Orwik

Rainfall-driven sex-ratio genes in African buffalo suggested by correlations between Y-chromosomal haplotype frequencies and foetal sex ratio.

ABSTRACT: BACKGROUND: The Y-chromosomal diversity in the African buffalo (Syncerus caffer) population of Kruger National Park (KNP) is characterized by rainfall-driven haplotype frequency shifts between year cohorts. Stable Y-chromosomal polymorphism... expand abstract is difficult to reconcile with haplotype frequency variations without assuming frequency-dependent selection or specific interactions in the population dynamics of X- and Y-chromosomal genes, since otherwise the fittest haplotype would inevitably sweep to fixation. Stable Y-chromosomal polymorphism due one of these factors only seems possible when there are Y-chromosomal distorters of an equal sex ratio, which act by negatively affecting X-gametes, or Y-chromosomal suppressors of a female-biased sex ratio. These sex-ratio (SR) genes modify (suppress) gamete transmission in their own favour at a fitness cost, allowing for stable polymorphism. RESULTS: Here we show temporal correlations between Y-chromosomal haplotype frequencies and foetal sex ratios in the KNP buffalo population, suggesting SR genes. Frequencies varied by a factor of five; too high to be alternatively explained by Y-chromosomal effects on pregnancy loss. Sex ratios were male-biased during wet and female-biased during dry periods (male proportion: 0.47-0.53), seasonally and annually. Both wet and dry periods were associated with a specific haplotype indicating a SR distorter and SR suppressor, respectively. CONCLUSIONS: The distinctive properties suggested for explaining Y-chromosomal polymorphism in African buffalo may not be restricted to this species alone. SR genes may play a broader and largely overlooked role in mammalian sex-ratio variation. collapse abstract

A host species-informative internal control for molecular assessment of African swine fever virus infection rates in the African sylvatic cycle Ornithodoros vector.

African swine fever virus (ASFV) infection in adult Ornithodoros porcinus (Murry 1877, sensuWalton 1979) ticks collected from warthog burrows in southern and East Africa was assessed using a duplex genomic amplification approach that is informative w... expand abstractith respect to the invertebrate host species and infecting sylvatic cycle virus. DNA extracted from individual ticks was used as template for the simultaneous amplification of a C-terminal 478-bp ASFV p72 gene region and a approximately 313-bp fragment of the tick mitochondrial 16S rRNA gene, under optimized reaction conditions. Within-warthog burrow infection rates ranged from 0% to 43% using this approach, and phylogenetic analysis of 16S gene sequences revealed the presence of three geographically discrete O. porcinus lineages, but no support for subspecies recognition. False negatives are precluded by the inclusion of host species-informative primers that ensure the DNA integrity of cytoplasmically located genome extracts. In addition, infection rate estimates are further improved as false positives arising from carry-over contamination when performing a two-step nested polymerase chain reaction are negated by the one-step approach. Phylogenetic comparison of full-length virus gene sequences with the partial C-terminal p72 gene target confirmed the epidemiological utility of the latter in a sylvatic setting. The method is therefore of particular value in studies assessing the prevalence and diversity of ASFV in relation to the African sylvatic tick vector and holds potential for investigating the role of alternative tick species in virus maintenance and transmission. collapse abstract

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 asympt... expand abstractomatic 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. collapse abstract

Mass mortality of adult male subantarctic fur seals: are alien mice the culprits?

BACKGROUND: Mass mortalities of marine mammals due to infectious agents are increasingly reported. However, in contrast to previous die-offs, which were indiscriminate with respect to sex and age, here we report a land-based mass mortality of Subanta... expand abstractrctic fur seals with apparent exclusivity to adult males. An infectious agent with a male-predilection is the most plausible explanation for this die-off. Although pathogens with gender-biased transmission and pathologies are unusual, rodents are known sources of male-biased infectious agents and the invasive Mus musculus house mouse, occurs in seal rookeries. METHODOLOGY/ PRINCIPAL FINDINGS: Molecular screening for male-biased pathogens in this potential rodent reservoir host revealed the absence of Cardiovirus and Leptospirosis genomes in heart and kidney samples, respectively, but identified a novel Streptococcus species with 30% prevalence in mouse kidneys. CONCLUSIONS/ SIGNIFICANCE: Inter-species transmission through environmental contamination with this novel bacterium, whose congenerics display male-bias and have links to infirmity in seals and terrestrial mammals (including humans), highlights the need to further evaluate disease risks posed by alien invasive mice to native species, on this and other islands. collapse abstract

Intraspecific patterns of mitochondrial variation in natural population fragments of a localized desert dung beetle species, Pachysoma gariepinum (Coleoptera: Scarabaeidae).

