Natural Infection, Immunity & Prevalence of PCV2Michael Murtaugh and Cheryl Dvorak

University of Minnesota, USA

AcknowledgementsCharles Haley and Eric Bush, USDA-APHISSuresh Tikoo, VIDO

SponsorsUniversity of Minnesota SDECBoehringer Ingelheim Vetmedica, Inc.

Canada 1999mPCV2b

PCV2a2001-2013

PCV2b2003-2013

2006-2013

China 2003

2012-2013

MN VDL Sequencing917 Isolates

1 2 3 4 5 6 7 8 9 10 11 12 13 14 150.5

5

50

500

Series11999

2001

2003

2005

2007

2009

2011

2013

Num

ber o

f Seq

uenc

es

Year of Isolation

490

Swine Finishing Herds in USA (n=187, pigs >20 weeks)

ViremiaPCV2 >99% of Herds Positive

Antibody>99% of Herds Positive

Average PCV2 titer >104 copies per ml

0

50

100

0-1011-20

21-3031-40

41-5051-60

61-7071-80

81-90

91-100

Within Herd Prevalence

Freq

uenc

y (N

umbe

r of F

arm

s)

0

100

200

300

400

500

600

2 3 4 5 6 7 8 9PCV2 DNA copies/ml (log10)

Freq

uenc

y (n

umbe

r of a

nim

als)

0

20

40

60

80

0-10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100

Within Herd Prevalence

Freq

uenc

y (N

umbe

r of F

arm

s)

In 2005, there was no PCVAD in the USA

Porcine Circovirus in 2006, USA

Porcine Circovirus in 2006 Pre-PCVAD, Pre-Vaccines

Swine Finishing Herds in USA (n=187, pigs >20 weeks)

ViremiaPCV2 >99% of Herds Positive

Antibody>99% of Herds Positive

Average PCV2 titer >104 copies per ml

0

50

100

0-1011-20

21-3031-40

41-5051-60

61-7071-80

81-90

91-100

Within Herd Prevalence

Freq

uenc

y (N

umbe

r of F

arm

s)

0

100

200

300

400

500

600

2 3 4 5 6 7 8 9PCV2 DNA copies/ml (log10)

Freq

uenc

y (n

umbe

r of a

nim

als)

0

20

40

60

80

0-10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100

Within Herd Prevalence

Freq

uenc

y (N

umbe

r of F

arm

s)

Puvanendiran et al. 2011. Virus Res 157:92-98.

A B AB -0

50

100

150

200

250

300

350

400

286

386

95

233

N=1000

PCV2a PCV2b PCV2a+PCV2b

Negative

29%

39%

9%

23%

PCV2b in 48% of pigsPCV2a in 38% of pigs : in 2006

PCV2a

PCV2b

qPCR

Rowland et al.

AB

B

AN

umbe

r per

bin

CT value

X=35.3

X=35.9

X=34.4

Level of Viremia is Not Affected by

Genotype of Infecting Viruses

Infection with PCV2a=PCV2b=

PCV2a+2b

• Pigs at finishing are viremic• Antibody is not controlling infection• What is the source of infection?

When do Pigs get Infected?

Sows are viremic

Sows are viremic

Virus in ColostrumVirus in Colostrum Virus in Oral fluidsVirus in Oral fluids

Pre-farrowing Sows are Infected and Shed PCV2

No effect of parity

No effect of parity

• Serum and swabs were collected pre-suckling• 78% of piglets were born viremic• All PCR-positive samples were PCV2b (n=219)

SerumSerum

Piglets are born Viremic

Skin SwabsSkin Swabs

PCV2 is present in pre-suckling piglet serum

PCV2 is present in pre-suckling piglet serum

• Non-viremic sows on Farms 2, 3, 5, and 6 gave birth to viremic piglets.

• Sows are PCV2 positive even in the absence of observable viremia.

Nonviremic Sows Produce Viremic Piglets

A Negative PCR Test is not Proof of Negative

Piglet skin

qPCR Detects Live, Infectious Virus in Pigs and Environment, Except on Sanitized Surfaces

Piglet serumSow Serum

Crate Bar

Serum IgGSerum IgG

• Anti-PCV2 antibodies are present in serum, colostrum, and oral fluids of sows• Sows from farm 3 and 5 were vaccinated and have universally high antibodies

Colostrum IgGColostrum IgG

Sows have High Levels of anti-PCV2 Antibodies

PCV2 Infection is Persistent

• Even in the presence of PCV2-specific antibodies, PCV2 viremia is maintained.

• Once an animal is infected, it is infected for life.

0 5 10 15 20 250

20

40

60

80

100Viral DNA levels

SowPiglets

Piglet age (weeks)

% P

CV2

posi

tive

pigs

0 5 10 15 20 250

1

2

3IgG Antibody levels

SowPiglets

Piglet age (weeks)

Ave

rage

OD

val

ue

Persistent infection: Vaccination Evidence

Young pigs (45 kg)

Old pigs (100 kg)

January neg* negMarch neg negMay 104 107

June neg negAugust neg negOctober neg negNovember neg negJanuary neg neg

One batch not vaccinated

Vaccination can suppress viremia to non-detectable levels. However, virus reappeared when vaccination was stopped.Vaccination does not cure infection.

• The farrowing environment is thoroughly contaminated with PCV2.

• Growing piglets are under constant viral challenge from the environment and from the sow.

• Piglets can be infected with PCV2 in utero, during birth, and from the environment.

virus

Maternal Ab

pigletantibodies

10-15 weeks

Pigs are Infected at Birth - Infection can be Lifelong

Six Years Later: What is the PCV2 Status

Viral loads are reduced.

Positive Negative0

10

20

30

40

50

60

70

80

90

Large Increase in PCR-negative pigs

20062012

% P

CV2

positi

ve p

igs

Change in PCR Status 2006 - 2012

Anti-

Rep

Anti-Cap

Infected + Vaccinated 81%

Vaccinated Only 13%

Background noise 3%

Negative 3%

Serological Status of Finishing Pigs - 2012

Vaccination Suppresses but does not Cure Infection

Young pigs (45 kg)

Old pigs (100 kg)

January neg* negMarch neg negMay 104 107

June neg negAugust neg negOctober neg negNovember neg negJanuary neg neg

One batch not vaccinated

Vaccination can suppress viremia to non-detectable levels. However, virus reappeared when vaccination was stopped.

Conclusion: PCV2 causes disease, but presence in lymph nodes does not prevent immune response to PCV2 vaccination.

Kristensen et al. 2011. Prev Vet Med 98:250.

Vaccination Works: Meta-Analysis (66 trials)

Vaccines against PCV2 improve growth Vaccines against PCV2 reduce mortality

How is vaccination working????????????

No one really knows the mechanism.

Vaccines do not induce robust antibody response.

Neutralizing antibodies exist but do not eliminate virus.

Cytotoxic T cells not a general feature of protein vaccines.

But, no question that it works.

Concluding Observations

PCV2 is a highly conserved virus displaying limited genetic diversity in the United States

PCV2 is endemic is swine herds; PCV2b is more common than PCV2a.

PCV2 exposure starts at birth; infection can be lifelong.

Vaccination effectively controls PCVAD and reduces infectious pressure, but does not eliminate virus.