What Is Mycoplasma bovis (M. bovis) in Cattle?

Mycoplasma bovis (M. bovis) is a bacterial pathogen that affects cattle worldwide, causing a variety of diseases that impact the welfare and productivity of beef and dairy herds. The organism’s ability to cause persistent infections presents a challenge to the agricultural industry, leading to efforts to understand and control its spread. It is a subject of ongoing research and strategic farm management.

Understanding Mycoplasma bovis Biology

Mycoplasma bovis belongs to a class of bacteria distinguished by their small size and a complete lack of a cell wall. This absence makes M. bovis naturally resistant to common antibiotics, such as penicillins and cephalosporins, which work by targeting cell wall synthesis. This intrinsic resistance complicates treatment efforts.

The organism’s biology allows it to evade the host’s immune system. M. bovis can alter the proteins on its surface, making it difficult for the cow’s immune defenses to recognize and respond. It can also form biofilms, which are communities of bacteria encased in a protective matrix that shields them from antibiotics and immune cells, contributing to chronic infections.

Common Illnesses Caused in Cattle

M. bovis is associated with several conditions in cattle. One of the primary illnesses is bovine respiratory disease, manifesting as severe and chronic pneumonia, particularly in young calves and feedlot cattle. Clinical signs include a harsh, dry cough, nasal discharge, and fever, with a poor response to standard antibiotic treatments often resulting in chronic abscesses within the lungs.

In dairy cows, M. bovis causes contagious mastitis, an infection of the udder that is difficult to manage. It can affect multiple quarters, leading to a dramatic drop in milk production and milk that appears watery or contains pus-like clots. The infection becomes chronic, resisting typical therapies, and affected cows are often removed from the herd due to high somatic cell counts and low production.

Another manifestation, especially in calves, is arthritis, which causes painful swelling in one or more joints and results in severe lameness. This condition can occur on its own or alongside pneumonia. Less frequently, M. bovis can lead to other issues such as middle ear infections (otitis), which may cause a head tilt, eye infections, and reproductive problems like abortions.

How M. bovis Spreads and is Identified

Mycoplasma bovis spreads through several routes. The primary mode of transmission is direct, nose-to-nose contact, which allows the bacteria to pass through respiratory secretions. It is also transmitted via aerosols when an infected animal coughs, making crowded conditions, such as in transport or feedlots, high-risk environments.

Indirect contact is another pathway for spread, as contaminated equipment, feeding utensils, and water sources can harbor the organism. A primary route of transmission is through milk, as calves can become infected by drinking from an infected cow. The introduction of a new animal that is a silent carrier—infected but not showing signs of illness—is how the disease often enters a previously clean herd.

Diagnosis of M. bovis requires laboratory testing, as clinical signs like pneumonia or arthritis are not unique to this pathogen. Definitive diagnosis requires lab tests on samples such as nasal swabs, lung tissue, joint fluid, or milk. The most reliable method is the polymerase chain reaction (PCR) test, which detects the bacterium’s genetic material. Bacterial culture is another option but is slow and difficult, while serology tests can indicate exposure but may not confirm active infection.

Managing M. bovis Infections and its Industry Impact

Managing M. bovis infections on farms is challenging. Treatment with antibiotics is often unsuccessful because of the bacterium’s natural resistance and ability to form protective biofilms. This leads to persistent infections that do not resolve. While some commercial vaccines exist, their effectiveness is considered low, offering limited protection.

Prevention and control rely on biosecurity and herd management. Key strategies include:

• Maintaining a “closed herd” where no new animals are introduced.
• Quarantining and testing any new animals to screen for carriers.
• Preventing contact with neighboring cattle through secure fencing.
• Ensuring proper on-farm hygiene and ventilation.
• Minimizing stress on animals to help control the spread.

The economic impact of M. bovis on the cattle industry is substantial. Losses stem from decreased milk production, reduced weight gain, treatment costs, and the culling of animals. Outbreaks can also lead to trade restrictions and significant costs associated with eradication programs. Mycoplasma bovis is not considered a significant risk to human health and is distinct from Mycobacterium bovis, the bacterium that causes bovine tuberculosis.