Pathogenesis of African swine fever virus inOrnithodorosticks

Pathogenicity and virulence of African swine fever virus

African swine fever (ASF) is a devastating disease with a high impact on the pork industry worldwide. ASF virus (ASFV) is a very complex pathogen, the sole member of the family Asfaviridae, which induces a state of immune suppression in the host through infection of myeloid cells and apoptosis of lymphocytes. Moreover, haemorrhages are the other main pathogenic effect of ASFV infection in pigs, related to the infection of endothelial cells, as well as the activation and structural changes of this cell population by proinflammatory cytokine upregulation within bystander monocytes and macrophages. There are still many gaps in the knowledge of the role of proteins produced by the ASFV, which is related to the difficulty in producing a safe and effective vaccine to combat the disease, although few candidates have been approved for use in Southeast Asia in the past couple of years.

Integrated control strategies for dengue, Zika, and Chikungunya virus infections

Arboviruses are a major threat to public health in tropical regions, encompassing over 534 distinct species, with 134 capable of causing diseases in humans. These viruses are transmitted through arthropod vectors that cause symptoms such as fever, headache, joint pains, and rash, in addition to more serious cases that can lead to death. Among the arboviruses, dengue virus stands out as the most prevalent, annually affecting approximately 16.2 million individuals solely in the Americas. Furthermore, the re-emergence of the Zika virus and the recurrent outbreaks of chikungunya in Africa, Asia, Europe, and the Americas, with one million cases reported annually, underscore the urgency of addressing this public health challenge. In this manuscript we discuss the epidemiology, viral structure, pathogenicity and integrated control strategies to combat arboviruses, and the most used tools, such as vaccines, monoclonal antibodies, treatment, etc., in addition to presenting future perspectives for the control of arboviruses. Currently, specific medications for treating arbovirus infections are lacking, and symptom management remains the primary approach. However, promising advancements have been made in certain treatments, such as Chloroquine, Niclosamide, and Isatin derivatives, which have demonstrated notable antiviral properties against these arboviruses in vitro and in vivo experiments. Additionally, various strategies within vector control approaches have shown significant promise in reducing arbovirus transmission rates. These encompass public education initiatives, targeted insecticide applications, and innovative approaches like manipulating mosquito bacterial symbionts, such as Wolbachia. In conclusion, combatting the global threat of arbovirus diseases needs a comprehensive approach integrating antiviral research, vaccination, and vector control. The continued efforts of research communities, alongside collaborative partnerships with public health authorities, are imperative to effectively address and mitigate the impact of these arboviral infections on public health worldwide.

An Updated Review of Ornithodoros Ticks as Reservoirs of African Swine Fever in Sub-Saharan Africa and Madagascar

This updated review provides an overview of the available information on Ornithodoros ticks as reservoirs and biological vectors of the ASF virus in Africa and Indian Ocean islands in order to update the current knowledge in this field, inclusive of an overview of available methods to investigate the presence of ticks in the natural environment and in domestic pig premises. In addition, it highlights the major areas of research that require attention in order to guide future investigations and fill knowledge gaps. The available information suggests that current knowledge is clearly insufficient to develop risk-based control and prevention strategies, which should be based on a sound understanding of genotype distribution and the potential for spillover from the source population. Studies on tick biology in the natural and domestic cycle, including genetics and systematics, represent another important knowledge gap. Considering the rapidly changing dynamics affecting the African continent (demographic growth, agricultural expansion, habitat transformation), anthropogenic factors influencing tick population distribution and ASF virus (ASFV) evolution in Africa are anticipated and have been recorded in southern Africa. This dynamic context, together with the current global trends of ASFV dissemination, highlights the need to prioritize further investigation on the acarological aspects linked with ASF ecology and evolution.

Susceptibility of Four Abalone Species, Haliotis gigantea, Haliotis discus discus, Haliotis discus hannai and Haliotis diversicolor, to Abalone asfa-like Virus

Abalone amyotrophia is a viral disease that causes mass mortality of juvenile Haliotis discus and H. madaka. Although the cause of this disease has yet to be identified, we had previously postulated a novel virus with partial genome sequence similarity to that of African swine fever virus is the causative agent and proposed abalone asfa-like virus (AbALV) as a provisional name. In this study, three species of juvenile abalone (H. gigantea, H. discus discus, and H. diversicolor) and four species of adult abalone (the above three species plus H. discus hannai) were experimentally infected, and their susceptibility to AbALV was investigated by recording mortality, quantitatively determining viral load by PCR, and conducting immunohistological studies. In the infection test using 7-month-old animals, H. gigantea, which was previously reported to be insusceptible to the disease, showed multiplication of the virus to the same extent as in H. discus discus, resulting in mass mortality. H. discus discus at 7 months old showed abnormal cell masses, notches in the edge of the shell and brown pigmentation inside of the shell, which are histopathological and external features of this disease, while H. gigantea did not show any of these characteristics despite suffering high mortality. Adult abalones had low mortality and viral replication in all species; however, all three species, except H. diversicolor, became carriers of the virus. In immunohistological observations, cells positive for viral antigens were detected predominantly in the gills of juvenile H. discus discus and H. gigantea, and mass mortality was observed in these species. In H. diversicolor, neither juvenile nor adult mortality from infection occurred, and the AbALV genome was not increased by experimental infection through cohabitation or injection. Our results suggest that H. gigantea, H. discus discus and H. discus hannai are susceptible to AbALV, while H. diversicolor is not. These results confirmed that AbALV is the etiological agent of abalone amyotrophia.

