Abstract
A healthy 20-month-old female beluga calf presented with sudden lethargy, cessation of nursing, and a swelling near the left pectoral fin. Aspiration revealed purulent material, from which samples were submitted for aerobic and anaerobic culture, and cytological analysis.
Nocardia paucivorans was isolated in pure culture from the aspirated sample. Its identity was confirmed by 16S rDNA sequencing. The isolate was sensitive to doxycycline, enrofloxacin, amikacin, trimethoprim/sulfa and erythromycin. In cetaceans, the antibiotic of choice is trimethoprim and sulfadiazine (TMS) at a ratio of 1:2.2,3 Prior to culture and sensitivity results, broad-spectrum antibiotic injections were used and the swelling was opened and drained, followed by daily flushing with a dilute chlorhexidine solution. Treatment with TMS medication and folic acid was started. Improvement was noted, but the calf developed a severe neutropenia followed by a non-responsive anemia and thrombocytopenia. TMS was discontinued, but probably due to a long half-life, the pancytopenia continued for five weeks. During this time, the calf was supported with extensive veterinary and husbandry measures to prevent opportunistic infections, including excellent daily nutrition, antifungal and antibiotic medication, stomach protectorants, and filgrastim ("Neupogen") to stimulate bone marrow. Within two weeks of filgrastim, the calf's blood values began to respond positively, although there was still limited motion in the left pectoral fin.
Six months later, when the calf was fully weaned, there was an episode of respiratory clinical signs and lethargy, which required treatment with corticosteroids and injectable antibiotics, in addition to the continuing oral medications. After two weeks of treatment, the calf appeared normal and ate well. Throughout the following twelve months, the calf had various flare-ups of lethargy and inappetence. As a result, oral antibiotic and antifungal medication were used continuously for the last year of life. Four months prior to death, the animal started to have more severe flare-ups that were not as responsive to previous treatments. Within four weeks of death, resting at the corner of pools, and having difficulty staying upright became more common. Bloodwork showed a progressive non-regenerative anemia. In the days before death, there were blood clots in her mouth on two separate occasions. The calf died at the age of 37 months of seemingly unrelated causes.
Gross necropsy revealed a large space-occupying mass walled off within the thorax, near the diaphragm. This mass contained blood and necrotic material. Microscopic examination showed the mass to be a dilated artery with extensive mural fibrosis and mild inflammation, suggesting that this was an aneurysm of unknown etiology.
Nocardia spp. are opportunistic pathogens of cetaceans, as they are ubiquitous in soil and water, most commonly entering the body through aerosol or inoculation routes.1,4 The forms of nocardiosis include pulmonary, systemic, central nervous system, extrapulmonary, cutaneous, subcutaneous, and actinomycetoma, with systemic being the most common in marine mammals.1,4 N. paucivorans was first identified from the respiratory secretions of a human suffering lung disease.5 We believe this to be the first time it has been isolated from a cetacean.
Acknowledgements
The authors wish to thank Dr. D. Martineau, College of Veterinary Medicine, University of Montreal, Montreal, Quebec Canada, Dr. S. Al Izzi, Dr. H. Dick, Idexx Reference Laboratories, Markham, Ontario Canada, and Dr. D. Slavic, Animal Health Laboratory, University of Guelph, Guelph, Ontario.
* Presenting author
Literature Cited
1. Dunn L, Buck JD, Robeck TR. 2001. Bacterial diseases of cetaceans and pinnipeds. In: Dierauf LA, Gulland FMD, editors. CRC Handbook of Marine Mammal Medicine. Boca Raton (FL): CRC Press. p 309–328.
2. Robeck TR, Dalton L. 1995. Subcutaneous Nocardiosis in a beluga whale. IAAAM 26th Annual Conference Proceedings, Mystic, CT; Pp. 27–28.
3. Schmitt T, Reidarson T, McBain J, St. Leger J, Dalton L, Jensen E, Beaman B. 2007. Management of cutaneous Nocardiosis in a beluga (Delphinapterus leucas) with novel trimethoprim sulfadiazine (1:2) formulation. IAAAM 38th Annual Conference Proceedings, Lake Buena Vista, FL; Pp.207.
4. St. Leger JA, Begeman L, Fleetwood M, Frasca Jr. S, Garner MM, Lair S, Trembley M, Linn J, Terio KA. 2009. Comparative pathology of Nocardiosis in marine mammals. Vet Pathol 46: 299–308.
5. Yassin AF, Rainey FA, Burghardt J, Brzezinka H, Mauch M, Schaal KP. 2000. Nocardia paucivorans sp. nov. Int J Syst Evol Microbiol 50: 803–809.