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June 2012 Archive for Dairy Today Healthline

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Dairy Today Healthline

Mycoplasma bovis, a Stealthy Invader

Jun 01, 2012

This pathogen poses a diverse set of challenges to calves.

Van Dyke 20small[1]By Tom Van Dyke, DVM, Manager of Veterinary Services, Merial
 
Pneumonia is one of the most frequent production-limiting conditions in both feedlot and dairy calves. 1 In recent years, Mycoplasma bovis (M.bovis) has exploded seemingly from nowhere to emerge as an important component of the Bovine Respiratory Disease (BRD) Complex.2 Taking its place among the major BRD bacterial players, such as Mannheimia haemolytica and Pasteurella multocida, M. bovis wields a unique set of weapons and poses a diverse set of challenges to calves.
 
The stealth qualities of M. bovis contribute to its ability to cause disease. Mycoplasma is able to manipulate or even turn off its surface antigens so that it may not be easily recognized by the calf's immune system. It is able to evade the calf's defenses further by "hiding out" in its own biofilm, and even stick to and disable the immune cells, which should be combating it. 3
 
Unlike its fellow BRD pathogens, Mannheimia and Pasteurella, M. bovis can cross membrane barriers easily and can be carried in blood to invade other tissues. M. bovis can live on the surface of the upper airway of asymptomatic animals from where it can potentially to spread to the lungs or other herdmates.2
 
M. bovis has potential to cause severe bronchopneumonia characterized by nodular lesions or small abscesses throughout the diseased tissue.1 Mycoplasma usually is thought to come in as a secondary infection, but can also be the primary infection in the BRD complex when calves are stressed or immune deficient.  Mycoplasma pneumonia has a more gradual or subtle onset and therefore is difficult to detect in early stages. Other syndromes associated with M. bovis include ear infections characterized by inflamed droopy ears, arthritis where one or more joints are swollen and painful, and contagious mastitis in lactating dairy cows.1
 
Mycoplasma pneumonia can be difficult to diagnose. Many diagnostic laboratories do not routinely detect M. bovis in submitted tissues or swabs because special media, equipment and techniques are required to grow it successfully. 3 Because pneumonia often is a mixed infection, the M. bovis contribution to the disease may go undetected. 1 Clinically, when pneumonia is accompanied by otitis (ear infection) or arthritis, M. bovis should be strongly suspected.1
 
M. bovis is spread by nose-to-nose contact or aerosol transmission from infected animals. 3 On dairy farms, baby calves can become infected when fed colostrum or waste milk from mastitic cows. 1 M. bovis will not last long in a hot, dry environment, but can survive for months on environmental surfaces in cool moist conditions.3 Simple exposure to infectious agents, however, is not sufficient cause for the development of disease in calves.4
 
Because of all the tricks M. bovis has up its sleeve, predictably control is challenging as well. Measures must be taken to minimize bacterial challenges and resistance. Testing and quarantining all incoming animals to the herd is ideal but not practical. Colostrum management and pasteurization of all waste milk before feeding it to baby calves is essential. Look for ways to reduce stress in handling, eliminate overcrowding and improve ventilation of calf barns. The use of Mycoplasma vaccines has yielded mixed results. 1 Vaccination and control of other respiratory diseases also are important to prevent Mycoplasma from gaining a foothold.2
 
M. bovis  pneumonia can be challenging to treat.  Because of its subtle and gradual onset, the disease may have advanced considerably before detected.  The lack of cell wall renders beta lactam antimicrobials, such as the cephalosporins and penicillins, ineffective. Fortunately, newer antimicrobials have been approved for the treatment of BRD associated with M. bovis, but successful therapy requires the maintenance of prolonged therapeutic levels of the drug for as long as 10 to 14 days.  Otherwise, relapses are common and full recovery less likely.2
 
The emergence of M. bovis has added yet another level of complexity to the BRD complex. Successful control, diagnosis and treatment will likely remain a challenge and require ongoing diligence.
 
©2012 Merial Limited, Duluth, GA. All rights reserved. RUMILGN1214 (05/12)
1 Smith GW. Mycoplasma Diseases of Calves. Virginia Veterinary Medical Association Conference Proceedings. 
  2012.
2 Currin JF, et al. Mycoplasma in Beef Cattle. Virginia Cooperative Extension Publication. 400-304.
3 Maunsell FP et al. Mycoplasma bovis Infections in Cattle. J Vet Intern Med. 2011;25:772–783.
4 McGuirk S and Ruegg P. Calf Diseases and Prevention. University of Wisconsin-Madison Publication. Available at www.uwex.edu/milkquality/pdf/calf_diseases_prevention.pdf.
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