Ed Metzger from Southwest Ontario Veterinary Service, Will ASF Start With A Wimper And Not With A Bang?


The Estonian wild boar population was infected with African Swine Fever (ASF) in September 2014 and the first domestic pig farm was affected in July 2015. Estonian and German researchers studied the sequence of events in 26 outbreaks in domestic pig herds with the goal of identifying estimates for the high-risk period of entry, the possible origin of the ASF virus and the mode of virus introduction. They also recorded how the disease played out clinically

on each farm. Now, with all of the talk of the devastation caused by ASF you might assume that it would present as an unmistakably severe disease outbreak as it entered the herd. You really couldn’t miss that it was ASF, right? Unfortunately, not so true.


The first clinical signs associated with ASF were usually mild and not specific to ASF despite the fact that most of these viruses were the more virulent types. In the beginning of individual farm outbreaks, morbidity and mortality were often limited to a single pen or unit of the farm. The spread of the virus within affected farms had been slow and the

contagiousness of the virus was relatively low. In none of the affected farms could the specific route of introduction be verified with certainty but the findings suggested that virus introduction occurred via indirect transmission routes due to insufficient biosecurity. The total herd incidence of outbreaks was similar across all three years, being 2.4% in

2015 and 2016, and 2.0% in 2017. All outbreaks occurred from June to September, during the warmest period of the year. The results suggest that the increase in ASF cases in local wild boar populations is the main risk factor leading to the infection of domestic farms with 88% of outbreaks occurring in areas where ASF virus was detected in wild boar prior to the outbreak, within a radius of 15 km from the outbreak farm.


Take Home Message


The “Time Bomb” that is ASF generally starts with a very slow and subtle fuse. We will really need to be in top form with respect to early detection. Be prepared to err on the side of caution if we want to shut this one down as early

as possible.


Submitted by Ed Metzger, DVM

Ref: Nurmoja I, Mõtus K, Kristian M, Niine T, Schulz K, Depner K, Viltrop A. Epidemiological analysis of the 2015-2017 African swine fever outbreaks in Estonia. Prev Vet Med. 2018 Oct 9. pii: S0167-5877(18)30361-1. doi:




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