Phylogenetic, population, and coalescent methods were used to examine the genetic structuring of Pachysoma gariepinum, a flightless dung beetle species endemic to the arid west coast of southern Africa that exhibits interrupted south to north morphol... expand abstractogical clinal variation along a distributional gradient. Mitochondrial cytochrome oxidase I sequence data of 67 individuals from 5 localities revealed the presence of 3 geographically distinct evolutionary lineages (with an overall nucleotide divergence of 5.7% and a per-locality divergence of 1.9-3.8%) which display significant levels of genetic structuring. The separation of the lineages was estimated to have occurred between 2.2 and 5.7 million years ago--which is the late Miocene, early Plio-Pleistocene era--possibly in response to the ebb and flow of the Orange and Holgat River systems as well as the interactions between the moving and stable sand dune systems. Moreover the species' current range appears to have been influenced by the formation of advective fog resulting in a constant source of water in an area with low precipitation thereby allowing for the beetles to radiate to areas that were previously inhospitable. Fu's F-statistics and population parameters based on recent mutations indicated that little to no recent population growth has occurred. This together with changing anthropogenic factors and the recovery of 3 geographically discrete management units, points to a need for census data in order to monitor and conserve the genetic diversity of this species. collapse abstract

Selection at the Y chromosome of the African buffalo driven by rainfall.

Selection coefficients at the mammalian Y chromosome typically do not deviate strongly from neutrality. Here we show that strong balancing selection, maintaining intermediate frequencies of DNA sequence variants, acts on the Y chromosome in two popul... expand abstractations of African buffalo (Syncerus caffer). Significant correlations exist between sequence variant frequencies and annual rainfall in the years before conception, with five- to eightfold frequency changes over short time periods. Annual rainfall variation drives the balancing of sequence variant frequencies, probably by affecting parental condition. We conclude that sequence variants confer improved male reproductive success after either dry or wet years, making the population composition and dynamics very sensitive to climate change. The mammalian Y chromosome, interacting with ecological processes, may affect male reproductive success much more strongly than previously thought. collapse abstract

Intra-genotypic resolution of African swine fever viruses from an East African domestic pig cycle: a combined p72-CVR approach.

Two of the 22 presently recognised African swine fever (ASF) virus p72 genotypes are genetically homogeneous and are associated with domestic pig cycles. Of these, genotype VIII comprises just two p72 variants, designated 'a' and 'b' in this study, a... expand abstractnd is confined to four East African countries where it has caused numerous outbreaks between 1961 and 2001. In order to resolve relationships within this homogeneous genotype, the central variable region (CVR) of the 9RL open reading frame of 38 viruses was characterised and the resulting dataset complemented with seven published sequences. Phylogenetic analysis of the 45 taxa resulted in seven discrete amino acid CVR lineages (A-G). CVR lineage F, 84 amino acids in length and spanning a 40-year period, comprised 26 isolates from Malawi, Mozambique, Zambia and Zimbabwe. The second largest lineage (E), consisted of 10 viruses causing outbreaks over a 10-year period in Zambia, Malawi and Mozambique whilst the remaining five lineages were country-specific and represented by four or less viruses with a maximum circulation period of three years. A combined p72-CVR analysis resulted in eight discrete lineages corresponding to eight unique p72-CVR combinations. One of these, b-F, appears to have arisen by convergent evolution or through an intra-genotypic recombination event, as the individual p72 and CVR gene phylogenies are incongruent. This raises the possibility of intra-genotypic recombination in ASF viruses for the first time. However, given the repetitive nature of the CVR region, convergent evolution cannot be excluded and may be the more likely explanation. collapse abstract

Genetic characterisation of African swine fever viruses from outbreaks in southern Africa (1973-1999).

African swine fever (ASF) is a highly lethal and economically significant disease of domestic pigs in the southern African sub-region, where outbreaks regularly occur. There is anecdotal evidence suggesting that trans-boundary movement of infected an... expand abstractimals may have played a role in precipitating widespread outbreaks in the past, however, since the 1970s outbreaks have generally been more localised, particularly in those countries where control of animal movement is strictly regulated. The origin and relatedness of regional ASF outbreaks was investigated here by means of a two-step genetic characterisation approach whereby p72 gene sequencing was used to delineate genotypes, prior to intra-genotypic resolution of viral relationships by central variable region (CVR) characterisation of the 9RL ORF. In this manner, regional virus heterogeneity and epidemiological links between outbreaks could be assessed for the first time through phylogenetic analysis of the C-terminal end of the p72 gene of viruses recovered from domestic pig outbreaks in southern Africa between 1973 and 1999. The phylogeny revealed the presence of 14 distinct p72 genotypes of which 6 (genotypes XVII-XXII) were considered novel. Eight of these were country-specific with the remaining six having a trans-boundary distribution. CVR products were heterogeneous in size ranging from 377bp to 533bp across the 14 southern African genotypes. Within-genotype CVR comparisons revealed the presence of a genotype XIX virus with an extended field presence in South Africa (1985-1996) and permitted discrimination between three genotype VII viruses that were identical across the p72 gene. collapse abstract

Intra- and inter-genotypic size variation in the central variable region of the 9RL open reading frame of diverse African swine fever viruses.

