Spatiotemporal analysis of African swine fever outbreaks on South African smallholder farms, 1993-2018.

African swine fever (ASF) is a contagious viral disease of swine worldwide. ASF in South Africa has for many years been confined to a controlled area in the northeast of the country that was proclaimed in 1935. Since 2012, outbreaks are more likely to occur in the historically ASF-free area. This study aimed to analyse the spatial and spatiotemporal structure of ASF outbreaks in South Africa between 1993 and 2018. Global space-time clustering of ASF outbreaks was investigated by the Diggle space-time K-function while Kulldorff's spatial scan statistic was applied to detect local cluster of ASF outbreaks. Globally, ASF outbreaks exhibit statistically significant spatial clustering. They have shown a significant negative space-time interaction at month scale (p = 0.003) but no significant space-time interaction at year scale (p = 0.577), revealing strong evidence that ASF cases that are close in space occur in months which are close and vice versa. In studying local area space-time clustering at both month and year scale, three significant local clusters associated with high-rate were detected. These clusters are localised in both the ASF-controlled area and outside the controlled area with radius varying from 60.84 km up to 271.43 km and risk ratio varying from 6.61 up to 17.70. At month scale, clusters with more outbreaks were observed between June 2017 and August 2017 and involved 22 outbreaks followed by the cluster that involved 13 outbreaks in January 2012. These results show the need to maintain high biosecurity standards on pig farms in both inside and outside the ASF-controlled areas.

The African swine fever epidemic in West Africa, 1996-2002.

African swine fever (ASF) is a contagious, highly fatal, haemorrhagic viral disease that only affects members of the Suidae family. Currently, no vaccine or treatment exists, so the disease has potentially devastating consequences for the pig industries, availability of affordable protein livelihoods and trade. This study aimed to consolidate historical information generated by working towards the control and eradication of ASF in previously unaffected countries in West Africa during 1996-2002. This descriptive analysis entailed the evaluation and review of archived records and reports of outbreaks, data from veterinary services, veterinary consultants and peer-reviewed publications. Specifically, the analysis focused on establishing the sequence of events in the spread of the disease throughout the region, as well as the possible sources and pathways (mostly human-driven, i.e., movement of pigs and swill feeding). The socio-economic aspects of the epidemic were also assessed. Finally, the prevention and control measures applied were described and evaluated. Major challenges for control that were identified involved lack of capacity to respond to an outbreak of animal disease and the nature of the pig sector in the affected countries. Most of the pigs were produced in low biosecurity subsistence husbandry systems. Actions taken by producers to limit economic losses due to the epidemic (e.g., illegal selling of pigs and infected pork, hiding of outbreaks) increased the risk of spread and frustrated control efforts. The disease has persisted in an endemic state ever since and has negatively affected pig production and marketing in most of these countries. The analysis of this information will allow a better understanding of the disease dynamics in a region infected for the first time, and learning how the prevention and control interventions that were implemented worked or failed. This will help the development of better tailored, sustainable and locally sound interventions. The authors provide a set of recommendations for ASF prevention and control.

Eradication of Transboundary Animal Diseases: Can the Rinderpest Success Story be Repeated?

A matrix system was developed to aid in the evaluation of the technical amenability to eradication, through mass vaccination, of transboundary animal diseases (TADs). The system involved evaluation of three basic criteria - disease management efficiency, surveillance and epidemiological factors - each in turn comprised of a number of elements (17 in all). On that basis, 25 TADs that have occurred or do occur in southern Africa and for which vaccines are available, in addition to rinderpest (incorporated as a yardstick because it has been eradicated worldwide), were ranked. Cluster analysis was also applied using the same criteria to the 26 diseases, creating division into three groups. One cluster contained only diseases transmitted by arthropods (e.g. African horse sickness and Rift Valley fever) and considered difficult to eradicate because technologies for managing parasitic arthropods on a large scale are unavailable, while a second cluster contained diseases that have been widely considered to be eradicable [rinderpest, canine rabies, the Eurasian serotypes of foot and mouth disease virus (O, A, C & Asia 1) and peste des petits ruminants] as well classical swine fever, Newcastle disease and lumpy skin disease. The third cluster contained all the other TADs evaluated with the implication that these constitute TADs that would be more difficult to eradicate. However, it is acknowledged that the scores assigned in the course of this study may be biased. The point is that the system proposed offers an objective method for assessment of the technical eradicability of TADs; the rankings and groupings derived during this study are less important than the provision of a systematic approach for further development and evaluation.

