Author details:
1 Veterinary Surveillance Department, Food and Veterinary Service, Riga, Latvia; 2 Faculty of Veterinary Medicine, Latvia University of Life Sciences and Technologies, Jelgava, Latvia; 3 Institute of Food Safety, Animal Health and Environment BIOR, Riga, Latvia; 4 Institute of Veterinary Medicine and Animal Sciences, Estonian University of Life Sciences, Tartu, Estonia; 5 Friedrich-Loeffler-Institut (FLI), Federal Research Institute for Animal Health, Greifswald-Insel Riems, Germany.
Abstract:
African swine fever (ASF) was first detected in Latvia in wild boar at the Eastern border in June 2014. Since then ASF has continued to spread in wild boar populations covering almost whole territory of the country. Sporadic outbreaks occurred at the same time in domestic pig holdings located in wild boar infected areas. Here we present the results of the epidemiological investigation in two large commercial farms. Several parameters were analyzed to determine the high risk period (HRP) and to investigate the ASF virus spread within the farm. Clinical data, mortality rates and laboratory results proved to be good indicators for estimating the HRP. The measures for early disease detection, particularly the enhanced passive surveillance that is targeting dead and sick pigs, were analyzed and discussed. Enhanced passive surveillance proved to be a key element to detect ASF at an early stage. The study also showed that ASF virus might spread slowly within a large farm depending mainly on direct contacts between pigs and the level of internal biosecurity. Findings suggest improvements in outbreak prevention, control measures and may contribute to a better understanding of ASF spreading patterns within large pig herds. Culling of all pigs in large commercial farms could be reconsidered under certain conditions.
Keywords: African swine fever; commercial farms; early detection; high risk period; disease control.
1. Ol,ševskis, E.; Guberti, V.; Seržants, M.; Westergaard, J.; Gallardo, C.; Rodze, I.; Depner, K. African swine
fever virus introduction into the EU in 2014: Experience of Latvia. Res. Vet. Sci. 2016, 105, 28–30. [CrossRef]
2. EFSA (European Food Safety Authority); Depner, K.; Gortazar, C.; Guberti, V.; Masiulis, M.; More, S.;
Olsevskis, E.; Thulke, H.-H.; Viltrop, A.; Wozniakowski, G.; et al. Scientific report on the epidemiological
analyses of African swine fever in the Baltic States and Poland. EFSA J. 2017, 15, e5068. [CrossRef]
3. EFSA (European Food Safety Authority); Cortinas Brahantes, J.; Gogin, A.; Richardson, J.; Gervelmeyer, A.
Scientific report on epidemiological analyses on African swine fever in the Baltic countries and Poland. EFSA
J. 2017, 15, e4732. [CrossRef]
4. Schulz, K.; Olsevskis, E.; Staubach, C.; Lamberga, K.; Serzants, M.; Cvetkova, S.; Conraths, F.J.; Sauter-Louis, C.
Epidemiological evaluation of Latvian control measures for African swine fever in wild boar on the basis of
surveillance data. Sci. Rep. 2019, 9, 4189. [CrossRef] [PubMed]
5. EFSA (European Food Safety Authority); Boklund, A.; Cay, B.; Depner, K.; Foldi, Z.; Guberti, V.; Masiulis, M.;
Miteva, A.; More, S.; Olsevskis, E.-H.; et al. Scientific report on the epidemiological analyse s of African
swinefever in the European Union (November 2017 until November 2018). EFSA J. 2018, 16, e5494. [CrossRef]
6. EFSA (European Food Safety Authority); Miteva, A.; Papanikolaou, A.; Gogin, A.; Boklund, A.; Bøtner, A.;
Linden, A.; Viltrop, A.; Schmidt, C.G.; Ivanciu, C.; et al. Scientic report on the epidemiological analyses
of African swine fever in the European Union (November 2018 to October2019). EFSA J. 2020, 18, e5996.
[CrossRef]
7. Pautienius, A.; Grigas, J.; Pileviciene, S.; Zagrabskaite, R.; Buitkuviene, J.; Pridotkas, G.; Stankevicius, R.;
Streimikyte, Z.; Salomskas, A.; Zienius, D.; et al. Prevalence and Spatiotemporal Distribution of African
Swine Fever in Lithuania, 2014–2017. Virol. J. 2018, 15, 177. [CrossRef]
8. Pejsak, Z.; Niemczuk, K.; Frant, M.; Mazur, M.; Pomorska-Mol, M.; Zietek-Barszcz, A.; Bocian, L.; Lyjak, M.;
Borowska, D.; Wozniakowski, G. Four Years of African Swine Fever in Poland. New Insights into
Epidemiology and Prognosis of Future Disease Spread. Pol. J. Vet. Sci. 2018, 21, 835–841.
9. Bellini, S.; Rutili, D.; Guberti, V. Preventive measures aimed at minimizing the risk of African swine fever
virus spread in pig farming systems. Acta Vet. Scand. 2016, 58, 82. [CrossRef]
10. Lamberga, K.; Seržants, M.; Ol,ševskis, E. African swine fever outbreak investigations in a large commercial
pig farm in Latvia: A case report. Berl. Munch. Tierarztl. Wochenschr. 2019, 132, 151–155.
11. European Commission. Council Directive 2002/60/EC of 27 June 2002 Laying Down Specific Provisions for
the Control of African Swine Fever and Amending Directive 92/119/EEC as Regards Teschen Disease and
African Swine Fever. 2002. Available online: https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:
02002L0060-20080903 (accessed on 18 June 2020).
12. Commission Implementing Decision 2014/709/EU of 9 October 2014 Concerning Animal Health Control
Measures Relating to African Swine Fever in Certain Member States and Repealing Implementing Decision
2014/178/EU. Available online: https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32014D0709
(accessed on 26 June 2020).
