Mycoplasma Bovis (M. Bovis) was first diagnosed in Ireland in 1994 and has been seen in many a farm outbreak since then. It is not a new disease by any sense of the word however the current widespread furore would suggest otherwise and perhaps it is only recently that we as an industry are starting to see the consequences of such a highly specialised pathogen on a national scale. With the current expansion level in the Irish dairy herd it is not surprising that with increasing numbers of animals within herd populations as well as the increasing pressures on farm systems that bugs such Mycoplasma Bovis that somewhat duked under the radar in the past and rumbled along have suddenly exploded on Irish farms, both beef and dairy. With widespread geographic movement of animals it is only inevitable that we see infectious diseases such as Mycoplasma Bovis rear its ugly head in all corners of the country and become ever more prevalent.
Mycoplasma Bovis is a highly specialised pathogen, known as atypical bacteria due its lack of cell wall and therefore inaccessible target of many antibiotics and is capable of exerting its damaging and sometimes catastrophic impact on the health, welfare and productivity of both beef and dairy cattle. M. Bovis presents itself in a number of ways during an outbreak of disease, it commonly presents as respiratory disease, otitis media (ear droop with head tilt), arthritis and mastitis and can be present in any combination of such clinical presentations simultaneously, the most common being polyarthritis and/or mastitis in dairy cows and often respiratory disease followed by polyarthritis in beef animals in feedlots. Other common presentations include its role the bovine respiratory disease complex, which although more often than not is present in company with 1 or more of the other pneumonia causing respiratory viruses or bacteria, it can be a pneumonia that is difficult to treat, it also supposedly responsible for otitis media and calves with head tilts and droopy ears although this is one presentation where it is more difficult to categorically confirm the presence of Mycoplasma Bovis.
The difficulty with Mycoplasma Bovis is that although sometimes highly pathogenic and infectious, capable of causing severe disease in a number of animals it is also a commensal and can live happily in the upper respiratory tract of healthy animals. Mycoplasma Bovis is best adapted at colonising mucosal surfaces where it can survive without causing any disease in the animal. The upper respiratory tract is the main known site of colonisation in cattle after exposure presumably by the aerosol route, nose to nose contact or indirectly by fomites such as feed utensils could all be responsible for transmission of infection. Cattle can also become infected with Mycoplasma Bovis by the udder and intramammary infection which can become another site of colonisation with the bug. Although shortly after infection the bug can be isolated from many tissues throughout the body, the udder and upper respiratory tract appear to be key in the persistence of Mycoplasma Bovis and subsequent shedding from that animal to the next. Calves fed milk infected with Mycoplasma Bovis can also become infected. Once a cow or calf become infected with Mycoplasma Bovis they can either become sick and show clinical signs associated with the disease or they may just become colonised where the bug settles itself in the upper respiratory tract for example in that animal and may not cause any clinical signs whatsoever. It is believed that once an animal does become infected that actually develops clinical signs of the disease whether that is infection by the upper respiratory tract or by the intrammamary route that they can become bacteraemic for a short time where the pathogen can exert its effects – such as settling out in joints for example and that after a short time the cow will develop an immune response and antibodies but the effects from the initial infection can be severe. For example if a cow gets an infected joint – after a short time the body will develop antibodies that protect the pathogen from crossing then blood –milk barrier or from moving to other parts of the body but the initial infection in the joint/s or wherever it reached initially can leave much longer damage, some cows can have swollen joints that are not appreciably lame but others can become so lame that they must euthanized on welfare grounds. Although mycoplasma infection should initiate an immune response and after initial infection the cow should have some immunity in theory so if they survive and get over this initial insult they can survive and get over it – the cow will always be susceptible to new infections via the udder and infections in the udder can be difficult to treat and often serve as a source of infection to other cows.
What can I do?
Firstly it is important to diagnose the actual pathogen – presumption can be very dangerous.
Joint fluid samples taken by your vet and sent to the lab for analysis in the case of swollen joints, milk samples taken for culture and or PCR testing in the lab in the case of mastitis, lung washes in the case of pneumonia outbreaks and post mortem samples can help diagnose mycoplasma. Blood testing is only useful as a screen to confirm if animals have ever met the disease but have little value in confirming the disease in a current outbreak as antibodies in blood could be present from historic exposure and animals can be perfectly healthy and have antibodies in the blood so a blood test will not confirm anything. Seeking veterinary advice is essential as if it is mycoplasma then it is essential to know for sure that is what you are dealing with, as cows can have many causes of mastitis, swollen joints/hock lesions for example and there a numerous causes of pneumonia mycoplasma can be wrongly implicated, nonetheless it is best to try and confirm diagnosis if it is suspected.
Approach to control of mycoplasma really is dependent on how it presents in your herd and always will require veterinary advice and intervention, if you are worried you may have the disease speak to you vet immediately. Mycoplasma mastitis control is based on the controls of contagious mastitis pathogens for example; milking infected cows last, cluster cleaning between cows, post milking teat disinfection etc. Mastitis cases can be difficult to treat and sometimes culling is the only option in non-responsive cases, this decision is case specific. Pneumonia outbreaks generally involve prompt identification of affected animals, choosing the appropriate therapy, segregation of sick animals, good husbandry and housing etc. Ottits in calves is similar – prompt id, segregation and treatment of sick calves, good hygiene and husbandry. There are many more and these only are examples of approach to mycoplasma problems, every farm will have different presentations of the disease and thus farm specific controls can be advised by your vet.
Like many infectious diseases, mycoplasma can be there and not causing any problems and equally well can be very damaging and extremely stressful when an outbreak does occur. Control within infected herds and prevention is key.