African swine fever (ASF) viruses are characterised by numerous p72 genotypes, but by low levels of intra-genotypic variation, particularly in domestic pig associated genotypes. As it is precisely these viral lineages that are involved in outbreaks o... expand abstractf the disease it is imperative that alternative, more informative gene regions be identified which are suitable for intra-genotypic resolution of relationships. To this end, the central variable region (CVR) of the 9RL open reading frame of diverse ASF viruses was amplified and product sizes scored and compared within and between genotypes. Results indicate that although product sizes are not genotype restricted, there is a high degree of intra-genotypic size variation particularly within the homogeneous p72 genotypes. Within one such genotype, the ESACWA virus genotype, 12 size-discrete CVR products were identified, four corresponding to viruses of west African origin and eight to viruses from countries where the disease is exotic, namely Europe, South America and the Caribbean. The high degree of size heterogeneity in the CVR of this genotype is significant and attests to the usefulness of the CVR gene marker in elucidating the epidemiology of African swine fever. collapse abstract

Retrospective genetic analysis of SAT-1 type foot-and-mouth disease outbreaks in southern Africa.

In areas where foot-and-mouth disease (FMD) is endemic in wildlife hosts, such as the Kruger National Park (KNP) in South Africa, control measures are in place that ensure that potentially infected antelope and buffalo do not come into close contact ... expand abstractwith domestic animals. In South Africa several SAT-1 outbreaks occurred nearly simultaneously in cattle and impala between 1971-1981. Phylogenetic analysis based on partial 1D gene nucleotide sequencing indicated that several of these outbreaks were linked and it is probable that disease spread from the intermediary impala antelope host to cattle in close proximity. Evidence was found for the involvement of viruses from a single KNP genotype in precipitating outbreaks in impala over a 10-year period. In addition, several unrelated outbreaks affecting cattle and impala occurred within a single year. Characterisation of outbreak strains from Botswana similarly revealed that a single genotype affected different species over a 10-year period and that transboundary spread of SAT-1 virus occurred on at least one occasion. This retrospective analysis of outbreak strains has clearly demonstrated that FMD control policies that address the role of antelope as intermediaries in disease transmission are crucial as these wildlife species play an important role in disease dissemination. collapse abstract

Molecular epidemiology of African swine fever in East Africa.

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 correspond... expand abstracting 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. collapse abstract

An investigation into the source and spread of foot and mouth disease virus from a wildlife conservancy in Zimbabwe.

African buffalo were introduced into a wildlife conservancy in the southeast of Zimbabwe in an effortto increase the conservancy's economic viability, which is primarily based on eco-tourism. The buffalo were infected with SAT serotypes (SAT-1, SAT-2... expand abstract and SAT-3) of foot and mouth disease (FMD) virus, and in order to isolate the conservancy and prevent the transmission of FMD to adjacent populations of domestic livestock, the conservancy was surrounded by a double-fence system, 1.8 m in height. The intention was to prevent the movement of both wildlife and domestic animals across the perimeter. However, two years after the buffalo were introduced, FMD occurred in cattle farmed just outside of the conservancy. Using serological and molecular diagnostic tests, epidemiological investigations showed that it was most likely that antelope (impala or kudu), infected through contact with the buffalo herd within the conservancy, had jumped over the fence and transmitted the virus to the cattle. collapse abstract

Foot and mouth disease in Mali: the current situation and proposed control strategies.

Two main reasons prompted the authors to write this paper. First, outbreaks of foot and mouth disease (FMD) have occurred repeatedly in Mali and neighbouring countries during the last decade. Secondly, there is a pressing need for control strategies,... expand abstract since the first molecular epidemiological studies of FMD virus in West Africa have demonstrated that FMD transmission across national boundaries is common in this region. The authors discuss the FMD outbreaks that occurred during the period of 1980 to 1996, which were reported to the Central Livestock Office in Mali by field veterinarians. The outbreaks in 1980 and 1982 were confined to the regions of Kayes and Gao, respectively. Between 1991 and 1992, outbreaks occurred in Segou, Sikasso and Bamako. In 1996, FMD outbreaks were reported in cattle populations throughout Mali, except in Kidal in the Sahara desert, where temperatures reach 45 degrees C. High mortality was reported in young animals, while morbidity approached 100% in adult cattle. collapse abstract

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... expand abstract 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. collapse abstract

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... expand abstract 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. collapse abstract

A first molecular epidemiological study of SAT-2 type foot-and-mouth disease viruses in West Africa.

