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Surveillance of classical swine fever in wild boar in Croatia from december 2005 to APRIL 2012

Structured non-random active surveillance (AS) of classical swine fever (CSF) in wild boar was established in Croatia in December 2005. Based on the data gathered before 2005 and in regards to CSF occurrence and risk the country was divided into CSF low risk and CSF high risk areas. AS is implemented by hunters and revisited on a yearly basis in order to account for information collected during the previous hunting season (HS). From December 2005 to April 2009 in CSF low risk areas number of wild boar to be included in the Program should have allowed for detection of CSF seroprevalence at 0.1 level with 0.95 confidence interval (CI) at a hunting ground (HG) level. In CSF high risk areas the sample size was calculated to allow for estimation of CSF seroprevalence of 0.5, with 0.95 CI and 0.1 precision. From 2005 to 2009 the hunting bag was assumed to be an approximation of actual wild boars population size per HG. After April 1, 2009 the design was adjusted to the situation on the field. In areas where CSF was directly or indirectly confirmed in wild boars, all hunted wild boars were supposed to be a subject of sampling for CSF virological and serological testing. In the rest of the country the sample size was determined to allow for detection of seroprevalence at 0.05 level as well as CSF seroprevalence and virological prevalence at 0.02 level, with 0.95 CI at the level of hunting area (HA) of size of 200 to 400 km2 , dependant on the risk status of the HA. Also estimated wild boar population size was used during this period when calculating number of wild boars to be sampled per HA. At the beginning of the implementation of the AS a low sampling rate allowed for no reliable inferences on CSF status in majority of HGs. Sensitivity of inferences from AS during the survey period at a HG or HA was increasing over time. Seven years of implementation of CSF surveillance in wild boar allowed for detection/demarcation of the areas in the country where CSF virus was circulating as early as in 2006 and as late as in 2009. The program also provided for information on evolution of CSF infection in two distinct HA of 250 km2 and 110 km2, as well as possible factors that were associated with limited the spread of the infection. Size of epidemiological unit (EU) is of relevance for sensible AS in wild boar and too large EU may lead to underestimation of the size of the problem. 259 STOP – CSF, International Scientific Conference, Novi Sad, Serbia, 2012 Long term implementation of AS and testing of more than 40, 000 wild boars during the study period, contributed to informed division of the country based on CSF risk and subsequent implementation of preventive measures on domestic pigs holdings in the vicinity of affected HG. AS allowed for collection of direct and indirect evidence to support the hypothesis which parts of Croatia are free from CSF infection in wild boar at 0.05 or 0.02 level with 95% CI. This status of the country is directly associated with movement and trade of pigs both domestic and wild without restriction.

wild boar ; CSF ; surveillance ; prevalence

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