Report on the First African Swine Fever Case in Greece

African swine fever (ASF) poses a major threat to swine health and welfare worldwide. After several European countries have reported cases of ASF, Greece confirmed officially the first positive case on 5 February 2020. The owner of a backyard farm in Nikoklia, a village in Serres regional unit, Central Macedonia, reported a loss of appetite, weakness, dyspnea, and the sudden death of 6 domestic pigs. Necropsy was performed in one gilt and findings were compatible with acute to subacute septicemic disease. Predominantly, hyperemic enlargement of spleen and lymph node enlargement and/or hemorrhage were observed. Description of vague clinical signs by the farmer suggested a limited resemblance to ASF-acute infection. However, the disease could not be ruled out once septicemic condition including splenomegaly, was diagnosed macroscopically at necropsy. In addition, considering the farm’s location near to ASF protection zones, a further diagnostic investigation followed. Confirmation of the disease was obtained using a series of diagnostic tests on several tissue samples. Further clinical, molecular, and epidemiologic evaluation of the farm was performed. According to the contingency plan, authorities euthanized all 31 pigs on the farm, whilst blood testing revealed ASF virus infection. Further emergency measures were implemented to contain the spread of the disease.

Detection of African swine fever virus genotype XV in a sylvatic cycle in Saadani National Park, Tanzania

African swine fever (ASF) is a severe haemorrhagic disease of domestic pigs caused by ASF virus (ASFV). ASFV is transmitted by soft ticks (Ornithodoros moubata complex group) and by direct transmission. In Africa, ASF is maintained in transmission cycles of asymptomatic infection involving wild suids, mainly warthogs (Phacochoerus africanus). ASF outbreaks have been reported in many parts of Tanzania; however, active surveillance has been limited to pig farms in a few geographical locations. There is an information gap on whether and where the sylvatic cycle may occur independently of domestic pigs. To explore the existence of a sylvatic cycle in Saadani National Park in Tanzania, blood and serum samples were collected from 19 warthogs selected using convenience sampling along vehicle-accessible transects within the national park. The ticks were sampled from warthog burrows. Blood samples and ticks were subjected to ASFV molecular diagnosis (PCR) and genotyping, and warthog sera were subjected to serological (indirect ELISA) testing for ASFV antibody detection. All warthog blood samples were PCR-negative, but 16/19 (84%) of the warthog sera were seropositive by ELISA confirming exposure of warthogs to ASFV. Of the ticks sampled, 20/111 (18%) were positive for ASFV by conventional PCR. Sequencing of the p72 virus gene fragments showed that ASF viruses detected in ticks belonged to genotype XV. The results confirm the existence of a sylvatic cycle of ASFV in Saadani National Park, Tanzania, that involves ticks and warthogs independent of domestic pigs. Our findings suggest that genotype XV previously reported in 2008 in Tanzania is likely to be widely distributed and involved in both wild and domestic infection cycles. Whole-genome sequencing and analysis of the ASFV genotype XV circulating in Tanzania is recommended to determine the phylogeny of the viruses.

Understanding African swine fever outbreaks in domestic pigs in a sylvatic endemic area: The case of the South African controlled area between 1977-2017

South Africa declared a controlled area for African swine fever (ASF) in 1935, consisting of the northern parts of Limpopo, Mpumalanga, North West and Kwa-Zulu Natal Provinces. The area was delineated based on the endemic presence of the sylvatic cycle of ASF, involving warthogs and argasid ticks. Occasionally, spillover occurs from the sylvatic cycle to domestic pigs, causing ASF outbreaks. In the period 1977 to 2017, 59 outbreaks of ASF were reported in domestic pigs within the ASF controlled area of South Africa. During these outbreaks, at least 4,031 domestic pigs either died or were culled. Season did not affect the number of reported ASF outbreaks, but the number of reported outbreaks in this area per year was thought to be slowly increasing, although not statistically significant. Outbreaks occurred predominantly in Limpopo province (93%) and were mostly due to contact (or suspected contact) with warthog or warthog carcasses. Clustering analysis of outbreaks found that the local municipalities of Ramotshere Moiloa, Lephalale and Thabazimbi had the highest relative risk for outbreaks. In 32 of the 59 outbreaks, the genotype of the ASF virus (ASFV) involved could be determined. Phylogenetic analysis of ASFVs detected in domestic pigs during the study period revealed that p72 genotypes I, III, IV, VII, VIII, XIX, XX, XXI and XXII had been involved in causing outbreaks within the ASF controlled area. No outbreaks were reported in the Kwa-Zulu Natal part of the controlled area during this period. South Africa is unlikely to eradicate all sources of ASFV as spillover from the sylvatic cycle in the controlled area continued to occur, but with the implementation of appropriate biosecurity measures pigs can be successfully farmed despite the presence of ASFV in African wild suids and soft ticks.

African Swine Fever Virus: An Emerging DNA Arbovirus

African swine fever virus (ASFV) is the sole member of the family Asfarviridae, and the only known DNA arbovirus. Since its identification in Kenya in 1921, ASFV has remained endemic in Africa, maintained in a sylvatic cycle between Ornithodoros soft ticks and warthogs (Phacochoerus africanus) which do not develop clinical disease with ASFV infection. However, ASFV causes a devastating and economically significant disease of domestic (Sus scrofa domesticus) and feral (Sus scrofa ferus) swine. There is no ASFV vaccine available, and current control measures consist of strict animal quarantine and culling procedures. The virus is highly stable and easily spreads by infected swine, contaminated pork products and fomites, or via transmission by the Ornithodoros vector. Competent Ornithodoros argasid soft tick vectors are known to exist not only in Africa, but also in parts of Europe and the Americas. Once ASFV is established in the argasid soft tick vector, eradication can be difficult due to the long lifespan of Ornithodoros ticks and their proclivity to inhabit the burrows of warthogs or pens and shelters of domestic pigs. Establishment of endemic ASFV infections in wild boar populations further complicates the control of ASF. Between the late 1950s and early 1980s, ASFV emerged in Europe, Russia and South America, but was mostly eradicated by the mid-1990s. In 2007, a highly virulent genotype II ASFV strain emerged in the Caucasus region and subsequently spread into the Russian Federation and Europe, where it has continued to circulate and spread. Most recently, ASFV emerged in China and has now spread to several neighboring countries in Southeast Asia. The high morbidity and mortality associated with ASFV, the lack of an efficacious vaccine, and the complex makeup of the ASFV virion and genome as well as its lifecycle, make this pathogen a serious threat to the global swine industry and national economies. Topics covered by this review include factors important for ASFV infection, replication, maintenance, and transmission, with attention to the role of the argasid tick vector and the sylvatic transmission cycle, current and future control strategies for ASF, and knowledge gaps regarding the virus itself, its vector and host species.

