Cattle Health: Mycoplasma In Beef Cattle

Mycoplasma is a tiny bacterium that has a long history of causing disease in the cattle industry. Beginning in the early 2000s, it has emerged as an important entity in Virginia.

Introduction

Mycoplasma was first isolated from cattle with pneumonia and arthritis at the Pasteur Institute 100 years ago. One strain of Mycoplasma was the cause of Contagious Bovine Pleuropneumonia (CBPP), one of the first diseases eradicated in the United States.

The current manifestation of the disease was first reported in the United States in the 1970s, but there were very few cases recognized in Virginia. In the summer of 2000, there was an explosion of new cases. Now the disease is widespread and individual cases can occur in almost any herd. Severe outbreaks can be devastating to producers. It is possible there was a low level of Mycoplasma bovis (M. bovis) present before 2000 that went undetected.

In a 2006 study, Mycoplasma bovis was present in 46 percent of cattle with normal lungs (Gagea, et al., 2006a), 85 percent of cattle with acute fibrinous pneumonia, and 98 percent of cattle with chronic pneumonia (Gagea, et al., 2006b). Mycoplasma grows slowly and requires a special medium so that if cultures are not performed specifically for the bacterium it will not be identified. Mycoplasma pneumonia primarily affects stocker and feeder calves but is occasionally found in nursing calves on cow-calf operations.

Transmission

There are many species of Mycoplasma but Mycoplasma pneumonia is most commonly caused by the bacterium M. bovis. The most likely method of spread for Mycoplasma is from calf-to-calf. This can occur by direct calf-to-calf contact, or through the air when calves are closely confined. Drenching and balling guns can spread the disease between calves. Even though M. bovis can live in the environment for short periods of time, spread of the disease by contamination of barns, feed troughs, trucks, etc. is not thought to be an important means of transmission.

As long as Mycoplasma remains in the upper respiratory tract it causes no clinical signs of disease. When the bacterium enters the lungs it causes a pneumonia that is somewhat different from the shipping fever pneumonia that most beef producers recognize. From the respiratory tract M. bovis can travel through the bloodstream where it is capable of entering joints, organs, and nerves (Maeda, et al., 2003). In beef cattle, Mycoplasma most commonly goes to the joints where it can cause a crippling arthritis and tenosynovitis (inflammation of the tendons and fluid in the joint). Mycoplasma can also infect the ears, eyes, udder, and genital tract.

Clinical Signs

Pneumonia

Mycoplasma bovis can, by itself, cause respiratory disease. However, the disease most often occurs when an initial stressor causes calves to develop traditional Bovine Respiratory Disease Complex (BRDC or shipping fever), and Mycoplasmosis develops seven to 14 days later. In this situation, because it is the third development in the disease complex it is often called a tertiary disease.

Bovine viral diarrhea virus (BVDV) has also been shown to suppress the immune system of cattle and predispose them to M. bovis pneumonia and other respiratory diseases.

Mycoplasma weakens the cattle’s immune system, and inhibits the respiratory tract’s own defenses against disease (Smith, 2002, p 559). Common clinical signs are a harsh hacking cough, a low-grade fever, mildly increased respiratory rate, mild depression, and runny eyes. Because Mycoplasma does not produce toxins like Mannheimia haemolytica, these calves initially do not look as sick as other calves with pneumonia. They are alert and have a fair appetite. However, if they are not treated early their condition will worsen dramatically and be much harder to treat. It may take seven to 14 days after the respiratory tract is infected before calves show dramatic clinical signs, and by this stage significant and often permanent damage has been done to the lungs. This scenario results in higher calf deaths and more “chronics.” Necropsy findings associated with Mycoplasma include small abscesses throughout the lung that have the appearance of scattered rice. Calves with pneumonia due to Mycoplasma do not respond as well to standard treatments for BRDC, and often relapse up to one month after initial treatment.

Source: Virginia Tech University Extension