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.

Special Issue "African Swine Fever and Other Swine Viral Diseases in Africa".

African swine fever (ASF) has become the swine disease of most global concern since its second escape from Africa in 2007 resulted in its spread to five continents and the consequent devastation of industrial to subsistence pig farming [...].

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.

Innovative Research Offers New Hope for Managing African Swine Fever Better in Resource-Limited Smallholder Farming Settings: A Timely Update.

African swine fever (ASF) in domestic pigs has, since its discovery in Africa more than a century ago, been associated with subsistence pig keeping with low levels of biosecurity. Likewise, smallholder and backyard pig farming in resource-limited settings have been notably affected during the ongoing epidemic in Eastern Europe, Asia, the Pacific, and Caribbean regions. Many challenges to managing ASF in such settings have been identified in the ongoing as well as previous epidemics. Consistent implementation of biosecurity at all nodes in the value chain remains most important for controlling and preventing ASF. Recent research from Asia, Africa, and Europe has provided science-based information that can be of value in overcoming some of the hurdles faced for implementing biosecurity in resource-limited contexts. In this narrative review we examine a selection of these studies elucidating innovative solutions such as shorter boiling times for inactivating ASF virus in swill, participatory planning of interventions for risk mitigation for ASF, better understanding of smallholder pig-keeper perceptions and constraints, modified culling, and safe alternatives for disposal of carcasses of pigs that have died of ASF. The aim of the review is to increase acceptance and implementation of science-based approaches that increase the feasibility of managing, and the possibility to prevent, ASF in resource-limited settings. This could contribute to protecting hundreds of thousands of livelihoods that depend upon pigs and enable small-scale pig production to reach its full potential for poverty alleviation and food security.

Experimental Infection of Domestic Pigs (Sus scrofa) with Rift Valley Fever Virus.

Rift valley fever (RVF), caused by the RVF virus (RVFV), is a vector-borne zoonotic disease that primarily affects domestic ruminants. Abortion storms and neonatal deaths characterise the disease in animals. Humans develop flu-like symptoms, which can progress to severe disease. The susceptibility of domestic pigs (Sus scrofa domesticus) to RVFV remains unresolved due to conflicting experimental infection results. To address this, we infected two groups of pregnant sows, neonates and weaners, each with a different RVFV isolate, and a third group of weaners with a mixture of the two viruses. Serum, blood and oral, nasal and rectal swabs were collected periodically, and two neonates and a weaner from group 1 and 2 euthanised from 2 days post infection (DPI), with necropsy and histopathology specimens collected. Sera and organ pools, blood and oronasorectal swabs were tested for RVFV antibodies and RNA. Results confirmed that pigs can be experimentally infected with RVFV, although subclinically, and that pregnant sows can abort following infection. Presence of viral RNA in oronasorectal swab pools on 28 DPI suggest that pigs may shed RVFV for at least one month. It is concluded that precautions should be applied when handling pig body fluids and carcasses during RVF outbreaks.

2023 International African Swine Fever Workshop: Critical Issues That Need to Be Addressed for ASF Control.

The 2023 International African Swine Fever Workshop (IASFW) took place in Beijing, China, on 18-20 September 2023. It was jointly organized by the U.S.-China Center for Animal Health (USCCAH) at Kansas State University (KSU) and the Chinese Veterinary Drug Association (CVDA) and sponsored by the United States Department of Agriculture Foreign Agricultural Service (USDA-FAS), Harbin Veterinary Research Institute, and Zoetis Inc. The objective of this workshop was to provide a platform for ASF researchers around the world to unite and share their knowledge and expertise on ASF control and prevention. A total of 24 outstanding ASF research scientists and experts from 10 countries attended this meeting. The workshop included presentations on current ASF research, opportunities for scientific collaboration, and discussions of lessons and experiences learned from China/Asia, Africa, and Europe. This article summarizes the meeting highlights and presents some critical issues that need to be addressed for ASF control and prevention in the future.

Review of the Pig-Adapted African Swine Fever Viruses in and Outside Africa.

