African swine fever virus (ASFV) was first reported in eastern Europe/Eurasia in 2007. Continued spread of ASFV has placed central European countries at risk, and in 2014, ASFV was detected in Lithuania and Poland. Sequencing showed the isolates are identical to a 2013 ASFV from Belarus but differ from ASFV isolated in Georgia in 2007.

A frican swine fever (ASF) is a complex and lethal viral disease affecting swine and has a significant socioeconomic impact on both the developed and developing world. It has a major negative effect on national, regional, and international trade and constrains pig production in affected areas. The devastating acute form of the disease is characterized, among other features, by functional and congestive-hemorrhagic disorders of the digestive and respiratory systems and causes around 100% mortality in infected pigs (1). Both European wild boars (Sus scrofa) and feral pigs are susceptible and exhibit clinical signs and mortality rates similar to those of domestic pigs. In contrast, African wild pigs (Phacochoerus and Potamochoerus spp.) are resistant to the disease (2-10).The causative agent of the disease, the ASF virus (ASFV), is a large double-stranded DNA virus and the only member of the Asfarviridae family, genus Asfivirus (11, 12). The virus genome is 170 to 192 kb long (13-17). ASF is endemic in sub-Saharan Africa, where it was first described in 1921 (18). Several outbreaks have occurred since then in Europe and South and Central America. In most non-African countries, the disease has been successfully eradicated, the only exception being Sardinia (Italy), where the disease is still endemic (19,20). In April 2007, the disease spread from East Africa to the Republic of Georgia (21), and outbreaks occurred in Armenia, Azerbaijan, and the Russian Federation (22). The ongoing spread of ASFV into adjacent eastern European countries, such as Ukraine (23,24) and Belarus (25), and the situation in Russia affecting both wild boars and domestic pigs placed neighboring areas in the European Union (EU) at risk for the spread of ASFV. The first cases of ASF in wild boars in Lithuania and Poland were reported in early 2014 in areas bordering . According to the World Organisation for Animal Health (OIE), during 2014, nearly 260 ASF cases or outbreaks in wild boars and domestic pigs were detected in EU countries (Latvia, Lithuania, Estonia, and Poland). This situation, combined with the uncertainty present in Belarus, has created a permanent risk of reintroducing ASF into the EU via wild boars or the illegal trade of contaminated pork products and waste (31).No vaccine is available to prevent ASF infection. The control and eradication measures applicable are based on classical disease control methods, including surveillance, epidemiological investigation, tracing of pigs, and stamping out in infected holdings. Citation Gallardo C, Nieto R, Soler A, Pelayo V, Fernández-Pinero J, MarkowskaDaniel I, Pridotkas G, Nurmoja I, Granta R, Simón A, Pérez C, Martín E, Fernández-Pacheco P, Arias M. 2015. Assessment of African swine fever diagnostic techniques as a response to the epidemic outbreaks in eastern European Union countries: how to improve surveillance and control programs.

An experimental infection was conducted to evaluate horizontal transmission, clinical, virological and humoral response induced in domestic pigs infected with African swine fever (ASF) genotype II virus circulating in 2014 into the European Union (EU). Ten naive pigs were placed in contact with eight pigs experimentally inoculated with the Lithuanian LT14/1490 ASF virus (ASFV) responsible for the first ASF case detected in wild boar in Lithuania in January 2014. Clinical examination and rectal temperature were recorded each day. Blood sampling from every animal was carried out twice weekly. Blood samples were examined for presence of ASF virus-specific antibodies and for determining the ASFV viral load. From the obtained results, it was concluded that the Lithuanian ASFV induced an acute disease which resulted in 94, 5% mortality. The disease was easily detected by real-time PCR prior to the onset of clinical signs and 33% of the animals seroconverted. All findings were in accordance with observations previously made in domestic pigs and wild boar when infected with ASF genotype II viruses characterized by a high virulence. One in-contact pig remained asymptomatic and survived the infection. The role of such animals in virus transmission would need further investigation.

Molecular epidemiology has proven to be an essential tool in the control of classical swine fever (CSF) and its use has significantly increased during the past two decades. Phylogenetic analysis is a prerequisite for virus tracing and thus allows implementing more effective control measures. So far, fragments of the 5´NTR (150 nucleotides, nt) and the E2 gene (190 nt) have frequently been used for phylogenetic analyses. The short sequence lengths represent a limiting factor for differentiation of closely related isolates and also for confidence levels of proposed CSFV groups and subgroups. In this study, we used a set of 33 CSFV isolates in order to determine the nucleotide sequences of a 3508–3510 nt region within the 5´ terminal third of the viral genome. Including 22 additional sequences from GenBank database different regions of the genome, comprising the formerly used short 5´NTR and E2 fragments as well as the genomic regions encoding the individual viral proteins Npro, C, Erns, E1, and E2, were compared with respect to variability and suitability for phylogenetic analysis. Full-length E2 encoding sequences (1119 nt) proved to be most suitable for reliable and statistically significant phylogeny and analyses revealed results as good as obtained with the much longer entire 5´NTR-E2 sequences. This strategy is therefore recommended by the EU and OIE Reference Laboratory for CSF as it provides a solid and improved basis for CSFV molecular epidemiology. Finally, the power of this method is illustrated by the phylogenetic analysis of closely related CSFV isolates from a recent outbreak in Lithuania.

BackgroundThe emergence in 2014 and persistence of African Swine Fever (ASF) in Lithuania has been linked to infected wild boar movement and close contact with the carcasses of other infected wild boars. Over time the number of reported cases of ASF in wild boars gradually increased, but no detailed epidemiological data has been available. Therefore, the objective of the present study was to determine ASF virus prevalence in wild boars and domestic pigs during the 2014–2017 period and further explore the current geographical distribution of the virus.ResultsOur study results show that ASF virus prevalence in hunted wild boars using PCR analysis increased from 0.83% (95% CI 0.69–0.98) to 2.27% (95% CI 2.05–2.48) from 2014 to 2016 respectively. However, there was a dramatic jump in the number of ASF positive wild boars cases in 2017 resulting in prevalence of 12.39% (95% CI 11.91–12.86) (p < 0.05).The average prevalence of ASF-specific antibodies in wild boar population during years 2014–2017 was 0.45% (95% CI 0.39–0.51) based on ELISA test results.Prevalence of ASF virus in domestic pigs ranged from 0.24% (95% CI 0.17% - 0.32) in 2015 to 2.74% (95% CI 2.33% - 3.15) in 2017. The average seasonal prevalence of ASF virus in pigs was statistically significant (p < 0.05) and ranged from 0% in spring to 3.68% (95% CI 3.32–4.05) in summer. Correlation between the pig density and number of recorded pig ASF cases in affected regions was only found in 2017 (R = 0.78, p < 0.05). No correlation was detected between the wild boar density and number of recorded pig or wild boar ASF - positive cases.ConclusionsThis study provides the first results of ASF virus prevalence changes in Lithuania during the 2014–2017. The overall results confirm the relatively high prevalence of ASF virus in wild boar that was gradually increasing from 2014 to 2017. In the last year of study, the number of ASF positive cases in both domestic pigs and wild boars had unexpectedly increased several times. A better understanding of current status of the disease will enable better control and prevent further spread of ASF virus in Western Europe.