New insights into the role of ticks in African swine fever epidemiology.

African swine fever (ASF), one of the most important diseases of swine, is present in many African countries, as well as in eastern Europe, Russia and Sardinia. It is caused by a complex virus, ASF virus (ASFV), for which neither vaccine nor treatment is available. ASFV affects swine of all breeds and ages, and also replicates in soft ticks of the genus Ornithodoros, facilitating ASFV persistence and reocurrence of disease. Depending on the involvement of these ticks, and the presence or not of sylvatic asymptomatic animals, several epidemiological cycles have been identified. The disease persists in East and southern African countries in a sylvatic cycle between O. porcinus (of the O. moubata species complex) and common warthogs. In some countries a domestic pig-tick cycle exists, whereas in other regions, notably West Africa, the role of soft ticks has not been demonstrated, and ASFV is transmitted between domestic pigs in the absence of tick vectors. Even in several East and Central African countries which have the sylvatic or domestic cycle, the majority of outbreaks are not associated with ticks or wild suids. In Europe, O. erraticus was detected and identified as a crucial vector for ASF maintenance in outdoor pig production on the Iberian Peninsula. However, in most parts of Europe, there is a lack of information about the distribution and role of Ornithodoros ticks in ASF persistence, particularly in eastern regions. This article reviews ASF epidemiology and its main characteristics, with a special focus on the distribution and role of soft ticks in ASF persistence in different settings. Information abouttick detection, control measures and future directions for research is also included.

International trade standards for commodities and products derived from animals: the need for a system that integrates food safety and animal disease risk management.

A case is made for greater emphasis to be placed on value chain management as an alternative to geographically based disease risk mitigation for trade in commodities and products derived from animals. The geographic approach is dependent upon achievement of freedom in countries or zones from infectious agents that cause so-called transboundary animal diseases, while value chain-based risk management depends upon mitigation of animal disease hazards potentially associated with specific commodities or products irrespective of the locality of production. This commodity-specific approach is founded on the same principles upon which international food safety standards are based, viz. hazard analysis critical control points (HACCP). Broader acceptance of a value chain approach enables animal disease risk management to be combined with food safety management by the integration of commodity-based trade and HACCP methodologies and thereby facilitates 'farm to fork' quality assurance. The latter is increasingly recognized as indispensable to food safety assurance and is therefore a pre-condition to safe trade. The biological principles upon which HACCP and commodity-based trade are based are essentially identical, potentially simplifying sanitary control in contrast to current separate international sanitary standards for food safety and animal disease risks that are difficult to reconcile. A value chain approach would not only enable more effective integration of food safety and animal disease risk management of foodstuffs derived from animals but would also ameliorate adverse environmental and associated socio-economic consequences of current sanitary standards based on the geographic distribution of animal infections. This is especially the case where vast veterinary cordon fencing systems are relied upon to separate livestock and wildlife as is the case in much of southern Africa. A value chain approach would thus be particularly beneficial to under-developed regions of the world such as southern Africa specifically and sub-Saharan Africa more generally where it would reduce incompatibility between attempts to expand and commercialize livestock production and the need to conserve the subcontinent's unparalleled wildlife and wilderness resources.

Balancing livestock production and wildlife conservation in and around southern Africa's transfrontier conservation areas.

