Download presentation

Presentation is loading. Please wait.

Published byMatthew Perkins Modified over 4 years ago

1
1 Risk of rabies introduction by non-commercial movement of pets The EFSA Journal (2006) 436 1-54, Assessment of the risk of rabies introduction into the UK, Ireland, Sweden, Malta, as a consequence of abandoning the serological test measuring protective antibodies to rabies P. Have, L. Alban, L.T. Berndtsson, F. Cliquet, P. Hostnik, S.C. Rodeia and M. Sanaa

2
2 Current legislation Regulation (EC) No 998/2003 –valid anti-rabies vaccination –waiting time of at least 21 days (COM 2005/91/EC) –derogations for UK, Ireland, Sweden and Malta to maintain serological test –review of derogations at the end of transitory period of 5 years following receipt of a scientific opinion of EFSA

3
3 EFSA mandate Commission requested EFSA to issue a scientific opinion on the risk assessment of rabies introduction into Ireland, the UK, Sweden and Malta, as a consequence of abandoning the serological test for antibody titration for rabies

4
4 Mandate cont To what extent the abandoning of the individual serological test for neutralising rabies-antibodies titration could be envisaged without increasing the risk If the need to maintain the serological test is scientifically justified, what is the regime to be considered as giving equivalent assurance

5
5 Approach Quantitative risk assessment based on –prevalence of rabies in the country of origin in pets –distribution of incubation periods of rabies –efficiency of establishing protective immunity by vaccination –specificity of the neutralization test for rabies (RFFIT or FAVN) –length of the waiting period

6
6 Model parameters Prevalence (P) –estimated from annual incidence data by assuming a mean incubation time of 38 days –pet population size estimated from 1.0 dog and 1.1 cats per 10 people P = incidence*38/(population at risk*365)

7
7 Model parameters distribution of incubation periods –Dogs: 1 week to several months –Cats: 9 days to 6 months described by a log-normal distribution with mean 38 days Incubation period

8
8 Model parameters Efficiency of vaccination (Ev) –assessed indirectly by measuring the antibody response –measured after first, single vaccination –absence of antibodies not always associated with loss of protection –interval between vaccination and testing major determinant –Ev of 98% used tentatively in this study

9
9 Model parameters Test specificity (Sp) –determines whether truly antibody-negative individuals are correctly assigned as such or whether some individuals are classified as false positive –FAVN test more specific than RFFIT –a tentative value of 99% is used here

10
10 Model parameters Length of waiting period (t) –Measured from time of vaccination –t will determine the residual prevalence P a of animals incubating rabies due to pre-vaccination exposure

11
11 Risk pathways

12
12 Type A risk

13
13 Type B risk

14
14 Model description Prevalence A and B prevalence Pa of animals already incubating rabies will gradually decrease as a result of developing clinical disease Pa = P * f(t) prevalence Pb of animals infected after the time of vaccination will gradually replace Pa Pb = P * (1- f(t))

15
15 Model description Risk A and B Type A risk Type B risk with vaccination Type B risk with vaccination and serology Ra = P * f(t) = Pa Rb = (1 - Ev) * Pb Rb = (1 – Sp) * (1 - Ev) * Pb

16
16 Model description Total risk Total risk R tot that an animal incubates rabies at time t after vaccination and serological testing is given by the sum of R a and R b : R tot = P * f(t) + (1 – Sp) * (1 - Ev) * Pb or R tot = P * (f(t) + (1 – Sp) * (1 - Ev) * (1- f(t))) or R tot = P * (1 – (Ev + Sp - Ev * Sp )*(1- f(t))

17
17 Model description modelling f(t) Sample an incubation period (ip) from the lognormal distribution Sample an interval between infection time and vaccination (int) from a uniform distribution between 0 and 365 days prior to vaccination F(t) calculated from positive values of ip-int 100.000 iterations

18
18 Model description non-linear least squares estimate of f(t) f(t) = exp(-0.0313*t) Rtot = P * (1 – (Ev + Sp - Ev * Sp )*(1- exp(-0.0313*t))

19
19 Effect of serological testing

Similar presentations

Presentation is loading. Please wait....

OK

Week 1.

Week 1.

© 2018 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google