Etiology of Contagious Bovine Pleuropneumonia
The causal organism in contagious bovine pleuropneumonia is Mycoplasma mycoides mycoides small colony type. (Also see Mycoplasma Pneumonias in Goats Mycoplasma Pneumonias in Goats Mycoplasma spp produce a variety of clinical signs in infected small ruminants. Severe respiratory disease outbreaks with high morbidity and mortality can be due to Mycoplasma capricolumcapripneumoniae read more .) Susceptible cattle become infected by inhaling droplets disseminated by coughing in affected cattle. Cattle that recover from the disease can become chronic carriers with chronic sequestra of infection in the lung. The organism can also be found in saliva, urine, fetal membranes, and uterine discharges. Transplacental infection of the fetus can occur. Viability of the organism in the environment is poor.
The incubation period varies, but most cases occur 3–8 weeks after exposure. In some localities, susceptible herds may show up to 70% morbidity. Mortality is likely to be ~50% in herds experiencing the disease for the first time. Of recovered animals, 25% may become carriers with chronic lung lesions in the form of sequestra of variable size. Because carriers may not be detectable clinically or serologically, they constitute a serious problem in control programs. Breed susceptibility, management systems, and general health of the animal are important factors that influence the infection.
Clinical Findings of Contagious Bovine Pleuropneumonia
In acute cases of contagious bovine pleuropneumonia, clinical signs include fever up to (41.5°C [107°F]); anorexia; and painful, difficult breathing. In hot climates, the animal often stands by itself in the shade, its head lowered and extended, its back slightly arched, and its elbows turned out. Percussion of the chest is painful; respiration is rapid, shallow, and abdominal. If the animal is forced to move quickly, the breathing becomes more distressed, and a soft, moist cough may result. The disease progresses rapidly, animals lose condition, and breathing becomes very labored, with a grunt at expiration. The animal becomes recumbent and dies after 1–3 weeks.
Chronically affected cattle usually exhibit clinical signs of varying intensity for 3–4 weeks, after which the lesions gradually resolve and the animals appear to recover. Subclinical cases occur and may be important as carriers. Infected calves may present primarily with polyarthritis that is evident as swelling of joints and lameness.
Lesions on Post-Mortem Examination
The thoracic cavity may contain up to 10 L of clear yellow or turbid fluid mixed with fibrin flakes, and the organs in the thorax are often covered by thick deposits of fibrin. The disease is largely unilateral, with more than 80%–90% of cases affecting only one lung. The affected portion is enlarged and solid. On section of the lung, the typical marbled appearance of pleuropneumonia is evident because of the widened interlobular septa and subpleural tissue that encloses gray, yellow, or red consolidated lung lobules. Microscopically, this is a severe, acute, fibrinous pneumonia with fibrinous pleurisy, thrombosis of pulmonary blood vessels, and areas of necrosis of lung tissue; the interstitial tissue is markedly thickened by edema fluid containing much fibrin. In chronic cases, the lesion has a necrotic center sequestered in a thick, fibrous capsule, and there may be fibrous pleural adhesions. Organisms may survive only within the inner capsule of these sequestra, and these animals may become carriers.
Diagnosis of Contagious Bovine Pleuropneumonia
Clinical signs, gross findings
Complement fixation test
C-ELISA, PCR assay or IFAT
Diagnosis of contagious bovine pleuropneumonia is based on clinical signs, including severe, often unilateral, pleuritis along with consolidation and fluid-distended interlobular septa, and the characteristic gross pathologic lesions of the lungs. Serological tests such as complement fixation, latex agglutination, or competitive ELISA tests can be used to aid definitive diagnosis. Confirmation is often by isolation of the mycoplasma followed by growth inhibition or immunofluorescence antibody test (IFAT) using hyperimmune rabbit sera against the mycoplasma, or increasingly, by PCR assay. Confirmation of serologic reactions can be made by immunoblotting test. As soon as an outbreak is suspected, culling and necropsy of presumptively infected cattle is advisable.
Control of Contagious Bovine Pleuropneumonia
Reportable disease (OIE A list)
Quarantine, restricted movement
Contagious bovine pleuropneumonia is a reportable disease listed by the OIE as one of 15 "A list" diseases. It has been eradicated in many countries by culling of all infected and exposed animals. In countries where cattle movement can readily be restricted, the disease can be eradicated by quarantine, blood testing, and culling. Where cattle cannot be confined, the transmission of infection can be limited by immunization with attenuated vaccine (eg, T1/44 strain). However, the vaccine is effective only if herd coverage within a country is high. Tracing the source of infected cattle detected at abattoirs, blood testing, and imposition of strict rules for cattle movement can aid in control of the disease in such areas.
Treatment is recommended only in endemic areas because the organisms may not be eliminated, and carriers may develop. Tylosin (10 mg/kg, IM, every 12 hours, for six injections) and danofloxacin 2.5% (2.5 mg/kg/day for 3 consecutive days) have been reported to be effective.
Contagious bovine pleuropneumonia is a highly infectious plague of cattle endemic to Africa and parts of Asia.
It is an OIE reportable A List disease.
Contagious bovine pleuropneumonia is due to Mycoplasma mycoidesmycoides.
The disease can cause a chronic carrier state with pulmonary sequestration.