Actinobacillus pleuropneumonia (APP) is a respiratory pathogen of swine that remains a deadly threat.

Actinobacillus pleuropneumonia (APP) is a bacterial infection that affects the respiratory system of pigs. APP can affect any age of swine, but it is most commonly observed in production flows of pigs from 40 lb. to market weight.

In positive production flows, the sows are usually carriers without clinical signs. These sows pass the organism to the piglets prior to weaning, but also pass antibodies via colostrum to piglets at birth. These antibodies will usually protect pigs from the clinical signs of APP until the end of the nursery stage or later, and can interfere with effective vaccination of piglets.

Clinical Signs of APP

Clinical signs include a rapid onset of pneumonia. The organism causes a hemorrhagic pneumonia. Prior to death or just after death, it is common to see blood coming from the nasal cavity of pigs. When postmortem examinations are done on pigs infected with APP, the common lesion features large areas of hemorrhage in the dorsal (upper) lobes of the lungs. This lesion is unusual and is found in an uncommon area for lung lesions. Most organisms cause lesions in the lower lung lobes or throughout the lungs without hemorrhage.

The lesions can turn into lung abscesses where the surface of the lung is stuck to the rib cage. These are found in postmortem examinations and at harvest time in the packing plant. These adhesions have a negative affect on performance.

There are several different classifications of APP organisms, called serotypes. In the United States, the most common APP serotypes are types 1, 5 and 7. We occasionally see other serotypes and non-typable isolates. Serotype 1 and 5 isolates tend to be the most severe, with relatively sudden onset and increased mortality. Some farms find they are positive by serology with less aggressive serotypes, with limited or no clinical signs.

Obtain An Accurate Diagnosis

When diagnosing this disease, the most common disease to rule out would be Actinobacillus suis. The sudden onset of mortality with Actinobacillus suis is also found with APP. The lesions are similar to APP but usually less severe.

Getting an accurate diagnosis is the most important part of APP control. Ruling out Actinobacillus suis and getting an antibiotic sensitivity test completed are both essential.

With the fast onset of disease, it is advisable to use injectable antibiotics to limit death loss. After completion of the antibiotic treatment, pigs can become susceptible again. Vaccination of piglets is the most common control tool we use. Vaccination success has been variable at times with both commercial and autogenous vaccines.

Case Study No. 1

We were called to a 2,000-head finishing site last fall to perform postmortem tests on pigs that had died overnight. This was a 1,500-sow farm with multiple site production. The farrowing and gestation stages were on two sites with nursery and finishing offsite. Weaning averaged 18 days of age. There had been numerous seedstock entries after a depopulation 10 years ago.

The finishing site had two, double-curtain-sided buildings divided into four rooms with four consecutive weeks of pig flow on site. The pigs ranged from 200 to 240 lb.

Postmortem examinations revealed mixed infections. The lesions revealed a viral component and a lesion resembling APP. Laboratory work confirmed a swine influenza virus (SIV) infection as well as APP serotype 5. We treated the group with injectible penicillin and saw a good response. This farm continues to experience mortality, but only when a virus such as SIV or porcine reproductive and respiratory syndrome sets up the lungs for the APP infection.

Case Study No. 2

We were called to do postmortem tests at a 3,000-head, single-site nursery. Weaned pigs were from a single source. Numerous 45-lb. pigs had died. All pigs had bloody noses and classic hemorrhagic lung lesions. An APP serotype 1 was isolated from submitted tissues. Treatment with injectable ceftiofur and feedgrade tilmicosin stopped mortality. This group was vaccinated with a commercial vaccine with serotypes 1, 5 and 7 and went to market without a relapse.


APP continues to be an organism of concern. It is always best to keep it out. Better serological tests have permitted better detection in seedstock sources and limited herd entry. For positive herds, tools to manage APP include multiple site production; all-in, all out by site; early weaning; antibiotics; and proper pig flow. Site depopulation removes the threat of APP as the organism does not survive well in the environment.