Dynamics of African swine fever virus (ASFV) infection in domestic pigs
infected with virulent, moderate virulent and attenuated genotype II
ASFV European isolates.
Abstract
This study aimed to compare the infection dynamics of three genotype II
African swine fever viruses (ASFV) circulating in Europe. Eighteen
domestic pigs divided into three groups were infected intramuscularly or
by direct contact with two haemadsorbent ASFVs (HAD) from Poland
(Pol16/DP/ OUT21) and Estonia (Est16/WB/Viru8), and with the Latvian
non-HAD ASFV (Lv17/WB/Rie1). Parameters such as symptoms, pathogenicity,
and distribution of the virus in tissues, humoral immune response, and
dissemination of the virus by blood, oropharyngeal and rectal routes
were investigated. The Polish ASFV caused a case of rapidly developing
fatal acute disease, while the Estonian ASFV caused acute to subacute
infections in the presence of surviving animals. In contrast, animals
infected with the ASFV from Latvia developed a more subtle, mild, or
even subclinical disease. Oral excretion was sporadic or even absent in
the attenuated group, whereas in animals that developed an acute or
subacute form of ASF, oral excretion began at the same time as in the
blood, or even 3 days earlier, and persisted up to 22 days. Regardless
of virulence, blood was the main route of transmission of ASFV and
infectious virus was isolated from persistently infected animals for at
least 19 days in the attenuated group and up to 44 days in the group of
moderate virulence. Rectal excretion was limited to the acute phase of
infection. In terms of diagnostics, the ASFV genome was detected in
contact pigs from oropharyngeal samples earlier than in blood,
independently of virulence and, together with blood, both samples could
cover a longer range to detect ASFV infection. The results presented
here provide quantitative data on the spread and excretion of ASFV
strains of different virulence among domestic pigs that can help to
better focus surveillance activities and thus increase the ability to
detect ASF introductions earlier.