African swine fever virus eradication in Africa

African Swine Fever Diagnosis in Africa: Challenges and Opportunities

The global spread of African swine fever (ASF) in recent decades has led to the need for technological advances in sampling and diagnostic techniques. The impetus for these has been the need to enable sampling by lay persons and to obtain at least a preliminary diagnosis in the field for early control measures to be put in place before final laboratory confirmation. In rural Africa, rapid diagnosis is hampered by challenges that include lack of infrastructure as well as human and financial resources. Lack of animal health personnel, access to affordable means to transport field samples to a laboratory, and lack of laboratories with the capacity to make the diagnosis result in severe under-reporting of ASF, especially in endemic areas. This review summarizes the challenges identified in gap analyses relevant to low- and middle-income countries, with a focus on Africa, and explore the opportunities provided by recent research to improve field diagnosis and quality of diagnostic samples used. Sampling techniques include invasive sampling techniques requiring trained personnel and non-invasive sampling requiring minimal training, sampling of decomposed carcass material, and preservation of samples in situations where cold chain maintenance cannot be guaranteed. Availability and efficacy of point-of-care (POC) tests for ASF has improved considerably in recent years and their application, as well as advantages and limitations, are discussed. The adequacy of existing laboratory diagnostic capacity is evaluated and opportunities for networking amongst reference and other laboratories offering diagnostic services are discussed. Maintaining laboratory diagnostic efficiency in the absence of samples during periods of quiescence is another issue that requires attention, and the role of improved laboratory networking is emphasized. Early diagnosis of ASF is key to managing the disease spread. Therefore, the establishment of the Africa Chapter of the Global African Swine Fever Research Alliance (GARA) increases opportunities for collaboration and networking among the veterinary diagnostic laboratories in the region.

High detection frequency and genetic diversity of porcine circovirus 3 (PCV-3) in Namibian backyard farms and warthogs

Since its first identification in 2015, porcine circovirus 3 (PCV-3) has been reported worldwide with a high frequency and in the presence of several clinical conditions, although its impact on pig health and productivity is still debated. Data on the presence of PCV-3 in Africa are, however, limited. A previous study performed on commercial pigs in Namibia failed to identify the pathogen. In the present study, the viral circulation in backyard farms, characterised by lower biosecurity measures and frequent animal exchange between farms, was assessed. The susceptibility of warthogs to PCV-3 infection and their potential epidemiological role were also evaluated. Tonsils from 77 pigs from backyard piggeries and 55 warthogs were collected in different regions of Namibia and tested by PCR. Positive samples were sequenced and compared to PCV-3 strains circulating globally. Forty-two out of 77 pigs (54.54 %) and 12 out of 55 warthogs (21.82 %) tested positive, demonstrating the presence of PCV-3 in the country and suggesting that the high biosecurity measures implemented in the commercial farms that previously tested negative for PCV-3 probably prevented viral introduction. The partial ORF2 gene was successfully sequenced in samples from 27 pigs and 6 warthogs. Genetically, the identified strains were part of 3 distinct groups which included both backyard pigs and warthogs from different regions of Namibia. There is also evidence for the occurrence of multiple introduction events most likely from Asian countries, either directly into Namibia or through other African countries. Considering the strict Namibian regulations on live animal importation, understanding the source of viral introduction is challenging, although semen importation or the habit of feeding backyard pigs with human food waste might have played a role. Pig exchanges between farms for breeding purposes or wildlife movements could also have been involved in PCV-3 dispersal within Namibia. Despite the significant advances in the field, further studies should be undertaken to properly understand PCV-3 epidemiology in Namibia and its impact on pig productivity and wildlife health.

Identification of the p34 Protein of African Swine Fever Virus as a Novel Viral Antigen with Protection Potential

African swine fever (ASF) is a highly contagious disease caused by African swine fever virus (ASFV), affecting domestic and wild boars. The polyprotein pp220 of ASFV is responsible for producing the major structural proteins p150, p37, p14, p34, and p5 via proteolytic processing. The p34 protein is the main component of the ASFV core shell. However, the immunologic properties of the p34 protein in vitro and in vivo remain unclear. The results showed that the recombinant p34 protein expressed in prokaryotes and eukaryotes could react with convalescent swine sera to ASFV, suggesting that p34 is an immunogenic protein. Significantly, anti-p34 antibodies were found to inhibit the replication of ASFV in target cells. Furthermore, rabbits immunized with the recombinant C-strain of classical swine fever virus containing p34 produced both anti-p34 humoral and cellular immune responses. In addition, the p34 protein could induce a cell-mediated immune response, and a T-cell epitope on the p34 protein was identified using immunoinformatics and enzyme-linked immunospot (ELIspot) assay. Our study demonstrates that the p34 protein is a novel antigen of ASFV with protective potential.

Actions and perceived impact of African swine fever control measures along the smallholder pig value chain in Uganda

Pig production in Uganda is constrained by African swine fever (ASF) which is endemic in the country. Current measures taken by the Government of Uganda in controlling ASF outbreaks include trade and livestock movement restrictions, called "quarantine." Little is known about the actions of, and impact of value chain actors in response to ASF quarantines. This study describes actions that different stakeholders in the smallholder pig value chain took, and the perceived economic impact, during ASF quarantines. Data was collected in ten focus group discussions (FGD) using participatory epidemiology tools and two key informants' (KIs) interviews with District Veterinary Officers (DVOs) of Kisoro and Moyo districts in Uganda. The results show that during ASF quarantine, pig value chain actors shifted their activities from formal places such as livestock markets, slaughter slabs, pork butcheries and pork joints to informal places such as farmers' homesteads. Farmers were perceived the most economically affected stakeholder group with forgone income due to unsold pigs, costs for implementing biosecurity measures and extra costs for feeding unsold pigs being the major perceived causes of the losses. The continued trade in pigs and pig products in informal marketplaces suggests that quarantine might not be effective for hindering activities that might spread ASF in these settings. The perceived economic losses provide an insight into the negative economic impact of the quarantine for the different stakeholders.

Tick-Borne Diseases of Humans and Animals in West Africa

Ticks are a significant group of arthropod vectors that transmit a large variety of pathogens responsible for human and animal diseases worldwide. Ticks are the second biggest transmitters of vector-borne diseases, behind mosquitoes. However, in West Africa, there is often only limited knowledge of tick-borne diseases. With the scarcity of appropriate diagnostic services, the prevalence of tick-borne diseases is generally underestimated in humans. In this review, we provide an update on tick-borne pathogens reported in people, animals and ticks in West Africa by microscopic, immunological and molecular methods. A systematic search was conducted in PubMed and Google Scholar. The selection criteria included all studies conducted in West Africa reporting the presence of Rickettsia, Borrelia, Anaplasma, Ehrlichia, Bartonella, Coxiella burnetii, Theileria, Babesia, Hepatozoon and Crimean-Congo haemorrhagic fever viruses in humans, animals or ticks. Our intention is to raise awareness of tick-borne diseases amongst human and animal health workers in West Africa, and also physicians working with tourists who have travelled to the region.

Innate immune escape and adaptive immune evasion of African swine fever virus: A review

African swine fever virus (ASFV) causes hemorrhagic fever in domestic and wild pigs. The continued spread of the virus in Africa, Europe and Asia threatens the global pig industry. The lack of an effective vaccine limits disease control. ASFV has evolved a variety of encoded immune escape proteins and can evade host adaptive immunity, inducing cellular inflammation, autophagy, or apoptosis in host cells. Frequent persistent infections hinder the development of a viral vaccine and impose technical barriers. Currently, knowledge of the virulence-related genes, main pathogenic genes and immunoregulatory mechanism of ASFV is not comprehensive. We explain that ASFV invades the host to regulate its inflammatory response, interferon production, antigen presentation and cellular immunity. Furthermore, we propose potential ideas for ASFV vaccine target design, such as knocking out high-virulence genes in ASFV and performing data mining to identify the main genes that induce antiviral responses. To support a rational strategy for vaccine development, a better understanding of how ASFV interacts with the host and regulates the host's response to infection is needed. We review the current knowledge about ASFV targeting of host innate and adaptive immunity and the mechanisms by which the affected immune pathways are suppressed.