The region in eastern, central and southern Africa (ECSA) where African swine fever (ASF) originated in a sylvatic cycle is home to all the p72 genotypes of ASF virus identified so far. While 20 of the 24 genotypes have been isolated from outbreaks in domestic pigs in the region, only five of the genotypes (I, II, VIII, IX, X) have an extended field presence associated with domestic pigs. Of the genotypes that appear to be strongly adapted to domestic pigs, two have spread beyond the African continent and have been the focus of efforts to develop vaccines against ASF. Most of the experimental ASF vaccines described do not protect against a wider spectrum of viruses and may be less useful in the event of incursions of different strains or where multiple genotypes co-exist. The other three pig-adapted strains that are currently restricted to the ECSA region might spread, and priority should be given to understanding not only the genetic and antigenic characteristics of these viruses but also their history. We review historic and current knowledge of the distribution of these five virus genotypes, and note that as was the case for genotype II, some pig-associated viruses have the propensity for geographical range expansion. These features are valuable for prioritizing vaccine-development efforts to ensure a swift response to virus escape. However, whilst ASF vaccines are critical for high-production systems, global food security relies on parallel efforts to improve biosecurity and pig production in Africa and on continued ASFV surveillance and characterisation in the ECSA region.

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.

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.

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 forward to improve the African situation and contribute to global prevention and control.

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.

Evidence-Based African Swine Fever Policies: Do We Address Virus and Host Adequately?

African swine fever (ASF) is one of the most threatening diseases for the pig farming sector worldwide. Prevention, control and eradication remain a challenge, especially in the absence of an effective vaccine or cure and despite the relatively low contagiousness of this pathogen in contrast to Classical Swine Fever or Foot and Mouth disease, for example. Usually lethal in pigs and wild boar, this viral transboundary animal disease has the potential to significantly disrupt global trade and threaten food security. This paper outlines the importance of a disease-specific legal framework, based on the latest scientific evidence in order to improve ASF control. It compares the legal basis for ASF control in a number of pig-producing regions globally, considering diverse production systems, taking into account current scientific evidence in relation to ASF spread and control. We argue that blanket policies that do not take into account disease-relevant characteristics of a biological agent, nor the specifics under which the host species are kept, can hamper disease control efforts and may prove disproportionate.

With or without a Vaccine-A Review of Complementary and Alternative Approaches to Managing African Swine Fever in Resource-Constrained Smallholder Settings.

The spectacular recent spread of African swine fever (ASF) in Eastern Europe and Asia has been strongly associated, as it is in the endemic areas in Africa, with free-ranging pig populations and low-biosecurity backyard pig farming. Managing the disease in wild boar populations and in circumstances where the disease in domestic pigs is largely driven by poverty is particularly challenging and may remain so even in the presence of effective vaccines. The only option currently available to prevent ASF is strict biosecurity. Among small-scale pig farmers biosecurity measures are often considered unaffordable or impossible to implement. However, as outbreaks of ASF are also unaffordable, the adoption of basic biosecurity measures is imperative to achieve control and prevent losses. Biosecurity measures can be adapted to fit smallholder contexts, culture and costs. A longer-term approach that could prove valuable particularly for free-ranging pig populations would be exploitation of innate resistance to the virus, which is fully effective in wild African suids and has been observed in some domestic pig populations in areas of prolonged endemicity. We explore available options for preventing ASF in terms of feasibility, practicality and affordability among domestic pig populations that are at greatest risk of exposure to ASF.

Investigation into eradication of African swine fever in domestic pigs from a previous outbreak (2016/17) area of South Africa.

A serological survey was conducted to evaluate the eradication of African swine fever (ASF) infection eighteen months after clinical surveillance and selective culling had been completed during domestic cycle outbreaks in parts of South Africa in 2016/17. Three hundred and twenty-two serum samples from 85 pig keepers were collected in the study area and tested for the presence of antibodies against the ASF virus (ASFV). None of the samples contained detectable levels of antibodies against ASFV. These results together with the findings from clinical surveillance following culling activities suggest that the disease had been eradicated from the domestic pig population in this area following the outbreaks. Questionnaire responses from the pig keepers in this area highlighted the need to implement basic biosecurity measures in smallholder pig keepers to prevent outbreaks of ASF in South Africa.

Investigation of African swine fever outbreaks in pigs outside the controlled areas of South Africa, 2012-2017.

