G.R. Thomson

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.

Genetic relationships between southern African SAT-2 isolates of foot-and-mouth-disease virus.

Sequencing of part of the 1D gene of foot-and-mouth disease virus was used to determine the relationships between SAT-2 viruses isolated from outbreaks which occurred in cattle in Zimbabwe and Namibia and in impala in South Africa between 1979 and 1989. The results demonstrated that the outbreaks in different countries were unrelated. Surprisingly close relationships were shown between all SAT-2 viruses isolated from cattle in Zimbabwe since 1983 but the two major epizootics which occurred in 1989 were caused by viruses which were clearly different. Conversely, two apparently unrelated outbreaks in impala in South Africa were caused by viruses which could not be distinguished.

The foot-and-mouth disease risk posed by African buffalo within wildlife conservancies to the cattle industry of Zimbabwe.

Quantification of the risk that African buffalo (Syncerus caffer) (isolated within wildlife conservancies in Zimbabwe by a double fencing system) would infect cattle outside the conservancies with foot-and-mouth disease (FMD) virus was assessed by scenario-pathway analysis. Of the five scenarios considered, the greatest annual risk (1:5000) for cattle would be from antelope jumping over the outer perimeter fence of the conservancy and infecting cattle on the outside. The other transmission scenarios (including air-borne transmission) had a FMD risk that was low to very low. Risk management would include means to prevent the escape of antelope from the conservancies and restriction of cattle density in the proximity of the perimeter fence.

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).

Molecular epidemiology of serotype O foot-and-mouth disease virus with emphasis on West and South Africa.

Genetic relationships of serotype O foot-and-mouth disease (FMD) viruses recovered from outbreaks of the disease in the West African countries of Niger, Burkina Faso and, Ghana (1988–1993) and those from South Africa (2000) were determined by partial VP1 gene characterization. A 581-bp fragment, corresponding to the C-terminus half of the 1D (VP1 gene) region was amplified and sequenced. An homologous region of 495 nucleotides was ultimately used to determine genetic relationships of serotype O viruses from the Middle East, Europe, South America, North Africa, East Africa, southern Africa and Asia. Seven distinct type O genotypes were identified by phylogenetic reconstruction, consisting of viruses from the following geographical regions: Genotype A: Asia, the Middle East, and South Africa, Genotype B: East Africa, Genotype C: West and North Africa, Genotype D: Taiwan and Russia, Genotype E: Angola and Venezuela, Genotype F: Western Europe, and Genotype G: Europe and South America. The genotypes constitute three different evolutionary lineages (I–III), which correspond to three discrete continental regions, some of which display inter-continental distributions due to introductions. Results further indicate that the outbreaks in Burkina Faso (1992) and Ghana (1993) are part of the same epizootic and that the strain involved in a recent outbreak of the disease in South Africa is most closely related (97% sequence identity) to a 1997 Bangladesh strain.

Genome variation in the SAT types of foot-and-mouth disease viruses prevalent in buffalo (Syncerus caffer) in the Kruger National Park and other regions of southern Africa, 1986-93

Dideoxy nucleotide sequencing of a portion of the 1D gene of SAT-type foot-and-mouth disease viruses (FMDV) was used to derive phylogenetic relationships between viruses recovered from the oesophageo-pharyngeal secretions of buffalo in the Kruger National Park as well as several other wildlife areas in southern Africa. The three serotypes differed from one another by more than 40% while intratypic variation did not exceed 29%. Within each type, isolates from particular countries were more closely related to one another than to isolates from other countries lending credence to previous observations that FMDV evolve independently in different regions of the subcontinent.