Vaccine matching. Reliability of foot-and-mouth disease r-values. determination

Transcription

1 Vaccine matching Reliability of foot-and-mouth disease r-values determination Interinstitutional Network for R&D in FMD (RIIDFA)- Argentina Veterinary and Agrochemical Research Centre (VAR) - Belgium

2 Protection against Podal Generalization. FMD vaccine potency testing in cattle using homologous and heterologous challenge strains PPG trials 10 PPG trials (160 bovines vaccinated with A 24 Cruzeiro + 20 controls) 6 homologous challenge trials (A 24 Cruzeiro strain) 4 heterologous challenge trials (A/Arg/01 strain) All animal trials were performed within an 11-month period (January-November 2006) Aims Determination of r-values r VNT and ELISA performed in three laboratories (SENASA, CEVAN and VAR) Serum samples taken at 30 dpv

3 There is not cross protection in vivo between A24 Cruzeiro and A/Arg/01 FMDV strains EXP # PPG A24 EPP VN A24 EPP ELISA A24 EXP # PPG A/Arg/01 EPP VN A/Arg/01 EPP ELISA A/Arg/ % 93% 89% 1 44% 2 94% 92% 90% 2 59% 3 94% 89% 3 56% ND 58% 4 93% 82% 4 25% ND 45% 5 88% 87% 5 13% ND 62% 6 84% 91% 6 13% ND 62% 7 94% 75% 78% 7 49% 8 81% 84% 81% 8 50% 9 88% 73% 86% 9 64% 10 75% 82% 88% 10 68% MEAN 88.5% 85.8% 86.2% MEAN 26.6% 56.1% 95% CI [ ] [ ] [ ] 95% CI [ ] [ ] SD 7.4% 4.2% SD 8.4% Serological assays: VN SENASA and lpelisa CEVAN

4 r-values: Interpretation of the results r 1 = reciprocal titer of reference serum against field virus reciprocal titer of reference serum against vaccine virus Virus neutralization test r-values (Rweyemamu M, 1984) r > 0.3 r <0.3 The field isolate is sufficiently similar to the vaccine strain that use of the vaccine is likely to confer protection against challenge with the field isolate. The field isolate is so different from the vaccine strain that the vaccine is unlikely to protect. ELISA r-values (Ferris and Donaldson, 1992) 0.4 < r < 1.0 Close relationship. A potent vaccine containing the vaccine strain is likely to confer protection. 0.2 < r < 0.39 The vaccine strain might be suitable for use if no closer match can be found provided that a potent vaccine is used and animals are preferably immunized more than once. r < 0.2 The vaccine strain is unlikely to protect against challenge with the field isolate.

5 n = 10 trials n = 10 trials r-values -95 %Confidence Intervals - VN Exp # Me an SD 95% CI Me dian CV% 1 0,19 0,09 0,13-0,25 0,21 47% 2 0,20 0,18 0,09-0,31 0,13 90% 3 0,24 0,12 0,17-0,31 0,25 50% 4 0,22 0,20 0,10-0,34 0,16 91% 5 0,19 0,12 0,12-0,26 0,18 63% 6 0,23 0,13 0,15-0,31 0,25 57% 7 0,34 0,12 0,27-0,41 0,31 35% 8 0,53 0,33 0,33-0,73 0,48 62% 9 0,39 0,26 0,23-0,55 0,28 67% 10 0,25 0,13 0,17-0,39 0,23 52% Me an 0,28 0,17 0,17-0,39 0,25 61% r -values- 95% confidence intervals - lpelisa Ex p. # Mean SD 95% CI Media n CV% 1 0,19 0,08 0,14-0,24 0,17 42% 2 0,26 0,16 0,16-0,36 0,25 62% 3 0,35 0,14 0,26-0,44 0,31 40% 4 0,33 0,16 0,23-0,43 0,29 48% 5 0,48 0,2 0,36-0,60 0,43 42% 6 0,28 0,11 0,21-0,35 0,26 39% 7 0,51 0,17 0,40-0,62 0,45 33% 8 0,45 0,17 0,34-0,56 0,48 38% 9 0,56 0,23 0,42-0,70 0,52 41% 10 0,60 0,28 0,43-0,77 0,56 47% Mean 0,40 0,17 0,29-0,51 0,37 43% Assay: VNT SENASA Assay: lpelisa CEVAN VN VAR: range and mean 0.19±0.13 [95%CI: ] lpelisa VAR: range and mean 0.20±0.06 [95%CI: ]

