From Georgia to Catalonia, this is how swine fever has evolved in the last twenty years

BarcelonaUntil last week, African swine fever (ASF) had not been detected in Spain for thirty years. The outbreak in Catalonia has already resulted in 13 positive cases among wild boar in the Collserola Natural Park, but its origin remains a mystery. The initial hypothesis that the virus arrived in Spain through a contaminated meat sample has lost traction in recent hours, because The Spanish government suspects that it may have come from a research center that studies the disease. And it has opened an investigation to clarify the matter. The key here is the sequencing of the virus, that is, the identification of the genetic mutations behind this pathogen, like a kind of ID card that makes it unique. According to the Ministry of Agriculture, the results of the analysis indicate that the genetic variants of the virus that caused the Catalan outbreak are more similar to those that began circulating in Georgia in 2007—which are commonly used in research centers—than to those currently affecting other countries.

2007 marks the beginning of the return of African swine fever (ASF) to Europe and Asia after the disease was considered eradicated, since "the virus has continued to spread over the last twenty years," explains Daniel Pérez Núñez, a postdoctoral researcher at the ASF virus laboratory of the Center for Molecular Biology, to ARA. That year, the disease entered Russia from Georgia and established itself in the south of the country, but it wasn't until 2011 that it began to spread northward. In just one year, the number of outbreaks reported by Russian authorities in the central region of the country increased significantly, and its presence was finally confirmed in Ukraine in 2012 and in Belarus in 2013, two countries that share borders with European Union member states.

More than a decade ago, the virus was knocking at Europe's door, but, according to the Ministry of Agriculture, those responsible for its spread across the countries of the Old Continent were, precisely, the eastern neighbors who detected it first. "The lack of transparency from these countries regarding the epidemiological situation, as well as the measures adopted to combat the disease, and the lack of cooperation with the European Union (EU), has been the main source of uncertainty when assessing the risk posed by the disease," argues the Spanish government. A year after its detection in Belarus, the virus's entry into EU countries was confirmed with positive cases in wild boar and domestic pigs in Lithuania, Latvia, Estonia, and Poland. It was then, in 2014, that Europe tightened measures to try to curb the spread of the virus and minimize the economic impact. Expansion across Europe and arrival in China

Despite European efforts to contain the virus, member states failed to stem the trickle of cases in wild boar and some domestic pig farms in northeastern Europe, and in 2017 the disease was detected for the first time in the Czech Republic and Romania. The year 2018 was key to the disease's spread: on the one hand, there was an increase in cases in already affected areas compared to the same period in previous years, and it continued to advance with its first appearance in Hungary, Belgium, and Bulgaria. On the other hand, African swine fever (ASF) was declared for the first time in China and "spread throughout the country," recalls Yolanda Revilla, director of the virus laboratory at the Severo Ochoa Molecular Biology Center.

Another factor to consider is that, in recent years, every summer has seen a significant increase in the number of reported cases, facilitating its spread, and more and more countries in our region have encountered the disease. In 2019, it was reported in Slovakia and Serbia; in 2020, it was detected for the first time in Greece and Germany; in 2022, in North Macedonia and Italy; in 2023, in Bosnia and Herzegovina, Croatia, Kosovo, and Sweden; and in 2024, in Montenegro and Albania. For all these reasons, experts were not alarmed when the first cases were detected in Collserola, although the sequencing of the virus has raised concerns about its origin, and they are now calling for a thorough investigation to determine, with absolute certainty, how this outbreak emerged.

Over these eighteen years, the virus has circulated in different countries, leading to progressive changes in its genome and resulting in various subgroups and variants that allow researchers to trace the pathogen and identify whether outbreaks are related. This is how the Ministry of Agriculture suggests that what is affecting wild boar in Catalonia does not correspond to what is currently being transmitted in other parts of Europe.

First cases in the 20th century

Until now The contaminated meat theory was the most plausible to scientists.Since the most common entry point for the virus in a disease-free country is through pork products that have been used as feed for other pigs. In 2021, for example, outbreaks were declared in the Dominican Republic and Haiti, and experts point to a container of contaminated meat from China as the source. In fact, it was first detected in Europe in the late 1950s, when it was introduced to Portugal from Angola precisely through food scraps. At that time, it spread to other European countries: Spain in 1960, France in 1964, Italy in 1967, Belgium in 1985, and the Netherlands in 1986. The disease was considered endemic in Portugal and Spain for decades, until 1995, when both countries...

For all these reasons, the Spanish government maintained until a week ago that "Spain was considered a paradigm in the eradication of this disease," since in the 1980s it implemented a program to detect infected animals and cull them until the population was completely eradicated. Now it remains to be seen what the real impact of the current outbreak is, and if it is contained, a year must pass without any new positive cases being identified before the disease can be declared eradicated again.

No vaccines (yet)

Another key reason why the spread of the disease hasn't slowed in recent years is the lack of vaccines, explains Revilla, who leads a laboratory working to develop one. "It's such a complex virus that obtaining a vaccine is very difficult," the expert reasons, also criticizing the lack of resources and support for their development. So far, the prevention strategy that has yielded "the most promising results" is a vaccine that uses an attenuated virus, meaning it only mildly infects animals to confer protection against the disease. However, other "safer" strategies are being tested in collaboration with the private sector. In fact, they will begin testing it next year on animals in Kenya, but the company has already warned that it won't be available to eradicate the current outbreak. The researcher estimates that, at the very least, it won't be available for another year, provided sufficient resources are allocated for its development.