Mycoplasma Disease in Cattle
In recent years, more than 20 species of Mycoplasma, Ureaplasma and Acholeplasma have been isolated from cattle with different diseases. All of the 20 aforementioned species have been referred to as the Mycoplasmas. It is generally believed that Mycoplasmas play a secondary role in infections, most often exacerbating pre-existing disease; but it has been shown that Mycoplasma bovis (M. bovis) can play a primary role. M. bovis is considered one of the more pathogenic species and is the most frequent Mycoplasma pathogen of pneumonia, mastitis, and arthritis in cattle. Meningitis, otitis media, kerato-conjunctivitis, decubital abscesses, vaginitis and/or abortion are other conditions which may be caused by M. bovis. In general, treatment of Mycoplasma diseases is difficult since Mycoplasma spp. lack a cell wall, which differentiates them from bacteria and are thus resistant to some commonly used antibiotics. Methods used for definitive diagnosis of Mycoplasma infection within an individual animal or herd include culture, fluorescent antibody test (FA-test), and/or serology. In addition, polymerase chain reaction (PCR) is a sensitive method which can be used. Selective media such as Friis or Hayflick's T-mycoplasma media are necessary for Mycoplasma culture and cultures must be kept at 10% CO2. To detect acute infection, paired serum samples are recommended, since rises in antibody titers occur 10-14 days after acute infection with certain Mycoplasma spp. PCR is an extremely sensitive method which can be used to confirm Mycoplasma infection.
Pneumonia: Two types of pneumonia are associated with Mycoplasma infections: contagious bovine pleuropneumonia and enzootic pneumonia of calves. Contagious bovine pleuropneumonia is caused by infection with Mycoplasma mycoides subsp. mycoides and is classified as a foreign animal disease. In "calf pneumonia", (enzootic pneumonia), Mycoplasma spp. are seldom the only pathogens isolated. Most commonly, there is primary and/or concurrent viral and/or bacterial infection. Common involved respiratory viruses are Parainfluenza 3 virus (PI3), Infectious bovine rhinotracheitis virus (IBR) and/or Bovine respiratory syncytial virus (BRSV). Common involved bacteria are Histophilus somni (H. somni), Pasteurella multocida, (P. multocida), and/or Mannhemia haemolytica (M. haemolytica). Most commonly, respiratory viruses are primary pathogens. However, M. dispar, M. bovis and Ureaplasma may also act as primary pathogens. Several species of Mycoplasma may be isolated from calves with pneumonia, but only a few of these species are considered pathogenic. Respiratory pathogenic Mycoplasma spp. include M. dispar, M. bovis, M. bovirhinus, M. bovigenitalium, Ureaplasma diversum. With the exception of M. bovis, these mycoplasmas can be found as normal flora of the upper respiratory tract. Pneumonia develops after their introduction into the lower respiratory tract, which is commonly preceded by impairment of mucociliary clearance and/or immune defense. Mycoplasmas can be introduced in a herd by subclinical Mycoplasma carriers. These cattle shed the organism through nasal discharge for months to years without showing clinical signs. Clinical signs observed in cattle with pure Mycoplasma pneumonia are coughing, induced by stress or movement, slight tachypnea, low grade fever and mild depression. Affected cattle usually retain a good appetite, which distinguishes this type of pneumonia from other viral and/or bacterial pneumonias. At necropsy, cranioventral areas of lungs are red-blue, firm and ooze purulent material on cut section. Histologically, there is chronic bronchointerstitial pneumonia charac-terized by peribronchiolar and perivascular lymphocytic cuffings, purulent bronchiolitis, accumulation of neutrophils and macrophages within alveolar lumens, epithelialization of alveolar septae and atelectasis. Due to prominent lymphocytic cuffings, this type of pneumonia is also called "cuffing pneumonia". Definitive diagnosis can be obtained through culture of a tracheal lavage fluid and/or tissue samples of lungs. In addition, fluorescent antibody tests for detection of antigen of distinct Mycoplasma spp. can be performed. Intramuscular application of oxytetra-cycline, erythromycin, or tylosin is recommended. In mixed infections with Mycoplasma spp. and bacteria, antibacterial therapy must be also effective against involved bacteria. Since "enzootic pneumonia" is a multifactorial disease associated with impaired pulmonary defense, proper management is also very important (i.e., adequate ventilation, prevention of overcrowding.
