Proceedings of the 10th International Colloquium on Paratuberculosis

#87
Evaluation <strong>of</strong> <strong>the</strong> surveillance system for MAP infection in Swedish cattle
Frössling J, Ågren ECC, Wahlström H, Lindberg A and Sternberg Lewerin S
Department <strong>of</strong> Disease Control and Epidemiology, National Veterinary Institute, SE-751 89
Uppsala, Sweden.
ABSTRACT
Previous investigations suggest that <strong>the</strong> prevalence <strong>of</strong> M. avium subsp. Paratuberculosis
(MAP) in Swedish cattle is close to zero and all recent cases have been linked to imported
animals (<strong>the</strong> two latest cases were detected in 2000 and 2005). According to Swedish
legislation clinical suspicions are notifiable and prompt <strong>of</strong>ficial investigations. Moreover,
eradication measures are taken on detection.
The aim <strong>of</strong> this study was to evaluate <strong>the</strong> surveillance system for MAP infection in
Swedish cattle and to estimate <strong>the</strong> probability <strong>of</strong> freedom from disease. Calculations <strong>of</strong>
surveillance sensitivities and probability <strong>of</strong> freedom were made using scenario-tree
modelling. This type <strong>of</strong> model allows inclusion <strong>of</strong> information from several different sources,
e.g. random or non-random surveillance data as well as documentations <strong>of</strong> differences in
risk.
The surveillance components identified and included in <strong>the</strong> present model were fallen
stock necropsies, screening <strong>of</strong> importing herds, surveys <strong>of</strong> dairy herds, surveillance
programme in beef herds and clinical surveillance. Import <strong>of</strong> animals and participation in <strong>the</strong>
on-going surveillance programme was specified for each tested herd, in order to adjust for
differences in risk. Calculations were made for each year from 2005 to 2008 and this formed
<strong>the</strong> basis for a final estimate covering <strong>the</strong> whole period until 2009. Data including <strong>the</strong> identity
<strong>of</strong> tested herds, <strong>the</strong> number <strong>of</strong> tested individuals etc. were collected from competent
authorities and animal health organisations.
Final estimates <strong>of</strong> <strong>the</strong> surveillance system sensitivities and <strong>the</strong> probability <strong>of</strong> freedom
from MAP infections at <strong>the</strong> end <strong>of</strong> 2008 are underway.
INTRODUCTION
Infection with M. avium subsp. Paratuberculosis (MAP) has been included in <strong>the</strong> Swedish
Epizootic Act (SFS 1999:657) since 1952. According to this legislation, clinical suspicions <strong>of</strong>
MAP are notifiable in all animal species and prompt <strong>of</strong>ficial investigations and eradication
measures upon detection.
In 1993, paratuberculosis was detected in an imported beef cow. This led to a thorough
tracing and <strong>the</strong> discovery <strong>of</strong> a few more infected herds; all <strong>of</strong> beef breeds and linked to
imported individuals (Engvall et al., 1994; Viske et al., 1996). Since <strong>the</strong>n, several activities
have been undertaken for <strong>the</strong> surveillance and control <strong>of</strong> MAP infections in Sweden
(Sternberg Lewerin et al., 2007; Anonymous, 2008). The purpose has been to eradicate MAP
from <strong>the</strong> cattle population and <strong>the</strong> results indicate that implemented strategies have been
successful. In order to evaluate <strong>the</strong> current probability <strong>of</strong> freedom, and to estimate <strong>the</strong>
contribution <strong>of</strong> <strong>the</strong> different surveillance components to this, a complete investigation <strong>of</strong> <strong>the</strong>
whole surveillance system regarding MAP infection in cattle has been requested. For MAP
infection, which is a slowly progressing disease, it has also been considered important that
this type <strong>of</strong> evaluation is performed while accounting for surveillance data from previous
years. It is not reasonable that results from just one year <strong>of</strong> surveillance would be sufficient to
significantly demonstrate freedom from MAP, as it takes several years for clinical disease to
develop.
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