Biodiversity conservation, of which the transfrontier conservation area movement is an integral part, and more effective livestock production/trade are pivotal to future rural development in southern Africa. For that reason, it is imperative to effectively ameliorate the obstacles that have impeded progress towards the coexistence of these two sectors for more than half a century. Transboundary animal diseases, foot and mouth disease in particular, have been and continue to be the most important of these obstacles. Fortunately, new developments in international sanitary standards applicable to trade in commodities and products derived from animals are beginning to make a solution possible. However, while progress in principle has been achieved, practical implementation remains problematic for technical reasons, exacerbated by inconsistent attitudes towards acceptance of non-traditional international trade standards. This paper describes the background to this situation, progress that has been achieved in the recent past and remaining difficulties that need to be overcome to advance towards achievement of balanced rural development in southern Africa.

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

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

Classical swine fever (hog cholera): review of aspects relevant to control.

Classical swine fever (CSF) has the ability to spread over large distances when human intervention such as illegal swill feeding facilitates its movement. This was apparent during 2005 when CSF appeared in South Africa (SA) after an absence of 87 years. In this review, various newly published developments in terms of the diagnosis of the disease and vaccination are described and applied to situations similar to SA. The role of wildlife such as feral pigs and European wild boar in the dissemination and maintenance of CSF virus are discussed, and the dearth of knowledge on the potential of other wild pig species prevalent on southern Africa noted. The modes of spread and control measures to prevent introduction as well as during outbreaks are discussed.

A pilot study of common health problems in smallholder pigs in Angónia and Boane districts, Mozambique.

A pilot survey was conducted in 2 districts in Mozambique to determine the most important health problems facing smallholder pig producers. While African swine fever is the most serious disease that affects pigs at all levels of production in Mozambique, it is likely that productivity is reduced by the presence of mange and gastrointestinal parasites, while in traditional systems the conditions are favourable for the development of porcine cysticercosis caused by the pork tapeworm Taenia solium, which poses a health risk to communities. Results of the pilot survey confirmed that, with the exception of African swine fever, ecto- and endoparasites are probably the most important health risks for producers. Porcine cysticercosis is more prevalent among pigs in traditional, free-ranging systems, while mange becomes a serious factor when pigs are permanently confined.

Tissue and cell tropism of African horse sickness virus demonstrated by immunoperoxidase labeling in natural and experimental infection in horses in South Africa.

Tissues from 196 experimental and confirmed natural cases of African horse sickness (all 9 serotypes) were examined with a standardized and validated immunohistochemical assay for detection of the causative virus. The study confirmed that heart and lung are the main target tissues for African horse sickness virus (across all serotypes), followed closely by spleen. It also indicated that microvascular endothelial cells and monocyte-macrophages are the main target cells for virus replication. The importance of monocytes as target cells was emphasized, with relatively few tissue macrophages containing antigen in the lung and spleen, respectively. The results were largely in agreement with those of previous studies, but the large number of cases examined permitted more precise description of the location and distribution of antigen in different tissues. Comparison with descriptions of tissue and cell tropism of other orbiviruses indicated similarity with African horse sickness. Immunohistochemistry was shown to be a useful and consistent technique for demonstrating target cells, but the difficulty of identifying cell types-in particular, different types of monocyte-macrophages-is a limitation.

Potential plant poisonings in dogs and cats in southern Africa.

Plant poisoning occurs less commonly in dogs and cats than in herbivorous livestock, but numerous cases have been documented worldwide, most of them caused by common and internationally widely cultivated ornamental garden and house plants. Few cases of poisoning of cats and dogs have been reported in southern Africa, but many of the plants that have caused poisoning in these species elsewhere are widely available in the subregion and are briefly reviewed in terms of toxic principles, toxicity, species affected, clinical signs, and prognosis. The list includes Melia azedarach (syringa), Brunfelsia spp. (yesterday, today and tomorrow), Datura stramonium (jimsonweed, stinkblaar), a wide variety of lilies and lily-like plants, cycads, plants that contain soluble oxalates, plants containing cardiac glycosides and other cardiotoxins and euphorbias (Euphorbia pulcherrima, E. tirucalli). Poisoning by plant products such as macadamia nuts, onions and garlic, grapes and raisins, cannabis (marijuana, dagga) or hashish and castor oil seed or seedcake is also discussed. Many of the poisonings are not usually fatal, but others frequently result in death unless rapid action is taken by the owner and the veterinarian, underlining the importance of awareness of the poisonous potential of a number of familiar plants.

