Selected aspects related to epidemiology, pathogenesis, immunity, and control of African swine fever

Abstract African swine fever (ASF) is currently one of the most severe viral infections of domestic pigs, wild boars, and other hosts belonging to Suidae family. ASF is also considered as the most complex and devastating infectious and haemorrhagic disease of swine due to its severe socio-economic impact and transboundary character. ASF it is a notifiable disease and due to the lack of specific treatment and vaccine, the disease can be only limited by the administrative measures comprising wild boar hunting and stamping out of affected pigs. ASF occurred for the first time in Kenya in 1921 while in Europe (Portugal) the virus was detected at the end of the 1950s. In spite of successful eradication of this threat in a number of affected regions, the virus remains endemic in both feral and domestic pigs in Africa and Sardinia. The ‘new era’ of ASF started in 2007 after its re-introduction to Georgia. Following its intensive expansion, the virus spread to other Caucasian countries, including the territory of the Russian Federation. In 2014 the virus reached Ukraine, Belarus, and, consequently, European Union countries: Lithuania, Latvia, Estonia, and Poland. The occurrence of ASF in wild boars and pigs had a severe impact on both epidemiology and economy because of the national and international transport and trade consequences. Up to date, starting from the February 2014, eighty ASF cases in wild boar and three outbreaks in domestic pigs have been diagnosed. Taking into account the diverse rate of spread in Poland, this review aims to present and discuss the current state of knowledge on ASF including its epidemiology, pathology, transmission, and perspectives of control.

Download Full-text

Territorial pattern between outbreaks of ASF among wild and domestic pigs in Ukraine

Scientific Messenger of LNU of Veterinary Medicine and Biotechnology ◽

10.32718/nvlvet10403 ◽

2021 ◽

Vol 23 (104) ◽

pp. 18-22

Author(s):

Ye. O. Dudnyk

Keyword(s):

Wild Boar ◽

African Swine Fever ◽

Weak Links ◽

Wild Boars ◽

Domestic Pigs ◽

Wild Pigs ◽

Animal Populations ◽

Focus Of Infection ◽

Epizootic Process

The article presents the results of the analysis of the epizootic situation in Ukraine regarding African swine fever among domestic and wild pigs from 2012 to 2020 and identifies the main sources of virus spread as well as weak links in the biological safety system of farms. When studying the statistical material of the Food and Agriculture Organization of the United Nations (FAO) and the State Service of Ukraine on Food Safety and Consumer Protection regarding animal morbidity, revealed a territorial pattern between the outbreaks of African swine fever among wild boars and domestic pigs of private farms and pig-breeding complexes, and proved the involvement of the European boar in the epizootic process as a natural reservoir and mobile focus of infection. Calculated the number of outbreaks of African swine fever among wild boars and domestic pigs within the same region and district, and studied the sequence of the emergence of foci on limited territories. Analyzed the natural focality of the disease, the probability of infection transmission to the domestic pig farm sector, and the role of infected objects in the spread of the virus among wild animal populations. From 2012 to 2020 inclusive, according to FAO statistics, 537 cases of African swine fever were recorded in Ukraine, 21.7 % of which were associated with wild boars. In 2017 and 2018, the role of the European wild boar in the epizootic process is best reflected, when 10.9 % (2017) and 20.4 % (2018) of outbreaks of African swine fever among domestic animals recorded in the same administrative districts, where during a year this desiase was detected among wild pigs. When analyzing statistical data of the recent years, the effectiveness of introducing more detailed monitoring of African swine fever among wild boars using modern laboratory methods and improving biosafety measures in the private sector and directly on hunting grounds has been proved. Further research is based on predicting the dynamics of the spread of African swine fever in Ukraine and the role of wild boar in this epizootic process. In addition, the role of wild boar in the spread of African swine fever in other countries and the most effective foreign methods of disease control and prevention will be analyzed.

Download Full-text

African Swine Fever in Wild Boar in Europe—A Review

Viruses ◽

10.3390/v13091717 ◽

2021 ◽

Vol 13 (9) ◽

pp. 1717

Author(s):

Carola Sauter-Louis ◽

Franz J. Conraths ◽

Carolina Probst ◽

Ulrike Blohm ◽

Katja Schulz ◽

...

