Arthritis is inflammation of the joints and is usually caused by bacterial infection. The condition occurs in pigs of all ages. Neonatal pigs may develop joint illness caused by Streptococcus suis type 1 and later at 3 weeks of age may be infected with Mycoplasma hyorhinis or Haemophilus parasuis (as a form of Glasser's Disease). Weaned pigs may develop arthritis due to Streptococcus suis type 2 and in some cases, Staphylococcus hyicus may be present. As pigs grow Mycoplasma hyosynoviae become more important as a cause of arthritis and finally in heavy finishers, gilts and adult breeding stock arthritis is often caused by Erysipelothrix rhusiopathiae or E. tonsillarum during erysipelas.
Arthritis arises when the joints which are sterile are invaded by bacteria from the bloodstream during disease and multiply to cause inflammation. The joint fluid increases in volume and contains inflammatory cells and there may be inflammation (synovitis) of the lining of the joint capsule (the synovium). The inflammation gives rise to heat in the joints the increase in fluid gives rise to swelling and pain leading to lameness. Arthritis heals gradually as the body's defenses eliminate infection but may remain chronic.
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The first signs of arthritis are usually reluctance to rise or lameness. Affected pigs are often lying down and require considerable disturbance to make them rise. Some may even shuffle on their knees rather than walk. They tend to stand with head held down and back arched. When they move they may use an affected leg less because of the pain from the affect joint and are lame. Badly affected animals may be unable to eat or lose condition because of the pain and even mildly affected animals may not grow at the same rate as unaffected littermates.
Arthritis may affect a single joint or a number of joints (polyarthritis). Examination of the affected leg or legs confirms the presence of arthritis. The affected joint will be swollen and painful if the disease responsible is active and will be hot to the touch. The animal may be fevered. Where the condition has been present for some time the joint may no longer be hot although it remains swollen and painful. Complete recovery can occur. Animals which have had chronic arthritis may have sores or calluses on their limbs where they have been lying or have unevenly worn horn on their hooves.
Arthritis must be suspected when lame animals are seen. They should be caught and the lesions felt carefully. In most cases the presence of heat and swelling in a joint is sufficient to suggest arthritis but arthritis of the hip and should joints cannot always be felt in well muscled pigs. In chronic disease the pain and some difficulty in flexure persist but the heat and swelling have subsided. The presence of arthritis may be confirmed in the live pig by taking a sample of the joint fluid (synovial fluid) which will contain pus and is often under pressure. More recently ultrasound has been used to identify arthritis in valuable animals. At post-mortem examination arthritic joints are swollen and when cut there is pus in the joint cavity in the early stages. The pus varies in amount color and consistency but its presence confirms that there is arthritis. The nature of the joint changes can provide some idea of the organism involved but this is determined by laboratory means usually by cultivating the organism concerned from the fluid. The presence of diseases such as erysipelas and Mycoplasma hyosynoviae infection can be confirmed using blood tests for antibody.
Treatment and control
Arthritis caused by bacteria can be treated successfully in pigs using antimicrobials given at an early stage of the disease. Once the infection has produced irreversible changes antimicrobial treatment may eliminate the bacteria but not cure the condition completely. Supportive treatment such as the use of corticosteriods and non-steroidal anti-inflammatories can improve the speed of cure and help control pain but few are available for pigs used as food animals. The treatments used vary with the disease. In erysipelas or streptococcal arthritis penicillin given by injection is rapidly effective but in mycoplasma arthritis linocmycin or tiamulin may be used. Arthritis may be prevented by protection against the specific diseases causing it. Regular vaccination protects against erysipelas arthritis in breeding stock and vaccination protects against Glasser's disease in younger pigs. Antibiotic treatment programs can protect against S. suis type 2 and prompt treatment of a litter may prevent the development of S. suis type 1 in piglets once the first case has been seen Where damage to feet and joints make arthritis more likely to follow bacterial infection (joint ill in piglets and mycoplasmal arthritis in finishers) correction of faults in flooring may contribute to control.