By Dr Peter Evans (on behalf of the Pig Vet Society)
Glässer’s disease is caused by bacteria known as Haemophilus parasuis (HPS). More than 15 different strains of HPS have been identified. The most obvious signs of HPS infection are fibrinous serositis (typical straw coloured fluid with strands of fibrin) and polyarthritis.It is important to note that HPS is often “found” as part of the normal bacterial flora of pigs in the absence of any pathological conditions. HPS is found in all pigs, including SPF/high health herds.
The bacteria are found mainly in the upper respiratory tract (nasal cavity). Very rarely will HPS be found in normal healthy lungs, but is often isolated when enzootic pneumonia infection or other respiratory pathogens, occurs. This would suggest that HPS is an opportunistic cause of lung infections.
The virulence of strains varies and there is evidence of cross-immunity between strains. I.e. less virulent strains may protect pigs from infections/disease caused by more virulent pathogenic strains.
Endemically infected sow herds pass passive immunity onto their piglets which protects them from disease for up to 12 weeks. An active immunity to HPS will develop in piglets should they still be protected by passive immunity and if there is sub-clinical infection.
Classically disease occurs in pigs two weeks old to four months of age. Disease in younger piglets would be associated with a failure in transfer of maternal immunity and in older piglets with a failure to produce active immunity.
Understanding the need to have a strong immunity both passive and active, can explain why the disease seems cyclical in some units. As the number of infected animals decreases over time the level of stimulation of the immune systems declines and consequently the level of immunity to HPS reduces.
At some point there will be pigs with no protection while others are carrying the disease. Should the carriers become stressed or infected with other diseases they begin shedding more HPS’s, infecting naïve pigs and an outbreak of Glässer’s flares.The outbreaks seen on SPF/high health farms as a result of low levels of innate immunity are often far worse than on conventional health farms.
It is also common to find that piglets born from gilts are more vulnerable.
Pathogenesis and clinical signs
Following a compromise in the immune status of pigs in particular some stressful event like weaning, transport, diet changes, temperature changes, ventilation failures, the HPS organism will get into the blood (=septicaemias develops) and settle on the membranes of joints and cavities (abdominal, chest and heart).
Following the colonisation of the bacteria disease follows rapidly. Affected pigs become depressed, feverish and reluctant to move (joint pain), struggle to breathe and sometimes show nervous symptoms.
The damage caused to lungs, pericardium (heart sac) lead to oxygen depravation with bluish colour being seen on ears, snouts and limbs. Death follows quite rapidly thereafter.
In some cases a chronic form of the disease may be evident which is characterised by poor growth and pale piglets. However, often due to pericarditis development these animals often die suddenly when stressed.
Post mortem signs include fluid filled cavities with fibrin strands in a straw coloured fluid.Diagnosis should be confirmed by bacterial isolation to differentiate from other diseases with similar symptoms. These include other septicaemic diseases like streptococcal infections, enterotoxaemic E. coli and acute erysipelas. Chronic Arthritis caused by Mycoplasma hyosynoviae is often diagnosed as Glässer’s — proper bacterial isolation and post mortems is necessary to differentiate.
Treatment and prevention
HPS are sensitive to a wide range of antibiotics including Penicillin’s, tetracyclines and sulphonamides. It is important to begin treatment of the group of pigs affected as early as possible due to the acute nature of Glässer’s disease.
Should the disease be a problem in suckling pigs — treatment is aimed at reducing the bacterial load in sows by treating them in-feed. Should the disease be a problem post-weaning preventative in-feed medication regimes should be followed. Vaccines are now commercially available and offer an alternate to antibiotics for the long term control.
Stress is a particularly important initiator of Glässer’s disease in the just weaned pig (as with many other diseases); the attention to facilitating weaning cannot be overemphasised.
Nicolet J 1992. Haemophilus parasuis. In Diseases of Swine 7th Edition. Iowa State University Press P 526-527.
Muirhead M, Alexander T 1997. Glässer’s Disease. In Managing pig Health and the Treatment of disease. Sheffield, UK, 5M Enterprises P 315-316.