Structures and implications of the C962R protein of African swine fever virus

African swine fever virus (ASFV) is highly contagious and can cause lethal disease in pigs. Although it has been extensively studied in the past, no vaccine or other useful treatment against ASFV is available. The genome of ASFV encodes more than 170 proteins, but the structures and functions for the majority of the proteins remain elusive, which hindered our understanding on the life cycle of ASFV and the development of ASFV-specific inhibitors. Here, we report the structural and biochemical studies of the highly conserved C962R protein of ASFV, showing that C962R is a multidomain protein. The N-terminal AEP domain is responsible for the DNA polymerization activity, whereas the DNA unwinding activity is catalyzed by the central SF3 helicase domain. The middle PriCT2 and D5_N domains and the C-terminal Tail domain all contribute to the DNA unwinding activity of C962R. C962R preferentially works on forked DNA, and likely functions in Base-excision repair (BER) or other repair pathway in ASFV. Although it is not essential for the replication of ASFV, C962R can serve as a model and provide mechanistic insight into the replicative primase proteins from many other species, such as nitratiruptor phage NrS-1, vaccinia virus (VACV) and other viruses.

Genetic analysis of African swine fever viruses based on E183L (p54) gene, circulating in South Sumatra and Lampung province, Indonesia

Background and Aim

African swine fever (ASF) is a disease that emerged in Indonesia in 2019 in the North Sumatra province and spread rapidly to other areas, such as South Sumatra and Lampung, in 2020. This study aimed to identify the phylogenetics of the ASF virus (ASFV) in the provinces of South Sumatra and Lampung.

Materials and Methods

Nine ASFV isolates collected from the Disease Investigation Center in Lampung were used in this study. The isolates were from ASF cases in South Sumatra and Lampung in 2020-2022. The isolates were sequenced and compared with other ASFV isolates to establish the virus genotype. Sequencing was performed using the complete E183L gene target encoding the p54 protein.

Results

This study showed that ASFV from South Sumatera and Lampung Province belongs to genotype II.

Conclusion

Based on the analysis of the E183L gene, all nine ASFV isolates that originated from South Sumatra and Lampung were identical to other genotype II ASFV isolates from Georgia, China, Vietnam, and Timor Leste.

High-Risk Regions of African Swine Fever Infection in Mozambique

African swine fever (ASF) is a transboundary infectious disease that can infect wild and domestic swine and requires enhanced surveillance between countries. In Mozambique, ASF has been reported across the country, spreading between provinces, mainly through the movement of pigs and their by-products. Subsequently, pigs from bordering countries were at risk of exposure. This study evaluated the spatiotemporal distribution and temporal trends of ASF in swine in Mozambique between 2000 and 2020. During this period, 28,624 cases of ASF were reported across three regions of the country. In total, the northern, central, and southern regions presented 64.9, 17.8, and 17.3% of the total cases, respectively. When analyzing the incidence risk (IR) of ASF per 100,000 pigs, the Cabo Delgado province had the highest IR (17,301.1), followed by the Maputo province (8868.6). In the space-time analysis, three clusters were formed in each region: (i) Cluster A involved the provinces of Cabo Delgado and Nampula (north), (ii) Cluster B involved the province of Maputo and the city of Maputo (south), and (iii) Cluster C consisted of the provinces of Manica and Sofala (central) in 2006. However, when analyzing the temporal trend in the provinces, most were found to be decreasing, except for Sofala, Inhambane, and Maputo, which had a stationary trend. To the best of our knowledge, this is the first study to evaluate the spatial distribution of ASF in Mozambique. These findings will contribute to increasing official ASF control programs by identifying high-risk areas and raising awareness of the importance of controlling the borders between provinces and countries to prevent their spread to other regions of the world.

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.

Co-created community contracts support biosecurity changes in a region where African swine fever is endemic - Part I: The methodology

In Northern Uganda more people live in poverty than elsewhere in the country. Small-scale pig-keeping is common and African swine fever (ASF) is endemic, spreading along the smallholder value chain. Biosecurity measures remain the only way to prevent and control the spread of ASF in this context. Previous research in the study area has shown that many stakeholders are aware of ASF, how it is spread and methods for prevention and control, but biosecurity implementation remains limited. Participatory approaches have been suggested in order to increase community engagement in relation to animal disease control, ensuring that disease prevention or control actions are guided by local people's priorities and the promotion of local ownership of disease control. The objective of this study was to investigate the capacity of participatory action at community level with a broad inclusion of stakeholders to initiate change and greater stakeholder ownership to improve biosecurity in the smallholder pig value chain. Specific attention was paid to the feasibility of co-created community contracts for this purpose. The study was carried out in Northern Uganda in six purposively selected villages and included both farmers and traders. Centred on co-created community contracts on biosecurity, the study comprised repeated group discussions, semi-structured and structured group and individual interviews, as well as field observations. At the first meeting, participants were presented with suggested biosecurity measures adapted for farmers and traders respectively. Participants discussed each measure, agreed which ones to implement for one year, and co-created a community contract to this effect. During the study period, repeated interviews were undertaken and implementation support was provided. Interview data was coded and thematically analysed. Great diversity was observed between communities with regard to which and how many measures were selected, illustrating heterogeneity in the possibilities of biosecurity implementation and the complexity of livelihood challenges. The methodology appeared to be effective at instigating change, with all the communities changing some of their biosecurity behaviour during the study period. The intensified communication and cooperation around pigs in the communities reinforced the sense of group identity and the capacity-building offered at the first meeting supported implementation and appeared to be more important than the physical contract. Participants reported feeling empowered and described how they shared their knowledge, educated their peers and acted as catalysts for wider biosecurity change in their communities. These are promising results and indicate a positive attitude to both the agreed measures and the methodology.

Multiepitope array as the key for African Swine Fever diagnosis

African Swine Fever (ASF) is an acute hemorrhagic fever affecting suids with high mortality and morbidity rate. The causal agent of ASF, the African Swine Fever Virus (ASFV), is an icosahedral virus of 200 nm diameter, composed of an outer envelope layer of host derivation and a linear 170-190 kb long dsDNA molecule. As of today, no efficient therapeutic intervention nor prophylactic measures exist to fight ASFV diffusion, underlining the importance of the early diagnosis and the need for efficient in-field screening of ASF. Recommended guidelines for the diagnosis of ASF are unpracticable in the desirable context of the rapid in-farm screening. In this view, the design of innovative diagnostics based on a panel of multiple ASFV epitopes would amend versatility and the analytical performances of the deliverable, ensuring high quality and accuracy standards worth of implementation in rapid in-field monitoring programs. Pursuing this view, we performed epitope prediction from the major AFSV structural proteins holding the potential to be targeted in innovative rapid diagnostic tests. Selected ASFV structural protein sequences were retrieved from data repositories and their tridimensional structure was computed. Linear and 3D protein structures were subjected to the prediction of the epitope sequences, that are likely to elicit antibody production, by independent bioinformatic tools, providing a list of candidate biomarkers whose batch employment held the potential suitability for the unbiased rapid in-field diagnosis and, in turn, might be implemented in screening programs, crowing the current monitoring and control campaigns that are currently running worldwide.

