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Human Brucellosis Exposure from a Harbor Porpoise
Abstract & Commentary
By Maria D. Mileno, MD
Associate Professor of Medicine, Division of Infectious Diseases, at Brown University, Alpert Medical School.
Dr. Mileno reports no financial relationships to this field of study.
Synopsis: A porpoise carcass on the southern coast of Maine was recovered by a rescue team affiliated with a marine mammal facility; a tissue sample sent for culture grew an organism with morphologic and microscopic characteristics of a Brucella species. The Centers for Disease Control and Preventiion confirmed the isolate as B. ceti and initiated an investigation to determine whether aerosol exposure occurred among the 4 individuals who performed the necropsy evaluation of the porpoise.
Source: Sears S., Colby K., Tiller R, et al. Human Exposures to Marine Brucella Isolated from a Harbor Porpoise - Maine, 2012. MMWR 2012;61(25):461-463
On January 28th 2012 a porpoise carcass found by a rescue team affiliated with a marine mammal facility underwent a necropsy at a small room in a university facility within 24 hours. It was undertaken by a faculty member, two students and a community volunteer. They each wore gowns and gloves, but they worked without respiratory precautions. Necrotic tissue was removed from the uterine horn. An electric saw with an oscillating blade was used to cut the skull to evaluate the brain. The same individuals who performed the necropsy also cleaned the room after the procedure. Air was exhausted from the room directly outdoors thus persons in adjacent rooms to the necropsy room were felt to have minimal to no risk for exposure to Brucella organisms.
A swab sample of uterine horn tissue was sent for culture to a laboratory specializing in veterinary diagnostics, and an isolate was successfully cultured; it was forwarded to another lab for further identification. This event had already triggered high suspicion for a potential Brucella species infection and standard biosafety level 3 (BSL-3) precautions were taken at both laboratories, including use of biosafety cabinet for specimen manipulation. CDC received the samples on February 15th for confirmatory testing and the isolate was identified by multilocus sequence typing as sequence type 23 - a known sequence type associated with harbor porpoises. DNA testing for marine species are limited, and given that it was from a cetacean, the isolate was likely B. ceti as opposed to B. pinnepedialis.
Since the staff members did not use respiratory protection while handling the porpoise or its specimens the four exposed staff members were advised to immediately begin a 3-week regimen of rifampicin and doxycycline for antimicrobial prophylaxis. They were to also conduct daily fever checks, undergo monitoring for symptoms of acute febrile illness weekly and have their serum tested for Brucella antibodies immediately, and at regular intervals for 24 weeks after the last known exposure. None of the four persons were found to have seroconverted nor did they become ill.
Brucellosis remains a significant worldwide economic and public health problem, especially in Mediterranean countries. Clinical manifestations of this zoonotic disease in humans are often nonspecific and variable making it difficult to recognize. Economically, brucellosis is an important disease of domesticated animals, yet the worldwide incidence of human brucellosis is unknown.
Much has been learned since 1887 when Sir David Bruce isolated B. melitensis from a sick patient and eradication programs were implemented in the U.S., however pockets of infection remain. B. abortus is a reproductive disease of cattle, bison, buffalo elk and camels, as well as secondary hosts such as goats, horses, dogs and wolves. This persistence of the organism in wildlife is an obstacle to its complete eradication in the U.S.1,2 Large populations of feral swine in California, Texas, Florida and Hawaii harbor Brucella organisms as well. Dogs are a principal reservoir of B. canis in the U.S. and disease outbreaks have been reported in kennels and shelters.3 Cases have also been reported among dog breeders and kennel workers who were exposed during the birthing process when exposed to infected tissues. Routes of transmission include foodborne exposures through ingestion of unpasteurized dairy projects. Direct or indirect exposure to the organism occurs through broken skin or mucous membranes when in contact with the aborted fetuses, placental fluids and tissues or during the slaughtering and butchering process. Aerosol transmission through inhalation or conjunctival inoculation do occur, but person-to-person transmission is very rare. An investigation of brucellosis cases among feral swine hunters led to the publication of an educational brochure for hunters by the USDA.
Among those working with marine mammals a few reports of human cases of neurobrucellosis exist.4 Populations at risk include American Indian/Alaska natives who hunt marine mammals, wildlife researchers, veterinary staff as well as marine mammal rescue workers, such as those who were those involved in this reported case.
Some of the other systemic consequences of brucellosis can be severe and unexpected. The epidemiologic and clinical characteristics of 44 cases of aortic brucellosis were recently summarized by Cascio et al through a review of the literature and two additional cases of their own. This cardiovascular complication of brucellosis involved the ascending thoracic aorta in 18 patients. In 16 it occurred as a consequence of endocarditis occurring during brucellosis, and the descending thoracic aorta or the abdominal aorta were involved in the remaining 30 cases. In these latter cases it was associated with spondylodiscitis of the lumbar spine in 13 patients. A history of symptoms indicative of brucellosis was not universally present.5
Brucellosis is one of the 10 most frequently reported laboratory acquired infections in the U.S. Infections are most often due to direct handling of the organism, or being in close vicinity to its handling. Routine clinical laboratory procedures completed outside of a biological safety cabinet have led to exposures as well as accidents due to equipment malfunctions. There will be newly published guidelines this year for safe work practices in human and animal medical diagnostic laboratories which address how isolates are tracked between labs, risk assessment for potentially exposed workers, and recommendations for post-exposure prophylaxis.