Mastitis. Although several Mycoplasma spp. (M. canadense, M. bovigenitalium, M. californicum) may cause mastitis, Mycoplasma bovis is the most prevalent. The disease spreads rapidly within a herd, thus the usual history in a farm with Mycoplasma mastitis is that several cows within a short period of time have acute mastitis in one or more quarters. All quarters are usually affected in lactating animals. In addition, the same farm may also have problems with lameness, reproductive problems, calf pneumonia, and adult cow respiratory disease. Cows affected with acute Mycoplasma mastitis have a dramatic drop in milk production. Affected quarters will be warm, swollen and light brown. On palpation, the parenchyma may be firm and often fine nodular. Drawn milk appears normal initially, but separates rapidly in a floccular deposit and a clear supernatant. Acute mastitis may be followed by chronic mastitis, intermittent acute flare-ups, or subclinical infection. Cows with subclinical infection can return to normal milk production, but they may continue to shed Mycoplasma spp. within milk. Mycoplasma spp. and, thus, Mycoplasma mastitis can be transmitted mechanically via handling, milking machines, and common udder wash solutions. Microscopically, acute infection causes neutrophilic mastitis characterized by neutrophilic infiltration of lobular interstitium, degeneration, and necrosis of alveolar epithelium and neutrophilic accumulation within alveoli, which is often followed by abscess formation. In subacute stages, macrophages predominate as inflammatory cells. Chronic Myco-plasma mastitis is characterized by hyperplasia of alveolar and ductular epithelium, aggregation of lymphocytes within interstitium and around ducts, interstitial fibrosis and lobular atrophy. For definitive diagnosis of Mycoplasma mastitis, culture of milk and/or udder parenchyma may be pursued. Immunoblot performed on milk samples is another method which can be used for diagnosis. As with other Mycoplasma diseases, Mycoplasma mastitis is difficult to treat. Thus, prevention by teat dipping, dry/lactating cow therapy, and proper maintenance of milking machine equipment is recommended. Once Mycoplasma mastitis is detected within a herd, identification of infected cattle and their strict separation or culling may be necessary, since the disease is highly contagious and often therapy resistant.
Arthritis: The incidence of Mycoplasma arthritis is increased in cattle herds with enzootic Mycoplasma mastitis and/or pneumonia, since Mycoplasma arthritis occurs commonly secondary to bovine affected with Mycoplasma pneumonia or mastitis due to hematogenous spread. Oral infection of calves from dams with Mycoplasma mastitis may also occur. Lameness caused by M. bovis is typically a result of polyarthritis and/or tendosynovitis. One clinical sign of Mycoplasma arthritis is marked lameness. Animals have pain during movement and/or at palpation of affected joints. Capsules of affected joints are warm, distended and fluctuant on palpation. Gross examination of the affected joints will show fibrinosuppurative synovitis and tenosynovitis with cartilage erosions. Affected joint capsules are distended by opaque, cream colored exudates, which often contains fibrin flakes. Eroded cartilage may be replaced by polypoid granulation tissue. The synovium is often reddened and edematous. Microscopically, there may be ulceration of synovial membranes and infiltration of synovia and joint capsule with neutrophils, macrophages, plasma cells and/or lymphocytes. Neutrophils may accumulate within the joint space and there may be hyperplasia of synovial cells and villi. Synovial vessels are often congested and occasionally thrombosed. Mycoplasma culture of tissue samples and/or synovial fluid may be pursued for definitive diagnosis. Treatment follows the protocol of any septic arthritis. Recommended is lavage of affected joints with a through-and-through flushing method, most likely on a daily basis over the next 1-2 weeks. Local antibiotic therapy may be used. Systemic antibiotic therapy is recommended, since there is commonly concurrent Mycoplasma mastitis and/or pneumonia. It must be considered that Mycoplasma spp. have a poor response to antibiotic therapy. Antibiotics effective in Mycoplasma-induced lameness include danofloxacin, enrofloxacin, and tylosin. Aspirin can be given for pain management.
-by Suzanne Brishard, Class of 2003
-edited by Dr. Sandra Schoeniger, ADDL Graduate Student
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