Artificial Insemination as an Alternative Transmission Route for African Swine Fever Virus

The rapid spread of the African swine fever virus (ASFV), causing severe disease with often high fatality rates in Eurasian suids, prevails as a threat for pig populations and dependent industries worldwide. Although advancing scientific progress continually enhances our understanding of ASFV pathogenesis, alternative transmission routes for ASFV have yet to be assessed. Here, we demonstrate that ASFV can efficiently be transferred from infected boars to naïve recipient gilts through artificial insemination (AI). In modern pig production, semen from boar studs often supplies many sow herds. Thus, the infection of a boar stud presents the risk of rapidly and widely distributing ASFV within or between countries. Daily blood and semen collection from four boars after intramuscular inoculation with ASFV strain 'Estonia 2014' resulted in the detection of ASFV genomes in the semen as early as 2 dpi, in blood at 1 dpi while semen quality remained largely unaffected. Ultimately, after insemination with extended semen, 7 of 14 gilts were ASFV positive by 7 days post insemination, and all gilts were ASFV positive by 35 days post insemination. Twelve out of 13 pregnant gilts aborted or resorbed at the onset of fever. A proportion of fetuses originating from the remaining gilt showed both abnormalities and replication of ASFV in fetal tissues. Thus, we present evidence for the efficient transmission of ASFV to gilts via AI and also to implanted embryos. These results underline the critical role that boar semen could play in ASFV transmission.

Development of a chromatographic lateral flow immunoassay for detection of African swine fever virus antigen in blood

African swine fever (ASF) is a highly lethal disease of domestic and wild swine caused by African swine fever virus (ASFV). The disease currently circulates in Africa, Europe, Asia and on the island of Hispaniola. The ongoing epizootics in Europe and Asia have produced millions of animal deaths and severe economic losses. No effective vaccine is available for ASF, making rapid and accurate detection of ASFV essential for disease mitigation strategies. Currently available diagnostics for ASFV possess significant limitations related to assay performance, deployability, and/or turn-around time; therefore there is an unmet need for pen-side diagnostic tests with sufficient sensitivity and specificity. A chromatographic lateral flow immunoassay (LFIA) was developed for the detection of ASFV antigen in EDTA-treated whole blood using monoclonal antibodies targeting the viral p30 protein. The assay requires only water to perform and provides results in 25 min, making it well-suited for field use. The LFIA was capable of detecting genotype I and genotype II strains of ASFV in EDTA blood from experimentally infected pigs at varying time-points after infection, though it was unable to detect a genotype X ASFV strain. Diagnostic sensitivity correlated with clinical disease severity, body temperature, and viral DNA levels, and was over 90% in animals showing moderate to severe ASF-related symptoms after challenge with virulent genotype II virus. The LFIA also showed a robust diagnostic specificity of over 98%, which is essential to field testing for a high consequence to foregin animal disease. The LFIA targeting the viral p30 protein can reliably detect ASFV in whole blood from animals showing moderate to severe clinical signs of infection with virulent genotype I and II isolates, making it a promising candidate for use as a field-deployable antigen detection assay. Additional evaluation using field samples and different virus strains is required to further assess the utility of this rapid diagnostic test.

A Naturally Occurring Microhomology-Mediated Deletion of Three Genes in African Swine Fever Virus Isolated from Two Sardinian Wild Boars

African swine fever virus (ASFV) is the etiological agent of a lethal disease of domestic pigs and wild boars. ASF threatens the pig industry worldwide due to the lack of a licensed vaccine or treatment. The disease has been endemic for more than 40 years in Sardinia (Italy), but an intense campaign pushed it close to eradication; virus circulation was last detected in wild boars in 2019. In this study, we present a genomic analysis of two ASFV strains isolated in Sardinia from two wild boars during the 2019 hunting season. Both isolates presented a deletion of 4342 base pairs near the 5' end of the genome, encompassing the genes MGF 360-6L, X69R, and MGF 300-1L. The phylogenetic evidence suggests that the deletion recently originated within the Sardinia ecosystem and that it is most likely the result of a non-allelic homologous recombination driven by a microhomology present in most Sardinian ASFV genomes. These results represent a striking example of a genomic feature promoting the rapid evolution of structural variations and plasticity in the ASFV genome. They also raise interesting questions about the functions of the deleted genes and the potential link between the evolutionary timing of the deletion appearance and the eradication campaign.

In Silico Characterization of African Swine Fever Virus Nucleoprotein p10 Interaction with DNA

African swine fever virus (ASFV) is the etiological agent of a highly contagious, hemorrhagic infectious swine disease, with a tremendous sanitary and economic impact on a global scale. Currently, there are no globally available vaccines or treatments. The p10 protein, a structural nucleoprotein encoded by ASFV, has been previously described as capable of binding double-stranded DNA (dsDNA), which may have implications for viral replication. However, the molecular mechanism that governs this interaction is still unknown, mostly due to the lack of a structural model for this protein. In this work, we have generated an ab initio model of the p10 protein and performed extensive structural characterization, using molecular dynamics simulations to identify the motifs and residues regulating DNA recognition. The helix-turn-helix motif identified at the C-terminal region of the protein was shown to be crucial to the dsDNA-binding efficiency. As with other DNA-binding proteins, two distinct serine and lysine-rich regions found in the two helices were identified as key players in the binding to DNA, whose importance was later validated using experimental binding assays. Altogether, these findings may contribute to a better understanding of the p10 function in ASFV replication.

Exploring the hurdles that remain for control of African swine fever in smallholder farming settings

To honour the 100 years anniversary of the first publication about African swine fever (ASF) a webinar with a particular focus on disease control in the smallholder sector was organized. This article is based on the webinar, summarizing the early history of ASF research, reflecting on the current global disease situation and bringing forward some suggestions that could contribute towards achieving control of ASF. The first description of ASF by R. Eustace Montgomery in 1921 laid the foundations for what we know about the disease today. Subsequent research confirmed its association with warthogs and soft ticks of the Ornithodoros moubata complex. During the latter half of the 21st century, exponential growth of pig production in Africa has led to a change in the ASF-epidemiology pattern. It is now dominated by a cycle involving domestic pigs and pork with virus spread driven by people. In 2007, a global ASF epidemic started, reaching large parts of Europe, Asia and the Americas. In Europe, this epidemic has primarily affected wild boar. In Asia, wild boar, smallholders and industrialized pig farms have been affected with impact on local, national and international pig value chains. Globally and historically, domestic pigs in smallholder settings are most frequently affected and the main driver of ASF virus transmission. Awaiting a safe and efficacious vaccine, we need to continue focus on other measures, such as biosecurity, for controlling the disease. However, smallholders face specific challenges linked to poverty and other structural factors in implementing biosecurity measures that can prevent spread. Improving biosecurity in the smallholder sector thus remains an important tool for preventing and controlling ASF. In this regard, interdisciplinary research can help to find new ways to promote safe practices, facilitate understanding and embrace smallholders' perspectives, engage stakeholders and adjust prevention and control policies to improve implementation.

African Swine Fever Virus: A Review

African swine fever (ASF) is a viral disease with a high fatality rate in both domestic pigs and wild boars. ASF has greatly challenged pig-raising countries and also negatively impacted regional and national trade of pork products. To date, ASF has spread throughout Africa, Europe, and Asia. The development of safe and effective ASF vaccines is urgently required for the control of ASF outbreaks. The ASF virus (ASFV), the causative agent of ASF, has a large genome and a complex structure. The functions of nearly half of its viral genes still remain to be explored. Knowledge on the structure and function of ASFV proteins, the mechanism underlying ASFV infection and immunity, and the identification of major immunogenicity genes will contribute to the development of an ASF vaccine. In this context, this paper reviews the available knowledge on the structure, replication, protein function, virulence genes, immune evasion, inactivation, vaccines, control, and diagnosis of ASFV.

