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Risk of rabies introduction by non-commercial movement of pets

Risk of rabies introduction by non-commercial movement of pets. P. Have, L. Alban, L.T. Berndtsson, F. Cliquet, P. Hostnik, S.C. Rodeia and M. Sanaa.

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Risk of rabies introduction by non-commercial movement of pets

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  1. Risk of rabies introduction by non-commercial movement of pets P. Have, L. Alban, L.T. Berndtsson, F. Cliquet, P. Hostnik, S.C. Rodeia and M. Sanaa 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”

  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. 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. Mandate cont’ • To what extent the abandoning of the individual serological test for neutralising rabies-antibodies titration could be envisagedwithout 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. 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. 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. Model parameters Incubation period • 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

  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. 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. Model parameters • Length of waiting period (t) • Measured from time of vaccination • t will determine the residual prevalence Pa of animals incubating rabies due to pre-vaccination exposure

  11. Risk pathways

  12. Type A risk

  13. Type B risk

  14. Model descriptionPrevalence 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. 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 Model descriptionRisk A and B

  16. Model descriptionTotal risk • Total risk Rtot that an animal incubates rabies at time t after vaccination and serological testing is given by the sum of Ra and Rb: Rtot = P * f(t) + (1 – Sp) * (1 - Ev) * Pb or Rtot = P * (f(t) + (1 – Sp) * (1 - Ev) * (1- f(t))) or Rtot = P * (1 – (Ev + Sp - Ev * Sp )*(1- f(t))

  17. Model descriptionmodelling 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. Model descriptionnon-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. Effect of serological testing

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