Statistical Exploration of Local Transmission Routes for African Swine Fever in Pigs in the Russian Federation, 2007-2014

Abstract

African swine fever (ASF) is a devastating viral disease of swine that is present in both pigs and wild boar in the western part of the Russian Federation and the eastern part of the European Union. It represents a significant threat for the European pig production industry as neither treatment nor vaccine is available. This study analysed the spatial and spatio-temporal distributions of ASF cases that were reported in domestic pigs and wild boar for assessing the likelihood of wild boar-to-domestic pig and farm-to-farm transmission routes in the epidemic that occurred from 2007 to 2014 in the Krasnodar and the Tver regions, two of the most affected areas of the Russian Federation. Results suggest that in both regions, the spatial proximity to an infectious farm was a strong risk factor for infection of a susceptible farm. In the Krasnodar region, the results of the statistical analysis suggest that the epidemics in wild boar and in domestic pigs were independent from each other. In contrast, there seemed to be a dependence between the two epidemics in the Tver region. But because outbreaks in domestic pigs were not statistically significantly clustered around wild boar cases, the joint spatial distribution of wild boar cases and of outbreaks in domestic pigs in the Tver region may be explained by regular spillovers from the domestic pig to the wild boar population. These findings confirm the need to maintain high biosecurity standards on pig farms and justify strict control measures targeted at domestic pig production such as culling of infected herds and local movement restrictions.

Relevant Measures to Prevent the Spread of African Swine Fever in the European Union Domestic Pig Sector

“…The risk of introduction and exposure to ASF depends on the epidemiological characteristics of the country, area, and type of farm (31, 70, 74–80). Pig production in Europe is highly heterogeneous with different biosecurity standards and productive levels (39, 81).…”

“…On breeding farms, semen (21, 40, 45), embryos, or ova should come from free-ASFV certified farms (15, 19, 44, 57). Visits should be discouraged (44, 45), limiting access to the farm and animals, to workers and veterinarian services (5, 31, 52, 63). If visitors enter the farm, visits should be registered and visitors should follow strict biosecurity measures regarding footwear and clothing (45, 47, 52, 57, 58, 64).…”

“…Key measures to prevent the introduction of ASF on commercial farms are to establish clear clean/dirty areas for personnel including changing rooms and shower (15, 18, 31, 49, 55) and to review logistical arrangement for entry of new animals. This measure will allow for the adequate identification of critical control points (15), which is particularly relevant since contaminated vehicles transporting pigs or carcasses are associated to a high risk of disease transmission (18, 70).…”

“…Moreover, internal audits or self-evaluation need to be periodically conducted to enforce biosecurity measures (15, 18). Furthermore, a set of rules on food for workers entering the farm should be clearly specify (31) and food should be restricted to eating rooms (15, 18) or not allowed (44, 52). …”

Modelling African swine fever presence and reported abundance in the Russian Federation using national surveillance data from 2007 to 2014

“…For example, although wild boar are considered not to have played a major role in the transmission of ASFv to domestic pigs (Iglesias et al, 2015;Vergne et al, 2015a), the use of wild boar density instead of the forest coverage would have allowed a more precise examination of wild boar's role in the epidemiology of ASF.…”