Investigation of a Mycobacterium bovis outbreak in cattle at a Colorado dairy in 2010

• Localización: JAVMA: Journal of the American Veterinary Medical Association, ISSN-e 0003-1488, Vol. 244, Nº. 7, 2014, págs. 805-812
• Idioma: inglés
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• Resumen

  • Objective�To describe an epidemiological investigation of a bovine tuberculosis outbreak on a Colorado dairy operation.

    Procedures�A cull dairy cow infected with Mycobacterium bovis (index cow) was detected at a Texas abattoir during routine slaughter surveillance and subsequent diagnostic testing. This initiated an epidemiological investigation that was performed in accordance with USDA regulations.

    Results�The index cow was traced back to a Colorado dairy (index herd). Of the 908 cattle in the index herd, 101 (11.1%; 86 adult cattle > 2 years old and 15 immature cattle = 2 years old) were infected with M bovis. Fourteen M bovis�infected cattle = 2 years old were identified on 5 additional premises that had purchased cattle from the index herd directly or indirectly. All 115 affected cattle were infected with the same genetic type (spoligotype) of M bovis. A substantial proportion of cattle that left the index herd during the 5 years previous to the identification of the index cow were untraceable because of a lack of unique animal identification and inadequate records.

    Conclusions and Clinical Relevance�Results indicated that neonatal calves can have an important role in the transmission of M bovis. Also, this report highlights the exigent need for unique individual identification of livestock, including neonatal animals, so that thorough epidemiological investigations of reportable (zoonotic or foreign animal) diseases can be conducted when necessary.

    Bovine tuberculosis is caused by Mycobacterium bovis, which is a zoonotic pathogen.1 In 1917, the USDA initiated a state-federal-industry eradication program to address bovine tuberculosis in cattle.2 Consequently, bovine tuberculosis has been nearly eliminated from US cattle herds, but intermittent M bovis infections continue to occur. From 2002 to 2011, national surveillance detected M bovis�infected cattle in 80 herds, including 25 (31%) dairy, 53 (66%) beef, and 2 (3%) mixed purpose herds.3 During this same period, M bovis�infected animals were detected in 9 captive cervid herds, including 1 each in 2003 and 2006, 2 in 2008, and 5 in 2009.3 National surveillance for bovine tuberculosis consists of antemortem surveillance, which includes CFT tests performed by USDA-accredited veterinarians, and slaughter inspection performed at federally inspected slaughter establishments.

    The purpose of an epidemiological investigation is to determine the origin of an infected individual and the potential spread of infection. In regard to livestock production, these investigations focus primarily on the origin and disposition of all animals that have resided at an affected premises for the 5 years prior to the discovery of the infected animal or as far back as producer records allow. During such an investigation, the tracing of sexually intact animals is emphasized because these animals typically live longer and thereby pose a greater risk for disease transmission than do neutered animals.

    Traditionally, it has been assumed that neonatal dairy bull calves, which are typically sold at 1 to 3 days old, pose a low risk for transmission of bovine tuberculosis because of the limited time they spend in the herd of origin and the fact that they are generally housed with similar calves that are destined for slaughter with minimal exposure to sexually intact cattle. However, this assumption is potentially flawed because neonatal calves are often exposed, albeit for a brief time, to colostrum and milk from adult cows, which could be contaminated with M bovis. Thus, these calves could become infected with M bovis prior to their sale at 1 to 3 days of age.4 Unfortunately, neonatal bull calves are frequently moved with little to no official or permanent identification from their birthplace to calf-raising operations or other noncommercial facilities. Lack of identification complicates tracking animal movement and limits the ability to determine the extent of animal exposure to the pathogen in question. The purpose of this report was to describe an epidemiological investigation of a bovine tuberculosis outbreak that began in a Colorado dairy herd in 2010 and resulted in M bovis�infected cattle being identified on 5 additional premises, presumably because of disease transmission by young calves.