Characterization of pathogenic and non-pathogenic African swine fever virus isolates from Ornithodoros erraticus inhabiting pig premises in Portugal

Abstract

Ten African swine fever virus isolates from the soft tick Ornithodoros erraticus collected on three farms in the province of Alentejo in Portugal were characterized by their ability to cause haemadsorption (HAD) of red blood cells to infected pig macrophages, using restriction enzyme site mapping of the virus genomes and by experimental infection of pigs. Six virus isolates induced haemadsorption and four were non-haemadsorbing (non-HAD) in pig macrophage cell cultures. The restriction enzyme site maps of two non-HAD viruses, when compared with a virulent HAD isolate, showed a deletion of 9?6 kbp in the fragment adjacent to the left terminal fragment and of 1?6 kbp in the right terminal fragment and an insertion of 0?2 kbp in the central region. The six HAD viruses isolated were pathogenic and produced typical acute African swine fever in pigs and the four non-HAD isolates were non-pathogenic. Pigs that were infected with non-HAD viruses were fully resistant or had a delay of up to 14 days in the onset of disease, after challenge with pathogenic Portuguese viruses. Non-HAD viruses could be transmitted by contact but with a lower efficiency (42-50 %) compared with HAD viruses (100 %). The clinical differences found between the virus isolates from the ticks could have implications for the long-term persistence of virus in the field because of the cross-protection produced by the non-pathogenic isolates. This may also explain the presence of seropositive pigs in herds in Alentejo where no clinical disease had been reported.

Pig Major Acute-Phase Protein and apolipoprotein A-I responses correlate with the clinical course of experimentally induced African Swine Fever and Aujeszky's disease

“…This viral infection has been the subject of a large number of studies related to different aspects of infection: pathogenesis, target cells, cytokine regulation [16,37] and apoptosis of infected cells [8,33]. The clinical course of ASF, the evolution of fever and the viremia titer profiles were very similar in animals inoculated with the same isolate and doses of the virus, as has been reported in the literature [4,33,34] but clinical signs are not sufficient to perform a differential diagnosis in the field. With respect to the serum markers reported here, the major changes in APP response were observed after 4 days p.i.…”

“…It is caused by a large, enveloped DNA virus that induces an acute haemorrhagic disease characterised by severe immune cell depletion and apoptosis induction in target and immune defence cells [33]. The clinical outcome of the disease ranges from lethal to moderately virulent or non-virulent according to the virus strain [4,34]. A generalised infection rapidly follows via the bloodstream and is associated with a high fever (up to 42 • C) and acute death of the animal.…”

No evidence of African swine fever virus replication in hard ticks

“…(Boinas et al, 2004) LIV 13/33 Spleen homogenate 5.5 (Rennie et al, 2000) Georgia 2007/1 Defibrinated blood 5.9 (Rowlands et al, 2008) Malta'78 Defibrinated blood 5.6 (Wilkinson et al, 1980) Netherlands'86 Defibrinated blood 5.4 (Terpstra and Wensvoort, 1986) Brazil'78 Defibrinated blood 5.4 (Mebus et al, 1978) …”

3.3 Afrikanische Schweinepest

“…Hierbei kann es zu Kontakten zwischen Ornithodoros Zecken und domestizierten Hausschweinen kommen (Thomson, 1985 . Auf dem afrikanischen Kontinent werden hingegen selten Kontakte zwischen afrikanischen Wildschweinearten und Hausschweinen beobachtet (Jori and Bastos, 2009, Thomson, 1985, Wilkinson, 1986 (Boinas et al, 2004). Indirekt kann man das Vorhandensein dieser speziellen Lederzeckenart mittels eines Antikörper-ELISAs feststellen (Canals et al, 1990, Oleaga-Pérez et al, 1993 (Montgomery, 1921).…”