Swine Circoviruses

Question 1

What are the characteristics of Porcine Circovirus (PCV)?

Answer 1

• Circoviridae
  
  • Circo = transverse
• ssDNA virus, circular, non-enveloped
  
  • one of the Smallest viruses known to infect mammals
• Infectious for months to years in the environment - very stable

Question 2

What are the different types of PCV?

Answer 2

• Porcine Circovirus Type 1 (PCV1)
  
  • non-pathogenic, 1974
• Porcine circovirus type 2 (PCV2)
  
  • Primary pathogenic circovirus - 1990
• Porcine circovirus type 3 (PCV3)
  
  • sill investigating - 2015

Question 3

What are the primary genotypes of PCV2?

Answer 3

• PCV2a - 1998 Canada, most vaccines based on this genotype
• PCV2b - associated with increased severity of disease
• PCV2d - 1012 US, now predominant genotype in US

Question 4

What are the key concepts for PCV2?

Answer 4

• Ubiquitous worldwide, 95% of US herds seropositive
• Cell target: actively dividing cells
• Hallmark lesion: Lymphoid Depletion
• Contributes to a collection of disease syndromes termed Porcine Circovirus Associated Disease (PCVAD)

Question 5

How is PCV2 Transmitted?

Answer 5

• Contact with infected pigs - oronasal and ocular secretions, urine, feces
• Environmental
  
  • Very difficult to eliminate PCV2 from enviornment
• Transplacental
• Contaminated fomites

Question 6

What is the Pathogenesis for PCCV2?

Answer 6

• Virus replication occurs in nucleus of actively dividing cells
  
  • dependent on host cell enzymes present in S phase of cell cycle for virus replication
• PCV2 alone rarely results in PCVAD
  
  • necessary but not sufficient
• Immune stimulation by co-factors usually necessary (⇡ cellular replication)
  
  • stress and environmental conditions
  • Pathogens: PRRSV, PPV, M. hyopneumoniae
  • ImmunizationsL PRRS MLV, KLH in IFA,
• Lymphocyte Proliferation ⇢ ⇡⇡ PCV2 replication ⇢ Lymphid depletion ⇢ Clinical PCVAD

Question 7

What are the disease syndromes of PCVAD?

Answer 7

1. Systemic disease or postweaning multisystemic wasting syndrome (PMWS)
2. Respiratory Disease (PCV2- associated pneumonia)
3. PCV2-associated enteritis
4. Subclinical infection
5. PCV2-associated reproductive failure - resembles PPV
6. Porcine dermatitis and nephropathy syndrome (PDNS)

Question 8

What is PMWS?

Answer 8

• Primarily affects pigs 8-18 weeks of age
• Morbidity 2-25%, Mortality 70-80%
• Clinical Signs:
  
  • muscle wasting, weight loss, progressive poor growth, ill thrift, jaundice or pallor, rough hair coat, diarrhea, dyspnea, pyrexia

Question 9

What are the gross lesions associated with PCVAD?

Answer 9

• Lungs fail to fully collapse, firm with mottling and consolidation
• lymph nodes enlarged and hemorrhagic
• Enteritis:
  
  • Intestines thickened
  • Exudate on mucosa
  • Grossly resembles proliferative enteritis caused by Lawsonia intreacellularis or Salmonellosis
• Acute pulmonary Edema - acute death of well-doing pigs

Question 10

What are the microscopic lesions associated with PCVAD?

Answer 10

• Pathognomonic: lymphoid depletion, histiocytic replacement of follicles, and infiltration of parafollicular areas by histocytes
  
  • LN, tonsils, spleen, thymus, Peyer’s patches, BALT
  • increases susceptibility to opportunistic infections
  • Greater PCV2 ⇢⇢ more severe depletion

Question 11

What are the Systemic inflammatory lesions seen with PCVAD?

Answer 11

• Macrophage and lymphocyte infiltration in many tissues
• lymphohistiocytic interstitial pneumonia
• Often includes multinucleated giant cells
• PCV2 inclusions - often in cytoplasm of macrophages
  
  • can be in the nucleus of many cell types

Question 12

What is the key histopathologic feature in fetuses that died from PCV2?

Answer 12

Fibrosing and/or necrotizing myocarditis

Question 13

What Is Porcine dermatitis and nephropathy Syndrome (PDNS)?

Answer 13

• Considered an immunocomplex disease - Type III Hypersensitivity
• NOT definitively caused by PCV2 - significantly reduced occurrence once PCV2 vaccination became widespread
• Primarily affects nursery and growing pigs
  
  • low prevalence <1%
  • high mortality 50-100%
• Pigs with acute disease die due to renal failure - ⇡⇡ creatinine and urea
• Signs:
  
  • Irregular red-to-purple papules and macules on skin of hind limbs and perineal area
  • decreased appetite, depression, listlessness, stiffness, and reluctance to ambulate, typically nonfebrile

Question 14

What are the gross lesions associated with PDNS?

Answer 14

• Firm, bilaterally enlarged pale kidneys
  
  • Petechiae on cortex
• Fluid in abdomen and thorax
• Enlarged hemorrhagic lymph nodes
• Occasionally splenic infarcts
• Skin hemorrhages, renal petechiae, and splenic infarcts also seen with CSFV and ASFV

Question 15

what are the microscopic lesions associated with PDNS?

Answer 15

• Systemic necrotizing inflammation
• fibrinonecrotizing glomerulonephritis
• Necrotizing vasculitis in skin
• Necrotizing vasculitis systemically in other organs
  
  • Spleen, LN, heart, adrenal gland

Question 16

How is PMWS diagnosed

Answer 16

1. Clinical signs of wasting or ill thrift
2. Gross and microscopic lesions characteristic of the disease
3. Viral antigen or DNA in lymphoid lesions

Question 17

How is PCV diagnosed?

Answer 17

• Virus is ubiquitous
• Ab detection: ELISA, IFA
• Viral DNA: PCR - high levels in serum linked to disease
• Visualizing viral DNA or Ag in tissues: ISH or IHC

Question 18

How is PCV2 Reproductive failure diagnosed?

Answer 18

• Late-term abortions and stillbirths
• Extensive fibrosing and/or necrotizing myocarditis
• High concentrations of PCV2 in fetal lesions

Question 19

What are the criteria for diagnosing PDNS?

Answer 19

• Hemorrhagic and necrotizing skin lesions and/or swollen and pale kidneys with generalized cortical petechiae
• Systemic necrotizing vasculitis and fibrinonecrotizing glomerulonephritis
• Detection of PCV2 not necessary for PDNA