A novel Asfarvirus-like virus identified as a potential cause of mass mortality of abalone

A novel Asfarvirus-like virus is proposed as the etiological agent responsible for mass mortality in abalone. The disease, called abalone amyotrophia, originally was recognized in the 1980s, but efforts to identify a causative agent were unsuccessful. We prepared a semi-purified fraction by nuclease treatment and ultracentrifugation of diseased abalone homogenate, and the existence of the etiological agent in the fraction was confirmed by a challenge test. Using next-generation sequencing and PCR-based epidemiological surveys, we obtained a partial sequence with similarity to a member of the family Asfarviridae. BLASTP analysis of the predicted proteins against a virus database resulted in 48 proteins encoded by the novel virus with top hits against proteins encoded by African swine fever virus (ASFV). Phylogenetic analyses of predicted proteins of the novel virus confirmed that ASFV represents the closest relative. Comparative genomic analysis revealed gene-order conservation between the novel virus and ASFV. In situ hybridization targeting the gene encoding the major capsid protein of the novel virus detected positive signals only in tissue from diseased abalone. The results of this study suggest that the putative causative agent should be considered a tentative new member of the family Asfarviridae, which we provisionally designate abalone asfa-like virus (AbALV).

Comparative vector competence of the Afrotropical soft tick Ornithodoros moubata and Palearctic species, O. erraticus and O. verrucosus, for African swine fever virus strains circulating in Eurasia

African swine fever (ASF) is a lethal hemorrhagic disease in domestic pigs and wild suids caused by African swine fever virus (ASFV), which threatens the swine industry globally. In its native African enzootic foci, ASFV is naturally circulating between soft ticks of the genus Ornithodoros, especially in the O. moubata group, and wild reservoir suids, such as warthogs (Phacochoerus spp.) that are bitten by infected soft ticks inhabiting their burrows. While the ability of some Afrotropical soft ticks to transmit and maintain ASFV is well established, the vector status of Palearctic soft tick species for ASFV strains currently circulating in Eurasia remains largely unknown. For example, the Iberian soft tick O. erraticus is a known vector and reservoir of ASFV, but its ability to transmit different ASFV strains has not been assessed since ASF re-emerged in Europe in 2007. Little is known about vector competence for ASFV in other species, such as O. verrucosus, which occurs in southern parts of Eastern Europe, including Ukraine and parts of Russia, and in the Caucasus. Therefore, we conducted transmission trials with two Palearctic soft tick species, O. erraticus and O. verrucosus, and the Afrotropical species O. moubata. We tested the ability of ticks to transmit virulent ASFV strains, including one of direct African origin (Liv13/33), and three from Eurasia that had been involved in previous (OurT88/1), and the current epizooties (Georgia2007/1 and Ukr12/Zapo). Our experimental results showed that O. moubata was able to transmit the African and Eurasian ASFV strains, whereas O. erraticus and O. verrucosus failed to transmit the Eurasian ASFV strains. However, naïve pigs showed clinical signs of ASF when inoculated with homogenates of crushed O. erraticus and O. verrucosus ticks that fed on viraemic pigs, which proved the infectiousness of ASFV contained in the ticks. These results documented that O. erraticus and O. verrucosus are unlikely to be capable vectors of ASFV strains currently circulating in Eurasia. Additionally, the persistence of infection in soft ticks for several months reaffirms that the infectious status of a given tick species is only part of the data required to assess its vector competence for ASFV.

Serum-Derived Extracellular Vesicles from African Swine Fever Virus-Infected Pigs Selectively Recruit Viral and Porcine Proteins

: African swine fever is a devastating hemorrhagic infectious disease, which affects domestic and wild swines (Susscrofa) of all breeds and ages, with a high lethality of up to 90-100% in naïve animals. The causative agent, African swine fever virus (ASFV), is a large and complex double-stranded DNA arbovirus which is currently spreading worldwide, with serious socioeconomic consequences. There is no treatment or effective vaccine commercially available, and most of the current research is focused on attenuated viral models, with limited success so far. Thus, new strategies are under investigation. Extracellular vesicles (EVs) have proven to be a promising new vaccination platform for veterinary diseases in situations in which conventional approaches have not been completely successful. Here, serum extracellular vesicles from infected pigs using two different ASFV viruses (OURT 88/3 and Benin ΔMGF), corresponding to a naturally attenuated virus and a deletion mutant, respectively, were characterized in order to determine possible differences in the content of swine and viral proteins in EV-enriched fractions. Firstly, EVs were characterized by their CD5, CD63, CD81 and CD163 surface expression. Secondly, ASFV proteins were detected on the surface of EVs from ASFV-infected pig serum. Finally, proteomic analysis revealed few specific proteins from ASFV in the EVs, but 942 swine proteins were detected in all EV preparations (negative controls, and OURT 88/3 and Benin ΔMGF-infected preparations). However, in samples from OURT 88/3-infected animals, only a small number of proteins were differentially identified compared to control uninfected animals. Fifty-six swine proteins (Group Benin) and seven proteins (Group OURT 88/3) were differentially detected on EVs when compared to the EV control group. Most of these were related to coagulation cascades. The results presented here could contribute to a better understanding of ASFV pathogenesis and immune/protective responses in the host.

