Formerly a “fringe” issue, lameness in swine production has become a priority in the face of recent veterinary and producer-driven lameness investigations showing that losses attributable to lameness can reach $23 per growing pig.1 Culls or mortality due to lameness and joint disease can routinely approach 1% to 5% of the total population.2 Thus, lameness presents a considerable financial burden and represents a significant animal well-being and welfare issue. In one investigation, lameness was the third most common cause of antibiotic treatment in finisher pigs.3 Lame pigs have difficulties defending themselves from targeted aggression by pen mates.4 Feed and water intake is reduced due to poor ambulation, balance, and pain.4 Lameness can be due to a single or multiple insults including metabolic bone disease, osteochondrosis dissecans, toxicosis (selenium or zinc), and/or infectious agents (Streptococcus suis, Haemophilus parasuis, Erysipelothrix rhusiopathiae, Actinobacillus suis, M. hyosynoviae, and M. hyorhinis).
Mycoplasma-associated arthritis is of increasing concern to swine producers and veterinarians. M. hyosynoviae and M. hyorhinis cause lameness and arthritis in growing pigs (Figure 1 and 2). Two of the preeminent swine diagnostic laboratories in the world, Iowa State University Veterinary Diagnostic Laboratory and University of Minnesota Veterinary Diagnostic Laboratory, have seen an increase in infectious arthritis due to M. hyorhinis and M. hyosynoviae over the last several years.5,6 The ISU-VDL diagnosed 890 cases of arthritis between 2003 and 2014. Mycoplasma-associated arthritis accounted for an average of 26% of arthritis cases overall all years, with an increasing frequency in recent years, up to 43% (45 of 106) in 2010 (Figure 3). Over the last four years, 9,329 PCR assays have been run to detect M. hyosynoviae and M. hyorhinis at the ISU-VDL costing the swine industry close to $300,000 in molecular diagnostics alone.Figure 3: Frequency of diagnosis of Mycoplasma hyosynoviae and Mycoplasma hyorhinis in cases of swine arthritis submitted to the ISU-VDL between 2005 and 2014.
M. hyosynoviae has an affinity for joints, causing a severe arthritis in pigs more than 10 weeks old.7,8 Clinical signs include soft, non-warm swellings of the tarsal joint in a majority of affected pigs. Affected animals move with great difficulty and lose weight due to inappetence. Disease may affect individual pigs or become an epidemic with 10 to 50% of pigs affected before reaching market weight.9
M. hyorhinis-associated disease has recently been identified as one of the main concerns of the U.S. pork industry10 and has been diagnosed in nearly every production system.11 Unlike M. hyosynoviae, M. hyorhinis also causes a polyserositis and is emerging as an important cause of mortality in nursery pigs (Figure 4-7).12 Most pigs appear to get colonized within one to two weeks post-weaning, with a sharp increase in the percentage of pigs colonized two to three weeks prior to the peak of mortality in the nursery; however, M. hyorhinis has been detected in the nasal cavity of newborn piglets a few hours after birth.13,14
The ISU-VDL diagnosed a total of 2,949 cases of septicemia due to S. suis, H. parasuis, or M. hyorhinis between 2005 and 2014. In 2010 M. hyorhinis accounted for 1.8% (four of 226) of these cases. This percentage has increased in recent years, up to 28% (134 of 606) in 2014 (Figure 8). Similarly, approximately 50% of the cases with polyserositis received at the MN-VDL from September 2009 to May 2010 show involvement of this etiology.15
Figure 4: Pig, heart, fibrinous and fibrosing epicarditis. Figure 5: Pig, peritoneal cavity, fibrinous peritonitis. Figure 6: Pig, heart, fibrinous and lymphoplasmacytic epicarditis. Figure 7: Pig, mesentery, purulent and lymphoplasmacytic mesenteritis. ISU-VDL.
Figure 8: Frequency of diagnosis of Mycoplasma hyorhinis, Haemophilus parasuis, and Streptococcus suis in cases of septicemia submitted to the ISU-VDL between 2005 and 2014.
Research improving diagnosis
Historically, diagnosis of infectious arthritis has focused on postmortem samples that include joint fluid to detect an infectious agent using culture and PCR along with histologic evaluation of formalin-fixed synovial tissue and identification of suggestive lesions. In the next few years, research currently being conducted at ISU College of Veterinary Medicine may provide the protocols necessary for the collection of joint fluid as an antemortem diagnostic sample for culture, PCR and cytology. These protocols will likely decrease the considerable financial burden of lameness in swine production.
Currently, swine producers and veterinarians are faced with the challenge of controlling Mycoplasma-associated arthritis and M. hyorhinis-associated disease without the tools necessary to prevent disease, monitor pathogen circulation or evaluate interventions. Currently, there are no commercially available immunologic assays or vaccines available for either agent despite a considerable need.
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