6 Classification of A 24 Cruzeiro log 10 serum titers VNT lpelisa Low Medium High Low Medium High CEVAN NA NA NA t < t 2.80 t >2.80 SENASA t < t 2.00 t >2.00 NA NA NA VAR t < t 2.26 t>2.26 t < t 2.41 t >2.41

7 VNT r-values for FMDV strain A/Arg/01 (trials 1-6) SENASA VN VAR VN Low Medium High Low Medium High r T, C SD %CI r G,C

8 lpelisa r-values for FMDV strain A/Arg/01 (trials 1-6) CEVAN lpelisa VAR lpelisa Low Medium High Low Medium High r TC, SD %CI r G,C lpelisa r-values for FMDV strains O1 Campos and C3 Indaial (trials 1-6) O1 Campos C3 Indaial Low Medium High Low Medium High r TC, SD %CI r G,C

9 VNT r-values for FMDV strain A/Arg/01 determined for the first four and the last four trials r T, C SENASA VN n=4 (trials 1-4) n= 4 (trials 7-10) Low Medium High Low Medium High na SD na 95%CI , na r T, C VAR VN n=4 (trials 1-4) n= 4 (trials 7-10) Low Medium High Low Medium High SD %CI

10 lpelisa r-values for FMDV strain A/Arg/01 as determined in the first four or in the last four trials CEVAN lpelisa n=4 (trials 1-4) n= 4 (trials 7-10) Low Medium High Low Medium High VAR lpelisa n=4 (trials 1-4) n= 4 (trials 7-10) Low Medium High Low Medium High na na na

11 Effect of pooling of sera on r-value determination Assay: VAR VN (trials 1-10) Pool identification All animals per PPG trial Protected animals per PPG trial Unprotected animals per PPG trial Randomly selected animals Randomly selected protected animals Randomly selected unprotected anim Nº of pools Nº of sera/pool rpool [95%CI] mean [95%CI] [95%CI] 0.048±0.034 a 0.207±0.098 a 0.186±0.125 a [ ] [ ] [ ] b 0.045± ± ±0.122 [ ] [ ] [ ] 0.055± ± ±0.122 [ ] [ ] [ ] 0.105± ± ±0.068 [ ] [ ] [ ] 0.057± ± ±0.042 [ ] [ ] [ ] 0.107± ± ±0.069 [ ] [ ] [ ] ri rt a mean ± SD; b 95%CI

12 Some conclusions... VN r G,C -values for medium and high serum titer classes from the A 24 Cruzeiro vaccinated animals are in line with the heterologous PPG outcome for the three testing laboratories, suggesting that the vaccine strain A 24 Cruzeiro is unlikely to protect against the field isolate A/Arg Arg/01. The corresponding lpelisa r-values are slightly higher and indicate a closer relationship between both strains (i.e. the vaccine strain might be suitable for use if no closer match can be found provided that a potent vaccine is used and animals are immunized preferably more than once). Pooling of serum samples significantly reduced the inter-animal and inter-trial trial variation, irrespective of the number of serum samples in the pool and the type of serum samples pooled. A consistently low r-value r was observed indicating that the A 24 Cruzeiro vaccine would be unlikely to confer protection against challenge with the A/Arg Arg/01 field strain.

13 More conclusions... Low titer sera are poor estimators of the relatedness between FMDV strains and its use should should be avoided for vaccine matching purposes. Medium to high titer sera result in r-value r estimates that more closely correlate to in vivo cross- protection studies. Appropriate determination of r-values r for two strains with demonstrated absence of cross- protection may also depend on the potency of the vaccine used to vaccinate cattle, especially since high potency vaccines generally lead to a more elevated serum titer post vaccination

14 RIIDFA VAR-Belgium Eduardo Palma Eduardo Maradei Blanca Robiolo Jose La Torre Claudia PérezP Alejandro PérezP Norberto Fondevila Eliana Smitsaart Nora Mattion Nesya Goris Tom Willems Kris De Clercq Thank you!