Review: Capripoxvirus Diseases: Current Status and Opportunities for Control

Lumpy skin disease, sheeppox and goatpox are high-impact diseases of domestic ruminants with a devastating effect on cattle, sheep and goat farming industries in endemic regions. In this article, we review the current geographical distribution, economic impact of an outbreak, epidemiology, transmission and immunity of capripoxvirus. The special focus of the article is to scrutinize the use of currently available vaccines to investigate the resource needs and challenges that will have to be overcome to improve disease control and eradication, and progress on the development of safer and more effective vaccines. In addition, field evaluation of the efficacy of the vaccines and the genomic database available for poxviruses are discussed.

Bacterial enteritis in ostrich (Struthio Camelus) chicks in the Western Cape Province, South Africa

Ostrich (Struthio camelus) chicks less than 3 mo age are observed to experience a high mortality rate that is often associated with enteritis. This study was undertaken to investigate the infectious bacteria implicated in ostrich chick enteritis. Postmortems were performed on 122 ostrich chicks aged from 1 d to 3 mo and intestinal samples were subjected to bacterial culture. Bacterial isolates were typed by PCR and serotyping. Escherichia coli (E. coli; 49%) was the most frequently isolated from the samples followed by Clostridium perfringens (C. perfringens; 20%), Enterococcus spp. (16%), and Salmonella spp. (7%). Of the E. coli, 39% were categorized as enteropathogenic E. coli, 4% enterotoxigenic E. coli, and no enterohaemorrhagic E. coli were found. The majority (93%) of C. perfringens was Type A and only 7% was Type E. C. perfringens Types B through D were not present. The netB gene that encodes NetB toxin was identified from 16% of the C. perfringens isolated. All the C. perfringens Type E harbored the netB gene and just 10% of the C. perfringens Type A had this gene. Three Salmonella serotypes were identified: Salmonella Muenchen (S. Muenchen; 80%), S. Hayindongo (13%), and S. Othmarschen (7%). The indication is that the cause of enteritis in ostrich chicks is bacterial-involving: enteropathogenic E. coli and enterotoxigenic E. coli; C. perfringens Types A and E (with the possible influence of netB gene); and S. Muenchen, S. Hayindongo, and S. Othmarschen.

Lumpy skin disease: attempted propagation in tick cell lines and presence of viral DNA in field ticks collected from naturally-infected cattle

Lumpy skin disease (LSD) is of substantial economic importance for the cattle industry in Africa and the Near and Middle East. Several insect species are thought to transmit the disease mechanically. Recent transmission studies have demonstrated the first evidence for a role of hard (ixodid) ticks as vectors of lumpy skin disease virus (LSDV). The aim of this study was to attempt in vitro growth of the virus in Rhipicephalus spp. tick cell lines and investigate in vivo the presence of the virus in ticks collected from cattle during LSD outbreaks in Egypt and South Africa. No evidence was obtained for replication of LSDV in tick cell lines although the virus was remarkably stable, remaining viable for 35 days at 28 °C in tick cell cultures, in growth medium used for tick cells and in phosphate buffered saline. Viral DNA was detected in two-thirds of the 56 field ticks, making this the first report of the presence of potentially virulent LSDV in ticks collected from naturally infected animals.

An improved method for determining virucidal efficacy of a chemical disinfectant using an electrical impedance assay

A major problem with the testing of virucidal efficacy using current protocols is that scoring of virus-induced cytopathic effect (CPE) is dependent on subjective visual interpretation using light microscopy. The current report details the use of an electrical impedance assay (xCELLigence, ACEA Biosciences) for its utility in virucidal efficacy testing. In this study, the xCELLigence system was used in a procedure developed from guidelines given by the Deutsche Vereiniging zur Bekämpfung der Viruskrankheiten (DVV) (German Association for the Control of Virus Diseases) in order to demonstrate the inactivation of infectious bursal disease virus using a commercial virucide. Although the modified DVV assay using the xCELLigence system yielded identical results (i.e. a 5-log10 reduction in viral infectivity) as the traditional DVV assay, the system allows virucidal efficacy and cytotoxicity to be measured in a more precise and reproducible fashion.

