Prevalence of Mycoplasma bovis in bovine pneumonia and arthritis

Samples from cattle with pneumonia and/or arthritis were cultured for Mycoplasma. When requested, the Mycoplasma isolates were further identified to species by polymerase chain reaction or restriction fragment length polymorphism. The records of all cases where mycoplasma testing was performed were examined and other infectious agents known to cause pneumonia or arthritis were recorded. Mycoplasma species were isolated from 85% of the lung samples and 69% of the joint samples. Eightyfour percent of the 81 Mycoplasma isolates that were further identified were M. bovis, which clearly made it the most common pathogenic agent identified in samples from cattle with pneumonia and/or arthritis. M. bovis appeared to play an important role in feedlot pneumonia and was the most common cause of arthritis. Unfortunately, treatment and prevention options are currently either ineffective or their effectiveness is unknown.


Summary
Samples from cattle with pneumonia and/or arthritis were cultured for Mycoplasma.
When requested, the Mycoplasma isolates were further identified to species by polymerase chain reaction or restriction fragment length polymorphism.The records of all cases where mycoplasma testing was performed were examined and other infectious agents known to cause pneumonia or arthritis were recorded.Mycoplasma species were isolated from 85% of the lung samples and 69% of the joint samples.Eighty-four percent of the 81 Mycoplasma isolates that were further identified were M. bovis, which clearly made it the most common pathogenic agent identified in samples from cattle with pneumonia and/or arthritis.M. bovis appeared to play an important role in feedlot pneumonia and was the most common cause of arthritis.Unfortunately, treatment and prevention options are currently either ineffective or their effectiveness is unknown.

Introduction
Pneumonia is the most common and serious disease problem that affects beef cattle.
Bacteria such as Mannheimia (Pasteurella) haemolytica, Pasteurella multocida, and Haemophilus somnus, and viruses such as infectious bovine rhinotracheitis virus, bovine virus diarrhea virus, parainfluenza type 3 virus, and bovine respiratory syncytial virus, acting independently or in association with one another, are considered to be the major causes of bovine pneumonia.Arcanobacterium (Actinomyces) pyogenes is frequently isolated from chronically infected lungs, but it is usually thought to invade after another agent has damaged the lungs.
Recently, there has been considerable interest in Mycoplasma bovis as a cause of pneumonia and arthritis that fails to respond to treatment.The purpose of this project was to first determine the frequency of isolation of Mycoplasma species, especially M. bovis, from bovine lung and joint samples submitted to the Kansas State University Veterinary Diagnostic Laboratory, and second to compare that frequency to the frequency for which other respiratory pathogens were identified.

Experimental Procedures
The records of bovine cases submitted between May1999 and December 2001 in which mycoplasma testing was performed were examined and the results recorded.Culture for Mycoplasma spp. was by inoculation onto Friis agar and by inoculation into Friis broth followed by subculture onto agar.Agar plates were examined between 2 and 10 days after inoculation for Mycoplasma colonies.When requested by the submitting veterinarian or owner, Mycoplasma isolates were identified to species by polymerase chain reaction (PCR) using species-specific primers or by restriction fragment length polymorphism of the DNA product obtained by PCR using genus-specific primers.Identification of other bacteria was by routine culture procedures, and identification of viruses was by fluorescent antibody staining and/or virus isolation.

Results and Discussion
Mycoplasma were isolated from 157 of 185 (84.9%) lung samples and from 82 of 119 (68.9%) joint samples (Table 1).In cases where both lung and joint samples were included in the same submission (Mycoplasma isolation was not requested for both types of samples in all cases), 27 of 30 (90.0%) lung samples and 28 of 37 (75.7%)joint samples were culture positive.Of the 81 Mycoplasma isolates identified as to species, 68 (83.9%) were M. bovis.There were six isolates of M. arginini, one each of M. alkalesence, M. bovirhinis, and M. canadense, and four that were not further identified after the PCR indicated they were not M. bovis.In 7 of the 13 cases where a non-M.bovis species was identified, M. bovis was also isolated from the sample.Other pathogens that were identified are listed in Table 1.
Mycoplasma species easily were the most common agents isolated from lung and joint samples from cattle with pneumonia and arthritis, and 84% of the isolates that were further identified were M. bovis.In many cases, pneumonic lungs contained no identifiable pathogen, except Mycoplasma, and a large majority of joint samples were culture-negative except for Mycoplasma.
A 1980 study from California reported that Mycoplasma species were isolated from 86% of the lungs from 500 feedlot cattle, and that 76% of the isolates that were identified were M. bovis alone or in combination with another Mycoplasma.Recently, M. bovis has been touted as an emerging disease of cattle and associated with the presence of multiple abscesses in the lungs of cattle with chronic bronchopneumonia.Examination of our records revealed that M. bovis was present in lungs from cattle with acute bronchopneumonia, chronic bronchopneumonia without abscesses, and acute interstititial pneumonia, as well as cases of chronic bronchopneumonia with abscesses.Our results, as well as the earlier report from California, indicate that M. bovis is common in the lungs of cattle dying of all types of pneumonia, and most likely it is not an emerging disease, but one that over the years has been underdiagnosed.
Most Mycoplasma species that have been isolated from cattle lungs do not cause any disease when put back into cattle.After infection with only M. bovis, most cattle do not become visibly sick, but the organism causes a small amount of lung damage from which M. bovis can be isolated for months.
Perhaps more importantly, M. bovis increases the severity of pneumonia caused by Mannheimia (Pasteurella) haemolytica and Pasteurella multocida, especially if the calves are infected with M. bovis before infection with other bacteria.Several people have found that on arrival at a feedlot, a large majority of cattle already have been exposed to M. bovis.After a month on feed, almost all feedlot cattle have been exposed, and after exposure most animals remain infected for months.Therefore, almost all cattle in most feedlots are infected with M. bovis, and one would expect to isolate the organism from a large proportion of pneumonic lungs, regardless of the cause of the pneumonia.This makes it very difficult be certain of the role of M. bovis in bovine pneumonia, but many veterinarians and researchers feel that it plays an important role, probably by increasing the severity of other respiratory infections.