Risk of African Swine Fever Virus Sylvatic Establishment and Spillover to Domestic Swine in the United States

African swine fever virus (ASFV) causes a high-consequence foreign animal disease that has emerged along international trade routes. Owing to high lethality and resulting trade sanctions, establishment of this disease in the United States would have devastating economic consequences. ASFV can be transmitted by soft ticks in the genus Ornithodoros or directly between swine, including domestic, feral, and wild swine. Consequently, the spatial risk of ASFV establishment depends on where susceptible animals, with or without competent vectors, co-occur. We synthesized county-level historical records of soft tick occurrence, current maps of feral swine distribution, and domestic swine inventory to evaluate the risk of ASFV establishment and spillover in the United States. Areas of California, Florida, and much of the southwestern United States were classified as high risk for ASFV establishment and spillover should an introduction event occur. Our analyses indicate that California, Texas, Georgia, and Florida are high-priority candidates for proactive risk reduction strategies. Domestic swine are often produced in high-biosecurity environments, mitigating health risks associated with contacting infected hosts and vectors. However, small-scale and organic pig producers in much of the southern United States remain more vulnerable to disease emergence.

A Review of African Swine Fever and the Potential for Introduction into the United States and the Possibility of Subsequent Establishment in Feral Swine and Native Ticks

African swine fever (ASF) is caused by African swine fever virus (ASFV), which can cause substantial morbidity and mortality events in swine. The virus can be transmitted via direct and indirect contacts with infected swine, their products, or competent vector species, especially Ornithodoros ticks. Africa and much of Eastern Europe are endemic for ASF; a viral introduction to countries that are currently ASF free could have severe economic consequences due to the loss of production from infected animals and the trade restrictions that would likely be imposed as a result of an outbreak. We identified vulnerabilities that could lead to ASFV introduction or persistence in the United States or other ASF-free regions. Both legal and illegal movements of live animals, as well as the importation of animal products, byproducts, and animal feed, pose a risk of virus introduction. Each route is described, and current regulations designed to prevent ASFV and other pathogens from entering the United States are outlined. Furthermore, existing ASFV research gaps are highlighted. Laboratory experiments to evaluate multiple species of Ornithodoros ticks that have yet to be characterized would be useful to understand vector competence, host preferences, and distribution of competent soft tick vectors in relation to high pig production areas as well as regions with high feral swine (wild boar or similar) densities. Knowledge relative to antigenic viral proteins that contribute to host response and determination of immune mechanisms that lead to protection are foundational in the quest for a vaccine. Finally, sampling of illegally imported and confiscated wild suid products for ASFV could shed light on the types of products being imported and provide a more informed perspective relative to the risk of ASFV importation.

Suidae and Tayassuidae

The Suidae and Tayassuidae live on all continents except Antarctica. True wild boars were indigenous to Europe and Asia and are the ancestors to the domestic pig; with whom they share the same scientific name Sus scrofa. Wild boars have been introduced to the Americas and many islands. Because of the close genetic relationship, in many areas they have interbred with domestic pigs and formed considerable populations of feral suids that represent wild boar and feral pig crosses. Wild suid populations are relatively hardy and most disease research has been focused on their potential as a reservoir for diseases of concern for commercial pig production. The Togian Island babirusa, pygmy hog, Visayan warty pig, Javan warty pig, and Chacoan peccary are endangered. For all species, hunting, habitat loss, and hybridization are important threats to conservation.

Tick-Borne Transmission of Murine Gammaherpesvirus 68

Herpesviruses are a large group of DNA viruses infecting mainly vertebrates. Murine gammaherpesvirus 68 (MHV68) is often used as a model in studies of the pathogenesis of clinically important human gammaherpesviruses such as Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus. This rodent virus appears to be geographically widespread; however, its natural transmission cycle is unknown. Following detection of MHV68 in field-collected ticks, including isolation of the virus from tick salivary glands and ovaries, we investigated whether MHV68 is a tick-borne virus. Uninfected Ixodes ricinus ticks were shown to acquire the virus by feeding on experimentally infected laboratory mice. The virus survived tick molting, and the molted ticks transmitted the virus to uninfected laboratory mice on which they subsequently fed. MHV68 was isolated from the tick salivary glands, consistent with transmission via tick saliva. The virus survived in ticks without loss of infectivity for at least 120 days, and subsequently was transmitted vertically from one tick generation to the next, surviving more than 500 days. Furthermore, the F1 generation (derived from F0 infected females) transmitted MHV68 to uninfected mice on which they fed, with MHV68 M3 gene transcripts detected in blood, lung, and spleen tissue of mice on which F1 nymphs and F1 adults engorged. These experimental data fulfill the transmission criteria that define an arthropod-borne virus (arbovirus), the largest biological group of viruses. Currently, African swine fever virus (ASFV) is the only DNA virus recognized as an arbovirus. Like ASFV, MHV68 showed evidence of pathogenesis in ticks. Previous studies have reported MHV68 in free-living ticks and in mammals commonly infested with I. ricinus, and neutralizing antibodies to MHV68 have been detected in large mammals (e.g., deer) including humans. Further studies are needed to determine if these reports are the result of tick-borne transmission of MHV68 in nature, and whether humans are at risk of infection.

Structural Insight into African Swine Fever Virus A179L-Mediated Inhibition of Apoptosis

