Expert workshop
A total of 24 potential disease pathways could be defined by combining
the information collected during expert and farmer interviews, and were
classified during the expert workshop according to the overall frequency
of occurrence and the specific likelihood of disease spread for ASF,
PRRS and EP.
Initial answers of the experts diverged most of the times (Supplementary
Table S3). Concerning the frequency of pathway occurrence, the same
answer was given by all experts in three cases, namely for the direct
trade between farms (high frequency), transport performed by the farmer
(moderate frequency), and visits by feed advisors (high frequency).
Unanimous initial answers about disease spread likelihood were observed
slightly more often: for seven pathways in the case of ASF, for eight in
the case of PRRS and for six in the case of EP.
The final scores on frequency of occurrence and likelihood spread, on
which the experts agreed after open discussion are presented in Table 3,
together with the overall relevance for the three diseases of interest
obtained by means of risk assessment matrices. Out of the ten
transport-related disease pathways, four seemed to have a high frequency
of occurrence, which, coupled with fair-to-high likelihood of disease
transmission, resulted in high-to-very-high relevance for ASF, PRRS
and/or EP spread. Another pathway with fair-to-high relevance for
disease spread was self-performed pig transports by the farmer (pathway
10). On the one hand, experts believed that farmers may wash
transporters less frequently after transports or may get in contact with
their colleagues more often than professional lorry drivers. On the
other hand, they pointed out that farmers are considerably less likely
than trader companies to visit several farms on the same day, hence
having a lower relevance for disease spread compared to transports
performed by traders.
Out of the five pathways in the farmer encounters area, two were
classified as highly relevant for PRRS transmission. These were
“sharing of other farming equipment” (pathway 14) and “going to the
carcass collection point” (pathway 15). “Sharing of pig farming
equipment” (pathway 13) may result in a higher likelihood of pig
disease transmission but happens less frequently, resulting in an
overall low-to-fairly-low relevance.
In the external collaborators area, the other carcass management-related
practice (pathway 16) was found to be highly relevant for the spread of
PRRS and ASF. Other on-farm visits from external collaborators consist
in manure trade between farms, veterinarian visits, feed advisor visits
and other official farm visits. Despite the high frequency of such
visits, these appear to have only low-to-moderately-low relevance for
propagation of ASF, as likelihood of spread was categorized as low.
However, they are considered as highly relevant for transmission of
PRRS, which can be propagated much more efficiently via fomites, as well
as for the transmission of EP in the case of feed advisors.
Finally, among the four environment-related contact pathways, the only
one relevant for disease spread is wild boar movements from farm to
farm, with relevance ranging from fairly high for ASF to high for PRRS
and EP.
Table 3 List of disease pathways
between Swiss pig holdings resulting from the final expert workshop. For
each pathway, the frequency of occurrence, and the likelihood of disease
propagation through it for ASF, PRRS and EP are reported. The three
rightmost columns show the overall relevance of pathways for the three
diseases of interest, as a product of frequency of occurrence and
likelihood of disease spread.