Thirty-one viruses causing SAT-2 outbreaks in seven West African countries between 1974 and 1991, and four viruses representative of East and Central Africa were genetically characterized in this study. Four major viral lineages (I-IV) were identifie... expand abstractd by phylogenetic analysis of an homologous 480 nucleotide region corresponding to the C-terminus end of VP1. Lineage I comprised two West African genotypes with viruses clustering according to year of isolation rather than geographical origin. Lineage II was represented by viruses isolated between 1979 and 1983 in two neighbouring West African countries, Senegal and The Gambia. Viruses from Nigeria and Eritrea, representative of West and East Africa respectively, constituted lineage III, whilst lineage IV, comprising viruses from Central and East Africa, was regionally and genetically distinct. This study revealed that unrestricted animal movement in West Africa is a major factor in disease dissemination and has also provided the first indication of trans-regional virus transmission. collapse abstract

Low linkage disequilibrium indicative of recombination in foot-and-mouth disease virus gene sequence alignments.

We have applied tests for detecting recombination to genes of foot-and-mouth disease virus (FMDV). Our approach estimated summary statistics of linkage disequilibrium (LD), which are sensitive to recombination. Using the genealogical relationships, r... expand abstractate heterogeneity and mutation parameters estimated from individual sets of aligned gene sequences, we simulated matching RNA sequence datasets without recombination. These simulated datasets allowed for recurrent mutations at any site to mimic homoplasy in virus sequence data and allow construction of null distributions for LD parameters expected in the absence of recombination. We tested for recombination in two ways: by comparing LD in observed data with corresponding null distributions obtained from simulated data; and by testing for a negative relationship between observed LD between pairs of polymorphic nucleotide sites and inter-site distance. We applied these tests to six FMDV datasets from four serotypes and found some evidence for recombination in all of them. collapse abstract

Suitability of currently available vaccines for controlling the major transboundary diseases that afflict sub-Saharan Africa.

Molecular epidemiology of SAT3-type foot-and-mouth disease.

VP1 gene nucleotide sequences of 51 SAT3-type foot-and-mouth disease (FMD) viruses from seven southern and eastern African countries were used to infer a gene phylogeny. Results obtained by phylogenetic analysis of the homologous 405 nt region corres... expand abstractponding to the C-terminal 128 amino acids of 1D and adjacent 7 amino acids of 2A indicate that there are six distinct virus lineages evolving independently in different geographical localities in accordance with the FMD topotype concept. Topotypes I-IV occur in southern Africa, whilst topotypes V and VI are unique to East Africa. Viruses of different topotypes differ from each other at 20% or more of the nucleotide sites, specified in this study. Despite the limited geographical distribution of this serotype, the level of intratypic variation is intermediate between that of SAT1 and SAT2, both of which are widely distributed in sub-Saharan Africa. Within SAT3, 37.3% and 47.4% of sites were completely conserved on nucleotide and amino acid levels, respectively. The locality-specific grouping of viruses permits accurate determination of the sources of outbreaks, whilst the high levels of variation within the immunodominant 1D protein has implications for the control of the disease through vaccination. collapse abstract

Retrospective genetic analysis of SAT-1 type foot-and-mouth disease outbreaks in West Africa (1975-1981).

The complete 1D genome region encoding the immunogenic and phylogenetically informative VP1 gene was genetically characterized for 23 South African Territories (SAT)-1 viruses causing foot-and-mouth (FMD) disease outbreaks in the West African region ... expand abstractbetween 1975 and 1981. The results indicate that two independent outbreaks occurred, the first involved two West African countries, namely Niger and Nigeria, whilst the second affected Nigeria alone. In the former epizootic, virus circulation spanned a period of 2 years, whilst in the latter virus was recovered from the field over a 3 year period. Comparison of the West African viruses with SAT-1 viruses from other regions on the continent revealed that the two West African lineages identified in this study are regionally distinct. Furthermore, variation in VP1 gene length was identified in SAT-1 viruses for the first time, further emphasizing the uniqueness of these pathogens in West Africa. This first retrospective analysis in which the molecular epidemiology of SAT-1 viruses in West Africa is reported, provides a useful measure of the regional variation of these viruses and is an essential first step in the establishment of a West African sequence database that will be a useful reference for future outbreak eventualities. collapse abstract

The implications of virus diversity within the SAT 2 serotype for control of foot-and-mouth disease in sub-Saharan Africa.

