VN May 2022

Vetnuus | May 2022 36 Mycoplasmas are some of the smallest free-living organisms found in nature that can self-replicate (in contrast to viruses), and they are capable of causing a myriad of infections. Mycoplasmas do not have a cell wall like bacteria and are thus classified separately from bacteria. The absence of a cell wall makes it inherently resistant to certain antibiotics. A complaint often encountered with Mycoplasma infections is that they are chronic and non-responsive to treatment. As a secondary component often involved in the bovine respiratory disease (BRD) complex, this pathogen plays a critical role in the economy of the beef sector. Mycoplasma bovis is the most common mycoplasma that causes disease in bovines, and the infections can range from pneumonia, arthritis, tenosynovitis, otitis or mastitis to name a few. Dairy calves often present with otitis and resultant neurologic symptoms like ataxia, head tilt, and nystagmus. At the same time, respiratory disease is most often observed in beef calves under commercial feedlot conditions. Some sources indicate that Mycoplasma bovis can survive for several days in the environment, whereas others contend with this statement. Regardless, however, this is not an important method of disease transmission. The infection mainly spreads via direct contact or short distance aerosol droplets from infected animals. The disease spreads quickly in commercial feedlots where animals are comingled from various sources and kept in relatively close quarters. The prevalence of infection in incoming cattle is reasonably low, at 0% – 7%, but increases to 40% and even 100% after two weeks in the feedlot in some studies, where the spread is likely more rapid in stressed cattle. It does not necessarily translate tomorbidity since animals can harbour an infection and be a carrier of this organism without having clinical (or subclinical) disease, as is the case with various other bacteria often involved in BRD. Typical bacterial pneumonia caused by organisms such as Mannheimia haemolytica , Pasteurella multocida and/or Histophilus somni will peak early in a feedlot feeding period (within the first three weeks), whereas Mycoplasma bovis related pneumonia peaks later, at about 60 days on feed. It is a slow-growing organism that usually presents as chronic non-responsive pneumonia or sudden lethal clinical pneumonia that shows massive lung damage on necropsy that leaves one wondering how they survived that long. As mentioned above, the organism grows slowly and colonises the affected body tissues. Haematogenous spread to various organs can occur, and chronic pneumonia with polyarthritis should place Mycoplasma bovis high on the clinician’s differential diagnostic list. This condition is commonly referred to as chronic pneumonia and polyarthritis syndrome (CPPS). Infections elicit a very robust immune response, but one of the reasons this organism can colonise body tissues and survive, even in the face of a robust immune response, is unique biological adaptations that enable it to evade the immune system. One of these mechanisms is the ability to change their surface protein expression, typical of the antigenic components of pathogens to which the immune system produces specific antibodies. An in vitro Regulars I Zoetis Livestock Column Zoetis Animal HealthPages FOR ANIMALS. FOR HEALTH. FOR YOU. Mycoplasma bovis : Chronic Pneumonia and Polyarthritis Syndrome Dr Schabort Froneman Zoetis South Africa (Pty) Ltd: Technical Manager: Ruminants