Programmed cell death is a tightly controlled process critical for the removal of damaged or infected cells. Pro- and antiapoptotic proteins of the Bcl-2 family are pivotal mediators of this process. African swine fever virus (ASFV) is a large DNA virus, the only member of the Asfarviridae family, and harbors A179L, a putative Bcl-2 like protein. A179L has been shown to bind to several proapoptotic Bcl-2 proteins; however, the hierarchy of binding and the structural basis for apoptosis inhibition are currently not understood. We systematically evaluated the ability of A179L to bind proapoptotic Bcl-2 family members and show that A179L is the first antiapoptotic Bcl-2 protein to bind to all major death-inducing mammalian Bcl-2 proteins. We then defined the structural basis for apoptosis inhibition of A179L by determining the crystal structures of A179L bound to both Bid and Bax BH3 motifs. Our findings provide a mechanistic understanding for the potent antiapoptotic activity of A179L by identifying it as the first panprodeath Bcl-2 binder and serve as a platform for more-detailed investigations into the role of A179L during ASFV infection.IMPORTANCE Numerous viruses have acquired strategies to subvert apoptosis by encoding proteins capable of sequestering proapoptotic host proteins. African swine fever virus (ASFV), a large DNA virus and the only member of the Asfarviridae family, encodes the protein A179L, which functions to prevent apoptosis. We show that A179L is unusual among antiapoptotic Bcl-2 proteins in being able to physically bind to all core death-inducing mammalian Bcl-2 proteins. Currently, little is known regarding the molecular interactions between A179L and the proapoptotic Bcl-2 members. Using the crystal structures of A179L bound to two of the identified proapoptotic Bcl-2 proteins, Bid and Bax, we now provide a three-dimensional (3D) view of how A179L sequesters host proapoptotic proteins, which is crucial for subverting premature host cell apoptosis.

An overview on Sardinia's soft ticks (Ixodida: Argasidae)

Knowledge about soft ticks (Ixodida: Argasidae) in Sardinia is incomplete and distribution data need to be updated. This work studies soft ticks on the island focusing on two species, Argas reflexus and Ornithodoros maritimus, both recently recorded. A total number of 12 specimens of these species of interest were collected between 2004 and 2015. This study reports for the first time the presence of O. maritimus in a coastal area in Italy, and more generally in a coastal area rather than small islands near the coastline, confirming the presence of this species on the island 20 years after its last recording. Moreover we confirm the presence of A. reflexus on the island, in the town of Cagliari and, for the first time, in the town of Quartu Sant'Elena. At the present state of knowledge, in Sardinia, Ornithodoros erraticus, which was actively looked for within the surveillance for African swine fever, an endemic disease since 1978 on the island, is not present. The presence of another species reported only once in Sardinia, Argas vespertilionis, needs further confirmation.

The African swine fever control zone in South Africa and its current relevance

African swine fever (ASF) has been reported in South Africa since the early 20th century. The disease has been controlled and confined to northern South Africa over the past 80 years by means of a well-defined boundary line, with strict control measures and movement restrictions north of this line. In 2012, the first outbreak of ASF outside the ASF control zone since 1996 occurred. The objective of this study was to evaluate the current relevance of the ASF control line as a demarcation line between endemic ASF (north) areas and ASF-free (south) area and to determine whether there was a need to realign its trajectory, given the recent outbreaks of ASF, global climate changes and urban development since the line's inception. A study of ASF determinants was conducted in an area 20 km north and 20 km south of the ASF control line, in Limpopo, Mpumalanga, North West and Gauteng provinces between May 2008 and September 2012. The study confirmed that warthogs, warthog burrows and the soft tick reservoir, Ornithodoros moubata, are present south of the ASF control line, but no virus or viral DNA was detected in these ticks. There appears to be an increasing trend in the diurnal maximum temperature and a decrease in humidity along the line, but the impact of these changes is uncertain. No discernible changes in minimum temperatures and average rainfall along the disease control line were observed between 1992 and 2014. Even though the reservoirs were found south of the ASF boundary line, the study concluded that there was no need to realign the trajectory of the ASF disease control line, with the exception of Limpopo Province. However, the provincial surveillance programmes for the reservoir, vector and ASF virus south of this line needs to be maintained and intensified as changing farming practices may favour the spread of ASF virus beyond the control line.

Identification of a New Genotype of African Swine Fever Virus in Domestic Pigs from Ethiopia

African swine fever (ASF) is an important emerging transboundary animal disease (TAD), which currently has an impact on many countries in Africa, Eastern Europe, the Caucasus and the Russian Federation. The current situation in Europe shows the ability of the virus to rapidly spread, which stands to threaten the global swine industry. At present, there is no viable vaccine to minimize spread of the disease and stamping out is the main source of control. In February 2011, Ethiopia had reported its first suspected outbreaks of ASF. Genomic analyses of the collected ASF virus (ASFV) strains were undertaken using 23 tissue samples collected from domestic swine in Ethiopia from 2011 to 2014. The analysis of Ethiopian ASFVs partial p72 gene sequence showed the identification of a new genotype, genotype XXIII, that shares a common ancestor with genotypes IX and X, which comprise isolates circulating in Eastern African countries and the Republic of Congo. Analysis of the p54 gene also followed the p72 pattern and the deduced amino acid sequence of the central variable region (CVR) of the B602L gene showed novel tetramer repeats not previously characterized.

Effect of O. porcinus Tick Salivary Gland Extract on the African Swine Fever Virus Infection in Domestic Pig

African swine fever is a haemorrhagic disease in pig production that can have disastrous financial consequences for farming. No vaccines are currently available and animal slaughtering or area zoning to restrict risk-related movements are the only effective measures to prevent the spread of the disease. Ornithodoros soft ticks are known to transmit the African swine fever virus (ASFV) to pigs in farms, following the natural epidemiologic cycle of the virus. Tick saliva has been shown to modulate the host physiological and immunological responses during feeding on skin, thus affecting viral infection. To better understand the interaction between soft tick, ASFV and pig at the bite location and the possible influence of tick saliva on pig infection by ASFV, salivary gland extract (SGE) of Ornithodoros porcinus, co-inoculated or not with ASFV, was used for intradermal auricular inoculation. Our results showed that, after the virus triggered the disease, pigs inoculated with virus and SGE presented greater hyperthermia than pigs inoculated with virus alone. The density of Langerhans cells was modulated at the tick bite or inoculation site, either through recruitment by ASFV or inhibition by SGE. Additionally, SGE and virus induced macrophage recruitment each. This effect was enhanced when they were co-inoculated. Finally, the co-inoculation of SGE and virus delayed the early local spread of virus to the first lymph node on the inoculation side. This study has shown that the effect of SGE was powerful enough to be quantified in pig both on the systemic and local immune response. We believe this model should be developed with infected tick and could improve knowledge of both tick vector competence and tick saliva immunomodulation.