Transcriptome profile of spleen tissues from locally-adapted Kenyan pigs (Sus scrofa) experimentally infected with three varying doses of a highly virulent African swine fever virus genotype IX isolate: Ken12/busia.1 (ken-1033)

Background

African swine fever (ASF) is a lethal hemorrhagic disease affecting domestic pigs resulting in up to 100% mortality rates caused by the ASF virus (ASFV). The locally-adapted pigs in South-western Kenya have been reported to be resilient to disease and harsh climatic conditions and tolerate ASF; however, the mechanisms by which this tolerance is sustained remain largely unknown. We evaluated the gene expression patterns in spleen tissues of these locally-adapted pigs in response to varying infective doses of ASFV to elucidate the virus-host interaction dynamics.

Methods

Locally adapted pigs (n = 14) were experimentally infected with a high dose (1x10⁶HAD₅₀), medium dose (1x10⁴HAD₅₀), and low dose (1x10²HAD₅₀) of the highly virulent genotype IX ASFV Ken12/busia.1 (Ken-1033) isolate diluted in PBS and followed through the course of infection for 29 days. The in vivo pig host and ASFV pathogen gene expression in spleen tissues from 10 pigs (including three from each infective group and one uninfected control) were analyzed in a dual-RNASeq fashion. We compared gene expression between three varying doses in the host and pathogen by contrasting experiment groups against the naïve control.

Results

A total of 4954 differentially expressed genes (DEGs) were detected after ASFV Ken12/1 infection, including 3055, 1771, and 128 DEGs in the high, medium, and low doses, respectively. Gene ontology and KEGG pathway analysis showed that the DEGs were enriched for genes involved in the innate immune response, inflammatory response, autophagy, and apoptosis in lethal dose groups. The surviving low dose group suppressed genes in pathways of physiopathological importance. We found a strong association between severe ASF pathogenesis in the high and medium dose groups with upregulation of proinflammatory cytokines and immunomodulation of cytokine expression possibly induced by overproduction of prostaglandin E synthase (4-fold; p < 0.05) or through downregulation of expression of M1-activating receptors, signal transductors, and transcription factors. The host-pathogen interaction resulted in induction of expression of immune-suppressive cytokines (IL-27), inactivation of autophagy and apoptosis through up-regulation of NUPR1 [5.7-fold (high dose) and 5.1-fold (medium dose) [p < 0.05] and IL7R expression. We detected repression of genes involved in MHC class II antigen processing and presentation, such as cathepsins, SLA-DQB1, SLA-DOB, SLA-DMB, SLA-DRA, and SLA-DQA in the medium and high dose groups. Additionally, the host-pathogen interaction activated the CD8⁺ cytotoxicity and neutrophil machinery by increasing the expression of neutrophils/CD8⁺ T effector cell-recruiting chemokines (CCL2, CXCL2, CXCL10, CCL23, CCL4, CXCL8, and CXCL13) in the lethal high and medium dose groups. The recovered pigs infected with ASFV at a low dose significantly repressed the expression of CXCL10, averting induction of T lymphocyte apoptosis and FUNDC1 that suppressed neutrophilia.

Conclusions

We provide the first in vivo gene expression profile data from locally-adapted pigs from south-western Kenya following experimental infection with a highly virulent ASFV genotype IX isolate at varying doses that mimic acute and mild disease. Our study showed that the locally-adapted pigs induced the expression of genes associated with tolerance to infection and repression of genes involved in inflammation at varying levels depending upon the ASFV dose administered.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08754-8.

Changes in Estimating the Wild Boar Carcasses Sampling Effort: Applying the EFSA ASF Exit Strategy by Means of the WBC-Counter Tool

African swine fever (ASF) is a devastating disease, resulting in the high mortality of domestic and wild pigs, spreading quickly around the world. Ensuring the prevention and early detection of the disease is even more crucial given the absence of licensed vaccines. As suggested by the European Commission, those countries which intend to provide evidence of freedom need to speed up passive surveillance of their wild boar populations. If this kind of surveillance is well-regulated in domestic pig farms, the country-specific activities to be put in place for wild populations need to be set based on wild boar density, hunting bags, the environment, and financial resources. Following the indications of the official EFSA opinion 2021, a practical interpretation of the strategy was implemented based on the failure probabilities of wrongly declaring the freedom of an area even if the disease is still present but undetected. This work aimed at providing a valid, applicative example of an exit strategy based on two different approaches: the first uses the wild boar density to estimate the number of carcasses need to complete the exit strategy, while the second estimates it from the number of wild boar hunted and tested. A practical free access tool, named WBC-Counter, was developed to automatically calculate the number of needed carcasses. The practical example was developed using the ASF data from Sardinia (Italian island). Sardinia is ASF endemic from 43 years, but the last ASFV detection dates back to 2019. The island is under consideration for ASF eradication declaration. The subsequent results provide a practical example for other countries in approaching the EFSA exit strategy in the best choices for its on-field application.

Adaptive Cellular Immunity against African Swine Fever Virus Infections

African swine fever virus (ASFV) remains a threat to global pig populations. Infections with ASFV lead to a hemorrhagic disease with up to 100% lethality in Eurasian domestic and wild pigs. Although myeloid cells are the main target cells for ASFV, T cell responses are impacted by the infection as well. The complex responses remain not well understood, and, consequently, there is no commercially available vaccine. Here, we review the current knowledge about the induction of antiviral T cell responses by cells of the myeloid lineage, as well as T cell responses in infected animals, recent efforts in vaccine research, and T cell epitopes present in ASFV.

One hundred years of African swine fever in Africa: where have we been, where are we now, where are we going?

One hundred years have passed since the first paper on African swine fever (ASF) was published by Montgomery in 1921. With no vaccine, ineffectiveness of prevention and control measures, and lack of common interest in eradicating the disease, ASF has proven to be one of the most devastating diseases because of its significant sanitary and socioeconomic consequences. The rapid spread of the disease on the European and Asian continents and its recent appearance in the Caribbean puts all countries at great risk because of global trade. The incidence of ASF has also increased on the African continent over the last few decades, extending its distribution far beyond the area in which the ancient sylvatic cycle is present with its complex epidemiological transmission pathways involving virus reservoirs in ticks and wild African Suidae. Both in that area and elsewhere, efficient transmission by infected domestic pigs and virus resistance in infected animal products and fomites mean that human driven factors along the pig value chain are the dominant impediments for its prevention, control, and eradication. Control efforts in Africa are furthermore hampered by the lack of information about the size and location of the fast-growing pig population, particularly in the dynamic smallholder sector that constitutes up to 90% of pig production in the region. A vaccine that will be both affordable and effective against multiple genotypes of the virus is not a short-term reality. Therefore, a strategy for management of ASF in sub-Saharan Africa is needed to provide a roadmap for the way forward for the continent. This review explores the progression of ASF and our knowledge of it through research over a century in Africa, our current understanding of ASF, and what must be done going forwards to improve the African situation and contribute to global prevention and control. This article is protected by copyright. All rights reserved.

Prioritisation of Provinces for African Swine Fever Intervention in South Africa through Decision Matrix Analysis

South Africa has experienced an increase in the number of African swine fever (ASF) outbreaks in domestic pigs in the last ten years. Intervention will be needed in the form of control and prevention strategies to minimise the impact of this disease in the country. The aim of this study is to prioritise which provinces resources should be allocated to for ASF intervention strategies, based on the risk factors identified as pertinent in South Africa. A multi-criteria decision analysis approach was followed using an analytic hierarchy process (AHP) method to determine the perceived risk of ASF outbreaks in domestic pigs per province. Nine risk factors applicable to the South African context were identified from literature. Data on the presence of these risk factors per province were collected from records and by means of a questionnaire. The risk factors were weighted by means of an AHP. The decision matrix determined that ASF intervention and prevention resources should be focused on Mpumalanga, Free State and Gauteng provinces in South Africa. Specific intervention strategies should be focused on the confinement of pigs, swill-feeding of pigs and buying/selling of pigs at auctions through a participatory approach with stakeholders.

