Over 1000 species of freshwater and saltwater catfish exist worldwide, with some weighing a few grams and others up to 200kg. They vary greatly in their adaptations to different ecological conditions. An Egyptian catfish, Malapterurus, contains electrical organs capable of causing a fatal electric shock in humans [1]. Candiru (genus Vandellia) is a small Amazonian catfish that is attracted to urine and may penetrate the urethral orifice of mammals, including humans, requiring surgical intervention [2]. Almost all catfish have the ability to inflict extremely painful wounds with their pectoral and dorsal spines (Figure 2). The freshwater catfish I. punctatus is capable of causing significant injury with its stings [1]. Contrary to popular belief, the prominent barbels (whiskers) characteristic of catfish are for sensory purposes only and are incapable of causing envenomation.
Envenomations generally occur when the catfish are being handled. They react to being grasped by lashing from side to side and locking their dorsal and pectoral spines, which are enclosed in an integumentary sheath containing venom glands, into a rigid and extended position (Figure 3).
These sharp spines may penetrate skin, in the process damaging the delicate integumental sheath and exposing the venom glands. The retrorse barb (upturned tip) that Ictaluridae possess on their spines is capable of lacerating skin, facilitating absorption of the venom and often necessitating surgical removal [1]. Catfish venom consists of hemolytic, dermonecrotic, edema-producing, and vasospastic factors, all of which have shown to be heat, pH, and lyophilization labile [3]. A second source of toxins, crinotoxins, is released by the epidermal cells of catfish skin upon agitation. These proteinaceous substances may coat the spine and become passively introduced into the wound upon skin breach [4]. Both venom and crinotoxin promote a marked localized inflammatory reaction, resulting in common findings of local erythema, throbbing pain, hemorrhage, edema, cyanosis, and lymphangitis [5]. Systemic manifestations are rare, and the majority of cases resolve without long-term sequelae [6]. However, disabling sequelae including amputation of the affected body part due to severe tissue necrosis and death have been reported [7].
Although an infrequent occurrence, the most serious long-term complications of catfish envenomations involve infections. Ictaluridae are freshwater catfish that generally inhabit stagnant and dirty waters, potentially increasing the risk of infection. The vasoconstrictive effects of catfish toxins may also add to the infection risk by decreasing blood flow to the affected tissue [8]. A variety of organisms have been reported to be responsible for causing secondary infection, including Klebsiella, Erysipelothrix, Nocardia, Chromobacterium, Sporothrix, Actinomyces, Pseudomonas, Staphylococcus, Morganella, Edwardsiella[7], Mycobacterium[9], Aeromonas, and Vibrio species [7]. Aeromonas and Vibrio species have been reported to be the most aggressive organisms for freshwater and saltwater infections, respectively, especially in immunocompromised patients [6, 7].
The genera Proteus and Morganella are motile, facultative anaerobic Gram-negative rods with peritrichous flagella, and are assigned to the Enterobacteriaceae family mainly on the basis of shared biochemical characteristics, including the ability to oxidatively deaminate phenylalanine and, in most cases, to hydrolyze urea. In human disease, most infections are associated with prolonged hospitalization and, specifically, from colonization of indwelling catheters and associated urinary tract infections [10].
Although Sarter and colleagues isolated Proteus vulgaris from a catfish farm in the Mekong Delta, Vietnam [11], the present case report is the first, to the best of our knowledge, to describe catfish envenomation resulting in secondary infection by Proteus vulgaris. Junqueira performed a microbiological evaluation of the catfish to determine the array of organisms directly isolated from the fish [12]. Of interest, neither Gram-positive bacteria nor fungi were detected in these samples, which included 13 different Enterobacteriaceae, the least frequent of which was Proteus species. In addition, whereas the aforementioned study isolated various bacterial species directly from catfish, our study demonstrates patient isolates in the setting of a clinical infection. A MEDLINE search over the past 30 years identified only two other case reports of M. morganii infection following catfish envenomation [13].
Effects from catfish toxins, such as pain, erythema, and edema, are difficult to differentiate from a local bacterial process. However, we suspect that our patient was infected with P. vulgaris and M. morganii secondary to catfish sting. The suspicion arose because in addition to the positive wound cultures for these organisms, the patient’s condition worsened after outpatient therapy with amoxicillin-clavulanate, to which M. morganii was resistant, and improved only after having received broad spectrum Gram-negative coverage with tobramycin and ciprofloxacin, which are antibiotics that target both bacteria. The persistence of local symptomatology for days into the hospital course further supports the interpretation that a bacterial infection was present because toxin-mediated symptoms are usually short-lived, whereas bacterial infections generally persist. Sources of these bacterial strains include both the catfish and its aquatic environment, as numerous bacterial species have been isolated from the water and sediment in which catfish inhabit [14].
Initial treatment of catfish envenomation should include aggressive cleaning of the wound and the surrounding area, with an attempt to remove any remnants of spinal sheath, as this radiolucent organic matter may promote inflammation and harbor virulent waterborne organisms. Plain radiographs should be done to evaluate for foreign material and gas in the wound. Initial treatment also includes prompt administration of tetanus prophylaxis and empiric antibiotics to cover Aeromonas and Vibrio strains in freshwater and saltwater accidents, respectively. The antibiotics of choice for empiric treatment of Aeromonas are fluoroquinolones, including ciprofloxacin and levofloxacin, due to their broad Gram-negative effects [15]. Of note, Aeromonas is often resistant to penicillins and cephalosporins. A recommended antibiotic regimen for empiric coverage of Vibrio species involves doxycycline with the addition of either ceftazidime or a fluoroquinolone. Antibiotics should be adjusted based on organisms isolated and susceptibility results. After initial management, the wound should be thoroughly cleansed, irrigated, explored, and debrided if necessary, after which the lesion should be left open. The affected extremity should then be splinted and the patient closely monitored. In our patient, the presence of healthy appearing deep tissues coupled with a progressive improvement of signs and symptoms led us to pursue a conservative approach.
Live catfish should be handled carefully with gloves to avoid accidental encounters with spines. One way to handle a live catfish out of water is to grasp it behind the pectoral fins, keeping the dorsal spine pressed down with the palm of the hand [7]. Another suggested method involves gently grasping the fish in an anterior-to-posterior direction so that the erect dorsal spine fits safely between the second and third digits [6].