Hiep B10

Overview Porcine pleuropneumonia, caused by Actinobacillus pleuropneumoniae, is a disease associated with intensive pig production. The incidence of pleuropneumonia tends to vary widely. Back to top

Causes There are several known common serotypes, all with the capability of causing disease but some more so than others. Pleuropneumonia is usually transmitted from pig to pig. Airborne transmission can also be important, especially in pig-dense areas. All ages of pigs are susceptible to this disease, but it is most commonly seen in growing pigs. The incidence of the disease tends to be quite high. It is not uncommon for over 50 percent of a herd to contract the disease. Without treatment, death rates tend to parallel incidence rates. Back to top

Symptoms The clinical course of pleuropneumonia can be peracute, acute, subacute or chronic. In the peracute form, pigs die very suddenly, generally with very high temperatures and very little, if any, respiratory signs. In the terminal phase, there may be severe breathing difficulties (dyspnea), with open-mouth breathing and a foamy, blood-tinged discharge from the nose and mouth. The skin on the nose, ears, legs and perhaps the whole body takes on a blue color from the lack of oxygen in the blood (cyanosis). In the acute form, animals are generally depressed, and they refuse to eat. Severe dyspnea, coughing and sometimes open-mouth breathing are also evident. Cardiac and circulatory failure also is the rule. In the subacute and chronic forms, there is little to no fever, and the intensity and spontaneity of the cough change considerably. Appetite tends to decrease, and many pigs that survive gain poorly. Pathologically, lesions of Actinobacillus pleuropneumoniae infections are confined almost entirely to the respiratory tract. Pleuropneumonia usually involves both lungs. The pneumonic areas are dark and solid. The thoracic cavity contains a blood-tinged fluid. If the course of the disease has been peracute or acute, the trachea and bronchi are often filled with a foamy, blood-tinged mucous discharge. Back to top

Diagnosis Diagnosis of Actinobacillus pleuropneumoniae infections is most commonly made by observation of the typical lung lesions during post-mortem examination, in combination with isolation and identification of the causative organism in the microbiology laboratory. As possible differential diagnoses, pleuritic pasteurellosis, hog cholera (classical swine fever), erysipelas and streptococcal infections must be considered in peracute and acute cases. It is not unusual to find mixed bacterial populations, with Actinobacillus pleuropneumoniae predominating, in a case that is eventually diagnosed as pleuropneumonia. A specific ELISA test for a specific serotype or groups of serotypes also is used for serum-profiling or for detection of subclinical carriers.

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Management Once Actinobacillus pleuropneumoniae has become established on a farm, it is difficult to eliminate the organism, in spite of extremely aggressive measures. Exercising care not to commingle latently or chronically infected pigs with those having no previous exposure is a step in the right direction. All-in, all-out pig flow is very important. Pigs should never move from an older group to a younger group. Vaccines for pleuropneumonia are available, but their efficacy seems to be highly variable from farm to farm, country to country and continent to continent. When the impact of the disease is high, depopulation of a herd and repopulation with animals from a negative herd is an effective means of eradicating the disease. This procedure must, of course, be accompanied by a thorough disinfection of the premises being depopulated. Eradication of A. pleuropneumoniae from sero-positive herds has been accomplished using a program that combines segregated early weaning with an aggressive therapy of ceftiofur in piglets (Scott A. Dee, University of Minnesota).