Clinical importance

Mycoplasma suis used to called Eperythrozoon suis until a few years ago. M. suis is a sporadic cause of anemia in growing pigs. Clinical presentation is rare unless the infection is associated with another infectious outbreak.

Etiology

Mycoplasma suis  causes the destruction of erythrocytes by damaging them while its binds to their surface. Additionally, it has been shown that the pathogen can invade the red blood cell and escape the immune response of the host. Growing pigs between 2 and 8 months  are most at risk of being infected. Most of the animals stay subclinical unless a co-infection with another pathogen or a stressful event occur. Transmission is most often direct from licking open wounds or cannibalism but indirect transmission through vectors such as biting insects and needles is also possible.

Associated symptoms

Mycoplasma suis infection can cause both an acute disease and a chronic infection.

An acute infection by M.suis displays signs associated with severe hemolysis. Affected pigs are pyretic, anorexic, restless and pale. They may show signs of icterus or cyanosis of the extremities such as the ears. Mortality can be seen but is rare if there is no co-infection.

A milder form of the disease is more common and uncharacteristic. Non-thrifty pigs which might appear more pale than usual or yellowish are the main clinical signs.

Poor reproductive performances associated with a low quality of lactation can be seen in affected sows.

Associated lesions

Macroscopic lesions

Pale tissues are often the only sign seen at necropsy. In chronic cases, icterus of the body is more evident and the spleen appears enlarged due to the increase in erythrocyte production.

Microscopic lesions

Mycoplasms can be seen on the surface of erythrocytes on a blood smear.

Diagnosis

Clinical signs and lesions are indicative of the disease. Whole blood collected in a tube with anticoagulant is the sample of choice. PCR and ELISA have been developed but may not be available for routine analysis. In this case, a simple blood smear can be used to identify the pathogen on the surface of the erythrocytes.

Differential diagnosis

Causes of anemia such as gastric ulcers, whipworms, iron deficiency should be considered.

Treatment, Prevention and Control

Antibiotic treatments using molecules such as tetracyclines can be used to treat affected animals. However, tetracyclines will not be able to reach M.suis inside of the red blood cell.

Preventing co-infection with pathogens such as Salmonella choleraesuis or PCVAD and limiting should help prevent a clinical outbreak. A large number of IM injections, stress, high stocking density, external parasites are risk factors to consider.