Ceva Worldwide
Open menu
rechercher Ceva Worldwide
  1. Ceva Swine Sites
  2. Home page
  3. Diseases
  4. A. Pleuropneumoniae

A. Pleuropneumoniae

Importance and impact of porcine pleuropneumonia

 

Actinobacillus pleuropneumoniae is the bacterium responsible for porcine pleuropneumonia. It causes high morbidity and sometimes significant mortality, particularly at the end of the finishing period. This recurrent disease results in major economic losses in the global swine industry.

 

Clinical forms and diagnostic challenges

 

  • Peracute and acute forms are easily diagnosed due to their obvious and distinctive clinical signs, as well as the typical appearance of pigs found dead, which helps differentiate the two forms.
  • The much less obvious clinical signs and low mortality of the subacute form are often missed and mistakenly confused with a subclinical form — interpreted as “no pleuropneumonia issue” by farm staff and sometimes even by veterinarians.

This is partly explained by the fact that farms endemic for A. pleuropneumoniae are often co-infected with other respiratory agents, such as M. hyopneumoniae, which is responsible for milder respiratory signs. It may also be due to a lack of consistent, high-quality daily monitoring on farms.
However, even truly subclinical pleuropneumonia will result in pathological lung lesions and, despite the absence of clinical signs, a decrease in average daily gain and feed efficiency.

The chronic form, which can develop from any form of pleuropneumonia, further reduces productivity due to pain, decreased respiratory capacity, and the possible reactivation of the disease from chronically infected tissues. Lesions are easily diagnosed through slaughterhouse surveys, such as the Ceva Lung Program (CLP).
Relying solely on clinical signs in a farm endemic for A. pleuropneumoniae, where all clinical manifestations may occur over time, does not allow for an accurate assessment of the true impact of the disease.

To evaluate pleuropneumonia in all its possible forms, pathological assessment of lung lesions remains the least biased method. Lung lesion scoring systems, such as CLP, are considered highly relevant for estimating the severity and losses associated with respiratory disease caused by A. pleuropneumoniae on farm.

 

Epidemiology, serovars and variability in virulence

 

In many cases, the exact infection status of a given pig for A. pleuropneumoniae is not known by the producer or the veterinarian. However, the bacterium is endemic worldwide, present in 80 to 90% of swine farms, and seven different serovars (strain variations) have been reported on farms.

The prevalence of serovars varies according to:

  • the country,
  • the region,
  • the year of the study.

International trade of breeding stock and finishing pigs plays a major role in the introduction of new serovars. Endemic serovars only truly disappear following a total depopulation / repopulation program.
To date, 19 serovars of A. pleuropneumoniae have been classified worldwide. Technically, there are only 18, since serovars 9 and 11 can be considered as one (serovar 9/11), as the difference in their capsular polysaccharide (CPS) loci is only a single amino acid, and they share identical toxin profiles (ApxI + ApxII).
The different serovars present variable levels of virulence, partially attributed to their Apx toxin profiles.
However, A. pleuropneumoniae is highly adaptable to environmental conditions, allowing it to survive and persist even under unfavourable conditions.
In extreme cases, it can enter a hibernation state in biofilm, associated with increased antimicrobial resistance and reduced virulence.
Conversely, it can increase its virulence in response to high levels of catecholamines in the host — hormones responsible for the “fight-or-flight” response.
Thus, a single serovar can exhibit different degrees of virulence depending on clinical conditions:

  • a typically low-virulence strain may cause a severe outbreak,
  • and a more virulent strain may result in mild disease.

 

Immunity, vaccination and control

 

In endemic farms, pleuropneumonia-related losses occur mainly during finishing, and severe outbreaks often arise at the end of the finishing period.
This is due to uniform maternal immunity provided by colostrum antibodies, which protect pigs until the end of the nursery phase.
The drawback is that these antibodies progressively reduce the protective vaccine response against A. pleuropneumoniae.
For this reason, it is crucial to determine the optimal timing for the first vaccination through cross-sectional serology.

ELISA titres targeting the ApxIV toxin, which is weakly or non-virulent and unique to natural infection (not induced by vaccination), are commonly used.
The three exotoxins ApxI, ApxII and ApxIII, as well as lipopolysaccharide (LPS), are the main virulence factors involved in both lung lesion development and protective immunity.

Together, ApxI–III constitute antigens capable of inducing cross-protection.
Other virulence factors are also described and studied, including membrane proteins, some of which are immunogenic and can improve vaccine efficacy.
A serovar-independent vaccination providing long duration of immunity and strong protection against pleuropneumonic lesions is a key component of any A. pleuropneumoniae control program.
Its importance continues to grow in the context of antimicrobial resistance, which is exacerbated by routine treatments.