Different routes and doses influence protection in pigs immunised with the naturally attenuated African swine fever virus isolate OURT88/3

- Protection induced by combinations of doses and routes of immunisation of pigs with ASFV isolate OUR T88/3 is described.
- Intranasal immunisations with low and moderate doses provided complete protection with persistent low virus genome levels.
- Intramuscular immunisations with low and moderate doses provided lower protection with undetectable virus genome levels.
- Increased IL-10 serum concentrations, sometimes together with increased IFNγ, was observed before death in not-protected pigs.
- Changes in serum concentrations of TNFα, IFNγ, IL-4 and IL-10 were not detected in none of immunised protected pigs.

This study compares different combinations of doses and routes of immunisation of pigs with low virulent African swine fever virus (ASFV) genotype I isolate OURT88/3, including the intramuscular and intranasal route, the latter not previously tested. Intranasal immunisations with low and moderate doses (103 and 104 TCID50) of OURT88/3 provided complete protection (100%) against challenge with virulent genotype I OURT88/1 isolate. Only mild and transient clinical reactions were observed in protected pigs. Transient moderate virus genome levels were detected in blood samples after challenge that decreased, but persisted until the end of the experiment in some animals. In contrast, pigs immunised intramuscularly with low and moderate doses (103 and 104 TCID50) displayed lower percentages of protection (50-66%), and low or undetectable levels of virus genome were detected in blood samples throughout the study. In addition, clinical courses observed in protected pigs were asymptomatic. In pigs that were not protected and developed acute ASF, an exacerbated increase of IL-10 sometimes accompanied by an increase of IFNγ was observed before euthanasia. These results showed that factors including delivery route and dose determine the outcome of immunisation with the naturally attenuated isolate OURT88/3.