Keyword(s):

Wild Boar ◽

Case Fatality ◽

African Swine Fever ◽

Hemorrhagic Fever ◽

Spatial Behavior ◽

Control Measures ◽

Disease Spread ◽

Domestic Pigs ◽

In The Wild ◽

Socio Economic Impact

The introduction of genotype II African swine fever (ASF) virus, presumably from Africa into Georgia in 2007, and its continuous spread through Europe and Asia as a panzootic disease of suids, continues to have a huge socio-economic impact. ASF is characterized by hemorrhagic fever leading to a high case/fatality ratio in pigs. In Europe, wild boar are especially affected. This review summarizes the currently available knowledge on ASF in wild boar in Europe. The current ASF panzootic is characterized by self-sustaining cycles of infection in the wild boar population. Spill-over and spill-back events occur from wild boar to domestic pigs and vice versa. The social structure of wild boar populations and the spatial behavior of the animals, a variety of ASF virus (ASFV) transmission mechanisms and persistence in the environment complicate the modeling of the disease. Control measures focus on the detection and removal of wild boar carcasses, in which ASFV can remain infectious for months. Further measures include the reduction in wild boar density and the limitation of wild boar movements through fences. Using these measures, the Czech Republic and Belgium succeeded in eliminating ASF in their territories, while the disease spread in others. So far, no vaccine is available to protect wild boar or domestic pigs reliably against ASF.

Download Full-text

Modelling the Spatial Distribution of ASF-Positive Wild Boar Carcasses in South Korea Using 2019–2020 National Surveillance Data

Animals ◽

10.3390/ani11051208 ◽

2021 ◽

Vol 11 (5) ◽

pp. 1208

Author(s):

Jun-Sik Lim ◽

Timothée Vergne ◽

Son-Il Pak ◽

Eutteum Kim

Keyword(s):

Spatial Distribution ◽

Risk Factor ◽

South Korea ◽

Wild Boar ◽

African Swine Fever Virus ◽

Significant Risk ◽

African Swine Fever ◽

Credible Interval ◽

Imperfect Detection ◽

Wild Boars

In September 2019, African swine fever (ASF) was reported in South Korea for the first time. Since then, more than 651 ASF cases in wild boars and 14 farm outbreaks have been notified in the country. Despite the efforts to eradicate ASF among wild boar populations, the number of reported ASF-positive wild boar carcasses have increased recently. The purpose of this study was to characterize the spatial distribution of ASF-positive wild boar carcasses to identify the risk factors associated with the presence and number of ASF-positive wild boar carcasses in the affected areas. Because surveillance efforts have substantially increased in early 2020, we divided the study into two periods (2 October 2019 to 19 January 2020, and 19 January to 28 April 2020) based on the number of reported cases and aggregated the number of reported ASF-positive carcasses into a regular grid of hexagons of 3-km diameter. To account for imperfect detection of positive carcasses, we adjusted spatial zero-inflated Poisson regression models to the number of ASF-positive wild boar carcasses per hexagon. During the first study period, proximity to North Korea was identified as the major risk factor for the presence of African swine fever virus. In addition, there were more positive carcasses reported in affected hexagons with high habitat suitability for wild boars, low heat load index (HLI), and high human density. During the second study period, proximity to an ASF-positive carcass reported during the first period was the only significant risk factor for the presence of ASF-positive carcasses. Additionally, low HLI and elevation were associated with an increased number of ASF-positive carcasses reported in the affected hexagons. Although the proportion of ASF-affected hexagons increased from 0.06 (95% credible interval (CrI): 0.05–0.07) to 0.09 (95% CrI: 0.08–0.10), the probability of reporting at least one positive carcass in ASF-affected hexagons increased from 0.49 (95% CrI: 0.41–0.57) to 0.73 (95% CrI: 0.66–0.81) between the two study periods. These results can be used to further advance risk-based surveillance strategies in the Republic of Korea.

Download Full-text

Copy Number and Prevalence of Porcine Endogenous Retroviruses (PERVs) in German Wild Boars

Viruses ◽

10.3390/v12040419 ◽

2020 ◽

Vol 12 (4) ◽

pp. 419

Author(s):

Luise Krüger ◽

Milena Stillfried ◽

Carolin Prinz ◽

Vanessa Schröder ◽

Lena Katharina Neubert ◽

...

