October 10, 2019
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Successful elimination of Mycoplasma hyopneumoniae (M. hyo) from a herd is often driven by sow farm status, according to Alyssa Betlach, DVM, Swine Vet Center. Betlach has researched M. hyo for several years in a PhD program at the University of Minnesota.
Within the industry, M. hyo continues to be a prevalent and economically important respiratory pathogen worldwide. Studies have shown that the disease can add $3 to $10 per pig due to decreased animal performance, including longer time to market and increased antimicrobial usage, she added.
Traits of M. hyo
Three unique features of M. hyo must be considered when developing a control plan. First, piglets are not born with M. hyo but often are colonized from their mothers, who shed it during farrowing. The bacterium colonizes in the lungs of the pigs and causes clinical signs in grow-finish due to the slow, chronic nature of the infection.
Second, M. hyo primarily resides in the respiratory tract by adhering to lung cilia. Therefore, “When you think of diagnostics and sampling, you need to consider that it resides deep in the lung,” Betlach said.
Third, shedding from M. hyo has been shown to last up to 240 days and transmission is very slow. One pig needs 4 to 6 weeks to transmit the disease to another pig versus the flu that is transmitted from one pig to 14 others in a 2-week period.
Elimination starts on sow farm
Current elimination programs have successfully removed M. hyo from many herds. But the methods for elimination continue to improve by focusing on gilt acclimatization and sow farm stability.
“We need to think about negative gilts,” Betlach said. “If you have a positive farm and you constantly bring in negative gilts, you are adding wood to that fire. Therefore, we need to think of ways to address this.
“Gilt acclimatization is something we should think about,” she continued. “Gilt acclimatization strategies are designed to stabilize the sow herd by promoting ways to minimize shedding at farrowing.”
Acclimatizing gilts
Three types of gilt acclimatization are used, namely vaccination, natural exposure and exposure using a herd-specific lung homogenate. Vaccination for M. hyo is commonly practiced as it can reduce the bacterial load and clinical severity. However, M. hyo vaccination does not prevent colonization and has minimal effect on altering transmission.
Natural exposure through the introduction of M. hyo-positive culls into a gilt development unit has been performed. However, this approach is less than ideal in larger herds, as it takes a long time for adequate exposure and requires a high number of positive culls. Studies have shown that it takes one positive cull to one or two gilts for successful exposure within a 4-week period.
Exposure using a herd-specific, M. hyo-positive lung homogenate has been performed in the field, via intra-tracheal or aerosol techniques. Intra-tracheal exposure is a more labor-intensive method and may not be as feasible in large populations, as approximately 50% to 70% of the herd will need to be exposed to be successful. Therefore, aerosol exposure using foggers has been explored. Recently, this method has been shown to be successful for M. hyo exposure while being more feasible to perform.
Diagnostics for M. hyo
Several sample types are used for the detection of M. hyo. It is important to consider the overall goal that you are trying to achieve, as this will determine what sampling method should be used.
“Serum is commonly used, and the cost is relatively low,” Betlach said. “This sample type is used to detect the presence of M. hyo antibodies and it is easy to collect. However, the ability to interpret diagnostic results can be difficult, especially in vaccinated herds as the presence of antibodies from the vaccine or infection cannot be differentiated.”
Other sample types, such as oral fluids, laryngeal swabs and tracheal sample, are used to detect the presence of M. hyo infection. Oral fluid samples are easy to take, and the results are easy to interpret, in most conditions. Oral fluid samples work best in chronic situations but are not sensitive enough to detect the pathogen in an acute infection.
Laryngeal swabs, which are convenient, require some employee training. Positives can be obtained at 7 to 14 days after infection, Betlach said. In comparison, tracheal samples appear to be more sensitive in acute and chronic situations. This sample type also requires additional training as false-negative results from poor sampling technique can occur. Due to their sensitivity, Betlach uses tracheal samples in elimination strategies.
“Diagnostics have improved over the years,” she added. “For M. hyo detection, it is critical to think about what sample type you are going to use and the time of infection, and to understand the question you want to answer.”