Nervous and Locomotor Systems

Mycoplasma hyosynoviae

Clinical importance

Mycoplasmas are among the top concerns of the swine industry; different species cause different clinical signs. Mycoplasma hyosynoviae causes arthritis and therefore lameness. It does not appear that there is any cross-immunity between Mycoplasma species, so each is treated as a separate agent. Mycoplasma hyosynoviae is ubiquitous in the US and has been reported in several European countries.

Etiology and transmission

Mycoplasma hyosynoviae is a small bacteria without a cell wall. The bacteria first replicates in the upper respiratory tract of pigs, colonizes the tonsils and can persist there forever. Indeed, asymptomatic pigs can become lifelong carrier. Interestingly, even though the sows can shed Mycoplasma in their oro-nasal secretions, pigs are not infected by the bacteria until they reach 4 weeks of age. At this time, pigs get infected by direct oro-nasal contact. Within 10 days post-inoculation the bacteria travels from the upper respiratory tract to the joints and cause arthritis. The migration mechanism of the bacteria is not currently known but osteochondrosis and trauma seem to be a risk factor.

Which population is more likely to be affected by M.hyosynoviae?

  1. Nursery pigs
  2. Growing-finishing pigs
  3. Adult sows

Associated symptoms

Mycoplasma hyosynoviae can affect pigs anywhere from 10 to 24 weeks of age. While the bacteria first colonizes the respiratory system, no symptom can be seen during this stage. The first of the clinical signs occur once the bacteria has systematically invaded the pig. Affected pigs show rough hair coat, arthritis, swelling of the joints, lameness. Pigs can often be seen sitting down like a dog, their hind legs on the side to relieve some pressure on the joints. Mortality is very low but morbidity can reach 50%. Clinical signs tend to decrease in intensity on their own after 10 days.

Associated lesions

Macroscopic lesions

The affected joints are filled with a yellow to brown, serofibrinous fluid associated with thickening and edema of the synovial membrane. villous hypertrophy on the synoviae.

Microscopic lesions

As a result of arthritis, the cells of affected synovial membranes display hyperplasia and hyperemia. Lymphocyte and macrophage invasion of the peripheral blood vessels can be seen, more severe as the infection becomes chronic.

Which of the following statement is true for M. hyorhinis and not for M.hyosynoviae?

  1. Affected pigs show signs of lameness.
  2. Pigs can be lifelong carrier in the tonsils.
  3. Severe fibrinous adhesions can be found in the thorax of affected pigs.


Clinical signs and lesions can be used to make a presumptive diagnosis. However, identification of the pathogen is the only definitive diagnosis. Swabbing joints from pigs that have been showing signs for three to four days generally produces the best samples. Swabs are then tested via PCR. Culture is challenging as M.hyorhinis tends to overgrow M.hyosynoviae. Serology is not typically used because many animals are subclinically infected.

Treatment, Prevention and Control

M.hyosynoviae is not susceptible to treatment by beta-lactams. Rather, tetracyclines, tiamulin, and lincomycin are common antibiotics used to treat this kind of infection. No effective commercial vaccine has been developed but autogenous ones can be developed. Since the mechanism by which the bacteria becomes systemic is unknown, providing a stress-free environment and limiting the trauma to the joints when picking up the pigs are the best prevention methods. A clean and well-ventilated environment is always good practice.


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Swine Diseases Copyright © by Perle Zhitnitskiy, DVM, MSpVM is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.