Keyword(s):

Wild Boar ◽

Copy Number ◽

Digital Pcr ◽

Endogenous Retroviruses ◽

Wild Boars ◽

Domestic Pigs ◽

Copy Numbers ◽

Cellular Genes ◽

Porcine Endogenous Retroviruses ◽

Different Populations

Porcine endogenous retroviruses (PERVs) are integrated in the genome of pigs and are transmitted like cellular genes from parents to the offspring. Whereas PERV-A and PERV-B are present in all pigs, PERV-C was found to be in many, but not all pigs. When PERV-C is present, recombination with PERV-A may happen and the PERV-A/C recombinants are characterized by a high replication rate. Until now, nothing has been known about the copy number of PERVs in wild boars and little is known about the prevalence of the phylogenetically youngest PERV-C in ancient wild boars. Here we investigated for the first time the copy number of PERVs in different populations of wild boars in and around Berlin using droplet digital PCR. Copy numbers between 3 and 69 per genome have been measured. A lower number but a higher variability was found compared to domestic pigs, including minipigs reported earlier (Fiebig et al., Xenotransplantation, 2018). The wild boar populations differed genetically and had been isolated during the existence of the Berlin wall. Despite this, the variations in copy number were larger in a single population compared to the differences between the populations. PERV-C was found in all 92 analyzed animals. Differences in the copy number of PERV in different organs of a single wild boar indicate that PERVs are also active in wild boars, replicating and infecting new cells as has been shown in domestic pigs.

Download Full-text

Clinical Course and Gross Pathological Findings in Wild Boar Infected with a Highly Virulent Strain of African Swine Fever Virus Genotype II

Pathogens ◽

10.3390/pathogens9090688 ◽

2020 ◽

Vol 9 (9) ◽

pp. 688 ◽

Cited By ~ 1

Author(s):

Antonio Rodríguez-Bertos ◽

Estefanía Cadenas-Fernández ◽

Agustín Rebollada-Merino ◽

Néstor Porras-González ◽

Francisco J. Mayoral-Alegre ◽

...

Keyword(s):

Wild Boar ◽

Clinical Course ◽

African Swine Fever Virus ◽

Virulent Strain ◽

African Swine Fever ◽

Pathological Findings ◽

Wild Boars ◽

Gross Pathology ◽

Highly Virulent ◽

Genotype Ii

African swine fever (ASF) is a notifiable disease that in recent years has spread remarkably in Europe and Asia. Eurasian wild boar (Sus scrofa) plays a key role in the maintenance and spread of the pathogen. Here we examined gross pathology of infection in wild boar with a highly virulent, hemadsorbing genotype II ASF virus (ASFV) strain. To this end, six wild boars were intramuscularly inoculated with the 10 HAD50 Arm07 ASFV strain, and 11 wild boars were allowed to come into direct contact with the inoculated animals. No animals survived the infection. Clinical course, gross pathological findings and viral genome quantification by PCR in tissues did not differ between intramuscularly inoculated or contact-infected animals. Postmortem analysis showed enlargement of liver and spleen; serosanguinous effusion in body cavities; and multiple hemorrhages in lungs, endocardium, brain, kidneys, urinary bladder, pancreas, and alimentary system. These results provide detailed insights into the gross pathology of wild boar infected with a highly virulent genotype II ASFV strain. From a didactic point of view, this detailed clinical course and macroscopic description may be essential for early postmortem detection of outbreaks in wild boar in the field and contribute to disease surveillance and prevention efforts.

Download Full-text

Comparative genome analysis of Erysipelothrix rhusiopathiae isolated from domestic pigs and wild boars suggests host adaptation and selective pressure from the use of antibiotics

Microbial Genomics ◽

10.1099/mgen.0.000412 ◽

2020 ◽

Vol 6 (8) ◽

Author(s):

Robert Söderlund ◽

Nicoletta Formenti ◽

Stefania Caló ◽

Mario Chiari ◽

Mate Zoric ◽

...

