Haemophilus Parasuis on the Rise


The organism Haemophilus parasuis (HPS) was first reported in 1910 by Glasser. It was associated with fibrinous serositis and polyarthritis. Through the years, it was considered a sporadic disease of high-health pigs.

However, in recent years, it has emerged as a significant bacterial disease. The concurrent emergence of new swine respiratory diseases, such as porcine circovirus-associated disease type 2, influenza viruses and porcine reproductive and respiratory syndrome (PRRS) virus, has contributed to its increased prevalence and severity.

Vaccines, antibiotics and other management strategies have not always been successful in the control of losses due to HPS.

Case Study No. 1

A gilt development facility receives weaner gilts from a breeding stock multiplier unit every nine weeks. The “nursery” is a section of the facility, but possible air exposure to older animals periodically occurs if doors in hallways are left open.

Four to five weeks after delivery, a portion of the pigs developed a mild cough with intense sneezing. Initially, it was suspected that the virus causing inclusion body rhinitis (IBR) was circulating.

However, some affected pigs started to lose weight and needed to be euthanized. Autopsies showed these animals had pericarditis and pleuritis. Diagnostics revealed positive results for HPS, but negative for IBR, swine influenza virus (SIV), PRRS, circovirus and Streptococcus suis.

The remaining animals were injected with a long-acting antibiotic (tetracycline). Subsequent groups were vaccinated for HPS upon arrival and given antibiotics in the water during the challenge period.

Following these treatment steps, minimal clinical disease has occurred and no animals have exhibited lesions at postmortem examination.

Case Study No. 2

A continuous-flow, wean-to-finish site received PRRS-negative pigs from a sow farm every eight weeks. Very few health issues were clinically visible until a respiratory break occurred. Pigs of all sizes/ages were affected. Pigs were visibly sick and the cough was the classic bark of influenza. Treatment was given via water, but death loss occurred with increasing frequency.

Postmortem examination revealed moderate pneumonia and severe pleuritis, pericarditis and peritonitis. Those lesions were characteristic for HPS and appeared to be the major cause for the deaths. Tissues were submitted for lab testing.

The diagnostic laboratory findings were influenza virus and HPS. Because the site was continuous flow, a concentrated effort was made to control the infectious agents. The losses due to HPS were contained by strategic antibiotic application and the use of a commercial vaccine. Future groups received HPS vaccine, which controlled the mortality problems and clinical signs.

This case demonstrates the importance of determining a control program for disease syndromes that have multiple causes. SIV vaccines have not been very effective in preventing overt disease. Newer strain-specific HPS vaccines have been very helpful in reducing clinical effects of an infection.

Once this wean-to-finish site went through four groups with normal mortality, vaccine use was stopped. No other producer receiving the same pigs from the same sow farm has seen clinical signs of HPS.

Case Study No. 3

A 1,200-sow farm was producing PRRS-negative pigs and started bringing in high-health weaner gilts. The owner decided to raise some pigs from his own production. These male pigs were housed in the same nursery with the new gilts.

Within two weeks, gilts were coughing and sneezing and exhibiting severe respiratory distress. Two were euthanized and lab results isolated pure HPS from the lungs. It was suspected the HPS originated in the in-house male pigs and then infected the weaner gilts. Antibiotics were put in water and feed for a short time. Future herd additions were vaccinated for HPS.


Haemophilus parasuis is a common bacteria residing in the respiratory tract of healthy pigs. Pigs are commonly infected from their dams during the first week of life. However, the introduction of animals from an outside source can trigger a disease outbreak, as there are numerous strains of the bacteria and each strain may have different virulence. Stress situations such as mixing and moving, along with poor ventilation in colder months can cause the bacteria to replicate rapidly and cause clinical disease.

A complete diagnostic workup is essential to getting specific identification of the organism and then developing a control strategy. Your health advisor can develop a control and monitoring program for your operation.  

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