Prevention and Control of African Swine Fever in the Smallholder Pig Value Chain in Northern Uganda: Thematic Analysis of Stakeholders' Perceptions

African swine fever (ASF) is endemic in Uganda and considered a major constraint to pig production. In the absence of a vaccine, biosecurity is key for ASF prevention and control. To improve prevention and control on farm and community level there is need for more knowledge on current application of biosecurity practises, and better understanding of how pig value chain actors perceive prevention and control. To achieve this, a qualitative interview study involving focus group discussions (FGD) was conducted with actors from the smallholder pig value chain in northern Uganda. Six villages were purposively selected based on previous outbreaks of ASF, preliminary perceived willingness to control ASF, and the representation of several different value chain actors in the village. Results indicated that biosecurity practises such as basic hygiene routines including safe carcass handling, minimising direct and indirect contacts between pigs or between pigs and people, trade restrictions and sharing of disease information were implemented in some of the villages. Thematic analysis based on grounded theory revealed six categories of data relating to ASF prevention and control. Together these categories form a logical framework including both enablers and hindrances for ASF prevention and control. In summary participants mostly had positive perceptions of ASF biosecurity, describing measures as effective. Participants further possessed knowledge of ASF and its transmission, some of which was in line with known scientific knowledge and some not. Nevertheless, participants were hindered from preventing and controlling ASF due to biosecurity costs and a need to prioritise family livelihood over disease transmission risks, incompatibility of current biosecurity practises with local culture, traditions and social contexts and finally lack of access to veterinarians or, occasionally, low-quality veterinary services. The constraints could be addressed by applying participatory processes in designing biosecurity measures to ensure better adaptation to local cultural and social contexts.

I267L Is Neither the Virulence- Nor the Replication-Related Gene of African Swine Fever Virus and Its Deletant Is an Ideal Fluorescent-Tagged Virulence Strain

African swine fever virus (ASFV) is the causative agent of African swine fever (ASF) which reaches up to 100% case fatality in domestic pigs and wild boar and causes significant economic losses in the swine industry. Lack of knowledge of the function of ASFV genes is a serious impediment to the development of the safe and effective vaccine. Herein, I267L was identified as a relative conserved gene and an early expressed gene. A recombinant virus (SY18ΔI267L) with I267L gene deletion was produced by replacing I267L of the virulent ASFV SY18 with enhanced green fluorescent protein (EGFP) cassette. The replication kinetics of SY18ΔI267L is similar to that of the parental isolate in vitro. Moreover, the doses of 10^2.0 TCID₅₀ (n = 5) and 10^5.0 TCID₅₀ (n = 5) SY18ΔI267L caused virulent phenotype, severe clinical signs, viremia, high viral load, and mortality in domestic pigs inoculated intramuscularly as the virulent parental virus strain. Therefore, the deletion of I267L does not affect the replication or the virulence of ASFV. Utilizing the fluorescent-tagged virulence deletant can be easy to gain a visual result in related research such as the inactivation effect of some drugs, disinfectants, extracts, etc. on ASFV.

The Role of Male Reproductive Organs in the Transmission of African Swine Fever-Implications for Transmission

African swine fever (ASF) has evolved from an exotic animal disease to a threat to global pig production. An important avenue for the wide-spread transmission of animal diseases is their dissemination through boar semen used for artificial insemination. In this context, we investigated the role of male reproductive organs in the transmission of ASF. Mature domestic boars and adolescent wild boars, inoculated with different ASF virus strains, were investigated by means of virological and pathological methods. Additionally, electron microscopy was employed to investigate in vitro inoculated sperm. The viral genome, antigens and the infectious virus could be found in all gonadal tissues and accessory sex glands. The viral antigen and viral mRNAs were mainly found in mononuclear cells of the respective tissues. However, some other cell types, including Leydig, endothelial and stromal cells, were also found positive. Using RNAScope, p72 mRNA could be found in scattered halo cells of the epididymal duct epithelium, which could point to the disruption of the barrier. No direct infection of spermatozoa was observed by immunohistochemistry, or electron microscopy. Taken together, our results strengthen the assumption that ASFV can be transmitted via boar semen. Future studies are needed to explore the excretion dynamics and transmission efficiency.

Prevention and Control Strategies of African Swine Fever and Progress on Pig Farm Repopulation in China

African swine fever (ASF) is a devastating disease in domestic and wild pigs. Since the first outbreak of ASF in August 2018 in China, the disease has spread throughout the country with an unprecedented speed, causing heavy losses to the pig and related industries. As a result, strategies for managing the disease are urgently needed. This paper summarizes the important aspects of three key elements about African swine fever virus (ASFV) transmission, including the sources of infection, transmission routes, and susceptible animals. It overviews the relevant prevention and control strategies, focusing on the research progress of ASFV vaccines, anti-ASFV drugs, ASFV-resistant pigs, efficient disinfection, and pig farm biosecurity. We then reviewed the key technical points concerning pig farm repopulation, which is critical to the pork industry. We hope to not only provide a theoretical basis but also practical strategies for effective dealing with the ASF epidemic and restoration of pig production.

Descriptive and Multivariate Analysis of the Pig Sector in North Macedonia and Its Implications for African Swine Fever Transmission

North Macedonia, a country in the Balkan region of Europe, is currently bordered to the north and east by countries with active African swine fever (ASF) outbreaks. The predominantly traditional backyard pig farming sector in this country is under imminent threat of disease incursion. The characteristics and practices of such sectors have rarely been described, and thus the implications for these factors on disease introduction and spread are poorly understood. Using a semi-structured questionnaire, 457 pig producers were interviewed, providing information on 77.7% of the pig population in North Macedonia. In addition, a pilot study of 25 pig producers in Kosovo was performed. This study aimed to provide a detailed description of the North Macedonian pig sector, to make comparisons with nearby Kosovo, and to identify areas with high-risk practices for targeted mitigation. Descriptive data were summarized. Results of the questionnaire were used to identify farm-level risk factors for disease introduction. These factors were used in the calculation of a biosecurity risk score. Kernel density estimation methods were used to generate density maps highlighting areas where the risk of disease introduction was particularly concentrated. Multiple correspondence analysis with hierarchical clustering on principal components was used to explore patterns in farm practices. Results show that farms were predominantly small-scale with high rates of turnover. Pig movement was predominantly local. The highest biosecurity risk scores were localized in the eastern regions of North Macedonia, concerningly the same regions with the highest frequency of wild boar sightings. Veterinarians were highly regarded, regularly utilized, and trusted sources of information. Practices that should be targeted for improvement include isolation of new pigs, and consistent application of basic sanitary practices including washing hands, use of disinfection mats, and separation of clean and dirty areas. This study provides the most complete description of the North Macedonian pig sector currently available. It also identifies regions and practices that could be targeted to mitigate the risk of disease incursion and spread. These results represent the first steps to quantify biosecurity gaps and high-risk behaviors in North Macedonia, providing baseline information to design risk-based, more cost-effective, prevention, surveillance, and control strategies.

Extension of Sylvatic Circulation of African Swine Fever Virus in Extralimital Warthogs in South Africa

Sylvatic circulation of African swine fever virus (ASFV) in warthogs and Ornithodoros ticks that live in warthog burrows historically occurred in northern South Africa. Outbreaks of the disease in domestic pigs originated in this region. A controlled area was declared in the north in 1935 and regulations were implemented to prevent transfer of potentially infected suids or products to the rest of the country. However, over the past six decades, warthogs have been widely translocated to the south where the extralimital animals have flourished to become an invasive species. Since 2016, there have been outbreaks of ASF in pigs outside the controlled area that cannot be linked to transfer of infected animals or products from the north. An investigation in 2008–2012 revealed that the presence of Ornithodoros ticks and ASFV in warthog burrows extended marginally across the boundary of the controlled area. We found serological evidence of ASFV circulation in extralimital warthogs further south in the central part of the country.

