Australian Livestock Export Corporation Limited
Meat and Livestock Australia
(Previously published online with the LiveCorp and MLA Veterinary Handbook Disease Finder)
(Image Source: Anexa Veterinary Services, NZ)
Description
Pneumonia refers to inflammation of the lungs. It may be accompanied by inflammation of the larger airways (bronchioles) and referred to as bronchopneumonia, or by inflammation of the pleura (outer surface of the lung, adjacent to the chest wall) and referred to as pleuropneumonia. Pneumonia in sheep and goats is often caused by infectious agents, particularly by a combination of bacteria and viruses.
In sheep and goats, the important infectious agents associated with pneumonia include:
- Viruses – Parainfluenza virus type-3 (PI-3), adenovirus, respiratory syncytial virus and caprine arthritis and encephalitis (CAE) virus (goats).
- Bacteria – Manehimia haemolytica, Pasteurella multocida, Haemophilus sp., Chlamydia sp., Salmonella sp., and Mycoplasma sp.
Non-infectious causes of pneumonia include parasitic (lungworms) and aspirations from incorrect drenching.
Many of the causal pathogens (viruses and bacteria including Mycoplasma) are normal residents of the upper respiratory tract in most sheep and goat flocks and herds in Australia. The most common sequence of events leading to pneumonia is thought to be initiated by stressors lowering the resistance of the animal and allowing an initial acute virus or mycoplasma infection to commence in the upper respiratory tract or lung. This compromises local defenses sufficiently to allow invasion and multiplication of secondary bacteria.
Animals more at risk of viral and bacterial pneumonia are young animals subjected to a range of stressors that are common in the export process including transportation, mixing with new animals, crowding, inadequate ventilation, dust, and sudden climatic changes.
Most viral and bacterial pneumonias develop acutely and are highly contagious in susceptible flocks with the potential to cause outbreaks of disease. Survivors are often chronically affected. In goats, pneumonia caused by caprine arthritisphalitis (CAE) virus is a chronic progressive pneumonia in adults. Lungworms may be acquired when grazing pastures in temperate climates before entering the export process.
Aspiration pneumonia is caused by incorrect drenching technique and might occur as part of fulfilling a pre-export protocol in an assembly point.
Animals with pneumonia may be more susceptible to heat stress and heat stress may exacerbate clinical signs and disease progression for animals with pneumonia.
Respiratory distress will occur if normal lung function is compromised. Progressive disease may also result in endotoxaemia and septicaemia. If the surface of the lungs and lining of the chest cavity become inflamed (pleurisy) there is severe pain. Death may occur when there is sufficient lung compromised to cause anoxia (usually when more than 70% of the lung is affected), or from overwhelming systemic infection including toxemia.
Clinical Signs and Diagnosis
Bacterial pneumonias are often first detected when an animal has died suddenly and is necropsied. Other animals may then be noticed to have signs, including reduced appetite, depression, rapid shallow breathing, coughing, and nasal discharge. Dyspnea (labored or difficult breathing) may follow minor exertion or rise in temperature as respiratory reserve is reduced.
Nasal and ocular discharge may result from dust, ammonia vapor, or fly worry. It can, however, be a result of viral infection of the upper respiratory tract and a prelude to pneumonia.
Pneumonias that cause persistent forced coughing in young sheep and goats can sometimes contribute to prolapse of the rectum.
Most lungworm infections are inapparent. Heavy infections may result in coughing that is reduced following anthelmintic treatment. They are susceptible to most modern drenches.
With bacterial pneumonias the anteroventral lobes are most affected. With viral and Mycoplasma pneumonias, all lobes may be involved with secondary bacteria invading the anteroventral lobes.
With lungworm, the lesions are grey to green nodules scattered throughout the caudal lobes. Sometimes tangles of white threadlike worms up to 5 cm long are found in mucus in the large airways. Lungworm lesions are usually an incidental finding in an animal necropsied for another disease.
Animals that aspirate usually develop severe pneumonia, decline quickly and die within a few days of the aspiration occurring. At necropsy, the anterior of one lung is usually more affected than the other. There is consolidation, liquefaction, and involvement of the pleura. The aspirated material can be difficult to recognize.
In the pneumonia of goats, associated with CAE virus, the infection becomes clinical only in older goats. At necropsy, the lungs are grey and firm. Laboratory determination of pathogens requires nasal swabs in transport media for virus detection and isolation, and acute and convalescent sera for virus serology. In dead animals, portions of affected lung should be submitted fixed in buffered formalin for histology and chilled for microbiology and virology.
Treatment
When infectious pneumonia is suspected, treat sick animals with antibiotics. Broad spectrum antibiotics are more likely to be effective than narrow spectrum antibiotics. Non-steroidal anti-inflammatory drugs may be warranted in valuable animals. Ensure ready access to feed and water. Severely affected animals should be euthanized without delay.
Use anthelmintic drenches where lungworm is suspected.
Prevention
Causative organisms are often ubiquitous and prevention generally involves management to reduce stressors that may increase the likelihood of disease. Options include avoiding mixing sheep of different origins, reducing crowding, ensuring good ventilation, and providing shelter against sudden climatic changes. Early detection, isolation and aggressive treatment with broad spectrum antibiotics may reduce the extent and severity of outbreaks of bacterial pneumonia.