Keyword(s):

Wild Boar ◽

Host Adaptation ◽

Extracellular Proteins ◽

Gene Variants ◽

Erysipelothrix Rhusiopathiae ◽

Content Type ◽

Wild Boars ◽

Domestic Pigs ◽

Resistance Determinants ◽

Capsule Production

The disease erysipelas caused by Erysipelothrix rhusiopathiae (ER) is a major concern in pig production. In the present study the genomes of ER from pigs (n=87), wild boars (n=71) and other sources (n=85) were compared in terms of whole-genome SNP variation, accessory genome content and the presence of genetic antibiotic resistance determinants. The aim was to investigate if genetic features among ER were associated with isolate origin in order to better estimate the risk of transmission of porcine-adapted strains from wild boars to free-range pigs and to increase our understanding of the evolution of ER. Pigs and wild boars carried isolates representing all ER clades, but clade one only occurred in healthy wild boars and healthy pigs. Several accessory genes or gene variants were found to be significantly associated with the pig and wild boar hosts, with genes predicted to encode cell wall-associated or extracellular proteins overrepresented. Gene variants associated with serovar determination and capsule production in serovars known to be pathogenic for pigs were found to be significantly associated with pigs as hosts. In total, 30 % of investigated pig isolates but only 6 % of wild boar isolates carried resistance genes, most commonly tetM (tetracycline) and lsa(E) together with lnu(B) (lincosamides, pleuromutilin and streptogramin A). The incidence of variably present genes including resistance determinants was weakly linked to phylogeny, indicating that host adaptation in ER has evolved multiple times in diverse lineages mediated by recombination and the acquisition of mobile genetic elements. The presented results support the occurrence of host-adapted ER strains, but they do not indicate frequent transmission between wild boars and domestic pigs. This article contains data hosted by Microreact.

Download Full-text

Characterization and management of interaction risks between livestock and wild ungulates on outdoor pig farms in Spain

Porcine Health Management ◽

10.1186/s40813-021-00246-7 ◽

2022 ◽

Vol 8 (1) ◽

Author(s):

Saúl Jiménez-Ruiz ◽

Eduardo Laguna ◽

Joaquín Vicente ◽

Ignacio García-Bocanegra ◽

Jordi Martínez-Guijosa ◽

...

Keyword(s):

Wild Boar ◽

Management Practices ◽

Risk Mitigation ◽

African Swine Fever ◽

Farming Systems ◽

Mediterranean Ecosystems ◽

Risk Scores ◽

Wild Ungulates ◽

Domestic Pigs ◽

Pig Farms

Abstract Background To control the transmission of relevant shared diseases, such as animal tuberculosis (TB) and African swine fever (ASF), it is essential to reduce the risk of interaction between livestock and wild ungulates. In Eastern and Central Europe, the current spread of ASF virus affecting wild boar and domestic pigs (especially those raised outdoors and/or in backyards) has devastated the pig sector in affected regions and is seriously threatening other exporting countries. Here, we evaluated the risk of wildlife-livestock interactions on 45 outdoor pig farms in Spain, the second largest pork producer in the EU and then proposed biosecurity-related actions. An integrated, systematic wildlife risk mitigation protocol based on interviews, questionnaires and field audits was developed and applied on each farm. Results Most of the interaction risk points were associated with water sources (84.2%; 701/832), mainly springs and ponds, which accounted for almost all the specific points with high or very high risk scores. The risk of interaction at feeding points (6.9%; 57/832) and those associated with facilities for livestock and/or game management (8.9%; 74/832) were rated as low and very low risk, respectively. Wild boar were present and hunted on 69% of the farms. Supplementary feeding for wild ungulate species (mainly wild boar) was provided on almost half (48.9%; 22/45) the surveyed farms. Risk mitigation actions were categorised to target water access, waterers, food, other livestock species, grazing, wildlife, and offal disposal. Of the total number of actions (n = 2016), 82.7% were identified as priority actions while 17.3% represented alternative options which were identified less cost-effective. On average, 37.1 (median: 32; range 14–113) action proposals per study farm were made and 2.0 (median: 1; range 0–4) per risk point. The mean estimated cost of implementing the proposed priority actions was 14,780 €/farm (25.7 €/hectare and 799.4 €/risk point). Conclusions This study expands the knowledge of interaction risks between domestic pigs and wild ungulates in outdoor pig farming systems and highlights the importance of considering local risks and management practices when designing and prioritising adapted wildlife risk mitigation and biosecurity actions. This practical and feasible protocol developed for Mediterranean ecosystems is easily transferable to professionals and can be adapted to extensive (outdoor) production or epidemiological systems in other European regions.