South Africa historically experienced sporadic African swine fever (ASF) outbreaks in domestic pigs in the northern parts of the country. This was subsequently indicated to be because of spillover from the sylvatic cycle of ASF between warthog and tampans (soft ticks) in the area. South Africa declared this area an ASF-controlled area in 1935, and the area is still controlled in terms of the Animal Diseases Act, 1984 (Act 35 of 1984). Two main epidemics of ASF in domestic pigs were identified outside of the South African ASF-controlled area. The first occurred in 2012 with outbreaks in Gauteng and Mpumalanga provinces, and the second occurred in 2016-2017 with outbreaks in the North West, Free State and Northern Cape provinces. These were the first ASF epidemics in South Africa associated with transmission of the disease via a domestic cycle. This study found that the spread of ASF in these epidemics was mainly via auctions, swill feeding and scavenging. These three aspects need to be addressed in terms of awareness and education on the disease including implementation of biosecurity measures in order to prevent future ASF outbreaks in South Africa. Specific biosecurity measures should be implemented in the semi-commercial sector to prevent ASF-infected pigs and pig products from being moved to naïve pigs and therefore spreading the disease.

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.

Seroprevalence of Rift valley fever in South African domestic and wild suids (1999-2016).

Rift valley fever (RVF) is a vector-borne viral disease of domestic ruminants, camels and man, characterized by widespread abortions and neonatal deaths in animals, and flu-like symptoms, which can progress to hepatitis and encephalitis in humans. The disease is endemic in Africa, Saudi Arabia and Yemen, and outbreaks occur after periods of high rainfall, or in environments supporting the proliferation of RVF virus (RVFV)-infected mosquito vectors. The domestic and wild animal maintenance hosts of RVFV, which may serve as sources of virus during inter-epidemic periods (IEPs) and contribute to occurrence of sporadic outbreaks, remain unknown, although reports indicate that the African buffalo (Syncerus caffer) may play a role. Due to the close proximity of the habitats of domestic pigs and warthogs to those of known domestic and wild ruminant RVFV maintenance hosts respectively, our study investigated their possible role in the epidemiology of RVF in South Africa by evaluating RVFV exposure and seroconversion in suids. A total of 107 warthog and 3,984 domestic pig sera from 2 and all 9 provinces of South Africa, respectively, were screened for presence of RVFV neutralizing antibodies using the virus neutralization test (VNT). Sero-positivity rates of 1.87% (95% CI: 0.01%-6.9%) and 0.68% (95% CI: 0.49%-1.04%) were observed for warthogs and domestic pigs, respectively, but true prevalence rates, taking test sensitivity and specificity into account, were lower for both groups. There was a strong association between the results of the two groups (χ2  = 0.75, p = .38), and differences in prevalence between the epidemic and IEPs were non-significant for all suid samples tested (p > .05). This study, which provides the first evidence of probable exposure and infection of South African domestic pigs and warthogs to RVFV, indicates that further investigations are warranted, to fully clarify the role of suids in the epidemiology of RVF.

Lack of evidence for long term carriers of African swine fever virus - a systematic review.

African swine fever (ASF) was first described in 1921 as a highly fatal and contagious disease which caused severe outbreaks among settlers' pigs in British East Africa. Since then the disease has expanded its geographical distribution and is currently present in large parts of Africa, Europe and Asia and considered a global threat. Although ASF is typically associated with very high case fatality rates, a certain proportion of infected animals will recover from the infection and survive. Early on it was speculated that such survivors may act as carriers of the virus, and the importance of such carries for disease persistence and spread has since then almost become an established truth. However, the scientific basis for such a role of carriers may be questioned. With this in mind, the objective of this study was to review the available literature in a systematic way and to evaluate the available scientific evidence. The selection of publications for the review was based on a database search, followed by a stepwise screening process in order to exclude duplicates and non-relevant publications based on pre-defined exclusion criteria. By this process the number of publications finally included was reduced from the 3664 hits identified in the initial database search to 39 publications, from which data was then extracted and analysed. Based on this it was clear that a definition of an ASF virus carrier is lacking, and that in general any survivor or seropositive animal has been referred to as carrier. It was also clear that evidence of any significant role of such a carrier is absent. Two types of "survivors" could be defined: 1) pigs that do not die but develop a persistent infection, characterised by periodic viraemia and often but not always accompanied by some signs of subacute to chronic disease, and 2) pigs which clear the infection independently of virulence of the virus, and which are not persistently infected and will not present with prolonged virus excretion. There is no evidence that suggests that any of these categories of survivors can be considered as "healthy" carriers, i.e. pigs that show no sign of disease but can transmit the virus to in-contact pigs. However, localized virus persistence in lymphoid tissues may occur to some extent in any of the categories of survivors, which in theory may cause infection after oral uptake. To what extent this is relevant in reality, however, can be questioned given the virus dose generally needed for oral infection.