Age affected: Weaners, growers/finishers.
Causes: Poor ventilation; chilling; bacterial, mycoplasmal and viral infections.
Effects: Inappetence, fever, cough, breathing difficulty, blue skin.
Pneumonia in pigs is caused mainly by viruses and bacteria, although lungworms can occasionally cause bronchitis. The viral diseases include Porcine Reproductive and Respiratory Syndrome (PRRS), swine influenza (SI), Porcine respiratory coronavirus (PRCv) and Aujeszky’s disease (AD) and the bacteria involved include Bordetella bronchiseptica, Haemophilus parasuis (Glässer's disease), Mycoplasma hyopneumoniae (Enzootic pneumonia), Actinobacillus pleuropneumoniae (pleuropneumonia), Streptococcus suis and Pasteurella multocida.
All can infect the lungs of non-immune pigs and most cause pneumonia alone, and combinations of one or more agents can cause severe disease. Infection is by the respiratory route in all cases, the organism colonising the tonsils (A. pleuropneumoniae, S. suis, H. parasuis), the trachea and bronchi (B. bronchiseptica, M. hyopneumoniae and swine influenza virus) and the lung. Those colonising the lung cause pneumonia directly by attacking the lining of the delicate alveoli where gas exchange takes place or the cells defending the lung, allowing organisms such as P. multocida to colonise.
Those in the trachea and bronchi paralyse the mechanism for expelling fluid and allow the accumulation of secretion and pus in the dependant portions of the lung in bronchopneumonia (as in enzootic pneumonia). As less lung is available, respiratory rates rise to maintain the animal.
Mode of transmission
Most pneumonia is caused by specific causal agents. In almost all cases, pneumonia is transmissible from pig to pig by aerosol, contact with other pigs and the oronasal route, with some infection possible from contaminated water, feed, clothing and implements. The actual mode of transmission and the mode of transmission from farm to farm depends upon the agent. In the case of some pneumonias where more than one agent is present (such as the Porcine Respiratory Disease Complex, PRDC), some of the organisms involved may be common inhabitants of the upper respiratory tract such as Pasteurella multocida, and this organism is capable of colonising damage caused by a number of primary agents.
Pigs with pneumonia may appear normal. Enzootic pneumonia is common, yet clinical signs are confined to coughing when roused and depression of weight gain in immune herds. In non-immune herds, even adults may develop severe pneumonia and some may die. The clinical signs of pneumonia include a rise in respiratory rate. This increases still further when pigs move or run and may become so severe that the animal resorts to mouth breathing in order to get air (severe pleuropneumonia). If the animal is restrained at this point, then exercise intolerance develops and pigs cannot pull away if held. Affected pigs are often recumbent and reluctant to rise.
They are often fevered and appear reddened. They may bury themselves in straw if this is present and become inappetent or even fail to drink (pleuropneumonia). Pneumonic pigs often lose condition rapidly as the energy needed to gain air is considerable, food intake has fallen drastically and the damage to the lungs leads to increased load on the heart, gradual heart failure and congestion (blue/purple colour) of the extremities. The condition may resolve completely (Swine Influenza), result in permanent lung damage (pleuropneumonia) or progress to death, sometimes with froth on the lips (pasteurellosis, pleuropneumonia).
Pneumonia should be considered when pigs go off their feed, fail to keep up with the group or lose condition.
Coughing is common and is most obvious early in the morning. Affected pigs may have reddened skins and raised respiratory rates. Their sides may heave when they are required to move far and on holding they may not have the energy to pull away. Rectal temperatures are often raised, but any fever may lead to a raised respiratory rate and respiratory disease must be confirmed. Harsh lung sounds, bubbling sounds and tracheal sounds can all be heard using a stethoscope, but pigs squeal loudly, making listening difficult. Diseases which cause pneumonia may have clinical signs which enable them to be distinguished.
Postmortem examination of pigs on farm, or of lungs at slaughter, confirms that pneumonia is present and can give an estimate of its identity and its extent. In conditions such as pleuropneumonia, the lungs are weighed and in enzootic pneumonia, the lung can be mapped and the extent of the damage related to likely production losses. The agents present can be confirmed by laboratory tests on affected lung or by the presence of serum antibody in recovered pigs.
Treatment and prevention
Treatment of pneumonia is possible when bacteria are involved but not when it is caused by viruses. However, bacteria colonise some viral diseases and recovery may be faster if antimicrobial treatment is given.
Seriously ill animals (pleuropneumonia) do not eat or drink, so antimicrobials must be given by injection, but it is most common to treat groups in water or feed. Mycoplasmas require tiamulin, valnemulin, lincomycin or fluoroquinolone and B. bronchiseptica requires antimicrobials which reach it on the bronchial epithelium such as trimethoprim sulphonamide. Ceftiofur is of value for pleuropneumonia and penicillins for streptococcal pneumonia.
Affected animals should be supported with warmth, space, feed and water and destroyed if they do not recover. Control of respiratory disease is best carried out by vaccination, and vaccines are now available for most of the diseases listed. Management by using all-in, all-out systems can reduce the level of pneumonia markedly and treatment of animals into airspaces can also reduce its severity and extent.
The easy transmission of pneumonias within a herd may make control difficult, but depopulation and restocking can eradicate most respiratory disease. Maintenance of the pigs in isolation with the purchase of disease-free breeding stock should prevent the appearance of most pneumonias.