Lameness in the nursery and respiratory problems or polyserositis can be caused by M. hyorhinis. Strains of M. hyorhinis can be isolated from joints, brain, liver, conjunctivae, tonsils, pneumonic lung tissues and nasal cavities.
M. hyorhinis infections are transmitted to young pigs from infected sows in farrowing pens or from older pigs in nursery and grower units. Disease commonly occurs between 3-10 weeks of age but may occasionally occur in older pigs. Mortality is lower than 10% but chronic disease has a negative effect on growth performance.
The clinical signs begin 3-10 days after exposure or stress. Slight fever is present for 4-5 days and pigs show a moderate reduction in appetite, are unwilling to move and have a low growth rate, roughened hair coat, huddled appearance, difficulty breathing and unusually no coughing. The joints are swollen from polyarthritis which causes lameness and some pigs may be affected for up to 6 months. Lameness and swollen joints in young pigs may also be caused by Streptococcus suis and Haemophilus parasuis infection.
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