SAT 2 is the serotype most often associated with outbreaks of foot-and-mouth disease (FMD) in livestock in southern and western Africa and is the only SAT type to have been recorded outside the African continent in the last decade. Its epidemiology i... expand abstracts complicated by the presence of African buffalo (Syncerus caffer), which play an important role in virus maintenance and transmission. To assess the level of genetic complexity of this serotype among viruses associated with both domestic livestock and wildlife, complete VP1 gene sequences of 53 viruses from 17 countries and three different host species were analysed. Phylogenetic analysis revealed eleven virus lineages, differing from each other by at least 20 % in pairwise nucleotide comparisons, four of which fall within the southern African region, two in West Africa and the remaining five in central and East Africa. No evidence of recombination between these lineages was detected, and thus we conclude that these are independently evolving virus lineages which occur primarily in discrete geographical localities in accordance with the FMD virus topotype concept. Applied to the whole phylogeny, rates of nucleotide substitution are significantly different between topotypes, but most individual topotypes evolve in accordance with a molecular clock at an average rate of approximately 0.002 substitutions per site per year. This study provides an indication of the intratypic complexity of the SAT 2 serotype at the continental level and emphasizes the value of molecular characterization of diverse FMD field strains for tracing the origin of outbreaks. collapse abstract

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... expand abstract 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. collapse abstract

Development of a TaqMan PCR assay with internal amplification control for the detection of African swine fever virus.

A closed-tube polymerase chain reaction (PCR) was developed to allow the rapid detection of African swine fever virus (ASFV) DNA. This assay targets the VP72 gene of ASFV and uses the 5'-nuclease assay (TaqMan) system to detect PCR amplicons, avoidin... expand abstractg tube opening and potential cross-contamination of post-PCR products. An artificial mimic was engineered with the TaqMan probe site replaced by a larger irrelevant DNA fragment allowing discrimination from ASFV by using two-colour TaqMan probe reporters. When added to the samples, successful amplification of this mimic demonstrated the absence of substances inhibitory to PCR, thereby validating negative results. Assay sensitivity was confirmed by obtaining positive signals with a representative selection of ASFV isolates. Many of the clinical and post-mortem features of ASF resemble those of classical swine fever (CSF) and porcine dermatitis and nephropathy syndrome (PDNS). Therefore, fast and reliable detection of ASFV is essential not only for the implementation of control measures to prevent the spread of ASF, but also in the differential diagnosis from CSF and PDNS. This assay should prove to be a valuable tool in the laboratory diagnosis of ASF and will complement existing molecular methods to provide rapid differential diagnosis in cases of suspected swine fever. collapse abstract

Foot and mouth disease in wildlife.

Review of the status and control of foot and mouth disease in sub-Saharan Africa.

Six of the seven serotypes of foot and mouth disease (FMD) virus (i.e. all but Asia 1) are prevalent in Africa although there are marked regional differences in distribution. Three of these serotypes are unique to Africa, namely the three South Afric... expand abstractan Territories (SAT) serotypes. Serotype C may also now be confined to Africa because it has not been reported elsewhere recently. In southern Africa at least, the SAT serotypes have an intimate and probably ancient association with African buffalo (Syncerus caffer) that is instrumental in their maintenance. Within each of the six prevalent serotypes, with the possible exception of C, there are a number of different lineages with more or less defined distributions (i.e. topotypes) that in some cases are sufficiently immunologically different from one another to require specific vaccines to ensure efficient control. This immunological diversity in prevalent serotypes and topotypes, in addition to uncontrolled animal movement in most parts of the continent, render FMD difficult to control in present circumstances. This fact, together with poorly developed intercontinental trade in animals and animal products has resulted in the control of FMD being afforded a low priority in most parts of the continent, although the northern and southern regions of the continent are an exception. As a consequence, eradication of FMD from Africa as a whole is not a prospect within the foreseeable future. In southern Africa, the use of fencing and other means to strictly control the movement of wildlife and livestock as well as judicious application of vaccine has resulted in countries of the region being able to access beef and other livestock markets in Europe and elsewhere in the developed world. Significant marketing of livestock and livestock products from Africa outside the continent is unlikely to be achieved unless similar approaches can be developed for other regions of Africa. This will result in continuing under-exploitation of a valuable resource in the arid and semi-arid regions of Africa, with increasing marginalisation of human populations living there. collapse abstract