Armanda D.S. Bastos

Foot and mouth disease in wildlife.

Occasionally foot and mouth disease (FMD) can be destructive of wildlife, as apparently occurred in South Africa in the late 19th century where large numbers of impala Aepyceros melampus succumbed, and more recently in Israel where high mortality occurred in mountain gazelles Gazella gazella (Macaulay, 1963; Shimshony, 1988). More usually, as is often the situation with domestic livestock in extensive production systems, infection of wildlife with FMD results in a relatively mild disease from which affected animals recover in a week or two. The significance of the disease for wildlife lies largely in the potential that clovenhoofed wild animals have for transmitting the disease to domestic livestock where, especially in intensive farming situations, the disease may be severely debilitating and result in serious economic losses for farmers. Perhaps more significant is the effect the presence of the disease (more precisely, the infection) has on international trade in livestock and livestock products. Therefore, the indirect effects of the infection often far outweigh the direct effects that it has on animals themselves, be they wild or domestic. Some wild ruminants also have the potential to become carriers of the infection i.e. the virus may persist in the absence of any obvious sign of disease. These animals, albeit extremely rarely, transmit the infection to cohorts of the same or other species with which they are in close contact. Until the end of the 19th century FMD was widespread throughout the world, but from the early 20th century the disease was progressively eradicated from the developed world because of its severe economic impact on intensive livestock production. Presently, North America, most of Europe, Australia and New Zealand among the major livestock rearing areas of the world are free of FMD. It persists currently in South America, most African countries, the Middle East, and many parts of south, central and south-east Asia. Major re-incursions of the disease have occurred recently in south-east Asia (Taiwan, Japan, South Korea and Indonesia), South America (Argentina, Uruguay and Brazil) and western Europe (UK, The Netherlands, France and Ireland). In some cases this has involved the transcontinental spread of the so-called pan-Asian topotype O virus from Asia. This occurred in September 2000 in South Africa (Sangare et al., 2001) and in February 2001 in the UK (Samuel and Knowles, 2001). Wildlife, however, has not been responsible for any of these re-incursions and, as far as is known, none became infected by either direct or indirect contact with domestic livestock during these incidents. On the other hand, fear of spread of the infection into collections of rare and valuable species, including zoological collections, has resulted in much conjecture as to how to protect these animals in the event of an epizootic. Furthermore, what the consequences would be in the event that measures taken to prevent infection prove ineffective is currently a subject of considerable debate. There has been a strong lobby to vaccinate such animals to protect them from infection but how effective that would be is a matter of opinion. Such action could interfere with the trading status of the country concerned. For countries that are members of the Office International des Epizooties (OIE), the international animal health organisation that sets international trading norms with respect to animals and animal products, to achieve the most favourable trading status (freedom from FMD without vaccination), no animals vaccinated against FMD within the last 12 months should be present on the territory of the country concerned. No distinction is made between wildlife and domestic live* Corresponding author. E-mail address: gavin.thomson@oau-ibar.org (G.R. Thomson). Virus Research 91 (2003) 145 /161

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

Summary. 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.

Persistent infection of African buffalo (Syncerus caffer) with SAT-type foot-and-mouth disease viruses: rate of fixation of mutations, antigenic change and interspecies transmission

Transmission of a plaque-purified SAT-2 foot-and-mouth disease virus (FMDV) occurred erratically from artificially infected African buffaloes in captivity to susceptible buffaloes and cattle in the same enclosure; in some instances transmission occurred only after contact between persistently infected carriers and susceptible animals lasting a number of months. Because the rate at which FMDV mutations accumulated in persistently infected buffaloes was approximately linear (1.64 percent nucleotide substitutions per year over the region of the 1D gene sequenced), both buffaloes and cattle that became infected some months after the start of the experiment were infected with viruses that differed from the original clone. The nucleotide differences were reflected in significant antigenic change. A SAT-1 FMDV from a separate experiment inadvertently infected some of the buffalo in the SAT-2 experiment. The SAT-1 FMDV also accumulated mutations at a constant rate in individual buffaloes (1.54 percent nucleotide changes per year) but the resultant antigenic variation was less than for SAT-2. It is concluded that persistently infected buffaloes in the wild constantly generate variants of SAT-1 and SAT-2 which explains the wide range of genomic and antigenic variants which occur in SAT-1 and SAT-2 viruses in southern Africa.

Natural transmission of foot-and-mouth disease virus between African buffalo (Syncerus caffer) and impala (Aepyceros melampus) in the Kruger National Park, South Africa.

VP1 gene sequences of SAT-2 type foot-and-mouth disease (FMD) viruses recovered from impala and African buffalo in the Kruger National Park (KNP) were used to determine intra- and interspecies relationships of viruses circulating in these wildlife populations. On this basis five distinct lineages of SAT-2 virus were identified in routine sampling of oesophageopharyngeal epithelium from buffalo between 1988 and 1996. Different lineages were associated with discrete geographic sampling localities. Over the period 1985-95, four unrelated epizootics occurred in impala in defined localities within the KNP. Evidence for natural transmission of FMD between buffalo and impala is presented for the most recent 1995 outbreak, with data linking the 1985 and 1988/9 impala epizootics to viruses associated with specific buffalo herds.

