Glaesserella parasuis is a common gram-negative bacterium found in swine populations worldwide. It was formerly known as Haemophilus parasuis until its renaming in 2020. This organism maintains a dual existence, acting as both a commensal, naturally present in the upper respiratory tract of healthy pigs, and a pathogen, capable of causing disease under certain conditions.
This bacterium can colonize piglets as early as two days after birth, residing in the trachea, nasal passages, or tonsils. While many pigs carry G. parasuis without showing signs of illness, specific strains can become virulent. The onset of disease often occurs when pigs experience stressors that compromise their immune system, allowing the bacteria to proliferate and spread beyond the respiratory tract.
Clinical Manifestations
The primary disease caused by Glaesserella parasuis is Glasser’s disease, also known as porcine polyserositis or infectious polyarthritis. This condition is characterized by systemic inflammation of the serous membranes. Affected pigs often develop polyserositis, an inflammation of membranes surrounding the lungs (pleuritis), heart (pericarditis), and abdominal organs (peritonitis).
In addition to polyserositis, pigs commonly exhibit polyarthritis, which is inflammation of multiple joints. This leads to noticeable lameness and swollen, painful joints. Neurological signs can also manifest due to meningitis, an inflammation of the membranes surrounding the brain and spinal cord. These signs include tremors, incoordination, and a recumbent posture.
Pneumonia, an inflammation of the lungs, can also occur. Other general clinical signs of Glasser’s disease include high fever, loss of appetite, depression, and in acute cases, sudden death. The severity and specific combination of symptoms can vary depending on factors such as the pig’s age, the virulence of the particular G. parasuis strain involved, and the presence of environmental stressors or co-existing infections.
Transmission and Identification
Glaesserella parasuis primarily spreads among pigs through direct contact and airborne transmission. This occurs via nose-to-nose contact, as well as through aerosol droplets released during coughing and sneezing. Healthy carrier pigs, which harbor the bacterium in their upper respiratory tract without showing symptoms, play a significant role in transmitting the organism within and between herds. These carriers can shed the bacteria in their nasal discharge for up to six months.
Outbreaks of Glasser’s disease are frequently triggered by various forms of stress that can compromise a pig’s immune system. Common stressors include mixing pigs from different sources, transportation, sudden environmental changes such as temperature fluctuations, overcrowding, and concurrent infections with other swine pathogens like Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) or swine influenza virus.
Diagnosis of Glasser’s disease begins with observing clinical signs and post-mortem findings, but these are not definitive due to symptom overlap with other swine diseases. Laboratory confirmation is essential. Samples collected for diagnosis include joint fluid, cerebrospinal fluid, lung tissue, and serosal swabs from affected areas.
Bacterial culture and isolation of G. parasuis from these samples can confirm its presence, though the bacterium is fastidious and fragile, making successful culture challenging. Polymerase Chain Reaction (PCR) is a widely used and highly sensitive diagnostic technique that detects the bacterium’s genetic material, even from dead bacteria, making it a reliable method for rapid and specific detection. Serology, which involves blood tests to detect antibodies against G. parasuis, indicates exposure to the bacterium but does not confirm an active infection or identify the specific serovar causing the disease.
Management and Control
Controlling Glaesserella parasuis infections involves a combination of preventive measures and prompt treatment strategies. Biosecurity practices are fundamental to limiting the introduction and spread of the bacterium. Implementing all-in/all-out production systems, which involve moving groups of pigs through facilities together and then completely emptying and disinfecting barns before the next group, significantly reduces pathogen transmission. Strict hygiene, proper ventilation, and appropriate stocking densities also help minimize stress and improve overall herd health.
Minimizing stressors for pigs is a key preventive action. This includes reducing stress during weaning, transportation, and environmental changes, as well as preventing overcrowding. Ensuring adequate colostrum intake for newborn piglets provides them with maternal antibodies, offering passive immunity that protects them early in life.
Vaccination is an effective strategy to reduce the incidence and severity of Glasser’s disease. Commercial vaccines are available, and some offer protection against common serovars, such as serovar 5. However, because G. parasuis has multiple serovars, and cross-protection between them can be limited, veterinarians may recommend autogenous vaccines tailored to the specific strains present on a farm. Vaccination programs should be customized in consultation with a veterinarian to ensure effectiveness.
For affected animals, early antibiotic intervention is important for successful treatment. Common classes of antibiotics effective against G. parasuis include penicillin, ampicillin, and ceftiofur, often administered by injection as sick pigs may not eat or drink. However, antibiotic resistance is a growing concern, with multidrug resistance reported in some strains. Therefore, antibiotic sensitivity testing is important to guide treatment choices and ensure the selected antibiotic will be effective against the specific strain causing the infection. Supportive care, such as anti-inflammatory drugs, can also be provided to alleviate symptoms and improve animal comfort.