13. Working Document SANTE/7112/2015/Rev. 3, Principles and Criteria for Geographically defining ASF
Regionalization. Available online: https://ec.europa.eu/food/sites/food/files/animals/docs/ad_controlmeasures_asf_wrk-doc-sante-2015-7112.pdf (accessed on 2 July 2020).
14. Arias, M.; Jurado, C.; Gallardo, C.; Fernandez-Pinero, J.; Sanchez-Vizcaino, J.M. Gaps in African swine fever:
Analysis and priorities. Transbound. Emerg. Dis. 2017, 1 (Suppl. 65), 235–247. [CrossRef]
15. Guinat, C.; Gubbins, S.; Vergne, T.; Gonzales, J.L.; Dixon, L.; Pfeiffer, D.U. Experimental pig-to-pig transmission
dynamics for African swine fever, Georgia 2007/1 strain. Epidemiol. Infect. 2016, 144, 25–34. [CrossRef]
[PubMed]
16. Pietschmann, J.; Guinat, C.; Beer, M.; Pronin, V.; Tauscher, K.; Petrov, A.; Keil, G.; Blome, S. Course and
transmission characteristics of oral low-dose infection of domestic pigs and European wild boar with a
Caucasian African swine fever virus isolate. Arch. Virol. 2015, 160, 1657–1667. [CrossRef] [PubMed]
17. Nurmoja, I.; Motus, K.; Kristian, M.; Niine, T.; Schulz, K.; Depner, K.; Viltrop, A. Epidemiological analysisof
the 2015–2017 African swine fever outbreaks in Estonia. Prev. Vet. Med. 2018. [CrossRef] [PubMed]
18. Zani, L.; Dietze, K.; Dimova, Z.; Forth, J.H.; Denev, D.; Depner, K.; Alexandrov, T. African Swine Fever in a
Bulgarian Backyard Farm—A Case Report. Vet. Sci. 2019, 6, 94. [CrossRef] [PubMed]
19. Chenais, E.; Depner, K.; Guberti, V.; Dietze, K.; Viltrop, A.; Ståhl, K. Epidemiological considerations on
African swine fever in Europe 2014–2018. Porc. Health Manag. 2019, 5, 6. [CrossRef]
20. European Commission (EC). Strategic Approach to the Management of African Swine Fever for the EU,
SANTE/7113/2015—Rev12. Available online: https://ec.europa.eu/food/sites/food/files/animals/docs/ad_
control-measures_asf_wrk-doc-sante-2015-7113.pdf (accessed on 11 June 2020).
21. Gabriel, C.; Blome, S.; Malogolovkin, A.; Parilov, S.; Kolbasov, D.; Teifke, J.P.; Beer, M. Characterization of
African swine fever virus Caucasus isolate in European wild boars. Emerg. Infect. Dis. 2011, 17, 2342–2345.
[CrossRef]
22. Blome, S.; Gabriel, C.; Beer, M. Pathogenesis of African swine fever in domestic pigs and European wild boar.
Virus Res. 2013, 173, 122–130. [CrossRef]
23. Ol,ševskis, E.; Schulz, K.; Staubach, C.; Seržants, M.; Lamberga, K.; Pule, D.; Ozoli ¯ n, š, J.; Conraths, F.;
Sauter-Louis, C. African swine fever in Latvian wild boar—A step closer to elimination. Running head:
Epidemiology of African swine fever in Latvia. Transbound. Emerg. Dis. 2020. [CrossRef]
24. Regulation (EU) 2016/429 of the European Parliament and of the Council of 9 March 2016 on Transmissible animal
diseases and amending and repealing certain acts in the area of animal health (‘Animal Health Law’); Council of the
European Union: Brussels, Belgium, 2016.
25. Gallardo, C.; Soler, A.; Nieto, R.; Cano, C.; Pelayo, V.; Sanchez, M.A.; Pridotkas, G.; Fernandez-Pinero, J.;
Briones, V.; Arias, M. Experimental Infection of Domestic Pigs with African Swine Fever Virus Lithuania
2014 Genotype II Field Isolate. Transbound. Emerg. Dis. 2015, 64, 300–304. [CrossRef]
26. Olesen, A.S.; Lohse, L.; Boklund, A.; Halasa, T.; Gallardo, C.; Pejsak, Z.; Belsham, G.J.; Rasmussen, T.B.;
Bøtner, A. Transmission of African swine fever virus from infected pigs by direct contact and aerosol routes.
Vet. Microbiol. 2017, 211, 92–102. [CrossRef] [PubMed]
27. European Commission. Commission Decision 2003/422/EC of 26 May 2003 Approving an African Swine Fever
Diagnostic Manual. 2003. Available online: https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:
32003D0422 (accessed on 18 June 2020).
28. Gallardo, C.; Fernández-Pinero, J.; Arias, M. African swine fever (ASF) diagnosis, an essential tool in the
epidemiological investigation. Virus Res. 2019, 271, 197676. [CrossRef] [PubMed]
29. Guiant, C.; Gogin, A.; Blome, S.; Keil, G.; Pollin, R.; Pfeiffer, D.U.; Dixon, L. Transmission routes of African
swine fever virus to domestic pigs: Current knowledge and future research directions. Vet. Rec. 2016, 178,
262–267. [CrossRef]
30. Lamberga, K.; (Veterinary Surveillance Department, Food and Veterinary Service, Riga, Latvia). Personal
communication with Food and Veterinary Service, 2020.
31. Penrith, M.-L.; Vosloo, W. Review of African swine fever: Transmission, spread and control. J. S. Afr. Vet.
Assoc. 2009, 80, 58–62