This swine pneumonia is important because it is difficult to raise pigs free from the organisms which cause the disease, it has been reported to occur wherever pigs are raised throughout the world, and it adversely affects feed intake and growth performance. This disease affects many pigs but does not cause many deaths unless severe secondary infections or complicating diseases occur. It has been called many different names including mycoplasmal pneumonia, mycoplasmal induced respiratory disease, enzootic pneumonia, and others. This pneumonia is a disease complex caused by Mycoplasma hyopneumoniae and made worse by Pasteurella multocida. Both of these organisms are very commonly isolated from the lungs of pigs. Pasteurella is easier to isolate and identify in the laboratory. Whenever mycoplasmal pneumonia is discussed in swine herds, the reality is that both mycoplasmal and pasteurella are present and involved in the disease.
The economic significance of mycoplasmal and pasteurella pneumonia is difficult to determine exactly. Estimates in the U.S. swine industry including reduced daily weight gain and antibiotics used to treat the disease are estimated to be $300,000,000 annually. Cost of pig deaths are not included in this number. A 1984 study showed that in 315 slaughter examinations of 9500 pigs, 99% of the herd and 70% of the pigs had pneumonia lesions typical of mycoplasmal pneumonia.
Coughing is the initial clinical sign noted in pigs with the disease. The cough is described as a dry, non-productive cough. Not all pigs in a pen will cough at once, but several may start to cough with others coughing in nearby pens. As pigs become sick, they eat less feed. This drop is difficult to detect because not all pigs are sick at once. As these pigs recover and start to eat, other pigs start to cough and they also decrease their feed intake. Some pigs that suffer serious secondary infections may thump or breathe with difficulty. These pigs require individualized treatment such as injections of antibiotics and isolation in a separate pen. Increased variation in growth results in uneven-sized pigs of the same age, or thin and small pigs. These pigs present a problem at the time of marketing since buildings are emptied to achieve all-in, all-out production.
Mycoplasma hyopneumoniae and Pasteurella multocida are spread from sows to piglets and from older pigs to younger pigs in finishing units. Pneumonia is worsened by daily temperature fluctuations, inadequate ventilation resulting in an accumulation of pig gases inside buildings, too much dust, too much humidity, moving and mixing of pigs resulting in fighting, continuous flow of pigs through buildings, and overcrowding. Daily observation of pigs and prompt treatment of sick pigs can decrease the severity of pneumonia.
Mycoplasmal pneumonia is diagnosed by routine slaughter examination of lungs. Lesions of mycoplasmal pneumonia are observed and lung samples can be taken and sent to specified diagnostic laboratories for confirmatory tests. Culture of lungs from a slaughter exam are less than ideal because the lung has been contaminated by scald vat water. Pasteurella multocida has been recovered from slaughter specimens, but mycoplasma is more difficult to isolate. Care must be taken not to overinterpret slaughter results because lung lesions will heal and become smaller as pigs age. Therefore, determining the economic effect of the disease on a herd is hard to do with slaughter examination. Serologic tests are available to detect antibodies against Mycoplasma hyopneumoniae. The tests include the enzyme-linked immunosorbent assay (ELISA), the complement fixation test, and the indirect hemagglutination test. These tests are best applied to herds of swine and not just to individual pigs.
Treatment and control of mycoplasmal pneumonia includes management, treatment, vaccination, and newer methods to eliminate the disease causing organisms. Treatment of affected pigs by antimicrobials in feed is limited with only lincomycin approved for sue in swine. Since the extra label drug usage policy does not apply to feed additives, other drugs are not available to use in feed. Vaccines for mycoplasmal pneumonia are commercially available. Medicated early weaning (MEW) is a method to obtain pigs free from mycoplasmal pneumonia which have been born to sows infected with the disease. Early studies indicated that it may be possible to achieve this goal. Health control programs such as specific pathogen free and others in Europe and the United Kingdom have attempted to raise pigs free from mycoplasmal pneumonia; however, many herds become reinfected with the disease at a later date.
All-in, all-out production from birth to market is a management scheme to control mycoplasmal pneumonia. This system does not eliminate the disease, but improves feed intake, feed conversion, daily weight gain, and lung lesions detected at slaughter. Mycoplasmal pneumonia is a challenge because once a herd is infected with the disease, it remains infected. Usually the herd health becomes worse over time as other diseases also infect the herd and complicate mycoplasmal pneumonia. Methods to control mycoplasmal pneumonia will not eliminate the disease unless a more aggressive method is adopted such as depopulation and repopulation or MEW. Theses should not be used without considering the location of the herd and assessing the risk of reinfection.
The take home message on mycoplasmal pneumonia is that it is difficult to raise pigs free from this disease. Mycoplasmal pneumonia actually is a disease caused by Mycoplasma hyopneumoniae but made worse by Pasteurella multocida. both organisms are present in most commercial and seedstock herds. Mycoplasmal pneumonia affects many pigs, but usually does not kill pigs. Only pigs which become overwhelmed by secondary infections or multiple diseases will die. The questions to ask is "how much is mycoplasmal pneumonia costing me?" This is difficult to answer in most herds, but the number of pigs coughing, the number of pigs requiring treatment, the treatment costs, days to market weight, variation in pig growth, and lung lesions at slaughter provide some information about the herd's status. Measuring the affects of the disease on feed intake, feed conversion, and daily weight gain offer economic information as to the affect of the disease on herd profitability. Thorough and ongoing diagnosis with help from a qualified diagnostic laboratory is essential to monitor other diseases which may complicate the pneumonia, and decrease the herd's profitability.