Bacterial Diseases of Reptiles
Bacterial diseases are common in reptiles, with most infections caused by opportunistic commensals that infect malnourished, poorly maintained, and immunosuppressed hosts. A comprehensive approach is required to ensure the success of a therapeutic plan. It is important not only to determine the causative agent but also to correct predisposing factors. Appropriate therapy in the absence of appropriate husbandry and nutrition will ultimately fail.
Cytology (or histopathology), gram stains, culture, and sensitivity are recommended to determine appropriate therapy. Many bacterial infections involve gram-negative bacteria, many of which are considered commensal. Anaerobic infections are not uncommon, but organisms can be difficult to culture. Gram-positive bacteria on smears, in conjunction with a negative culture, may indicate an anaerobic infection. Alternatively, if a therapeutic choice was based on aerobic culture and sensitivity and response is poor, then the presence of an anaerobe should be considered. The routine use of broad-spectrum antibacterials implies a low level of skill on the part of the clinician and is not in keeping with current antimicrobial stewardship recommendations.
A number of infectious conditions are similar in appearance, regardless of species. Septicemia is a common cause of death. The systemic disease may be preceded by trauma, localized infection, parasitism, or environmental stressors. Aeromonas and Pseudomonas spp are frequently isolated; the former may be transmitted by ectoparasites. Death may be peracute or follow a protracted course. Common terminal signs are respiratory distress, lethargy, convulsions, and incoordination. Petechiae may be found on the ventrum, and chelonians develop erythema of the plastron. Sanitation and husbandry can be significant factors in reducing outbreaks. Affected reptiles should be isolated, and antibiotic therapy initiated.
Classically, SCUD is a shell disease of aquatic turtles caused by Citrobacter freundii; however, various bacteria have been isolated from diseased skin and shell. Serratia spp may act synergistically by facilitating entry of C freundii. The scutes are pitted and may slough with an underlying purulent discharge. Anorexia, lethargy, and petechial hemorrhages on the shell and skin are seen; liver necrosis and abscessation is also common. Wound debridement and systemic antibiotics are recommended. Good sanitation is paramount for prevention.
Another shell disease of turtles is caused by Vibrio (Beneckea) chitinovora, a common infectious agent of crustaceans. Erythema and pitting of the shell with ulceration is seen. Septicemia is uncommon. Topical iodine is recommended in addition to antibiotics. The practice of feeding crayfish is often implicated in this condition and should be discouraged.
Ulcerative dermatitis (scale rot) is seen in snakes and lizards kept in unhygienic conditions with excessive humidity and moisture. Moist, contaminated bedding allows bacterial and fungal growth that, when coupled with exposure to fecal degradation products and skin damage from inappropriate floor heating, can predispose to small cutaneous erosions. Secondary infection with Aeromonas spp, Pseudomonas spp, and a number of other bacteria may result in septicemia and death if untreated. Erythema, necrosis, and ulceration of the dermis, and an exudative discharge are common. Although lesions are often sequelae of skin injuries, they more often develop from within, as is the case with classic necrotic dermatitis in the ball python. The disease can develop even when these animals are maintained under pristine conditions, so it is not simply a matter of excessive moisture and poor hygiene. The condition starts with hemorrhage into scales, followed by pustules that eventually lead to open and ulcerated lesions. Debridement and treatment with systemic antibiotics, topical antibiotic ointment, and excellent hygiene and husbandry are essential.
Blister disease has traditionally been considered a separate entity but is simply an early stage of ulcerative (necrotic) dermatitis. The cutaneous involvement is characterized by pustules or blisters that may resolve without development of ulcerative lesions if treatment is started early. A low-grade thermal injury may mimic blister disease because of the potential development of fluid-filled vesicles.
Focal infections caused by traumatic injuries, bite wounds, and often made more likely by poor management are seen in all orders of reptiles. Subcutaneous abscesses are seen as nodules or swellings. Differential diagnoses include parasitic nodules, tumors, and hematomas. Isolates of the anaerobic organism Peptostreptococcus and of the aerobes Pseudomonas, Aeromonas, Serratia, Salmonella, Micrococcus, Erysipelothrix, Citrobacter freundii, Morganella morganii, Proteus, Staphylococcus, Streptococcus, Escherichia coli, Klebsiella, and Dermatophilus have been recovered from reptilian abscesses, often in combinations. Small, localized abscesses should be completely excised to avoid recurrence. Larger abscesses should be marsupialized, followed by aggressive local wound treatment, including daily antiseptic lavage. The lining of the abscess must be thoroughly scraped to remove as much material as possible. Systemic antibiotics are seldom necessary after complete excision. Anaerobic bacteria are common in these lesions.
Visceral abscessation may occur as a result of hematogenous infection or intestinal translocation. Abscesses of the female reproductive system and liver are common and often result in coelomitis. Surgical intervention is indicated; systemic antibiotics alone are rarely, if ever, successful.
