Lung Diseases in Cattle

define bovine respiratory disease (BRD)

a complex condition caused by a combination of infectious agents, a weakened immune system in the host, and other environmental stressors. These factors collectively lead to the development of bronchopneumonia.

what viral pathogens are associated with BRD?

bovine herpesvirus type 1 (BHV-1), parainfluenza-3 virus (PI3), bovine viral diarrhea virus (BVDV), and bovine respiratory syncytial virus (BRSV)

what bacterial pathogens are associated with BRD?

Mannheimia haemolytica, Mycoplasma bovis, Pasteurella multocida, and Histophilus somni

what is bovine acute fibrinous pneumonia?

aka shipping fever or pneumonic pasteurellosis, primarily affects older cattle and has a low morbidity but high mortality rate; toxigenic strains of Mannheimia haemolytica or Pasteurella multocida invade the lungs, releasing bacterial toxins that cause tissue necrosis and in severe cases lead to pleuropneumonia.

how do cattle with bovine acute fibrinous pneumonia present clinically?

depression, fever, and a cough; PM examination reveals a bronchopneumonia with fibrin on the pleura, extensive necrosis, and interlobular septal expansion due to edema. Survivors may develop pulmonary abscesses, bronchiectasis and bronchiolitis obliterans.

what is bovine enzootic pneumonia?

aka calf pneumonia; a common respiratory disease affecting calves less than one-year of age; it arises from a combination of infectious causes and/or environmental factors that compromise respiratory defenses, enabling opportunistic bacteria to infect the lungs

what PM findings are seen in calves with bovine enzootic pneumonia?

bronchopneumonia, characterized by dark red cranioventral lung consolidation and suppurative exudate. When Histophilus somni is involved, additional lesions may also develop in the brain and heart.

where is Mycoplasma bovis pneumonia most prevalent?

in feedlot cattle in Europe and North America; NZ was considered free of M. bovis until July 2017 when the disease was confirmed in the South Island

what is a common feature and clinical signs of M. bovis infection?

chronic pneumonia that is non-responsive to treatment; clinical signs are non-specific and usually indistinguishable from other causes of pneumonia

what are the four main morphological patterns of pneumonia?

caseonecrotic bronchopneumonia

bronchopneumonia with foci of coagulation necrosis

suppurative bronchopneumonia without necrosis

chronic bronchopneumonia with abscessation

what are other disease syndromes associated with M. bovis infection?

arthritis, otitis media, mastitis, abortion, and keratoconjunctivitis

what does Mycobacterium bovis cause?

tuberculosis in cattle and other mammals, including humans, making it a zoonotic disease. Disease manifestation depends on the infection route (inhalation or ingestion).

what clinical signs to animals infected with Mycobacterium bovis have?

chronic weight loss, weakness, fluctuating fever, cough, exercise intolerance, and lymphadenitis, although many remain asymptomatic

gross lesions and histopathology associated with Mycobacterium bovis?

encapsulated, pale-yellow tubercles (nodules) with caseous and variably mineralized cores; granulomatous inflammation primarily affects the lungs and lymph nodes (retropharyngeal, tracheobronchial, mediastinal, and mesenteric)

Histologically: M. bovis lesions  are multicentric and feature  necrosis, mineralization, and multinucleated giant cells surrounded by epithelioid macrophages, lymphocytes, and plasma cells. Acid-fast bacteria are present in low to moderate numbers within macrophages and necrotic areas

what is Mortierella wolfii?

an environmental fungus that enters the lungs through inhalation before spreading systemically via circulation

what effect does M. wolfii have in cattle?

non-pregnant → infection remains asymptomatic

pregnant → fungus preferentially colonizes the placenta, leading to severe placentitis and abortion; uterine contractions during abortion can force necrotic material and fungi into placental veins, forming emboli that travel to the lungs

how does embolic pneumonia in cattle infected with M. wolfii look like?

emboli cause infarction and invade lung tissue; extensive necrosis and inflammation may lead to fibrin and hemorrhage within the pleural cavity

affected cattle typically die within 2 days of developing respiratory signs

what is the histopathology of M. wolfii?

fibrin, edema, necrotic debris, and fungal hyphae are abundant

if survival extends beyond a few days, macrophages and neutrophils become more prominent

what is lungworm that affects cattle?

Dictyocaulus viviparus is a sporadic parasitic disease that primarily affects calves in extensive pastoral systems most commonly in late summer and autumn. The extent of lesions depends on host susceptibility and parasite load.

what clinical signs develop in animals infected with lungworm?

signs typically develop around three weeks after ingestion of infective L3 larvae, including coughing, tachypnoea, dyspnoea, weight loss, and, in severe cases, death.

what lesions do we expect to find with lungworm infection?

lesions vary from interstitial pneumonia (larval migration), chronic bronchitis (adult parasites in bronchi) to granulomatous pneumonia (eggs, larvae). The dorsocaudal and ventrocaudal regions of lungs are most commonly affected, with large, wedge-shaped, often depressed, red to grey, consolidated foci at the posterior edge of the caudal lung lobes

what are two respiratory toxins that occasionally lead to severe lung disease in cattle?

4-ipomeanol from mouldy kumara and L-tryptophan from regrowing pastures

what is the pathogenesis of toxic pneumonia?

toxins enter the bloodstream and are metabolized by club cells in the distal bronchioles, leading to the release of free radicals that damage type I pneumocytes, resulting in alveolar and interstitial oedema

what clinical signs are seen with toxic pneumonia?

dyspnoea, typically appear 1–2 weeks after toxin exposure

lesions associated with toxic pneumonia?

diffusely enlarged, rubbery lungs with rib imprints, often accompanied by severe emphysema. Histologically, acute lesions show interstitial oedema and fibrin, while type II pneumocyte hyperplasia develops in surviving cattle

what is hypersensitivity pneumonia?

a disease triggered by allergens, primarily inhaled fungal spores from moldy hay or Dictyocaulus viviparus larvae, leading to the formation of antibody-antigen complexes

what is the pathogenesis of hypersensitivity pneumonia?

antigen-antibody complexes are deposited in the pulmonary interstitium and activate an immune response that causes tissue damage

what are the acute and chronic forms of hypersensitivity pneumonia?

Acute cases resemble toxic pneumonia, causing severe pulmonary oedema and necrosis. The more common chronic form results from repeated mild interstitial damage, leading to progressive fibrosis