“ Contribution of MLV PRRS
vaccination to the control and
eventual eradication of PRRS”.
Date
24 August 2012
Marc Martens, DVM
MSD AH
Disease spreading factors
2
2
Biological Warfare Principle:
Bacteria
or virus
PRRS
CSF
App
FMD
Aujeszky
3
3
Does vaccination prevent spreading of
disease agent?
Quality important
protected
4
economical
protection
Biological
protection
(virus
excretion
stopped)
4
No, vaccination reduces spreading
Gilt pool very
important
Less virus
excretion
Less virus to infect protected pig
Hygiene
Barriers
Not enough virus to infect a protected pig
5
5
PRRSV genotypes (Stadejek et al., 2006)
Belarus
Lelystad, EU vaccines
(Porcilis®,…)
Spain, Poland,
Italy, Denmark,
Germany, Netherlands
Thailand, USA
Belarus
Lithuania
VR-2332, US vaccines
(Ingelvac® ,…) USA,
China, Japan,
Thailand, Europe
6
Porcilis PRRS, Strain origin and characteristics
1. Parent strain isolated from a sow with no clinical symptoms
related to PRRS
2. Low pathogenic field isolate from Germany
3. Capacity to destroy PAM
4. Growth only on PAM
After attenuation process
1. No longer capable to destroy PAM
2. Also back-passage virus could not destroy PAM
3. Growing on VERO cells
4. Reduced capacity to spread
7
Field
virus
Attenuation
Vaccine strains
8
Ro:
how many animals (farms) are infected by 1 infected
animal (farm)
Ro < 1  Infection dies out because less than 1 animal
9
is infected by 1 infected
animal
9
2011 ISERPD Barcelona/ESPHM Finland
Several MSD AH internal trials were
performed to calculate the transmission ratio
of the PRRS vaccine virus. For the EU MLV
vaccine results of trials varied between 0.1
and 0.04. So the vaccine-virus will dy out in
the population and not interfere with
eradication programs 10
11
Reduction of transmision
Group 2
n=10
(7V+3C)
Separation by
plastic
Separation by
plastic
Group 1
N=11
(7V+4C)
pen A
Strain 1
pen B
1m
Intranasal challenge
Contacts-1
n=5
(4V+1C)
1m
Strain 2
Contacts-2
n=5
(3V+2C)
V = vaccinated
C = controls non vaccinated
12
Plastic curtain
(21, 23, 24, 26,
27, 34, 61, 67, 68,
72, 75)
Plastic curtain
Group 1
n =11
(7V+4C)
Strain 1
Contacts
n=5
(4V+1C)
(25, 28, 33, 36,
66)
21 days later
Group 2
n=10
(7V+3C)
(22, 29, 30, 35,
37, 63, 70, 73, 76,
77)
Strain 2
Contacts
N=5
(3V+2C)
RT-PCR+
seronegative
(32, 62, 64, 69,
71)
V = vacunados
C = controles no vacunados
13
Strain 1
Not-vaccinated
Vaccinated
3.5
3
Log10 viremia (TCID50)
Log10 viremia (TCID50)
3.5
2.5
2
1.5
1
0.5
0
3
2.5
2
1.5
1
0.5
0
0
3
6
9
23
12
26
72
15
18
21
0
3
75
6
21
Not-vaccinated
24
27
12
34
61
15
67
18
21
68
Strain 2
Vaccinated
3.5
3.5
3
Log10 viremia (TCID50)
Log10 viremia (TCID50)
9
2.5
2
1.5
1
0.5
0
3
2.5
2
1.5
1
0.5
0
0
3
6
9
29
12
35
63
15
18
21
0
14
3
6
22
9
30
37
12
70
73
15
76
77
18
21
2006 IPVS Kopenhagen/2007 Emerg. Dis. Congr. Krakow
French studies show that MLV vaccination leads
to PCR/ELISA negative output of breeding farms
15
2006 Tieraerztliche Praxis
Austrian trial showing the benefit of MLV
vaccine at longer term not only to control but
also eliminate PRRS from the progeny of
breeding sows
16
2010 IPVS Vancouver
Dutch colleagues describe the contribution of
MLV vaccine applied intradermally (IDAL) in
producing PRRS-free output from (re)
infected SPF farms
17
Effective vaccination will result in:
• Increased virus dosage needed to establish field
infection
• Decreased level of virus excretion
• Decreased duration of virus excretion
• Resulting in a reduced transmission of field virus
18
18
Thanks for your attention
19
19