A quadruple protection procedure for resuming pig production in small-scale ASFV-positive farms in China

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African swine fever outbreak has caused serious economic losses in China. Pork supply in consequence faces huge demand.

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The small-scale farms in China are encountering difficulties in raising pigs.

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A comprehensive procedure was tested in 35 small pig farms that had been confirmed with African swine fever virus.

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During a one-year study, 100 percent of porkers and 98.8 percent of sows were healthy respectively.

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An effective biosafety procedure was developed for production of pigs in small-scale farms in China.

African swine fever (ASF) outbreak has caused serious economic losses in Asia since 2018. As ASF is a new emerging disease, many farmers hesitate to raise pigs before biosafety procedures were evaluated to be effective. To support small-scale farms in resuming pig production, a comprehensive procedure, called the quadruple protection procedure (QPP), was tested in 35 small farms which had been confirmed with African swine fever virus (ASFV). The QPP takes care of the farms' construction, environmental disinfection, regular immunization, and feed quality. Qualified daily management was supplemented as well. During a one-year survey four disinfectants and one piece of equipment were used in higher frequency. A 7- or 15-day empty period after the disinfection was suitable when it was combined with the rest of the protection measures from QPP. Totally 18,730 porkers and 3,006 sows were healthy by the end of the study with percentage of 100 and 98.8, respectively, indicating that QPP could protect pigs in small-scale farms from pathogens within China. This study developed an effective protective procedure system for small-scale farms to produce pigs under the risk of ASF outbreak.

In vitro primary porcine alveolar macrophage cell toxicity and African swine fever virus inactivation using five commercially supply compound disinfectants under various condition

Efficacy of African swine fever virus (ASFV) inactivation using five commercially supply compound disinfectants was evaluated under various condition. Virucidal efficacy demonstrated that products A and E could inactivate at 1:800 within 1 min for both temperatures, while products B, C and D inactivated at 1:400. However, product D could inactivate at 1:800 when the exposure time was extended to 30 min and effected only 20°C. In addition, the cytotoxicity demonstrated that products A, B, C, D and E did not significantly affect to cell at 1:51,200, 1:12,800, 1:12,800, 1:25,600 and 1:12,800 dilution, respectively. In conclusion, these disinfectants could inactivate ASFV, however, the application of these products should be performed under safety precautions to prevent cytotoxicity in humans and animals.

The effectiveness of community-led initiatives in livestock disease control: a case of African swine fever in rural areas of Uganda

Proper implementation of biosecurity is currently the only control measure of African swine fever (ASF) in the absence of an effective vaccine or drug against the disease. Despite the efforts that Uganda's local and central governments have invested to reduce livestock diseases, ASF outbreaks still persist in the country. In this study, we assessed the effectiveness of community-led initiatives in the control of ASF in Mukono District, central Uganda. In Mukono district, a community-led pilot program was initiated where stakeholders in the pig value chain organized themselves into an ASF control task force to enforce on-farm and pig value chain activities intended to limit the spread of ASF. Semi-structured interviews with pig famers (n = 211) were conducted in two areas with contrasting practices: one with active community-initiated and monitored ASF control initiatives since 2016 (Kasawo and Namuganga) and the other without such initiative as the control (Mpunge and Ntenjeru). A significant decline (Wilcoxon ranked sign test: Z =  - 5.412, p = 0.000) in the annual frequency of ASF outbreaks in both Kasawo and Namuganga sub-counties was observed after the implementation of community-led initiatives. The level of practice of most ASF control measures was significantly higher (p < 0.01) in sub-counties that instituted community-led ASF control initiatives than in the control sub-counties. The results of this study demonstrate the power of community-led initiatives in reducing ASF disease outbreaks in endemic areas.

In vitro cytotoxicity and virucidal efficacy of potassium hydrogen peroxymonosulfate compared to quaternary ammonium compound under various concentrations, exposure times and temperatures against African swine fever virus

BACKGROUND AND AIM

The selection and proper application of disinfectants are crucial to the prevention of many diseases, so disinfectants must be evaluated before being used for the prevention of African swine fever (ASF). Three disinfectant products belonging to the group of potassium hydrogen peroxymonosulfates, product A and product B, and a quaternary ammonium compound called product C, were examined in vitro for host cell cytotoxicity and the efficacy of ASF virus inactivation. The study parameters included various concentrations, exposure times, temperatures, and degrees of cytotoxicity.

MATERIALS AND METHODS

Three disinfectant products were evaluated for cytotoxicity using primary porcine alveolar macrophage (PAM) cells at dilutions from 1:200 to 1:51,200. Disinfectants in concentrations of 1:200, 1:400, and 1:800 were prepared, the pH and the virucidal activity were tested. An equal volume of each dilution was mixed with the ASF virus and incubated at room temperature (20°C) or on ice (4°C) for 1 min, 5 min, or 30 min. Hemadsorption (HAD) or rosette formation was observed using an inverted microscope for 5 days after inoculation, and the virus titer was calculated as HAD50/mL. Each treatment and virus control were tested in triplicate, and the titers were reported as means and standard deviations. The reduction factor was used to measure inactivation.

RESULTS

Products A, B, and C at 1:400, 1:800, and 1:25,600 of dilution, respectively, did not show significant cytotoxic effects on PAM cells. Products A and B could inactivate ASF virus at 1:200 dilution within 5 min after exposure at 4°C. However, at 20°C, the exposure time had to be extended to 30 min to inactivate the virus. Product C could inactivate the virus at 1:400 dilution within 5 min under both temperature conditions, whereas at 1:800 dilution, the exposure time had to be extended to 30 min to completely inactivate the virus at 20°C.

CONCLUSION

All disinfectants could inactivate ASF virus in various concentrations, under appropriate exposure times and reaction temperatures, and there was no evidence of host cell cytotoxicity. For the control of ASF in pig farms, the appropriate concentration, ambient temperature, and contact time of these disinfectants should be taken into account.

Serological and molecular epidemiological study on swine influenza in Zambia

Influenza A viruses (IAVs) cause highly contagious respiratory diseases in humans and animals. In 2009, a swine-origin pandemic H1N1 IAV, designated A(H1N1)pdm09 virus, spread worldwide, and has since frequently been introduced into pig populations. Since novel reassortant IAVs with pandemic potential may emerge in pigs, surveillance for IAV in pigs is therefore necessary not only for the pig industry but also for public health. However, epidemiological information on IAV infection of pigs in Africa remains sparse. In this study, we collected 246 serum and 605 nasal swab samples from pigs in Zambia during the years 2011-2018. Serological analyses revealed that 49% and 32% of the sera collected in 2011 were positive for hemagglutination-inhibition (HI) and neutralizing antibodies against A(H1N1)pdm09 virus, respectively, whereas less than 5.3% of sera collected during the following period (2012-2018) were positive in both serological tests. The positive rate and the neutralization titres to A(H1N1)pdm09 virus were higher than those to classical swine H1N1 and H1N2 IAVs. On the other hand, the positive rate for swine H3N2 IAV was very low in the pig population in Zambia in 2011-2018 (5.3% and 0% in HI and neutralization tests, respectively). From nasal swab samples, we isolated one H3N2 and eight H1N1 IAV strains with an isolation rate of 1.5%. Phylogenetic analyses of all eight gene segments revealed that the isolated IAVs were closely related to human IAV strains belonging to A(H1N1)pdm09 and seasonal H3N2 lineages. Our findings indicate that reverse zoonotic transmission from humans to pigs occurred during the study period in Zambia and highlight the need for continued surveillance to monitor the status of IAVs circulating in swine populations in Africa.