Subspectacle abscessation is seen in snakes, and conjunctivitis is seen in the other orders. Severity ranges from mild inflammation to panophthalmitis and may occur as a result of ascending infectious stomatitis (see below). Topical antibiotic ointments are used in turtles, lizards without spectacles, and crocodilians. In snakes and lizards with spectacles, drainage is achieved by surgically removing a small wedge from the spectacle and flushing the subspectacular space and lacrimal duct with an antibiotic solution (eg, gentamicin). Some affected reptiles, especially turtles, may need supplemental vitamin A.
Infectious stomatitis is reported in snakes, lizards, and turtles and characterized early by petechiae in the oral cavity; caseous material develops along the dental arcades as the condition worsens. In severe cases, infection spreads to cause osteomyelitis of the mandible and maxilla. Aeromonas and Pseudomonas spp, common oral inhabitants, are most frequently isolated, along with a variety of other gram-negative and gram-positive aerobic and anaerobic bacteria. Respiratory or intestinal infection may develop in poorly managed cases. Surgical debridement, repeated irrigation with antiseptics, systemic antibiotics, and supportive therapy are indicated. In severe cases with ulceration or granuloma formation, aggressive surgery may be indicated. Vitamin supplementation, especially with vitamins A and C, has been advocated but does not always affect the disease course.
Respiratory infections are common; the incidence can be influenced by respiratory or systemic parasitism, unfavorable environmental temperatures or humidity, insufficient ventilation, unsanitary conditions, concurrent disease, and malnutrition. Open-mouth breathing, nasal or glottal discharge, and dyspnea are frequent signs. Aeromonas and Pseudomonas spp are frequently isolated, but many respiratory infections are mixed. Septicemia may develop in severe or protracted cases. Treatment consists of improving husbandry and initiating systemic antibiotics after the collection of diagnostic material. Nebulization therapy with antibiotics diluted in saline, in combination with acetylcysteine, has been used together with parenteral antibiotics. Reptiles with respiratory infections should be maintained at the mid to upper end of their preferred optimal temperature zone. Increased temperatures are important not only to stimulate the immune system but also to help mobilize respiratory secretions. Turtles and lizards often have an underlying vitamin A deficiency and require dietary correction.
Mycoplasmosis is a known cause of rhinitis and upper respiratory tract disease in chelonians and polyserositis in crocodilians. In chelonians, the disease has been associated with population declines, and the disease is often chronic and/or intermittent. In American alligators, mycoplasmosis results in severe systemic disease and frequently death. A variety of Mycoplasma species have been isolated. PCR and serologic diagnostic aids have been developed, and treatment using tetracyclines and macrolides has been advocated.
Ear infections occur frequently in turtles, especially box turtles and aquatic turtles. Marked swelling is seen at the tympanic membrane, and caseous material is present. Proteus spp, Pseudomonas spp, Citrobacter spp, Morganella morganii, Enterobacter spp, and other bacteria have been isolated. The tympanic membrane must be incised, followed by complete removal of all inspissated material. Surgical treatment is usually curative as long as all infection is removed and the Eustachian tube is patent. The open area should be flushed with diluted povidone-iodine until the area heals by second intention. Systemic antibiotics are rarely, if ever, required. Ear infections may be secondary to hypovitaminosis A or ascending infection from the oral cavity.
Often traumatic in origin, infectious cloacitis is characterized by edema and hemopurulent discharge. Cloacal calculi may lodge in the cloaca and predispose to local inflammation and swelling unless removed. In pericloacal abscesses, the infection often migrates craniad. Ascending urinary or genital tract infections are common sequelae. Aggressive therapy, including surgical debridement, local wound treatment, and appropriate systemic antibiotics, are indicated. Fecal examinations should be performed to identify potential parasitic causes, and radiography may help identify causes of tenesmus.
Although previously reported in the reptile literature as Paget disease, this condition is now thought to be a chronic bacterial osteomyelitis of the spine. Traditionally, Paget disease is characterized by repeated episodes of osteoclastic bone resorption and deposition, leading to dense, brittle bones. Commonly reported in snakes, these proliferative and progressive spinal lesions have been investigated and are thought to be associated with chronic bacterial infections, most commonly involving Salmonella spp in snakes. Diagnosis is by biopsy or blood culture. Longterm antibiotic therapy may be helpful, but the prognosis is typically guarded to poor.
Mycobacterial infections are more often associated with chronic wasting in wild, imported reptiles and are seen as granulomatous lesions at necropsy; however, infections are also seen in captive bred animals. Chelonians generally exhibit pulmonary involvement, whereas lizards, snakes, and crocodilians commonly show visceral granulomas. The common species isolated are Mycobacterium ulcerans, M chelonae, M haemophilum, and M marinum. All are cultured at reduced temperatures and may require months for growth. Rifampin and isoniazid are hepatotoxic, and the longterm administration required is unlikely to be safe. There are no reports of successful treatment, and most cases are euthanized at an advanced stage of presentation.
Salmonella have been frequently isolated from clinically healthy reptiles and should be considered part of the GI flora. The zoonotic nature of these commensal organisms must be considered when handling or treating reptiles. Attempts to eliminate these microorganisms from reptiles and their eggs have been unsuccessful and are not recommended. Veterinarians and reptile owners should be aware of the informational brochures available from the Association of Reptile and Amphibian Veterinarians