Review of African swine fever: transmission, spread and control.

African swine fever is one of the most important and serious diseases of domestic pigs. Its highly contagious nature and ability to spread over long distances make it one of the most feared diseases, since its devastating effects on pig production have been experienced not only in most of sub-Saharan Africa but also in western Europe, the Caribbean, Brazil and, most recently, the Caucasus. Unlike most diseases of livestock, there is no vaccine, and therefore prevention relies entirely upon preventing contact between the virus and the susceptible host. In order to do so it is necessary to understand the way in which the virus is transmitted and spreads. By implementing strict biosecurity measures that place barriers between the source of virus and the pigs it is possible to prevent infection. However, this has implications for free-ranging pig husbandry systems that are widespread in developing countries. Attempts to produce a vaccine are ongoing and new technology offers some hope for the future, but this will not remove the necessity for implementing adequate biosecurity on pig farms.

Poisonous plants of veterinary and human importance in southern Africa.

Southern Africa is inherently rich in flora, where the habitat and climatic conditions range from arid environments to lush, sub-tropical greenery. Needless to say, with such diversity in plant life there are numerous indigenous poisonous plants, and when naturalised exotic species and toxic garden varieties are added the list of potential poisonous plants increases. The economically important poisonous plants affecting livestock and other plant poisonings of veterinary significance are briefly reviewed. In addition, a synopsis of the more common plant poisonings in humans is presented. Many of the plants mentioned in this review are also used ethnobotanically for treatment of disease in humans and animals and it is essential to be mindful of their toxic potential.

African swine fever in Mozambique: review, risk factors and considerations for control.

African swine fever (ASF) is the most important disease that constrains pig production in Mozambique. Until 1994 it was apparently restricted to the central and northern provinces, but since 1994 outbreaks have been experienced throughout the country. ASF causes severe economic losses both in the small commercial sector and among the large numbers of small-scale producers in the family sector in rural and peri-urban areas. The history of ASF in Mozambique since its first confirmation in 1960 is briefly reviewed, recent outbreaks are reported, and the available information on the virus genotypes that have been responsible for some of the outbreaks is presented. Epidemiological factors that contribute to ASF outbreaks and strategies for limiting the negative effects of the disease in the different pig farming sectors in Mozambique, including raising farmer and community awareness, are discussed.

Certification for regional and international trade in livestock commodities: the need to balance credibility and enterprise.

The current system for the certification of internationally traded animal commodities can act as a barrier to developing countries accessing high-value international markets. In this Viewpoint article, Gavin Thomson and colleagues discuss the situation as it stands and identify inconsistencies with respect to the certification process. They suggest ways to address the lack of capacity for credible certification in some developing countries that will encourage market access for livestock commodities. They emphasise the role of mechanisms other than demonstrating that an area of production is free from a range of animal diseases, arguing that this could be of significant benefit to developing regions and countries, but that a reliable and independent system of certification based on international standards is essential.

International trade in livestock and livestock products: the need for a commodity-based approach.

International animal health standards designed to facilitate safe trade in livestock and livestock products are set by the Office International des Epizooties (OIE) under the Sanitary and Phytosanitary Agreement of the World Trade Organization (WTO) and documented in the OIE's Terrestrial Animal Health Code. A core principle of the Code is the need for countries to eradicate important transboundary animal diseases (TADs) to reduce the risk of exporting disease to trading partners. International food safety standards are set by the Codex Alimentarius Commission, administered jointly by the World Health Organization and the Food and Agriculture Organization of the United Nations. The goal of global eradication of most TADs is unachievable for the foreseeable future, other than in the case of rinderpest, and this prevents many countries, especially developing nations, from engaging in international trade under WTO rules. This paper proposes an alternative, commodity-based approach to the formulation of international animal health and food safety standards, based on the fact that different commodities pose very different risks when it comes to the spread of human and animal pathogens. Therefore, the risk mitigation strategies required are equally commodity-dependent. The authors conclude that more focused commodity standards would improve access to international markets for all countries, especially those in the developing world. For this objective to be realised, credible and independent certification is required.