Experimental Infection of Ornithodoros erraticus sensu stricto with Two Portuguese African Swine Fever Virus Strains. Study of Factors Involved in the Dynamics of Infection in Ticks

African swine fever (ASF) is a frequently devastating hemorrhagic disease of domestic pigs and wild boar and Ornithodoros erraticus sensu stricto argasid ticks are the only biological vectors of African swine fever virus (ASFV) known to occur in Europe. Recently this disease emerged in Eastern Europe and Russian Federation, showing a huge potential for a rapid spread between countries. There is some risk of re-emergence of ASF in the countries where these ticks exist, that can contribute for the persistence of infection and compromise control measures. In this study we aimed to identify factors that determine the probability of infection and its dynamics in the tick vector Ornithodoros erraticus sensu stricto, with two Portuguese strains of ASFV. Our results suggest that these ticks have a high likelihood of excreting the two haemadsorbing ASF viruses of different host origins and that, in field surveys, the analysis of adults and 5th nymphal stage can provide the best chance of detecting virus infection. The results also indicate that infection of pigs with highly virulent ASF viruses will promote higher rates of infection and a higher likelihood for virus excretion by ticks. Nevertheless, there is also a risk, although lower, that ticks can become infected on pigs that have overcome the acute phase of infection, which was simulated in our study by membrane feeding ticks with low titres of virus. We believe these results can be valuable in designing and interpreting the results of ASF control programmes, and future work can also be undertaken as our dataset is released under open access, to perform studies in risk assessment for ASFV persistence in a region where O. erraticus sensu stricto ticks are present.

Evaluation of hemostaseological status of pigs experimentally infected with African swine fever virus

African swine fever is a highly contagious hemorrhagic disease of pigs caused by African swine fever virus (ASFV). Hemorrhages are the most frequently reported lesions in acute and subacute forms of ASF. Hemorrhagic lesions are accompanied by impaired hemostasis, which includes thrombocytopenia and changes in the coagulation system. In the present study, experimental infection was conducted to elucidate whether a highly virulent ASFV genotype II circulating in the Trans-Caucasus and Eastern Europe affects the hemostasis of infected pigs. Platelet count changes and platelet size, as well as coagulation parameters were evaluated upon experimental infection. In contrast to other ASFV strains, ASFV genotype II showed a significant decrease in the number of platelets from 3rd dpi onwards. Furthermore, a decrease in platelet size was observed throughout the entire period of experiment. A significant increase in the number of platelet aggregates was observed from the beginning of infection. Unlike other ASFV strains, ASFV genotype II induced a slight shortening of an activated partial thromboplastin time (aPTT) throughout the experiment. Thrombin time (TT) was prolonged from day 5 onwards, whereas no changes in prothrombin time (PT) were found upon infection. The level of d-dimers was permanently higher than in control with a peak on day 3 post-infection. ASFV induced a significant decrease in the level of fibrinogen from day 5 till the end of experiment. Thus, it can be concluded that ASFV genotype II isolated in Armenia affects the hemostasis of infected pigs and causes changes that differ from that of other ASFV strains described previously.

A comparative analysis on the synonymous codon usage pattern in viral functional genes and their translational initiation region of ASFV

The synonymous codon usage pattern of African swine fever virus (ASFV), the similarity degree of the synonymous codon usage between this virus and some organisms and the synonymous codon usage bias for the translation initiation region of viral functional genes in the whole genome of ASFV have been investigated by some simply statistical analyses. Although both GC12% (the GC content at the first and second codon positions) and GC3% (the GC content at the third codon position) of viral functional genes have a large fluctuation, the significant correlations between GC12 and GC3% and between GC3% and the first principal axis of principle component analysis on the relative synonymous codon usage of the viral functional genes imply that mutation pressure of ASFV plays an important role in the synonymous codon usage pattern. Turning to the synonymous codon usage of this virus, the codons with U/A end predominate in the synonymous codon family for the same amino acid and a weak codon usage bias in both leading and lagging strands suggests that strand compositional asymmetry does not take part in the formation of codon usage in ASFV. The interaction between the absolute codon usage bias and GC3% suggests that other selections take part in the formation of codon usage, except for the mutation pressure. It is noted that the similarity degree of codon usage between ASFV and soft tick is higher than that between the virus and the pig, suggesting that the soft tick plays a more important role than the pig in the codon usage pattern of ASFV. The translational initiation region of the viral functional genes generally have a strong tendency to select some synonymous codons with low GC content, suggesting that the synonymous codon usage bias caused by translation selection from the host takes part in modulating the translation initiation efficiency of ASFV functional genes.

Review of the sylvatic cycle of African swine fever in sub-Saharan Africa and the Indian ocean

African swine fever (ASF) is a major limiting factor for pig production in most of the countries in Sub-Saharan Africa and the Indian Ocean. In the absence of vaccine, a good understanding of the ecology and epidemiology of the disease is fundamental to implement effective control measures. In selected countries of Southern and East Africa, the association between Ornithodoros moubata ticks and warthogs has been described in detail in the literature. However, for many other countries in the region, information related to the sylvatic cycle is lacking or incomplete. In West African countries, for instance, the role of wild pigs in the epidemiology of ASF has never been demonstrated and the existence and potential impact of a sylvatic cycle involving an association between soft ticks and warthogs is questionable. In other countries, other wild pig species such as the bushpigs (Potamochoerus spp.) can also be asymptomatically infected by the virus but their role in the epidemiology of the disease is unclear and might differ according to geographic regions. In addition, the methods and techniques required to study the role of wild hosts in ASF virus (ASFV) epidemiology and ecology are very specific and differ from the more traditional methods to study domestic pigs or other tick species. The aim of this review is (i) to provide a descriptive list of the methodologies implemented to study the role of wild hosts in African swine fever, (ii) to compile the available knowledge about the sylvatic cycle of ASFV in different regions of Sub-Saharan Africa and the Indian Ocean in addition to the one that has been described for East and Southern Africa, and (iii) to discuss current methodologies and available knowledge in order to identify new orientations for further field and experimental surveys.

