Semi-quantitative risk assessment of African swine fever virus introduction in pig farms

Abstract

A semi-quantitative risk assessment was developed to classify pig farms in terms of the probability of introduction of African swine fever virus (ASFV). Following on-farm data collection via a specific checklist, we applied a modified failure mode and effect analysis (FMEA) to calculate the risk priority codes (RPC's), indicating increasing risk levels ranging from 1 to 5. The importance of biosecurity measures was attributed by experts. To consider geographic risk factors, we classified pig farms based on local density of farmed pigs, and on the estimated wild boar population density. The combination of RPC's with geographical risk factors resulted into a final ranking of pig farms in terms of the risk of ASFV introduction. Furthermore, the estimation of frequency and levels of non-compliance with biosecurity measures was used to identify weak points in risk prevention at farm level. The outcome of the risk assessment was affected by choices in assigning non-compliance scores and importance to specific components of biosecurity. The method was applied in 60 commercial farms in major pig production areas in Italy. Furthermore, we applied a reduced version of our checklist in 12 non-commercial/small commercial (≤20 pigs) farms in the northern Apennines. In commercial farms, highest RPC's were obtained for biosecurity measures associated with personnel practices and farm buildings/planimetry. Intervention should be addressed to training of personnel on biosecurity and ASF, to avoid contacts with other pig herds, and to improve practices in the entrance into the farm. Sharing trucks with other farms, and loading/unloading of pigs were other weak points. Fencing was classified as insufficient in 70% of the commercial farms. Among these farms, breeding units were characterised by the lowest risk of ASFV introduction (although differences among median ranks were not statistically significant: P-value = 0.07; Kruskal–Wallis test), and increasing herd size was not significantly correlated with a higher risk (Kendall's τ = −0.13; P-value = 0.14). Density of farmed pig was greatest in the main pig production area in northern Italy. Conversely, exposure to wild boars was greatest for non-commercial/small commercial farms on the Apennines, which were also characterised by non-compliance with critical biosecurity measures.

Biosecurity and Hygiene Procedures in Pig Farms: Effects of a Tailor-Made Approach as Monitored by Environmental Samples

“…The results showed that breeding/nursery farms totalized a higher mean biosecurity score than fattening farms, according to Silva et al [ 53 ] and Scollo et al [ 54 ], since these were most likely to undergo certification and annual monitoring by the official veterinary service. Moreover, breeding farms are at the top of the sanitary pyramid in pig production; they have a high sanitary status and a reduced risk of the introduction of pathogens [ 55 ].…”

Semi-Quantitative Risk Assessment of African Swine Fever Virus Introduction in Outdoor Pig Farms

“…For data collection on farms, we used a checklist that was developed by Scollo et al [ 12 ] and contained 98 items, mostly with dichotomous answers. Eighteen new items were added to the original checklist to consider specific characteristics of outdoor farming.…”

“…Items were divided into 28 so-called sub-criteria, which were assigned five-level non-compliance scores, ranging from 1 (high compliance with biosecurity measures) to 5 (lowest level of compliance), based upon the proportion of items that were assigned a positive answer, indicating compliance with biosecurity [ 12 ] ( Table 1 ). In the few cases where sub-criteria include five mutually exclusive options, presented in increasing order of non-compliance level (e.g., B2 and B3, see supplementary material ), only one of these options was chosen, based upon objective data collection in the farm: the corresponding order, from 1 to 5, was assigned as the non-compliance score for the specific item.…”

“…Sub-criteria were assigned five-level importance scores by expert elicitation, with the collaboration of eight experts from countries affected by ASF, with experience in pig management and ASF control. The importance of the original 24 sub-criteria from [ 12 ] within the six main criteria was calculated using a modified Borda method [ 15 ]. During the evaluation of the sub-criteria by the expert panel, some of the items were considered of crucial importance for biosecurity against the introduction of ASFV in pig farms, and those were defined as critical items ( Table S1 in supplementary material ).…”

“…Recently, in the framework of a research project, we applied a semi-quantitative risk assessment method to classify and rank pig farms in terms of the risk of introduction of ASFV, which takes into account the relative importance of the different transmission pathways [ 12 ]. The study was focused on commercial farms, but considering the current epidemiological situation and the growing relevance of the outdoor farming system, the study was expanded to outdoor pig farms.…”