What is Mycoplasma suis disease in pigs? How to detect it using the Giemsa staining method?

Mycoplasma suis in pigs is the causative agent of infectious anemia, leading to fever, pallor, and poor growth. Join Fivevet to explore the clinical signs, pathogenesis, and effective detection methods using Giemsa staining in veterinary diagnosis. 1. What is Mycoplasma suis disease in pigs?
Haemoplasma, also known as blood-parasitic Mycoplasma, is a group of very small bacteria with diverse shapes and no cell wall. They live parasitically by attaching directly to the surface of the host’s red blood cells.
Although they are commonly referred to as “blood parasites,” biologically, Haemoplasma belongs to the Mycoplasma group of bacteria and is not classified as a parasite in the classical biological sense.
Haemoplasma bacteria are highly adapted to the blood environment and are closely dependent on the host. Glucose metabolism in the blood is believed to be their main source of energy. To date, parasitism outside the circulatory system has not been reported.
Many species of Haemoplasma have been identified in different mammals, including livestock, wild animals, and humans. In pigs, the main Haemoplasma species include:

• Mycoplasma suis
• Mycoplasma parvum
• Candidatus Mycoplasma haemosuis

2. What disease does Mycoplasma suis cause in pigs?
Mycoplasma suis (M. suis, formerly known as Eperythrozoon suis) belongs to the genus Mycoplasma and is a hemotropic (blood-parasitizing) bacterium. It is spherical or oval in shape, with a size of approximately 0.8–2.5 µm, and can be observed under a light microscope using oil immersion (1,000× magnification).
M. suis primarily survives by attaching to the surface of red blood cells. To date, it has not been successfully cultured in artificial media and can only grow in live pigs. Due to this characteristic, it is classified as a hemotropic bacterium.
Mycoplasma suis is the causative agent of Infectious Anemia in Pigs (IAP). The disease affects pigs of all ages, including weaned pigs, growing-finishing pigs, gilts, and sows. It can lead to anemia, jaundice, coagulation disorders, and hemorrhage.
3. Clinical signs and pathology of Mycoplasma suis infection in pigs
Mycoplasma suis infection can present in two main forms: acute and chronic, with severity depending on the pig’s immune status and management conditions.
3.1. Acute form
In the acute phase, M. suis causes infectious anemia with the following typical signs:
- Pale skin and mucous membranes, jaundice due to intravascular hemolysis.
- Subcutaneous hemorrhages, urticaria (skin rash).
- Necrosis and cyanosis in ears, tail, and peripheral areas.
- High fever, lethargy, reduced feed intake, increased respiratory rate.
In breeding sows, the disease may also cause:
- Lactation disorders.
- Reproductive cycle disturbances.
- Abortion.
The acute form often occurs during stressful periods such as weaning, farrowing, or regrouping, and may lead to mortality in piglets.
3.2. Chronic form
In the chronic phase, clinical signs are usually mild or subclinical:
- Persistent mild anemia.
- Low bacterial load in the blood.
- Reduced growth rate and decreased production performance.
Chronic M. suis infection increases the risk of secondary enteric and respiratory diseases, reduces average daily gain, lowers slaughter weight, and decreases birth weight of piglets.
4. Transmission routes of Mycoplasma suis in pig herds
Haemoplasmas are primarily transmitted through blood. In pigs, the main transmission routes include:
- Fighting between animals.
- Reuse of needles.
- Management practices such as castration and tail docking.
- Transmission via blood-sucking insects such as lice, horseflies, and mosquitoes.
- Vertical transmission from sow to piglet.
5. Diagnosis of Mycoplasma suis infection in pigs
Diagnosing Mycoplasma suis (Haemoplasma) infection is challenging due to its unique biological characteristics. Currently, the main diagnostic methods include:
5.1. Bacterial culture
To date, porcine Haemoplasma cannot be cultured under in vitro conditions. Animal experimentation is the only way to propagate the organism, but this is not practical for routine diagnosis.
5.2. Microscopic examination
Since culture is not possible, examination of stained blood smears is the traditional and commonly used diagnostic method in practice.
The most commonly used staining method is Giemsa staining. Depending on the stain and pH, Haemoplasma can be observed with the following characteristics:
- Small dots or clusters.
- Light red to reddish-purple color.
- Attached to the surface of red blood cells or found free in the plasma.
5.3. Molecular methods
Conventional PCR and quantitative PCR (qPCR) are widely used to directly detect the pathogen in blood samples by amplifying specific Haemoplasma genes.
5.4. Serological methods
Currently, serological methods are not widely applied in field diagnosis due to the lack of commercially available ELISA kits for detecting antibodies against M. suis.
6. Giemsa staining procedure for blood smears to detect Mycoplasma suis
6.1. Principle of Giemsa staining
Cells are spread as a thin smear and fixed onto a glass slide using absolute methanol. Cellular components such as the membrane, cytoplasm, and nucleus take up the Giemsa stain differently, allowing visualization of hemotropic bacteria under a microscope.
6.2. Indications
- Blood smears.
- Biological fluid smears (bronchial fluid, serous fluids, peritoneal fluid, etc.).
6.3. Equipment and reagents
- Pipettes and tips.
- Clean glass slides.
- Stock Giemsa stain.
- Phosphate buffer solution (pH 6.8).
- Absolute methanol.
- Distilled water.
6.4. Giemsa staining procedure
Step 1: Fixation
Fix the blood or biological fluid smear with absolute methanol for 1–3 minutes, then allow it to air dry.
Step 2: Staining
Place the slide on a staining rack and cover the entire smear with diluted Giemsa solution (5–10%) prepared in phosphate buffer (pH 6.8).
Staining time:
20–30 minutes for blood smears.
30–45 minutes for biological fluid smears.
Step 3: Rinsing
Gently rinse under running water.
Note: Do not discard the stain before rinsing, and avoid directing a strong stream of water directly onto the smear surface.
Step 4: Drying and examination
Allow the slide to air dry, then examine under a light microscope using oil immersion (×1000 magnification). 6.5. Interpretation of results
- Acute form: Mycoplasma suis appears in high density, densely attached to the surface of red blood cells, and may cause deformation of erythrocytes.
- Chronic form: The bacteria appear sparsely with low numbers. Red blood cells are damaged and show weaker staining. This article was prepared by FiveLab – the Veterinary Diagnostic, Testing and Inspection Center under Central Veterinary Medicine Joint Stock Company No. 5 (Fivevet).
 
Frequently Asked Questions:
1. What is Mycoplasma suis?
Mycoplasma suis is a blood-parasitizing bacterium in pigs that attaches to the surface of red blood cells and causes infectious anemia. It was previously known as Eperythrozoon suis.
2. What are the clinical signs of Mycoplasma suis infection in pigs?
Infected pigs may show anemia, pale skin, jaundice, fever, rapid breathing, and lethargy. In severe cases, subcutaneous hemorrhages and cyanosis of the ears and tail may occur. In sows, it can also cause abortion, reduced milk production, and reproductive disorders.
3. Can Mycoplasma suis be cultured in the laboratory?
Currently, Mycoplasma suis cannot be cultured under artificial conditions. The bacterium only grows in live pigs, so culture is not used for routine diagnosis.
4. Why is Giemsa staining used to detect Mycoplasma suis?
Since the bacterium cannot be cultured, Giemsa-stained blood smears are a traditional method that allows direct observation of M. suis attached to red blood cells under a microscope.
5. How does Mycoplasma suis affect pig productivity?
The disease leads to reduced growth rate, poor weight gain, decreased reproductive performance, and increased susceptibility to secondary infections, resulting in significant economic losses for farmers.