Co-circulation of two genetically distinct viruses in an outbreak of African swine fever in Mozambique: no evidence for individual co-infection.

In 1998, domestic pigs originating from villages within a 40 km radius of Ulongwe in the northern Tete Province of Mozambique were held in a quarantine facility for a 3-month period prior to their importation into South Africa. Eight of a total of 25 pigs died within the first 3 weeks of quarantine of what appeared clinically and on post mortem examination to be African swine fever (ASF). Organs were collected and preserved in formol-glycerosaline and the presence of ASF virus in these specimens was confirmed by three independent polymerase chain reaction (PCR) tests. Two gene regions were characterised, namely the C-terminus end of the major immunodominant protein VP72 and the central variable region (CVR) of the 9RL open reading frame (ORF). Results confirmed the presence of two genetically distinct viruses circulating simultaneously within a single outbreak focus. However, despite the pigs being housed within the same facility, no evidence of co-infection was observed within individual animals. Comparison of the two 1998 virus variants with viruses causing historical outbreaks of the disease in Mozambique revealed that these viruses belong to two distinct genotypes which are unrelated to viruses causing outbreaks between 1960 and 1994. In addition, the CVR and p72 gene regions of one of the 1998 Mozambique virus variants (variant-40) was shown to be identical to the virus recovered from an ASF outbreak in Madagascar in the same year, whilst the other (variant-92) was identical to a 1988 pig isolate from Zambia.

An investigation into natural resistance to African swine fever in domestic pigs from an endemic area in southern Africa.

A population of domestic pigs in northern Mozambique with increased resistance to the pathogenic effects of African swine fever (ASF) virus was identified by the high prevalence of circulating antibodies to ASF virus. An attempt was made to establish whether the resistance in this population was heritable. Some of these pigs were acquired and transported to a quarantine facility and allowed to breed naturally. Offspring of the resistant pigs were transferred to a high security facility where they were challenged with two ASF viruses, one of which was isolated from one of the Mozambican pigs and the other a genetically closely-related virus from Madagascar. All but one of the 105 offspring challenged developed acute ASF and died. It therefore appears that the resistance demonstrated by these pigs is not inherited by their offspring, or could not be expressed under the conditions of the experiment. The question remains therefore as to the mechanism whereby pigs in the population from which the experimental pigs were derived co-existed with virulent ASF viruses.

Genotyping field strains of African swine fever virus by partial p72 gene characterisation.

A PCR-based sequencing method was developed which permits detection and characterization of African swine fever virus (ASFV) variants within 5 and 48 h, respectively, of receipt of a clinical specimen. Amplification of a 478 bp fragment corresponding to the C-terminal end of the p72 gene, confirms virus presence with genetic characterization being achieved by nucleotide sequence determination and phylogenetic analysis. The method was applied to 55 viruses including those representative of the major ASF lineages identified previously by restriction fragment length polymorphism (RFLP) analysis. Results confirmed that the p72 genotyping method identifies the same major viral groupings. Characterization of additional viruses of diverse geographical, species and temporal origin using the PCR-based method indicated the presence of ten major ASF genotypes on the African continent, the largest of which comprised a group of genetically homogeneous viruses recovered from outbreaks in Europe, South America, the Caribbean and West Africa (the ESAC-WA genotype). In contrast, viruses from southern and East African countries were heterogeneous, with multiple genotypes being present within individual countries. This study provides a rapid and accurate means of determining the genotype of field and outbreak strains of ASF and is therefore useful for molecular epidemiological clarification of ASF.