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Download Volume 25 - No 1: Mycobacterium bovis
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JOHNS HOPKINS U N I V E R S I T Y Department of Pathology 600 N. Wolfe Street / Baltimore MD 21287-7093 (410) 955-5077 / FAX (410) 614-8087 Division of Medical Microbiology THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER Vol. 25, No. 01 Tuesday, January 3, 2006 A. Provided by Sharon Wallace, Division of Outbreak Investigation, Maryland Department of Health and Mental Hygiene. There is no information available at this time. B. The Johns Hopkins Hospital, Department of Pathology, Information provided by, Todd B. Sheridan, M.D. Clinical Presentation: A 15-month-old boy presented with fever and diarrhea. He was treated for gastroenteritis over the course of 4 weeks, requiring several intermittent admissions. He eventually developed abdominal distension and tenderness, leading to laparotomy for suspected ruptured appendix. Intraoperatively, multiple enlarged lymph nodes were noted, and the appendix appeared intact. Tuberculous peritonitis was diagnosed based on these and other findings, and treatment was initiated. The boy died 4 days later. Organism: Mycobacterium bovis is a member of the Mycobacterium tuberculosis complex, along with Mycobacterium tuberculosis, Mycobacterium africanum, Mycobacterium microti, Mycobacterium bovis subsp. caprae (M. caprae), and Mycobacterium tuberculosis subsp. canettii (M. canettii). M. bovis mainly causes disease in cattle (“bovine tuberculosis”), but it may infect many animals including dogs, cats, pigs and rabbits. Infection in humans was more common prior to pasteurization of cow’s milk and slaughter of infected cattle. The above case was reported in MMWR 2005:54(24);605-8. The report summarized 35 cases of M. bovis infection identified in New York City between 2001 and 2004. Similar to the current Maryland outbreak of 5 cases in the past 18 months, epidemiologic investigation revealed the cases were predominantly related to consumption of unpasteurized, fresh cheese (queso fresco) imported from Mexico or Central America. Clinical Manifestations: M. bovis infections in humans are more likely to produce extrapulmonary manifestations, especially in children. Gastrointestinal tract infection is the most common, with diffuse lymphadenopathy, diarrhea, abdominal pain and swelling. Cervical lymphadenopathy is also common and may be the main presenting feature. Pulmonary infection is similar to M. tuberculosis infection. In adults, reactivation of prior M. bovis infection is more common, and disseminated disease may occur with similar characteristics to disseminated M. tuberculosis infection. Prior to cattle surveillance and technologic advancements, farmers often developed cutaneous infections from milking cows, and osteomyelitis was a common sequelae. Human-to-human transmission is controversial, and in the NYC outbreak, no supportive evidence of human-to-human transmission was identified. M. bovis is often recovered in the urine; it should be remembered that BCG, an attenuated strain of M. bovis, is often used as intravesical therapy for carcinoma-in-situ. Positive cultures in this scenario may represent strains that are not completely attenuated, and may represent true infectious cystitis. Diagnosis: M. bovis is an acid-fast bacillus, similar in appearance to M. tuberculosis (MTB) but often described as shorter and plumper, less curved and less beaded. It grows very slowly, often requiring up to 6-8 weeks for growth. M. bovis will grow on Lowenstein-Jensen and Middlebrook 7H11 media but prefers medium with 0.4% pyruvate and no glycerol. It is differentiated from MTB by biochemical tests; M. bovis is niacin-negative, often resistant to pyrazinamide, will not grow in media containing thiophene-2-carboxylic acid hydrazide, and does not reduce nitrates to nitrites. BCG strains of M. bovis grow more rapidly (3-4 weeks), but are otherwise similar. Molecular methods of speciation of mycobacterial species are available; most are PCR-based and target the 16S rRNA gene, using genetic probes for detection. M. bovis cannot be distinguished from MTB on the basis of 16SrDNA sequencing or the currently available non-amplified commercial probes. Treatment: Treatment of M. bovis infections is similar to that of MTB, though pyrazinamide should not be used. In the NYC outbreak, 49% of isolates were resistant to pyrazinamide, 40% were resistant to pyrazinamide and streptomycin, 6% were resistant to pyrazinamide, isoniazid and pyrazinamide, 3% were resistant to pyrazinamide and isoniazid, and 3% showed no resistance. References: Koneman, et al. Color Atlas and Textbook of Diagnostic Microbiology, 5th ed., Lippincott-Raven, Philadelphia, 1997. Winters A, Driver C, Macaraig M, et al. Human tuberculosis caused by Mycobacterium bovis— New York City, 2001-2004. MMWR 2005, 54(24);605-8. http://www.dhmh.state.md.us/publ-rel/html/2005/pr121205.htm. Last accessed 12/13/05. http://pathology5.pathology.jhmi.edu/micro/v21n15.htm. Last accessed 12/13/05.