Between April 2000 and June 2000, two clusters of Chinese alligators (Alligator sinensis) presented with dermatitis, the first cluster of six and the second of two, and one most recently in August 2002. The ages of onset of clinical signs were one at four years old, two at five years old, three at six years old and four at seven years old. They weighed between 0.34 kg to 2.38 kg. Four died one to three months after presentation, three resolved in three months, but had a recurrence a year later of which they finally died, and three are currently alive. These skin lesions varied from being erythemic, ulcerative, and necrotic with exposure of the underlying muscularis. They were located on various parts of the body such as the face, mandibles, on the ventrum, dorsal trunk (scapulae), lateral trunk, femoral region and tail. One had a concomitant problem of the eye with corneal edema and blepharospasm, which finally resolved. Treatment of each animal typically consisted of most of the following:
1. Ceftazidime 20 mg/kg SQ q 72 hours for eight to 14 treatments;
2. Acriflavin in water as a continuous bath 35 mg/ml with water changes three times a week;
3. Betadine scrub of the skin lesions;
4. Topical application of either silver sulphadiazine two percent cream or Iodex R ointment;
5. Itraconazole 25 mg/kg (range 21 to 28 mg/kg) q 72 hours for six to 14 treatments; in some cases, this was started three months post presentation;
6. Baytril 5 mg/kg SQ SID x 14 days; this was usually started after the Ceftazidime regime was complete and lesions were not resolved;
7. Debridement of lesions;
8. Using a full spectrum light source of 300 watts such as the self-ballasted mercury vapor lamp;
9. Moving outdoors for natural light, since most cases occurred indoors; it was thought that a contributing factor might have been the lighting;
10. Force-feeding as necessary, as many began losing weight as they stopped feeding; and
11. Use of brackish water or saltwater--this was tried later in place of the acriflavin.
Diagnostics included blood analyses and skin biopsies. Blood collected from the tail vein, and a complete blood count (CBC) and chemistry panel were performed. Leukocytosis was seen in three cases ranging from 16.92 to 28.3 x 103/UL (ISIS range 7.875 +/- 3.369) with a combination of lymphocytosis, monocytosis, basophilia or azurophilia. Elevations in AST (306-317 IU/L, ISIS range 141 +/- 67), glucose (289 mg/dl, ISIS range 123 +/- 21), uric acid (14 mg/dl, ISIS range 0.9 +/- 0.4), and alkaline phosphatase (103 mg/dl, ISIS range 35 +/- 10) were also observed.
One skin biopsy was described as: acute to subacute suppurative parakeratotic bacterial dermatitis (severe) with general comments that the infection appeared to be due to colonization of the skin from outside the animal and not as a result of septicemia. There was no evidence of a viral, fungal or nematode etiology. Special stains were positive for fungi (yeasts) and bacteria (gram-positive cocci and gram-negative bacilli). Another skin biopsy was described as: multifocal exudative hyperkeratotic dermatitis with gram-positive cocci (Staphylococcus spp.) and fungal hyphae (Aspergillus, Penicillium, Candida spp.).
Histopathology results pertaining to the integument often returned as ulcerative dermatitis with intralesional fungal hyphae and filamentous bacteria. Additional descriptions were perivascular dermatitis, hyperkeratosis, exudative hyperkeratosis and ulceration. Several carcasses showed postmortem autolysis. Other organ system findings were septicemia (suspect); liver: multifocal granulomatous hepatitis (possibly sporozoan); kidney: interstitial nephritis, acute tubular necrosis, glomerulonephritis; lung: interstitial pneumonia, bronchopneumonia, pulmonary congestion; thyroid: granuloma with follicular atrophy; spleen: histocytosis; gastrointestinal: chronic atrophic gastritis, granulomatous enteritis with intralesional fungal hyphae.
At the time of this report, the exact etiology for the dermatitis found in these Chinese alligators is still undetermined. Environmental factors such as natural sunlight and water temperature are most likely contributory factors. Almost all of the cases have occurred indoors. The problem appears to be seasonal, occurring mostly in the summer months. The high humidity of the Houston weather predisposes a fungal growth in a compromised animal and a secondary bacterial infection sets in. Treatment has to be initiated early and aggressively, and must be continuous and long-term, with accompanying supportive therapy such as force-feeding and fluid therapy. This is seen in the cases that have survived. Further diagnostics such as skin cultures (fungal and bacterial), serology and radiographs may be helpful.
The author wishes to thank the Houston Zoo management for supporting and funding her attendance at this conference. She also wishes to thank the veterinary and herpetology staff for their assistance in the medical handling of these cases.