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Risk Assessment of Rabies Introduction via Pet Movement: EFSA Journal Summary

This article presents a risk assessment of rabies introduction into the UK, Ireland, Sweden, and Malta due to abandoning the serological test for protective antibodies. It discusses the current legislation, mandates, approach, and model parameters utilized. The study evaluates the prevalence of rabies, incubation periods, vaccination efficiency, test specificity, and waiting periods. Different risk pathways and models are described, including Type A and Type B risks with and without vaccination and serology. The total risk calculation and modeling methodology are elaborated upon, along with the effects of serological testing.

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Risk Assessment of Rabies Introduction via Pet Movement: EFSA Journal Summary

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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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