Abstract

In September 2004 a male, 23 year-old Atlantic bottlenose dolphin (Tursiops truncatus) housed at the National Aquarium in Baltimore (NAIB) presented with lethargy and decreased appetite. Blood analysis showed a leukocytosis (24,000/µl), marked neutrophilia, monocytosis, and lymphopenia. Gamma-glutamyltransferase (1,200IU/l), aspartate aminotransferase, alanine aminotransferase, total bilirubin and sedimentation rate were all elevated. Ultrasound examination of the abdomen revealed increased echogenicity in the left lobes of the liver and thickened blood vessels and bile ducts. Based on these findings treatment with broad-spectrum antibiotics and low-dose prednisone was initiated.

At week 7, respiratory irritation (marked "chuffing") was reported, followed by a bleeding event with frank hemorrhage expelled from the blowhole. Samples from the respiratory tract showed acid-fast beaded bacterial rods, large numbers of neutrophils, and erythrocytes. Large numbers of acid-fast organisms and neutrophils were also found in gastric and fecal samples. Cultures plated onto Mitchison agar (7H11) grew colonies within 48hrs that stained acid-fast positive. Identification via polymerase chain reaction at the University of Texas confirmed the organism to be Mycobacterium abscessus.

Based on culture and sensitivity testing, literature reviews, and consultations with physicians specialized in infectious disease at the Johns Hopkins University and the University of Maryland School of Medicine, antibiotics were changed to amikacin (12-14mg/kg IM SID), clarithromycin (3.5mg/kg PO BID), and cefixime (2mg/kg PO BID).¹ In an attempt to increase pulmonary drug levels, a nebulizer was constructed utilizing a 5-gallon plastic container with three one-way valves and a rubber cup to place over the blowhole. Saline and amikacin were used for nebulization (10 min BID), with oxygen provided at 6 L/min. Acetylcysteine was added periodically as an expectorant.

At week 9, after pre-treatment with vitamin K1, an ultrasound-guided liver biopsy showed a non-specific, subacute, multifocal, moderate hepatitis and cholestasis. Ultrasound at that time demonstrated severe abdominal fluid but we were unable to sample it by abdominocentesis. His peripheral vasculature was shut-down at this time, but normal blood flow returned as he stabilized. The beta-lactam and cephalosporin hybrid imipenem (4mg/kg IM BID) was added to the protocol due to the effectiveness of this drug against M. abscessus in humans. Severe thrombocytopenia (5,000/µl) was noted approximately 72 hours after starting imipenem. The thrombocyte level returned to normal after drug withdrawal. This side effect has been reported in humans, but it is unknown if this was a true drug reaction.

The animal slowly resumed normal food intake, and showed weight gain and increased activity. Serum levels of clarithromycin and amikacin were assessed and the doses were deemed appropriate.

The dolphin remained stable until week 22, when he showed a sudden drop in appetite and condition. A marked leukocytosis of 70,000/µl was present with a regenerative left shift. Gastric samples showed high levels of neutrophils, and repeated aerobic cultures grew pure Pseudomonas sp. Endoscopy of the esophagus and first chamber of the stomach showed an esophagitis and esophageal ulceration. At the time of submission, he is under intensive management, and his long-term prognosis is still considered grave.

While the true etiology of the disease in this animal is unknown, one component of it is a Mycobacterium abscessus infection. M. abscessus is an atypical mycobacterium that causes pulmonary disease in humans, and belongs to the same phylogenetic group as M. chelonae. Infection is typically reported in people with severe lung pathology such as cystic fibrosis or other mycobacterial disease.^2,3,4 Not all humans with positive sputum cultures have active disease.⁵ Cutaneous and subcutaneous lesions are also reported following inoculation of the bacteria into wounds or surgical sites.^2,6,7 In humans, the disease may be manageable with long term triple antibiotic cocktails and surgical resection, but is often progressive and fatal.^2,8,9 There has been no report of horizontal transmission between affected individuals.¹⁰ There has been one report of an M. abscessus cutaneous infection in a beluga (Delphinapterus leucas) which was managed for one year before the animal was euthanized.¹¹ The organism is a ubiquitous saprophyte that can grow in municipal water.¹² It was grown from multiple saltwater systems at the NAIB. Acid-fast cytology has been carried out on all the dolphins at NAIB and animals at another institution. All animals have been negative, except for one animal that has periodically been acid-fast positive on cytology and culture, but shows no evidence of clinical disease.

Acknowledgements

An enormous number of people have been involved in this case. We'd like to thank Dr. Michael Wise; Dr. Forrest Townsend, Dr. Tom Reidarson and Dr. Mike Walsh; Dr. Dan Petrus; Dr. Karen Carol and Dr. Trish Perl at Johns Hopkins University; Dr. Pamela Wood and Dr. Eli Perenchevich at the University of Maryland; Dr. Chuck Peloquin at the National Jewish Research Center; Chris Steinert, Laura Curley, Jill Arnold, Christina Steinert, Suzy Ridenour, Sue Hunter and all the marine mammal staff and volunteers.

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