Pathogenesis of African swine fever in domestic pigs and European wild boar

African swine fever (ASF) is among the most important viral diseases that can affect domestic and feral pigs. Both clinical signs and pathomorphological changes vary considerably depending on strain virulence and host factors. Acute infections with highly virulent virus strains lead to a clinical course that resembles a viral haemorrhagic fever that is characterized by pronounced depletion of lymphoid tissues, apoptosis of lymphocyte subsets, and impairment of haemostasis and immune functions. It is generally accepted that most lesions can be attributed to cytokine-mediated interactions triggered by infected and activated monocytes and macrophages, rather than by virus-induced direct cell damage. Nevertheless, most pathogenetic mechanisms are far from being understood. This review summarizes the current knowledge and discusses implications and research gaps.

Epidemiology of African swine fever virus

African swine fever virus used to occur primarily in Africa. There had been occasional incursions into Europe or America which apart from the endemic situation on the island of Sardinia always had been successfully controlled. But following an introduction of the virus in 2007, it now has expanded its geographical distribution into Caucasus and Eastern Europe where it has not been controlled, to date. African swine fever affects domestic and wild pig species, and can involve tick vectors. The ability of the virus to survive within a particular ecosystem is defined by the ecology of its wild host populations and the characteristics of livestock production systems, which influence host and vector species densities and interrelationships. African swine fever has high morbidity in naïve pig populations and can result in very high mortality. There is no vaccine or treatment available. Apart from stamping out and movement control, there are no control measures, thereby potentially resulting in extreme losses for producers. Prevention and control of the infection requires good understanding of its epidemiology, so that targeted measures can be instigated.

African swine fever virus infection in Ornithodoros ticks

African swine fever virus (ASFV) is an arbovirus which is vectored by soft ticks of the Ornithodoros spp. and in the sylvatic cycle infects wart hogs and bush pigs. ASFV infection of domestic swine causes a high mortality disease. On the other hand, ASFV infection of the tick can result in a high-titered and persistent infection depending upon the ASFV isolate and the tick combination. Recently, morphological, classical virology (titration) and recombinant ASFV have been used to study the cellular, molecular and genetic interactions that occur between ASFV and its host tick.

Molecular characterization of African swine fever virus isolates originating from outbreaks in the Russian Federation between 2007 and 2011

African swine fever is one of the most important viral diseases of pigs and which caused significant economic damage on the pig production worldwide. Nowadays, it is still present on the African continent, in Transcaucasus countries (TCC), on Island of Sardinia and in Russia. Outbreaks of the disease have been reported in Russia for the last four years, affected especially the Southern Federal District of the country. Since 2010, a new outbreak area has been observed in the Northwestern Federal District. In order to study the evolution of African swine fever virus (ASFV) isolates, strains were collected in the Russian Federation from 2007 to 2011 and investigated by means of partial sequencing and fragment length polymorphism. In detail, 7 variable regions, namely B646L, E183L, I196L, B602L, I73R/I329R, I78R/I215L and KP86R were investigated. Phylogenetic analyses revealed 100% nucleotide identity of B646L and E183L gene sequences of all examined isolates. All isolates formed one genetic cluster within genotype II. Moreover, no amplified fragment length polymorphism (AFLP) was observed for B602L, I196L, I73R/I329R, and I78R/I215L genes. The flanking primers used to amplify the KP86R gene failed to amplify a product in all the isolates. The obtained data strongly suggests that only one ASFV virus variant caused the outbreaks from 2007 to 2011 in the territory of the Russian Federation.

African swine fever viruses with two different genotypes, both of which occur in domestic pigs, are associated with ticks and adult warthogs, respectively, at a single geographical site

The role of the ancestral sylvatic cycle of the African swine fever virus (ASFV) is not well understood in the endemic areas of eastern Africa. We therefore analysed the ASF infection status on samples collected from 51 free-ranging warthogs (Phacocherus africanus) and 1576 Ornithodorus porcinus ticks from 26 independent warthog burrows at a single ranch in Kenya. Abattoir samples from 83 domestic pigs without clinical symptoms, originating from specific locations with no recent reported ASF outbreaks were included in this study. All samples were derived from areas of central Kenya, where ASF outbreaks have been reported in the past. Infection with ASFV was confirmed in 22 % of O. porcinus pools, 3.22 % of adult warthog serum samples and 49 % of domestic pig serum samples by using p72-based PCR. All of the warthog sera were positive for anti-ASFV antibodies, investigated by using ELISA, but none of the domestic pig sera were positive. Twenty O. porcinus-, 12 domestic pig- and three warthog-derived viruses were genotyped at four polymorphic loci. The ASFV isolates from ticks and domestic pigs clustered within p72 genotype X. By contrast, ASF viruses genotyped directly from warthog sera, at same locality as the tick isolates, were within p72 genotype IX and genetically similar to viruses causing recent ASF outbreaks in Kenya and Uganda. This represents the first report of the co-existence of different ASFV genotypes in warthog burrow-associated ticks and adult wild warthogs. The data from this and earlier studies suggest transfer of viruses of at least two different p72 genotypes, from wild to domestic pigs in East Africa.