Genetic heterogeneity of SAT-1 type foot-and-mouth disease viruses in southern Africa

Summary. Genetic relationships of 50 SAT-1 type foot-and-mouth disease viruses were determined by phylogenetic analysis of an homologous 417 nucleotide region encoding the C-terminal half of the VP1 gene and part of the 2A segment. Viruses obtained from persistently-infected African buffalo populations were selected in order to assess the regional genetic variation within the host species and compared with ten viruses recovered from recent and historical cases of clinical infection. Phylogenetic reconstructions identified three independently evolving buffalo virus lineages within southern Africa, that correspond with the following discrete geographic localities: (1) South Africa and southern Zimbabwe, (2) Namibia, Botswana and western Zimbabwe, and (3) Zambia, Malawi and northern Zimbabwe. This strict geographic grouping of viruses derived from buffalo was shown to be useful for determining the origin of recent SAT-1 epizootics in livestock.The percentage of conserved amino acid sites across the 50 SAT-1 viruses compared in this study was 50%. Most mutations were clustered within three discrete hypervariable regions, which coincide with the immunogenic G-H loop, H-I loop and C-terminus region of the protein. Despite the high levels of variation within the primary sequence, secondary structural features appear to be conserved.

Molecular epidemiology of African swine fever in East Africa

Summary.African swine fever (ASF) a lethal, viral hemorrhagic disease of domestic pigs, first reported from East Africa in 1921, is still widespread in this region. In order to assess field heterogeneity at the regional level, nucleotide sequences corresponding to the C-terminal end of the p72 gene were determined for 77 ASF viruses of diverse temporal and species origin occurring in eight East African countries. The number of sites completely conserved across all East African sequences characterized in this study was 84.2% and 86.8% on nucleotide and amino acid level, respectively. Phylogenetic analysis of a homologous 404 bp region revealed the presence of thirteen East African genotypes, of which eight appear to be country specific. An East African, pig-associated, homogeneous virus lineage linked to outbreaks in Mozambique, Zambia and Malawi over a 23 year period was demonstrated. In addition, genotype I (ESACWA) viruses were identified in East African sylvatic hosts for the first time which is significant as this genotype was previously thought to be restricted to the West African region where it occurs only in domestic pigs. The presence of discrete epidemiological cycles in East Africa and recovery of multiple genotypes affirms the epidemiological complexity of ASF in this region.

Role of wild suids in the epidemiology of African swine fever.

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

Genetic heterogeneity in the foot-and-mouth disease virus Leader and 3C proteinases.

The Leader and 3C proteinases of foot-and-mouth disease virus (FMDV) are responsible for almost all the proteolytic processing events of the viral polyprotein precursor. Investigation into the genetic heterogeneity of the regions encoding these proteins from isolates of six FMDV serotypes revealed the 3C proteinase to be more conserved than the Leader proteinase. Maximum likelihood analysis indicated similar phylogenetic groupings for the non-structural protein coding regions of both the Leader and 3C. These groupings were different from the structural VP1 protein coding region which, as shown previously, grouped according to serotype. Two distinct clades were apparent for both the Leader and 3C coding regions: one comprising of serotypes A, O and C together with SAT (South African Territories) isolates from eastern Africa. The other clade consisted of SAT isolates originating from southern Africa. Only one virus isolate, obtained from a buffalo in Uganda, did not conform to this phylogenetic pattern. This SAT 1 virus grouped with types A, O and C in the Leader analysis, but with the southern African SAT types in the 3C analysis, implicating intertypic recombination. The leader proteinases of southern African SAT type isolates differed from those present in European type isolates, particularly in the self-processing region. A three-dimensional structure was modeled for the Leader proteinase of one of the SAT type viruses, ZIM/7/83/2, and compared with the previously elucidated crystal structure of O(1)Kaufbeuren Leader proteinase. The active sites of the two leaders were found to superimpose closely, despite the observed sequence variation between the two molecules. Comparison of the 3C proteinase P1 cleavage sites suggested that the FMDV 3C proteinase may possess a broader substrate specificity, as observed in hepatitis A virus 3C proteinase.

African swine fever virus eradication in Africa

African swine fever was reported in domestic pigs in 26 African countries during the period 2009-2011. The virus exists in an ancient sylvatic cycle between warthogs (Phacochoerus africanus) and argasid ticks of the Ornithodoros moubata complex in many of the countries reporting outbreaks and in two further countries in the region. Eradication of the virus from the countries in eastern and southern Africa where the classic sylvatic cycle occurs is clearly not an option. However, the virus has become endemic in domestic pigs in 20 countries and the great majority of outbreaks in recent decades, even in some countries where the sylvatic cycle occurs, have been associated with movement of infected pigs and pig meat. Pig production and marketing and ASF control in Africa have been examined in order to identify risk factors for the maintenance and spread of ASF. These include large pig populations, traditional free-range husbandry systems, lack of biosecurity in semi-intensive and intensive husbandry systems, lack of organisation in both pig production and pig marketing that results in lack of incentives for investment in pig farming, and ineffective management of ASF. Most of these factors are linked to poverty, yet pigs are recognised as a livestock species that can be used to improve livelihoods and contribute significantly to food security. The changes needed and how they might be implemented in order to reduce the risk of ASF to pig producers in Africa and to the rest of the world are explored.

Possibility of sexual transmission of foot-and- mouth disease from African buffalo to cattle

Clinical implication Persistent remnants of vitelline arteries and veins should be considered in the differential diagnosis of colic in foals. In the present case, the recurrent signs of colic were probably due to the strangulation of an intestinal segment and the fibrinous peritonitis. The foal died of septicaemia. Exploratory laparotomy is the most obvious way to diagnose such congenital anomalies. During the curative resection of the strangulating band, the viability of the affected intestine should always be thoroughly evaluated (Kleinhaus and others 1974).