Bovis ISSN 2398-2993

Mycobacterium bovis

Contributor(s): Veronica Fowler , Tammy Hassel

Introduction

Classification

Taxonomy

  • Kingdom: bacteria.
  • Phylum: actinobacteria.
  • Order: actinomycetales.
  • Suborder: corynebacterineae.
  • Family: mycobacteriaceae.
  • Genus: mycobacterium - closely related to Corynebacterium Nocardia and Rhodococcus.

Etymology

  • GK: myces - a fungus; bakterion - a small rod.

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Clinical Effects

Epidemiology

Habitat

  • M. bovis has been found in several wild mammal species.

Life cycle

  • The symptoms of bTB usually take months to develop in cattle. Infections can also remain dormant for years and reactivate during periods of stress or in old age.
  • An animal can spread the disease to many other herd mates before it begins to manifest clinical signs.

Transmission

  • In most cases, M. bovis is transmitted between cattle in aerosols during close contact. This mainly occurs due to the introduction of infected (undetected-sub-clinical) cattle into new herds.
  • Some animals become infected when they ingest the organism; this route may be particularly important in calves that nurse from infected cows.
  • Spread can also occur through contaminated equipment, animal waste, feed and pasture.

Pathological effects

  • Emaciation.
  • Fever.
  • Weakness.
  • Loss of appetite.
  • Swollen lymph nodes.
  • Moist cough that gets worse in the morning and during cold weather or exercise.
  • Abscesses/lesions in various organs, especially the lungs (only visible upon post mortem examination).
  • Virulence is linked to the bacterias ability to affect macrophages and dendritic cells.

Control

Control via animal

  • The standard control measure bTB is to perform the tuberculin skin test and slaughter any individuals which show a reaction.
  • Frequency of testing is dependent on the annual incidence of bTB within the region and ranges from 12 - 48 months.
  • bTB is mainly spread into new herds through the movement of infected cattle that have not been detected:
    • All cattle moving out of a herd on an annual (or more frequent) testing frequency are subject to pre-movement testing.
    • All cattle moving out of a breakdown herd (where one or more animals fails a bTB test) are subject to pre-movement testing.
  • If bTB is detected, restrictions are put in place (a TB2 Restriction Notice is issued to the farm) so that animals may not be moved on or off the affected farm until further tests show that the herd is clear:
    • After a reactor is confirmed by post mortem and/or culture a herd must have two clear tests 60 days apart.
  • Routine meat inspections in abattoirs are important for surveillance of disease.

Control via chemotherapies

  • bTB is not treated in cattle as it is uneconomic.

Control via environment

  • Segregation from wildlife reservoirs:
    • Ensure they cannot access farm buildings and feed stores.
    • Fence off areas around badger setts to keep cattle out while allowing badgers free access.
  • Hygiene controls on the farm:
    • ​​​Good hygiene practices, for example, long term storage of manure and only spreading manure on arable land, restricting the production of aerosols from spreading, avoidance of shared grazing with other herds, only feed waste milk to calves if it has been boiled or pasteurised Milk acidification, avoid sharing equipment with other farmers Tuberculosis Colostrum Milk replacers.

Vaccination

  • No effective vaccination currently exists, although extensive R&D is being performed to develop one.

Other countermeasures

  • Hygiene training on farms to help manage the control of bTB spread.

Diagnosis

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Further Reading

Publications

Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Davidson J A, Loutet M G, O'Connor C, Kearns C, Smith R M, Lalor M K, Thomas H L, Abubakar I & Zenner D (2017) Epidemiology of Mycobacterium bovis Disease in Humans in England, Wales, and Northern Ireland, 2002-2014. Emerg Infect Dis (3), 377-386 PubMed.
  • Pérez-Lago L, Navarro Y & García-de-Viedma D (2014) Current knowledge and pending
    challenges in zoonosis caused by Mycobacterium bovis: a review.
    Res Vet Sci 97 PubMed.
  • Fitzgerald S D & Kaneene J B (2013) Wildlife reservoirs of bovine tuberculosis worldwide: hosts, pathology, surveillance, and control. Vet Pathol 50 (3), 488-99 PubMed.
  • Fine A E, Bolin C A, Gardiner J C, Kaneene J B (2011) A study of the persistence of Mycobacterium bovis in the environment under natural weather conditions in Michigan, USA. Vet Med Int.
  • de la Rua-Domenech R (2006) Human Mycobacterium bovis infection in the United Kingdom: Incidence, risks, control measures and review of the zoonotic aspects of bovine tuberculosis. Tuberculosis (Edinb) 86 (2), 77-109 PubMed.
  • Buddle B M, Wedlock D N & Denis M (2006) Progress in the development of tuberculosis vaccines for cattle and wildlife. Vet Microbiol 112 (2-4), 191-200 PubMed.
  • Cousins D V (2001) Mycobacterium bovis infection and control in domestic livestock. Rev Sci Tech (1), 71-85. 
  • O'Reilly L M & Daborn C J (1995) The epidemiology of Mycobacterium bovis infections in
    animals and man: a review.
    Tuber Lung Dis 76 (1), 1-46 PubMed.
  • Grange J M & Yates M D (1994) Zoonotic aspects of Mycobacterium bovis infection. Vet
    Microbiol
    40 (1-2), 137-51 PubMed.
  • Hardie R M & Watson J M (1992) Mycobacterium bovis in England and Wales: past, present
    and future.
    Epidemiol Infect 109 (1), 23-33 PubMed.

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