Download Full-text

Risk Assessment of African Swine Fever Virus Exposure to Sus scrofa in Japan Via Pork Products Brought in Air Passengers’ Luggage

Pathogens ◽

10.3390/pathogens9040302 ◽

2020 ◽

Vol 9 (4) ◽

pp. 302

Author(s):

Satoshi Ito ◽

Jaime Bosch ◽

Cristina Jurado ◽

José Manuel Sánchez-Vizcaíno ◽

Norikazu Isoda

Keyword(s):

Risk Assessment ◽

Wild Boar ◽

African Swine Fever Virus ◽

African Swine Fever ◽

Domestic Pigs ◽

Pork Products ◽

Risk Assessment Models ◽

Annual Probability ◽

Virus Exposure ◽

Stochastic Risk

In recent years, African swine fever (ASF) has become prevalent in many areas, including Asia. The repeated detection of the ASF virus (ASFV) genome in pork products brought in air passenger’s luggage (PPAP) was also reported from Japanese airports. In the present study, the risk of ASFV exposure to susceptible hosts in Japan via three different pathways was assessed. Two quantitative stochastic risk assessment models were built to estimate the annual probability of ASFV exposure to domestic pigs, which could be attributed to foreign job trainees or foreign tourists. A semi-quantitative stochastic model was built to assess the risk of ASFV exposure to wild boar caused by foreign tourists. The overall mean annual probability of ASFV exposure to domestic pigs via PPAP carried by foreign job trainees was 0.169 [95% confidence interval (CI): 0.000–0.600], whereas that by foreign tourists was 0.050 [95% CI: 0.000–0.214], corresponding to approximately one introduction every 5.9 and 20 years, respectively. The risk of ASFV exposure to domestic pigs was dispersed over the country, whereas that of wild boar was generally higher in the western part of Japan, indicating that the characteristics of the potential ASF risk in each prefecture were varied.

Download Full-text

Impaired T‐cell responses in domestic pigs and wild boar upon infection with a highly virulent African swine fever virus strain

Transboundary and Emerging Diseases ◽

10.1111/tbed.13678 ◽

2020 ◽

Vol 67 (6) ◽

pp. 3016-3032 ◽

Cited By ~ 2

Author(s):

Jane Hühr ◽

Alexander Schäfer ◽

Theresa Schwaiger ◽

Laura Zani ◽

Julia Sehl ◽

...

Keyword(s):

T Cell ◽

Wild Boar ◽

Virus Strain ◽

African Swine Fever Virus ◽

African Swine Fever ◽

T Cell Responses ◽

Fever Virus ◽

Domestic Pigs ◽

Cell Responses ◽

Highly Virulent

Download Full-text

Comparative Pathology of Domestic Pigs and Wild Boar Infected with the Moderately Virulent African Swine Fever Virus Strain “Estonia 2014”

Pathogens ◽

10.3390/pathogens9080662 ◽

2020 ◽

Vol 9 (8) ◽

pp. 662

Author(s):

Julia Sehl ◽

Jutta Pikalo ◽

Alexander Schäfer ◽

Kati Franzke ◽

Katrin Pannhorst ◽

...

Keyword(s):

Wild Boar ◽

Viral Antigen ◽

African Swine Fever Virus ◽

African Swine Fever ◽

Fever Virus ◽

Kinetic Experiment ◽

Domestic Pigs ◽

Hunting Bag ◽

North Eastern ◽

The Baltic

Endemically infected European wild boar are considered a major reservoir of African swine fever virus in Europe. While high lethality was observed in the majority of field cases, strains of moderate virulence occurred in the Baltic States. One of these, “Estonia 2014”, led to a higher number of clinically healthy, antibody-positive animals in the hunting bag of North-Eastern Estonia. Experimental characterization showed high virulence in wild boar but moderate virulence in domestic pigs. Putative pathogenic differences between wild boar and domestic pigs are unresolved and comparative pathological studies are limited. We here report on a kinetic experiment in both subspecies. Three animals each were euthanized at 4, 7, and 10 days post infection (dpi). Clinical data confirmed higher virulence in wild boar although macroscopy and viral genome load in blood and tissues were comparable in both subspecies. The percentage of viral antigen positive myeloid cells tested by flow cytometry did not differ significantly in most tissues. Only immunohistochemistry revealed consistently higher viral antigen loads in wild boar tissues in particular 7 dpi, whereas domestic pigs already eliminated the virus. The moderate virulence in domestic pigs could be explained by a more effective viral clearance.

Download Full-text