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Natural Infection, Immunity & Prevalence of PCV2 - Dr. Michael Murtaugh and Dr. Cheryl Dvorak, University of Minnesota, USA , from the Boehringer Ingelheim Pre-AASV Conference, February 28, 2014 - Dallas, TX More presentations at http://www.swinecast.com/2014-boehringer-ingelheim-aasv
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Natural Infec-on, Immunity & Prevalence of PCV2
Michael Murtaugh and Cheryl Dvorak University of Minnesota, USA
Acknowledgements Charles Haley and Eric Bush, USDA-‐APHIS Suresh Tikoo, VIDO
Sponsors University of Minnesota SDEC Boehringer Ingelheim Vetmedica, Inc.
Canada 1999 mPCV2b
PCV2a 2001-‐2013
PCV2b 2003-‐2013
2006-‐2013
China 2003
2012-‐2013
MN VDL Sequencing 917 Isolates
0.02
0.5
5
50
500
1 3 5 7 9 11 13 15 Series1
1999
2001
2003
2005
2007
2009
2011
2013
Num
ber o
f Seq
uences
Year of Isola-on
490
Swine Finishing Herds in USA (n=187, pigs >20 weeks)
Viremia PCV2 >99% of Herds Posi-ve
An-body >99% of Herds Posi-ve
Average PCV2 -ter >104 copies per ml
0
50
100
Within Herd Prevalence
Freq
uency (Num
ber o
f Farms)
0
100
200
300
400
500
600
2 3 4 5 6 7 8 9 PCV2 DNA copies/ml (log10)
Freq
uency (num
ber o
f animals)
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
uency (Num
ber o
f Farms)
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)
Viremia PCV2 >99% of Herds Posi-ve
An-body >99% of Herds Posi-ve
Average PCV2 -ter >104 copies per ml
0
50
100
Within Herd Prevalence
Freq
uency (Num
ber o
f Farms)
0
100
200
300
400
500
600
2 3 4 5 6 7 8 9 PCV2 DNA copies/ml (log10)
Freq
uency (num
ber o
f animals)
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
uency (Num
ber o
f Farms)
Puvanendiran et al. 2011. Virus Res 157:92-‐98.
0
50
100
150
200
250
300
350
400
A B AB -
286
386
95
233
N=1000
PCV2a PCV2b PCV2a+ PCV2b
Negative
29%
39%
9%
23%
PCV2b in 48% of pigs PCV2a in 38% of pigs : in 2006
PCV2a
PCV2b
qPCR
Rowland et al.
AB
B
A Num
ber p
er bin
CT value
X=35.3
X=35.9
X=34.4
Level of Viremia is Not Affected by Genotype of
Infec-ng Viruses
Infec-on with PCV2a=PCV2b=
PCV2a+2b
• Pigs at finishing are viremic • An-body is not controlling infec-on • What is the source of infec-on?
When do Pigs get Infected?
Sows are viremic
Virus in Colostrum Virus in Oral fluids
Pre-‐farrowing Sows are Infected and Shed PCV2
No effect of parity
• Serum and swabs were collected pre-‐suckling • 78% of piglets were born viremic • All PCR-‐posi-ve samples were PCV2b (n=219)
Serum
Piglets are born Viremic
Skin Swabs
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 posi-ve even in the absence of observable viremia.
Nonviremic Sows Produce Viremic Piglets
A Nega-ve PCR Test is not Proof of Nega-ve
Piglet skin
qPCR Detects Live, Infec-ous Virus in Pigs and Environment, Except on Sani-zed Surfaces
Piglet serum Sow Serum
Crate Bar
Serum IgG
• An--‐PCV2 an-bodies are present in serum, colostrum, and oral fluids of sows • Sows from farm 3 and 5 were vaccinated and have universally high an-bodies
Colostrum IgG
Sows have High Levels of an--‐PCV2 An-bodies
PCV2 Infec-on is Persistent
• Even in the presence of PCV2-‐specific an-bodies, PCV2 viremia is maintained.
• Once an animal is infected, it is infected for life.
0
20
40
60
80
100
0 5 10 15 20 25 % PCV
2 po
si-v
e pigs
Piglet age (weeks)
Viral DNA levels
Sow Piglets
0
1
2
3
0 5 10 15 20 25
Average OD value
Piglet age (weeks)
IgG An-body levels
Sow Piglets
Persistent infec-on: Vaccina-on Evidence
Young pigs (45 kg)
Old pigs (100 kg)
January neg* neg March neg neg May 104 107 June neg neg August neg neg October neg neg November neg neg January 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
piglet antibodies
10-15 weeks
Pigs are Infected at Birth -‐ Infec-on can be Lifelong
Six Years Later: What is the PCV2 Status
A B AB A B AB102
103
104
105
106
107
108
109
1010
Vira
l co
pie
s/m
l
2006 2012
Viral loads are reduced.
0
10
20
30
40
50
60
70
80
90
Posi-ve Nega-ve
% PCV
2 po
si-v
e pigs
Large Increase in PCR-‐nega-ve pigs
2006
2012
Change in PCR Status 2006 -‐ 2012
a" " b"c" " d"
An--‐Re
p
An--‐Cap
Infected + Vaccinated 81%
Vaccinated Only 13%
Background noise 3%
Nega-ve 3%
Serological Status of Finishing Pigs -‐ 2012
Vaccina-on Suppresses but does not Cure Infec-on
Young pigs (45 kg)
Old pigs (100 kg)
January neg* neg March neg neg May 104 107 June neg neg August neg neg October neg neg November neg neg January 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 vaccina-on.
Kristensen et al. 2011. Prev Vet Med 98:250.
Vaccina-on Works: Meta-‐Analysis (66 trials)
Vaccines against PCV2 improve growth Vaccines against PCV2 reduce mortality
How is vaccina-on working????????????
§ No one really knows the mechanism.
§ Vaccines do not induce robust an-body response.
§ Neutralizing an-bodies exist but do not eliminate virus.
§ Cytotoxic T cells not a general feature of protein vaccines.
§ But, no ques-on that it works.
Concluding Observa-ons
v PCV2 is a highly conserved virus displaying limited gene-c diversity in the United States
v PCV2 is endemic is swine herds; PCV2b is more common than PCV2a.
v PCV2 exposure starts at birth; infec-on can be lifelong. v Vaccina-on effec-vely controls PCVAD and reduces
infec-ous pressure, but does not eliminate virus.
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