Tuberculosis

Pathogen

Tuberculosis is an ancient disease that can infect many animal species, including humans. It is usually caused by a bacterium of the Mycobacterium tuberculosis complex, which includes M. tuberculosis (which is considered primarily a pathogen in humans), M. bovis (which is normally the causative agent of tuberculosis in ruminants, and is often called bovine tuberculosis or bovine tuberculosis), and several other species.

Susceptible species

It is important to realize that these bacteria can infect not only normal, usual hosts, but also other animal species (including humans). For example, M. tuberculosis can also be found in dogs and horses[1,2] and M. bovis in humans[3]. The oldest known case appears to be from the extinct long-horned bison (Bison cf. antiquus), from which genetic material was isolated from bone lesions[4].

Signs in animals

In chronic disease, lesions are an indication of the disease. The tissue damage consists of nodules with a creamy white content, and the animal is usually thin or emaciated. However, other diseases can also present a similar picture, but with a different pathogen. Therefore, it is necessary to perform further tests (microscopy and identification of the bacterium by means of cultures or molecular research methods). In addition, it must be taken into account that early and small injuries are so inconspicuous that they are easily overlooked. It is not possible to rule out tuberculosis based on macroscopic examination[5].

Infection of animals

The bacterium is usually spread through the air in the form of small droplets released when an infected animal sneezes or coughs and are inhaled. This is why the disease usually starts in the lungs. The bacterium can also be spread through direct contact between animals and the body fluids of sick animals.

Infection of people

Transmission of M. bovis to humans usually occurs through the consumption of unpasteurized milk from infected cows.

Geographical distribution

In the majority of European countries tuberculosis in domestic animals / livestock has been controlled thanks to the stringent testing of cattle.

However, in some countries certain wildlife species are infected and act as a reservoir of disease. For example, M. bovis is present in wild boar (Sus scrofa) and red deer (Cervus elaphus) in France and Spain and in badgers (Meles meles) in the UK and Ireland [6,7,8]. M. caprae, another member of the M. tuberculosis complex, occurs in red deer, cattle and people in Austria and South Germany [9,10].

The Netherlands has a TB-free status although individual cases of infected cattle being imported are reported almost every year [11]. In the Netherlands, during the period from December 2012 until April 2014, 104 badgers were tested for the presence of Mycobacterium tuberculosis complex bacteria as part of a joint project between the DWHC and the Central Veterinary institute in Lelystad; all samples were negative (for more details see the published study results: https://www.dwhc.nl/en/geen-tbc-dassen-nederland/).

 

Sources

  1. Accidental infection of veterinary personnel with Mycobacterium tuberculosis at necropsy: a case study. Posthaus H, Bodmer T, Alves L, Oevermann A, Schiller I, Rhodes SG, Zimmerli S. Vet Microbiol. 2011 May 5;149(3-4):374-80.
  2. Pulmonary disease due to Mycobacterium tuberculosis in a horse: Zoonotic concerns and limitations of antemortem testing. Lyashchenko KP, Greenwald R, Esfandiari J, Lecu A, Waters WR, Posthaus H, Bodmer T, Janssens JP, Aloisio F, Graubner C, Grosclaude E, Piersigilli A, Schiller I. Vet Med Int. 2012;2012:642145.
  3. Human Mycobacterium bovis infection in the United Kingdom: Incidence, risks, control measures and review of the zoonotic aspects of bovine tuberculosis. de la Rua-Domenech R.,. Tuberculosis (Edinb). 2006 Mar;86(2):77-109
  4. Mycobacterium tuberculosis complex DNA from an extinct bison dated 17,000 years before the present. Rothschild BM, Martin LD, Lev G, Bercovier H, Bar-Gal GK, Greenblatt C, Donoghue H, Spigelman M, Brittain D. Clin Infect Dis. 2001 Aug 1;33(3):305-11.
  5. A review of infection of wildlife hosts with Mycobacterium bovis and the diagnostic difficulties of the ‘no visible lesion’ presentation. Gavier-Widén D, Cooke MM, Gallagher J, Chambers MA, Gortázar C. N Z Vet J. 2009 Jun;57(3):122-31.
  6. Mycobacterium bovis in wildlife in France. Zanella G, Durand B, Hars J, Moutou F, Garin-Bastuji B, Duvauchelle A, Fermé M, Karoui C, Boschiroli ML. Zoonoses Public Health. 2012 Sep;59 Suppl 2:170-8.
  7. Progress in the control of bovine tuberculosis in Spanish wildlife. Gortazar C, Vicente J, Boadella M, Ballesteros C, Galindo RC, Garrido J, Aranaz A, de la Fuente J. Vet Microbiol. 2011 Jul 5;151(1-2):170-8.
  8. Bovine tuberculosis infection in wild mammals in the South-West region of England: a survey of prevalence and a semi-quantitative assessment of the relative risks to cattle. Delahay RJ, Smith GC, Barlow AM, Walker N, Harris A, Clifton-Hadley RS, Cheeseman CL.Vet J. 2007 Mar;173(2):287-301.
  9. Infection of red deer, cattle, and humans with Mycobacterium bovis subsp. caprae in western Austria. Prodinger WM, Eigentler A, Allerberger F, Schönbauer M, Glawischnig W. J Clin Microbiol. 2002 Jun;40(6):2270-2.
  10. Tuberculosis in cattle – surprisingly re-emerging or continuously present?. Moser I, Köhler H, Menge C. Tierarztl Prax Ausg G Grosstiere Nutztiere. 2014;42(4):240-9; German
  11. Spierenburg, M.A.H, Valkenburg, S.M. & Zijderveld, F.G. van (2014). Import van met TBC besmette runderen uit officieel vrije lidstaten. Tijdschrift voor Diergeneeskunde 12: 28-31

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