# Modelling as a tool to identify key measures to reduce Salmonella prevalence in slaughter pigs

Amandine Lurette, Suzanne Touzeau, Pauline Ezanno, Thierry Hoch, Christine Fourichon, Henri H. Seegers, Catherine C. Belloc

► To cite this version:

Amandine Lurette, Suzanne Touzeau, Pauline Ezanno, Thierry Hoch, Christine Fourichon, et al. Modelling as a tool to identify key measures to reduce Salmonella prevalence in slaughter pigs. 1. International Conference on Infectious Disease Dynamics (Epidemics), Dec 2008, Asilomar, United States. 2008. [hal-02813018](https://hal.inrae.fr/hal-02813018)

HAL Id: hal-02813018

https://hal.inrae.fr/hal-02813018

Submitted on 7 Aug 2023

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# Modelling as a tool to identify key measures to reduce *Salmonella* prevalence in slaughter pigs

A. Lurette<fnref n="1" />, S.Touzeau<fnref n="2" />, P. Ezanno<fnref n="1" />, T. Hoch<fnref n="1" />, C. Fourichon<fnref n="1" />, H. Seegers<fnref n="1" />, C. Belloc<fnref n="1" />

## INTRODUCTION

The control of *Salmonella* in pigs is a major public health concern.

The objective of this study was to demonstrate how the modelling approach developed allows to determine better ways of applying control measures: animals targeted, periods of application and the measure of efficiency required; in order to significantly reduce the *Salmonella* prevalence in pigs.

<figure><img src="image_2.png" /></figure>

## MATERIALS & METHODS

A stochastic mathematical model representing both the pig and sow populations within a farrow-to-finish herd and the *Salmonella* spread was used (Lurette *et al.*, 2008) (Fig. 1).

<figure><img src="image_3.png" /><figcaption>Figure 1. General framework of the epidemiological model</figcaption></figure>

### Measures to test :

- Optimize the implementation of existing measures → acidified food Farzan et al., 2006

- Identify new potential measures and their implementation → vaccination Roesler et al., 2006

### Representation in the model :

- Hypothesis on implied mechanisms → effect on three epidemiological parameters: infection probability (*p*<sub>i</sub>), quantity shed (*Q*) and re-activation probability (*βr*) → 3 reduction levels (25, 50 & 90%) from their default value.

- Selection of animals and duration → 2 types of measure

* Measure 1) either on sows or pigs during their lifetime

* Measure 2) on lactating sows, on post-weaning or on finishing pigs

## RESULTS

<table><caption>Table 1. Mean seroprevalence in groups of delivered pigs according to reduction in the probability of infection (*p*<sub>i</sub>) or of the quantity shed (*Q*). Reference : default values for all parameters</caption><thead><tr><th rowspan="2">Animal Targeted</th><th rowspan="2">Reference</th><th colspan="3">Infection probability</th><th colspan="3">Quantity shed</th></tr><tr><th><i>p</i><sub>i</sub></th><th>50</th><th>90</th><th><i>Q</i></th><th>50</th><th>90</th></tr></thead><tbody><tr><td colspan="8"><strong>Measure 1)</strong></td></tr><tr><td>Sows</td><td>19.8</td><td>10.1</td><td>1.9</td><td>0.2</td><td>15.2</td><td>13.4</td><td>4.1</td></tr><tr><td>Pigs</td><td>19.8</td><td>16</td><td>13.1</td><td>7.7</td><td>19.5</td><td>16.8</td><td>10.8</td></tr><tr><td colspan="8"><strong>Measure 2)</strong></td></tr><tr><td>Lactating sows</td><td>19.8</td><td>19.8</td><td>19.6</td><td>18.7</td><td>17.2</td><td>15.4</td><td>7.1</td></tr><tr><td>Finishing pigs</td><td>19.8</td><td>15.9</td><td>10.9</td><td>6.3</td><td>19.8</td><td>19.8</td><td>19.8</td></tr></tbody></table>

<figure><img src="image_4.png" /></figure>

Scenarios decreasing the mean seroprevalence differ according to the parameter considered, its level of reduction and the animal targeted (Tab. 1 & Fig. 2). A mean seroprevalence in groups of delivered pigs equal or less to 5% can be obtained by:

- Reducing the quantity of bacteria shed by the sows by 90%,

- Reducing both the probability of infection and the quantity shed by 25% and 50% respectively.

Moreover, when also combined with a reduction of the reactivation probability, the scenario can lead to a mean seroprevalence under 1%.

<figure><img src="image_5.png" /><figcaption>Figure 2. Mean seroprevalence in groups of delivered pigs according to the reduction in the probability of infection (*p*<sub>i</sub>), the quantity shed (*Q*) and the reactivation probability (*βr*).</figcaption></figure>

## DISCUSSION

Preliminary results that determine the required effect of a control measure on infection parameters.

Further experimental studies are needed to confirm such effects are attainable.

Moreover, our model allows to assess the effects of combinations of control measures.

<footnote n="1">¹INRA, ENVN, UMR1300 Bio-agression Epidémiologie et Analyse de Risque, BP 40706, F-44307 Nantes, France,</footnote>

<footnote n="2">²INRA, UR341 Mathématiques et Informatique Appliquées, F-78350 Jouy-en-Josas, France</footnote>