Genotype I African swine fever viruses emerged in domestic pigs in China and caused chronic infection

The Georgia-07-like genotype II African swine fever virus (ASFV) with high virulence has been prevalent in China since 2018. Here, we report that genotype I ASFVs have now also emerged in China. Two non-haemadsorbing genotype I ASFVs, HeN/ZZ-P1/21 and SD/DY-I/21, were isolated from pig farms in Henan and Shandong province, respectively. Phylogenetic analysis of the whole genome sequences suggested that both isolates share high similarity with NH/P68 and OURT88/3, two genotype I ASFVs isolated in Portugal in the last century. Animal challenge testing revealed that SD/DY-I/21 shows low virulence and efficient transmissibility in pigs, and causes mild onset of infection and chronic disease. SD/DY-I/21 was found to cause necrotic skin lesions and joint swelling. The emergence of genotype I ASFVs will present more problems and challenges for the control and prevention of African swine fever in China.

First Genomic Evidence of Dual African Swine Fever Virus Infection: Case Report from Recent and Historical Outbreaks in Sardinia

African swine fever virus (ASFV) is one of the pathogens of highest concern worldwide. Despite different virus lineages co-circulating in several areas, dual infections in the same animal have been rarely observed, suggesting that ASF superinfections are infrequent events. Here we present the first genome-wide detection and analysis of two intragenotype dual ASFV infections. The dual infections have been detected in a hunted wild boar and in a pig carcass, both infected by ASFV genotype I in Sardinia in 1984 and 2018, respectively. We characterize the genetic differences between the two sequences, their intra-host frequency, and their phylogenetic relationship among fully sequenced ASFV strains from Sardinia. Both dual infections involve pairs of closely related but different viruses that were circulating in Sardinia in the same period. The results imply that dual ASFV infections or similar ASFV strains are more common than expected, especially in ASF endemic areas, albeit difficult to detect.

Spatial-Temporal Movements of Free Ranging Pigs at the Wildlife-Livestock Interface of Murchison Falls National Park, Uganda: Potential of Disease Control at a Local Scale

In many Ugandan rural communities, pigs are generally kept under traditional smallholder systems without basic biosecurity measures in place. In some instances, these systems are at the livestock-wildlife interface, as it is the case in Nwoya district, which is bordered by Murchison Falls National Park (MFNP). This pig system has potential for the maintenance and transmission of pathogens like African swine fever (ASF) between different herds, and also with wild pigs (warthogs and bushpigs). In this paper, we describe the spatial and temporal pattern of the movements of free ranging domestic pigs in a rural setting in Northern Uganda where ASF is endemic. We also determine their use of habitat to highlight the potential interaction hotspots between domestic pigs and between domestic and wild pig populations. We fitted 10 free-ranging domestic pigs owned by different homesteads with GPS harnesses during rainy and dry seasons. The pig home range, daily distance, activity pattern and habitat use were calculated. Our results show that the maximum area covered (MCP 100%) by the pigs varied between 35,965 and 475,077 m². The core area varied from 1,317 to 50,769 m². The pigs' home ranges were significantly bigger during the dry season than during the rainy season (Wilcoxon test, W = 22, p = 0.04). The mean full day (24 h) distance was longer in the dry season than in the rainy season (Student test, t = 2.7, p = 0.03). The pigs were mostly located within their own homestead, but they also used other homesteads, grass and crop fields. This study highlights that free-ranging domestic pigs may cover a wide area, especially during the dry season. Interestingly, the home range of pigs from different herds may overlap with areas used by wild pigs which share crops and other resources in this area. This study provides insights into a better understanding of the potential for spread of diseases such as ASF at small-scale and can be used to raise awareness of such risks and to better target implementation of preventive measures.

Review of African swine fever outbreaks history in South Africa: From 1926 to 2018

The article reviews the outbreaks and distribution of African swine fever (ASF) in South Africa since the first probable outbreak that occurred in the Koedoesrand Ward in 1926. Retrospective data on the ASF outbreaks in South Africa were obtained from the World Organisation for Animal Health (OIE) disease database and the South African veterinary services annual reports in addition to published articles and online sources. South Africa has experienced many outbreaks that can be divided into 2 time periods: the period before the development of the OIE diseases database (1993) and the period after. More than 141 outbreaks of ASF were reported during the first period. Since the development of OIE disease database, 72 outbreaks directly involving 2968 cases, 2187 dead and 2358 killed pigs mainly in smallholder pig farms were reported. The median number of cases for a given ASF outbreak is 17, but in 50% of outbreaks no pigs were killed for prevention. The most important ASF outbreak was reported in April 2014 in the Greater Zeerust district (North West province) involving 326 cases and 1462 killed pigs. However, the outbreak with highest mortality involving 250 pigs was reported in 2016 (Free State province). According to phylogenetic analysis, nine p72 genotypes (I, III, IV, VII, VIII, XIX, XX, XXI and XXII) have been identified in South Africa. Season-wise, more outbreaks were recorded during summer. It was also observed that the OIE disease database could contain errors that would have been introduced through compiled forms at country level. Spatiotemporal studies on ASF outbreaks in South Africa are therefore required in order to assess statistically and quantitatively the clustering of outbreaks over space and time.

Age-related viral load and severity of systemic pathological lesions in acute naturally occurring African swine fever virus genotype II infections

African swine fever (ASF) causes a contagious hemorrhagic disease in all ages of pigs without sex predilections. The objective of this study was to determine the age-related viral loads and severity of systemic pathological lesions among three different swine group ages (weaned pigs, fattening pigs, and sows) during a recent outbreak of acute ASF in Vietnam. Age-related viral loads were determined in 5 major organs (lung, liver, spleen, kidney, and lymph node) by immunohistochemistry as well as in the blood by real-time polymerase chain reaction (PCR). Age-related systemic pathological lesions were analyzed in the listed organs among three age groups. Weaned pigs had significantly (p < 0.05) higher levels of viral loads in their lung, liver, lymph nodes and blood than in those of fattening pigs and sows. Fattening pigs had significantly (p < 0.05) higher scores of macroscopic lung and lymphoid lesions, and microscopic liver lesions compared with those of weaned pigs and sows. The results of this study demonstrated that viral loads were age-related in acute naturally occurring ASF but the severity of pathological lesions was not correlated with the level of viral loads in the five major organs.

Proteomics informed by transcriptomics for a qualitative and quantitative analysis of the sialoproteome of adult Ornithodoros moubata ticks

Background

The argasid tick Ornithodoros moubata is the main vector in mainland Africa of African swine fever virus and the spirochete Borrelia duttoni, which causes human relapsing fever. The elimination of populations of O. moubata would contribute to the prevention and control of these two serious diseases. Anti-tick vaccines are an eco-friendly and sustainable means of eliminating tick populations. Tick saliva forms part of the tick-host interface, and knowledge of its composition is key to the identification and selection of vaccine candidate antigens. The aim of the present work is to increase the body of data on the composition of the saliva proteome of adult O. moubata ticks, particularly of females, since in-depth knowledge of the O. moubata sialome will allow the identification and selection of novel salivary antigens as targets for tick vaccines.

Methods

We analysed samples of female and male saliva using two different mass spectrometry (MS) approaches: data-dependent acquisition liquid chromatography-tandem MS (LC–MS/MS) and sequential window acquisition of all theoretical fragment ion spectra–MS (SWATH-MS). To maximise the number of proteins identified, a proteomics informed by transcriptomics analysis was applied using the O. moubata salivary transcriptomic dataset previously obtained by RNA-Seq.

Results

SWATH-MS proved to be superior to LC–MS/MS for the study of female saliva, since it identified 61.2% more proteins than the latter, the reproducibility of results was enhanced with its use, and it provided a quantitative picture of salivary components. In total, we identified 299 non-redundant proteins in the saliva of O. moubata, and quantified the expression of 165 of these in both male and female saliva, among which 13 were significantly overexpressed in females and 40 in males. These results indicate important quantitative differences in the saliva proteome between the sexes.

