Recent research conducted at the Institute of Virology and Immunology in Mittelhäusern in collaboration with the University of Bern has revealed that the hygienic status of pigs plays an important role in the development of the disease caused by the African swine fever virus. The results, which have just been published in the journal PLOS Pathogens, will contribute eventually to vaccine development, researchers say.

The complexity of the ASF virus explains the lack of a safe and effective vaccine. The virus causes a fatal hemorrhagic fever in domestic pigs and wild boars. With hundreds of millions of animals affected in Africa, Europe and Asia, this disease has major socioeconomic consequences for the farmers and the global food industry. For this reason, the Institute of Virology and Immunology – the Swiss reference laboratory for ASF – investigates the immune responses needed to induce protection in pigs.

Virulent strains of ASF virus that circulate currently in Europe, Asia and in the Caribbean are fatal within days regardless of the hygienic status of the pigs. Consequently, the research aimed at investigating the immune responses in pigs uses attenuated ASF virus strains, although such strains can still be fatal in certain cases.

By infecting pigs with an attenuated ASF virus strain, the research groups at the IVI and the University of Bern, led by Nicolas Ruggli, Charaf Benarafa and Artur Summerfield, discovered that domestic pigs with a very high hygienic and health status experienced a milder and shorter form of the illness followed by complete recovery. By contrast, farm pigs with a standard conventional hygienic status suffered from protracted disease with a 50% lethality rate.

The analysis of their immune system before and during the infection suggests that a higher baseline immune activation has important consequences for the severity of the disease and the inflammatory responses. According to Charaf Benarafa, a veterinarian and immunologist, these differences in the baseline activation of the immune system in relation to the hygienic status are key factors in determining the progression of ASF during an infection with an attenuated strain.

In conclusion, Nicolas Ruggli, a veterinarian and virologist, explains that these results are very important, specifically for the development of live-attenuated vaccines against ASF and, more generally, for our understanding of host-pathogen interactions in hemorrhagic fevers.

Although Switzerland is currently free of ASF, the IVI is studying the characteristic features of the ASF virus strains circulating in Europe. Keeping abreast of the latest findings is vital to ensure effective and safe diagnosis if the disease arrives in Switzerland, and to provide the Swiss Veterinary Service with critical information on virological, immunological, clinical and pathological aspects.

The ASF virus is large and complex with a genome of more than 160 genes, half of which have unknown function. The challenges arise from the fundamental properties of this virus that infects the macrophages and hijacks the immune system. From the experimental standpoint, studies are conducted with cell cultures and pigs, and require a high-containment laboratory like the one at the IVI.

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