Risk of rabies introduction by non commercial movement of pets
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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

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”


Current legislation

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


Efsa mandate

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


Mandate cont

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


Approach

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


Model parameters

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)


Model parameters1

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


Model parameters2

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


Model parameters3

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


Model parameters4

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


Risk pathways

Risk pathways


Type a risk

Type A risk


Type b risk

Type B risk


Model description prevalence a and b

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))


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

Model descriptionRisk A and B


Model description total risk

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))


Model description modelling f t

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


Model description non linear least squares estimate of f t

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))


Effect of serological testing

Effect of serological testing


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