Conclusions

This work expands our knowledge of the O. moubata sialome, particularly that of females, by increasing the number of identified novel salivary proteins, which have different functions at the tick–host feeding interface. This new knowledge taken together with information on the O. moubata sialotranscriptome will allow a more rational selection of salivary candidates as antigen targets for tick vaccine development.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04892-2.

Molecular characterization of African Swine fever viruses in Burkina Faso, Mali, and Senegal 1989-2016: Genetic diversity of ASFV in West Africa

African swine fever (ASF) has been endemic in sub-Saharan Africa since the 1960s. Following its introduction in Senegal, in 1957, ASF steadily progressed through West Africa, reaching Burkina Faso in 2003, and later Mali in 2016. Despite the heavy burden of disease on pig production, little information is available on the genetic diversity of Africa swine fever virus (ASFV) in Burkina Faso, Mali and Senegal. Here, we used real-time PCR ASFV to detect the ASFV genome in samples collected between 1989 and 2016, in Burkina Faso, Mali and Senegal, and conventional approaches for isolate characterization. The C-terminal end of the p72 protein gene, the full E183L gene and the central variable region (CVR) within the B602L gene in ASFV genome were sequenced and compared to publicly available sequences. ASFV genome was found in 27 samples, 19 from Burkina Faso, three from Mali and five from Senegal. The phylogenetic analyses showed that all viruses belong to genotype I, with the ASFVs from Burkina Faso and Mali grouping with genotype Ia and ASFV serogroup 4, and those from Senegal with genotype Ib and the ASFV serogroup 1. The analysis of the CVR tetrameric tandem repeat sequences (TRS) showed four TRS variants in Burkina Faso, two in Senegal and one in Mali. The three countries did not share any common TRS, and all CVRs of this study differed from previously reported CVRs in West Africa, except for Senegal. Three of the five isolates from Senegal fully matched with the CVR, p72 and p54 sequences from ASFV IC96 collected during the 1996 ASF outbreak in Ivory Coast. This study shows the spread of the same ASFV strains across countries, highlighting the importance of continuous monitoring of ASFV isolates. It also calls for an urgent need to establish a regional plan for the control and eradication of ASF in West Africa.

Acute toxicity of piggery effluent and veterinary pharmaceutical cocktail on freshwater organisms

Intensive livestock farming has increased the use of veterinary pharmaceuticals in many developing countries, and this is considered a significant concern to the freshwater ecosystem. However, the information on the potential acute toxicity of piggery effluent waste and the veterinary pharmaceutical effluent discharged into the aquatic environment is limited. This study assessed the adverse effect of a piggery effluent and the cocktail mixtures of high- and low-level doses of three frequently occurring veterinary pharmaceuticals (tetracycline (TETR), ivermectin (IVER), and salicylic acid (SALA)) on freshwater organisms using three representative freshwater biotests organisms: Pseudokirchneriella subcapitata (P. subcapitata), Daphnia magna (D. magna), and Tetrahymena thermophila (T. thermophila). The freshwater organism test results showed that the 24-h and 48-h EC₅₀ algal toxicity to P. subcapitata exposed to 10% unfiltered piggery effluent were 25.6 and 49.3% respectively while the 24-h LC₅₀ value to Cladocera, D. magna exposed to unfiltered piggery effluent was 23.2 (17.7-30.4)%. The 24-h EC₅₀ protozoan toxicity to T. thermophila exposed to 1% HLD veterinary pharmaceuticals was 0.014 μg/L. Thus, the study established the different sensitivities of freshwater organisms to various percentage levels of piggery effluent and high- and low-level doses of veterinary pharmaceutical. The piggery effluent and the pharmaceutical cocktail mixtures have potential toxicological effects on the freshwater ecosystem.

An outbreak of African swine fever in small-scale pigs, Gauteng, South Africa, July 2020

OBJECTIVES

Since 2012, outbreaks of African swine fever (ASF) in domestic pigs have increased outside of South Africa's ASF control zone. This study describes the epidemiological investigation and findings of an ASF outbreak in a small-scale pig unit in Gauteng Province and makes recommendations to prevent future outbreaks.

METHODS

PCR testing and molecular analysis were performed on pig tissue samples. Veterinary services conducted epidemiological investigations, forward and backward tracing, and surveillance. Farm management and biosecurity practices were assessed. Quarantine, culling, carcass disposal, and disinfection were implemented.

RESULTS

ASF virus genotype I was detected. A concurrent ASF outbreak in neighbouring Mpumalanga Province was identified as a possible source. Inadequate biosecurity measures probably facilitated viral transmission. Potential mechanisms for the introduction of the ASF virus include swill feeding practices, free roaming of pigs, scavenging, illegal slaughter, and trade of pig products within the community.

CONCLUSIONS

Molecular typing of the ASF virus linked the outbreak to an ongoing ASF outbreak in Mpumalanga Province. Pig enterprises with poor biosecurity practices may face greater risk of ASF introduction. Small-scale pig keepers should be targeted for ASF awareness and education campaigns. Innovative and cost-effective biosecurity solutions are needed in this resource-poor setting.

Do wild suids from Ndumo Game Reserve, South Africa, play a role in the maintenance and transmission of African swine fever to domestic pigs?

Warthogs (Phacochoerus africanus) and bushpigs (Potamochoerus larvatus) are considered as the wild reservoirs of ASF. They are both present in Ndumo Game Reserve (NGR), located in the Northern South African Province of KwaZulu on the border with Mozambique. In that area, the occurrence of tick-warthog sylvatic cycle of ASF has been suspected for years. To assess if wild suids represent a risk of ASF virus spillover to domestic pigs, wild suid abundance and incursions outside NGR boundaries were estimated using transect counts, fence patrols and camera traps. Also, the presence of Ornithodoros ticks was explored in 35 warthog burrows within NGR. In addition, blood samples were taken from 67 domestic pig farms located outside NGR to be tested for ASF antibodies. Information on interactions between domestic and wild suids and ASF occurrence was gathered using interviews with pig farmers (n = 254) in the study area. In conclusion, the bushpigs and warthog's population estimates in NGR are 5 and 3-5 individuals/km² , respectively. Both species move out of the reserve regularly (15.4 warthogs/day and 6.35 bushpigs/day), with movements significantly increasing in the dry season. Some farmers observed warthogs and bushpigs as far as 8 and 19 km from NGR, respectively, but no reports of direct wild-domestic suids interactions or ASF outbreaks. Also, no soft ticks were detected in all warthog burrows and all the pig blood samples were negative for ASF antibodies. The absence of ticks in warthog burrows, the absence of antibodies in pigs sampled, the absence of reported outbreaks, and no familiarity with ASF in the study area, suggest that a sylvatic cycle of ASF is, at present, unlikely in NGR. This conclusion must be confirmed by a larger survey of warthog burrows and monitoring potential antibodies in warthogs from NGR.

Development of Diagnostic Tests Provides Technical Support for the Control of African Swine Fever

African swine fever is a highly contagious global disease caused by the African swine fever virus. Since African swine fever (ASF) was introduced to Georgia in 2007, it has spread to many Eurasian countries at an extremely fast speed. It has recently spread to China and other major pig-producing countries in southeast Asia, threatening global pork production and food security. As there is no available vaccine at present, prevention and control must be carried out based on early detection and strict biosecurity measures. Early detection should be based on the rapid identification of the disease on the spot, followed by laboratory diagnosis, which is essential for disease control. In this review, we introduced the prevalence, transmission routes, eradication control strategies, and diagnostic methods of ASF. We reviewed the various methods of diagnosing ASF, focusing on their technical characteristics and clinical test results. Finally, we give some prospects for improving the diagnosis strategy in the future.