Conference 07 - 2011 Case: 01 20111026

Signalment:

A 400 pound cross-bred calf (Bos taurus), age and gender unknown.Lung and liver tissues of the calf have been submitted to the necropsy section of the ADRDL-SDSU with a history of respiratory signs ("Well vaccinated, small feedlot calves. Having trouble with Mycoplasma sp.?").

Gross Description:

Gross necropsy results not reported.

Histopathologic Description:

Lung: There is diffuse infiltration of neutrophils and accumulation of fibrin and edema fluid in the airways. There are multifocal pulmonary necrotic areas surrounded by a zone of the inflammatory cells, primarily neutrophils and fewer macrophages. In addition to that there is also diffuse infiltration of neutrophils and accumulation of fibrin in the pleura.

The pulmonary blood vessels are congested.

Morphologic Diagnosis:

Bronchopneumonia, fibrino-suppurative, subacute, diffuse, severe, with multifocal areas of abscessation; diffuse fibrinosuppurative pleuritis.

Lab Results:

Mycoplasmasp. and H. somni have been isolated from the lung.
The bovine virus isolation and the FA for BVD, IBR and BRSV results were negative.

Condition:

Mycoplasma bovis, Histophilus somni

Contributor Comment:

Calf pneumonia is one of the major problems in beef and dairy sectors. It is the most common post-mortem diagnosis in calves at 1-5 months of age. Although it is associated with low mortality, it is highly infectious in nature, affecting more than 50% of young calves. Affected calves suffer from low growth rate. It is a multifactorial disease including a number of bacterial, viral and fungal pathogens.

Calf pneumonia occurs due to a complex interaction between host, environment and pathogen. Young calves with low immunity are highly susceptible to this disease. Among various bacterial agents that cause pulmonary infections, Mycoplasma and Histophilus are most common.

Mycoplasma bovis was first reported in the United States in the 1970s. The high number of new cases was reported in the summer of 2000. After that, M. bovis has been found almost in every herd. A study conducted in 2006 revealed a 46% prevalence of Mycoplasma bovis in lungs of normal cattle(3). Calves suffering from Mycoplasma pneumonia show low grade fever, tachycardia and mild depression.

H. somni is another important cause of bovine pneumonia(1,4). H. somni is also associated with a wide variety of other cattle diseases including abortion, infertility and arthritis(4). H. somni pneumonia is characterized grossly by grey to red consolidation of the cranio-ventral lung, involving from 5 to 80% of total lung volume(1). Tracheobronchial and mediastinal lymph nodes are typically edematous, with fibrinous pleuritis seen irregularly(1,3). Histologically, the suppurative necrotizing bronchopneumonia is the most common histopathologic identification of bacterial pulmonary infections.

Note: Multiple blocks were used for the slides submission; therefore not all the participants will get the same copy of the slides.

JPC Diagnosis:

1. Lung: Pleuropneumonia, fibrinosuppurative and necrotizing, diffuse, severe, with marked intralobular edema and lymphatic fibrin thrombi.
2. Lung: Bronchopneumonia, fibrinosuppurative and necrotizing, with marked suppurative bronchilitis and bronchiectasis.

Conference Comment:

There was marked slide variation, and some slides did not contain both sections of lung. The two sections of lung demonstrated the distinctly different histomorphologies of each entity.

One section contains multiple ectatic bronchioles filled with caseonecrotic material within areas of profound atelectasis characteristic of mycoplasmal pneumonia.. Bronchiolar-associated lymphoid tissue (BALT) is depleted, which is characteristic of enzootic bovine pneumonia. Affected cattle often present with otitis media, as mycoplasma preferentially colonize areas of the body lined by ciliated epithelium (such as airways).

The other section of lung exhibit necrosuppurative bronchopneumonia whichis more typical of gram-negative bacteria, such as Mannheimia hemolytic or Histophilus somni. In affected lungs, alveoli are filled with fibrin and leukocytes and larger areas of coagulative necrosis may become sequestra. Grossly, affected areas of lung will be sharply demarcated from adjacent lung, and the presence of large amounts of fibrin and cellular exudate will give it a firm feel(2).

References:

1. Andrews JJ, Anderson TD, Slife LN, Stevenson GW: Microscopic lesions associated with the isolation of Haemophilus somnus from pneumonic bovine lungs. Vet Pathol 22:131-136, 1985.
2. Caswell JL, Williams KJ. Respiratory system. In: Maxie MG, ed. Jubb, Kenedy, and Palmers Pathology of Domestic Animals. 5th ed. Philadelphia, PA:Saunders Elsevier; 2007:601-5, 610-5.
3. Gagea MI, Bateman KG, van Dreumel T, McEwen J, Carman S, Archambault M, Shanahan RA, Caswell JL: Diseases and pathogens associated with mortality in Ontario beef feedlots. J Vet Diagn Invest 18:18-28, 2006.
4. Kwiecien JM, Little PB: Haemophilus somnus and reproductive disease in the cow: A review. Can Vet J 32: 595-601, 1991.