other than domestic cats has not been widely observed. There have been very few reported cases in northern California.6 This case report illustrates a case of zoonotic transmission of S. schenckii by rodent bite in northern California. Our patient had no history of travel. Transmission via rodent bite is extremely uncommon. The fungus may have been directly inoculated from the rodent's mouth or the patient may have received an indirect inoculation of fungal spores from dirt into the wound caused by the bite. The diagnosis of sporotrichosis relies on isolation of the organism. Often the number of organisms in superficial exudate or scrapings is so low that culture is unrevealing. Biopsy and culture of tissue may be more helpful. With biopsy, histologic evaluation may demonstrate the typical oval to cigar-shaped yeast forms or asteroid bodies. In our patient, histology was not helpful and culture of exudate was misleading, while culture of tissue revealed the diagnosis. Generally, serology is not useful or widely available and antigen assays are not available. Culture generally (89% of the time) takes about 8 days to see growth.7 Spontaneous resolution of sporotrichosis is rare and therefore most patients require treatment. For cutaneous and lymphocutaneous disease in children in the United States, itraconazole is the agent of choice. The dose is 6 to 10 mg/kg up to a maximum of 400 mg orally daily for 2 to 4 weeks after all lesions are resolved, usually for a total of 3 to 6 months.7 Oral solution taken on an empty stomach is preferred due to improved absorption characteristics, if the patient can tolerate it without gastrointestinal upset. If capsules are used they should be given with a full meal, which enhances their absorption. Avoid coadministration with antacids. Oral saturated potassium iodide has efficacy similar to itraconazole and is still used in some countries because it is less costly, but it has many adverse effects including metallic taste, enlarged salivary glands, GI intolerance, rash, and fever. Terbinafine has lower cure rates and higher relapse rates than itraconazole. Fluconazole is less effective than the above medications and should be used only if the patient cannot tolerate itraconazole. Ketoconazole should not be used. Posaconazole is a promising therapeutic agent with good in vitro sensitivity but in vivo studies are lacking.8 Interestingly, local hyperthermia has been known for decades to reduce the size of lesions,7 but is impractical because it takes weeks of daily application of heat to the lesion using systems that will warm the tissue to 42°C to 43°C. The rare occurrence of transmission via rat bite combined with the fact that this nonendemic organism is rarely diagnosed in northern California makes this a unique case considering the patient's lack of travel outside of the region. Itraconazole therapy was well tolerated and curative with no relapse.FIGURE 1.: Ulcerative lesion on the radial aspect of the proximal interphalangeal joint of the right index finger 8 weeks following rodent bite.