PHOTO: CEVA SANTÉ ANIMALE
PARTNER FEATURE ▶▶▶
Preventing M. hyo and PCV2 to control PRDC
As knowledge grows of lung health problems in pigs, it is increasingly clear that porcine circovirus 2 is playing an important role in the severity of Porcine Respiratory Disease Complex. The virus is often present in co-infections with other pathogens, especially Mycoplasma hyopneumoniae.
BY ROMAN KREJCI, CEVA SANTÉ ANIMALE P
Pig lungs show- ing M. hyo lesions on top.
orcine Respiratory Disease Complex (PRDC) causes substantial economic losses in the swine industry due to decreased growth rate, increased feed con- version ratio, increased treatment costs and in-
creased mortality. Morbidity rates associated with PRDC may range from 30% to 70%, and mortality rates may be between 4% and 6% or even higher in affected farms. PRDC develops as a consequence of coinfections of multiple primary viral and bacterial micro-organisms; apart from My- coplasma hyopneumoniae (M. hyo), viruses like porcine circo- virus type 2 (PCV2), Porcine Reproductive and Respiratory Syndrome virus (PRRSv) and swine influenza virus are the most frequently found. Other viral pathogens – Aujeszky’s
disease virus, porcine respiratory coronavirus (PRCv) – and bacteria Actinobacillus pleuropneumoniae (App) or Streptococ- cus suis may be involved. Pasteurella multocida and Glaesserel- la parasuis are the most frequent secondary bacteria, compli- cating pneumonia. However, as a true multifactorial disease, environmental conditions, population size, management strategies and pig-specific factors such as age and breed also play critical roles in the outcome of PRDC.
Role of PCV2 in PRDC PCV2 is now widely accepted to be an important pathogen in PRDC. PCV2 antigens have been demonstrated in the cyto- plasm of pulmonary macrophages, the bronchiolar epithelium and endothelial cells, which suggests that PCV2 may contrib- ute to the severity and duration of PRDC. PCV2 is frequently confirmed as a cause of respiratory disease (see Figure 2). PCV2 can cause respiratory lesions in the absence of systemic lymphoid damage; that specific condition has been referred to as PCV2 lung disease (PCV2-LD). PCV2-LD is diagnosed when clinical signs like respiratory distress or dyspnoea are present, characteristic pulmonary lesions are observed in the absence of lymphoid lesions and a moderate to high amount of PCV2 is detected in the lungs but there is a lack of virus in lymphoid tissues. However, it was demonstrated that PCV2- LD is probably a negligible condition in the field, and PCV2 mainly contributes to PRDC in relation to PCV2 systemic dis- ease occurrence. PCV2 is determined to be associated with PRDC when PCV2 antigen is associated with characteristic lung lesions. Those lesions include necrotising and ulcerative bronchiolitis, granulomatous inflammation in the alveolar septa and mixed inflammation and fibroplasias in the lamina propria and peribronchiolar areas.
Co-infection with other pathogens A co-infection of PCV2 with another bacterial pathogen is frequently diagnosed in PRDC. In a retrospective study de- scribing the association of PCV2 with PRDC, PCV2 was found in 81%, the combination of PCV2 and P. multocida in 36%, followed by PCV2 and M. hyo in 31% cases. The results of that survey indicate that PCV2 is widely prevalent in pigs with PRDC and should be considered a major respiratory pathogen.
10 ▶ PIG PROGRESS | Volume 38, No. 4, 2022
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