Clinical Manifestiation and Diagnosis of PCVAD
PCV2 is associated with several disease manifestations. The most widely known and perhaps the biggest problem is the diseases widely known as postweaning multisystemic wasting syndrome (PMWS) but now better described as systemic infection with PCV2. PCV2-associated respiratory disease is very important and increasingly diagnosed. PCV2-associated reproductive disorders, enteritis, and porcine dermatitis and nephropathy syndrome (PDNS) are less commonly observed but very important manifestations of disease associated with PCV2.
Severe systemic infection of PCV2 (formerly known as PMWS) is the most common manifestation of PCV2-associated disease world wide. The primary clinical signs include weight loss or decreased rate of weight gain, paleness or icterus, and gauntness and ill thrift. Diagnosis of severe systemic PCV2 infection is based on the confirmation of lymphoid depletion and/or granulomatous inflammation in the lymphoid tissues by histopathological examination and demonstration of PCV2 antigen associated with the lymphoid lesions. Mild-to-severe lymphohistiocytic inflammation in one or several other organs associated with PCV2 antigen is also commonly observed in pigs with severe systemic PCV2-associated disease.
PCV2-associated pneumonia is the most common manifestation of PCV2 infection in cases submitted to the ISU-VDL. These pigs have manifest ill thrift and labored respiration and often cough. Most pigs with PCV2-associated pneumonia are also coinfected with PRRSV, or SIV, and/or Mycoplasma hyopneumoniae (M. hyopneumoniae) and/or a variety of opportunistic bacteria. The basis for concluding that PCV2 is involved in respiratory disease is that PCV2 antigen is associated with characteristic microscopic lung lesions. Lesions characteristic of PCV2-associated pneumonia include necrotizing and ulcerative bronchiolitis, bronchiolitis obliterans fibrosa, mixed inflammation and fibroplasia in the lamina propria and peribronchiolar areas, and granulomatous inflammation in the alveolar septa.
Cases of PCV2-associated enteritis are not uncommon. Most of the PCV2-associated enteritis cases are from grow-finish pigs. PCV2-associated enteritis cases often clinically and grossly resemble subacute or chronic ileitis. Pigs typically have a history of weight loss and dark colored diarrhea. The intestinal mucosa is grossly thickened and mesenteric lymph nodes enlarged. Microscopic examination confirms the presence of granulomatous enteritis, and the absence of crypt hyperplasia typical of Lawsonia intracellularis-induced proliferative enteritis. Confirmation is by immunohistochemical demonstration of abundant PCV2 antigen associated with the granulomatous enteritis lesions.
PCV2-associated reproductive failure is uncommonly diagnosed. PCV2-associated abortions are typically sporadic in occurrence, occur in gilts and are characterized by increased numbers of mummified fetuses. When confirmed, PCV2-induced abortions or reproductive losses in the pregnant animal it is typically characterized by fetal lymphohistiocytic myocarditis and/or myocardial fibrosis and confirmed by immunohistochemical demonstration of abundant amounts of PCV2 antigen associated with the myocardial lesions. We have recently observed a case where boars in a boar stud were coinfected with PCV2 and M. hyo. and P. multocida type D resulting in respiratory and systemic disease with fevers and ill thrift and infertility and shedding of PCV2 in the semen.
PCV2-associated porcine dermatitis and nephropathy syndrome (PDNS) is typically sporadic within the group of pigs involving less that 0.5% of the group. PDNS may precede or occur during outbreaks of severe systemic infection with PCV2. When we diagnose PDNS we almost always demonstrate PCV2 infection in the skin, or kidney, and/or lymphoid tissues of the affected pigs.