A host species-informative internal control for molecular assessment of African swine fever virus infection rates in the African sylvatic cycle Ornithodoros vector

African swine fever virus (ASFV) infection in adult Ornithodoros porcinus (Murry 1877, sensuWalton 1979) ticks collected from warthog burrows in southern and East Africa was assessed using a duplex genomic amplification approach that is informative with respect to the invertebrate host species and infecting sylvatic cycle virus. DNA extracted from individual ticks was used as template for the simultaneous amplification of a C-terminal 478-bp ASFV p72 gene region and a approximately 313-bp fragment of the tick mitochondrial 16S rRNA gene, under optimized reaction conditions. Within-warthog burrow infection rates ranged from 0% to 43% using this approach, and phylogenetic analysis of 16S gene sequences revealed the presence of three geographically discrete O. porcinus lineages, but no support for subspecies recognition. False negatives are precluded by the inclusion of host species-informative primers that ensure the DNA integrity of cytoplasmically located genome extracts. In addition, infection rate estimates are further improved as false positives arising from carry-over contamination when performing a two-step nested polymerase chain reaction are negated by the one-step approach. Phylogenetic comparison of full-length virus gene sequences with the partial C-terminal p72 gene target confirmed the epidemiological utility of the latter in a sylvatic setting. The method is therefore of particular value in studies assessing the prevalence and diversity of ASFV in relation to the African sylvatic tick vector and holds potential for investigating the role of alternative tick species in virus maintenance and transmission.

The CD2v protein enhances African swine fever virus replication in the tick vector, Ornithodoros erraticus

The NH/P68 non-haemadsorbing (non-HAD) African swine fever virus (ASFV) isolate contains frameshift mutations in the EP402R and adjacent EP153R genes. These encode, respectively, the protein (CD2v) that is required for the haemadsorption (HAD) of swine erythrocytes to ASFV-infected cells and a C-type lectin protein. Two recombinant HAD viruses were constructed in this parental strain. In one of these the intact EP153R gene sequence was restored. Although restoration of the HAD phenotype did not increase virus virulence in pigs, a significant increase was observed in the number of pigs which developed viraemia. These HAD recombinant viruses replicated to titres approximately 1000-fold higher than the parental non-HAD isolate when membrane fed to Ornithodoros erraticus ticks. Inoculation of the non-HAD isolate across the gut wall increased viral replication to levels comparable to that of the HAD recombinant viruses. These results demonstrate a novel role for the CD2v protein in virus replication in ticks.

Role of wild suids in the epidemiology of African swine fever

There is presently no vaccine to combat African swine fever (ASF), a viral hemorrhagic fever of domestic pigs that causes up to 100% morbidity and mortality in naive, commercial pig populations. In its endemic setting, ASF virus cycles between asymptomatic warthogs and soft ticks, with persistence in exotic locations being ascribed to the almost global distribution of susceptible soft tick and suid hosts. An understanding of the role played by diverse hosts in the epidemiology of this multi-host disease is crucial for effective disease control. Unlike the intensively studied Ornithodoros tick vector, the role of many wild suids remains obscure, despite growing recognition for suid-exclusive virus cycling, without the agency of the argasid tick, at some localities. Because the four wild suid genera, Phacochoerus, Potamochoerus, Hylochoerus, and Sus differ from each other in taxonomy, distribution, ecology, reservoir host potential, virus shedding, ASF symptomology, and domestic-pig contact potential, their role in disease epidemiology is also varied. This first consolidated summary of ASF epidemiology in relation to wild suids summarizes current knowledge and identifies information gaps and future research priorities crucial for formulating effective disease control strategies.

Phenotype-based identification of host genes required for replication of African swine fever virus

African swine fever virus (ASFV) produces a fatal acute hemorrhagic fever in domesticated pigs that potentially is a worldwide economic threat. Using an expressed sequence tag (EST) library-based antisense method of random gene inactivation and a phenotypic screen for limitation of ASFV replication in cultured human cells, we identified six host genes whose cellular functions are required by ASFV. These included three loci, BAT3 (HLA-B-associated transcript 3), C1qTNF (C1q and tumor necrosis factor-related protein 6), and TOM40 (translocase of outer mitochondrial membrane 40), for which antisense expression from a tetracycline-regulated promoter resulted in reversible inhibition of ASFV production by >99%. The effects of antisense transcription of the BAT3 EST and also of expression in the sense orientation of this EST, which encodes amino acid residues 450 to 518 of the mature BAT3 protein, were investigated more extensively. Sense expression of the BAT3 peptide, which appears to reversibly interfere with BAT3 function by a dominant negative mechanism, resulted in decreased synthesis of viral DNA and proteins early after ASFV infection, altered transcription of apoptosis-related genes as determined by cDNA microarray analysis, and increased cellular sensitivity to staurosporine-induced apoptosis. Antisense transcription of BAT3 reduced ASFV production without affecting abundance of the virus macromolecules we assayed. Our results, which demonstrate the utility of EST-based functional screens for the detection of host genes exploited by pathogenic viruses, reveal a novel collection of cellular genes previously not known to be required for ASFV infection.

Kinetics of African swine fever virus infection in Ornithodoros erraticus ticks

The kinetics of African swine fever virus (ASFV) infection in Ornithodoros erraticus ticks were investigated in specimens collected in the field at different times following an outbreak of the disease in Portugal in 1999 and in ticks infected experimentally with a virus isolated from a tick collected during this outbreak. In ticks collected from the field, initial screening for ASFV was carried out by PCR, followed by attempts to isolate the virus in macrophage cultures. Considering total numbers of ticks tested independently of developmental stages, ASFV DNA was detected in 42.3, 26.4 and 22.4% of specimens collected at weeks 0, 32 and 63 following the outbreak, respectively. Although virus was not isolated from most of these ticks, the proportion of isolations from large nymphs and adults increased between weeks 0 and 32 from 2 to 9 % and from 5 to 11.5%, respectively. These results, together with the higher virus titres at week 32, suggest that virus replication occurred. In contrast, virus isolations from small nymphs decreased over this period, from 5 to 1.3%. At week 63, infection rates decreased for all stages. Experimental infections showed the occurrence of virus replication within 4 weeks post-feeding and maintenance of high titres in almost 100% of ticks until 20 weeks post-infection. At weeks 41 and 61, a drop in virus titres and infection rates was observed. Relevant to the understanding of African swine fever epidemiology, our results show that ASFV replicates and persists in O. erraticus, but a viral clearance occurs at later times in both natural and experimental infections.