Eperythrozoonosis (Mycoplasma suis infection)

Occurrence: North America, Europe, Taiwan, Japan, China.
Age affected: Newborn, piglets pre-weaning, weaners (growers/ finishers, sows, boars)
Causes: Bacterium - Mycoplasma suis; biting insects, dirty needles.
Effects: Pale skin, fever, jaundice, poor growth, infertility.

Causes

The causal agent of eperythrozoonosis is the bacterium Mycoplasma suis, but the disease is still often referred to as eperythrozoonosis. M. suis is rod-shaped, coccoid or ring-like and is located on the membrane of the red blood cell.

This unusual habitat means that it cannot be grown in the laboratory at present and many aspects of its biology are not yet clear. Infection is oral or by injection of the organism. After infection, M. suis begins to multiply and causes disease in as little as 5-6 days. At the onset of clinical signs, up to 80% of the red blood cells are infected. M. suis causes increased fragility of the red blood cell membranes leading to their breakdown, which results in anaemia and mild jaundice.

The organism metabolises blood glucose very quickly and low blood glucose levels develop during infection because the consumption of blood glucose exceeds the rate at which it can be formed or released into the blood. Levels of liver enzymes and bilirubin (a breakdown product of haemoglobin from the red blood cells) rise and clotting of the blood within the blood vessels occurs. Recovering pigs develop antibodies, with a peak which lasts 2 months. PRRS may be a predisposing factor.

Mode of transmission

Infection can be transmitted to non-immune pigs by bites from lice (Haematopinus suis), mosquitoes (China), infected needles, rough handling (nasal snares) and the ingestion of blood, urine or secretions containing M. suis. In utero transmission has been described. Infection is usually introduced to a farm in carrier pigs.

There is clear evidence that administration of corticosteroids increases numbers of the organism in the blood. Haemoplasma (M. suis) from human infections in China have been found to resemble closely M. suis from pigs. Antibody to the organism is more common in pig keepers than in controls elsewhere in the world.

Clinical signs

Neonatal pigs 0-5 days of age become pale and may be jaundiced and then recover leaving the animals uneven in size. In weaned pigs, varying degrees of unthriftiness, jaundice (with raised blood bilirubin) and anaemia occur. The tips of the ears may be cyanotic (blue) and mottled. In sows these signs are accompanied by fever (40-41.5°C, 104-107°F) and oedema with effects on reproduction such as abortion and an increase in stillbirths. Infection may be sub-clinical.

Eperythrozoonosis is suspected when piglets or older pigs appear pale, jaundiced, or where sows develop fever, oedema and abort or produce excessive stillbirths. Confirmation is by laboratory means. The organisms are demonstrated on the surface of red blood cells in stained blood smears, particularly at the onset of clinical signs.

Blood films should be made directly when blood is taken for best results. The Polymerase Chain Reaction for the DNA of M. suis is increasingly used for confirmation of infection. Antibody can be detected, using whole organisms or recombinant proteins in an ELISA test. Serology detects herd infection but is unreliable for individuals.

Postmortem lesions

Dead piglets are anaemic with watery blood, icterus (jaundice) of the carcase, enlargement of the liver and spleen and fluid in all body cavities with reddening of the bone marrow. These findings reinforce the suspicion of eperythrozoonosis. Confirmation is by laboratory means.

Treatment and prevention

Tetracyclines should be given to affected animals by injection, or orally to infected animals at risk of disease for 14 days. This will eliminate disease but no infection in all cases. Symptomatic treatment may also be required.

Control is based upon reducing exposure of susceptible pigs to the blood of infected animals. Control of lice and the use of clean syringes for each animal may reduce transmission by the parenteral (injection) route. Transmission in utero can only be prevented by treatment of the pregnant sow with antimicrobials such as the tetracyclines.

Special note

The organism is closely related to one found in humans.