Evidence of lumpy skin disease virus over-wintering by transstadial persistence in Amblyomma hebraeum and transovarial persistence in Rhipicephalus decoloratus ticks

Lumpy skin disease is a debilitating cattle disease caused by the lumpy skin disease virus (LSDV), belonging to the genus Capripoxvirus. Epidemics of the disease usually occur in summer, when insect activity is high. Limited information is available on how LSDV persists during inter-epidemic periods. Transmission of LSDV by mosquitoes such as Aedes aegypti has been shown to be mechanical, there is no carrier state in cattle and the role of wildlife in the epidemiology of the disease seems to be of minor importance. Recent studies in ticks have shown transstadial persistence of LSDV in Rhipicephalus appendiculatus and Amblyomma hebraeum as well as transovarial persistence of the virus in Rhipicephalus decoloratus, R. appendiculatus and A. hebraeum. The over-wintering of ticks off the host as part of their life cycles is well known: A. hebraeum and R. appendiculatus over-winter, for example, on the ground as engorged nymphs/unfed (emergent) adults while R. decoloratus over-winters on the ground as engorged females. In this study, transstadial and transovarial persistence of LSDV from experimentally infected A. hebraeum nymphs and R. decoloratus females after exposure to cold temperatures of 5 °C at night and 20 °C during the day for 2 months was reported. This observation suggests possible over-wintering of the virus in these tick species.

Detection of lumpy skin disease virus in saliva of ticks fed on lumpy skin disease virus-infected cattle

Lumpy skin disease is an economically important disease of cattle that is caused by the lumpy skin disease virus (LSDV), which belongs to the genus Capripoxvirus. It is endemic in Africa and outbreaks have also been reported in the Middle-East. Transmission has mostly been associated with blood-feeding insects but recently, the authors have demonstrated mechanical transmission by Rhipicephalus appendiculatus as well as mechanical/intrastadial and transstadial transmission by Amblyomma hebraeum. Saliva is the medium of transmission of pathogens transmitted by biting arthropods and, simultaneously, it potentiates infection in the vertebrate host. This study aimed to detect LSDV in saliva of A. hebraeum and R. appendiculatus adult ticks fed, as nymphs or as adults, on LSDV-infected animals, thereby also demonstrating transstadial or mechanical/intrastadial passage of the virus in these ticks. Saliva samples were tested for LSDV by real-time PCR and virus isolation. Supernatants obtained from virus isolation were further tested by real-time PCR to confirm that the cytopathic effects observed were due to LSDV. Lumpy skin disease virus was detected, for the first time, in saliva samples of both A. hebraeum and R. appendiculatus ticks. At the same time, mechanical/intrastadial and transstadial passage of the virus was demonstrated and confirmed in R. appendiculatus and A. hebraeum.

Evidence of transstadial and mechanical transmission of lumpy skin disease virus by Amblyomma hebraeum ticks

Lumpy skin disease (LSD) is an economically important disease caused by LSD virus (LSDV), a Capripoxvirus, characterized by fever and circumscribed skin lesions. It is suspected to be transmitted mechanically by biting flies. To assess the vector potential of Amblyomma hebraeum in transmission of LSDV, mechanical/intrastadial and transstadial modes of transmission of the virus by this tick species were investigated. Two cattle were artificially infected as sources (donors) of infection to ticks. Ticks were infected as either nymphs or adults. Male A. hebraeum ticks were partially fed on donor animals and transferred to recipient animals to test for mechanical/intrastadial transmission. Nymphal A. hebraeum were fed to repletion on donor animals. The emergent adult ticks were placed on recipient animals to test for transstadial transmission of the virus. Successful transmission of LSDV infection was determined in recipient animals by monitoring development of clinical signs, testing of blood for the presence of LSDV by real-time PCR, virus isolation and the serum neutralization test. This report provides further evidence of mechanical/intrastadial and, for the first time, transstadial transmission of LSDV by A. hebraeum. These findings implicate A. hebraeum as a possible maintenance host in the epidemiology of the disease.

Detection and characterisation of papillomavirus in skin lesions of giraffe and sable antelope in South Africa

Papillomavirus was detected electron microscopically in cutaneous fibropapillomas of a giraffe (Giraffa camelopardalis) and a sable antelope (Hippotragus niger). The virus particles measured 45 nm in diameter. Histopathologically, the lesions showed histopathological features similar to those of equine sarcoid as well as positive immunoperoxidase-staining of tissue sections for papillomavirus antigen. Polymerase chain reaction (PCR) detected bovine papillomavirus (BPV) DNA. Bovine papillomavirus-1 was characterised by real-time PCR in the sable and giraffe, and cloning and sequencing of the PCR product revealed a similarity to BPV-1. As in the 1st giraffe, the lesions from a 2nd giraffe revealed locally malignant pleomorphism, possibly indicating the lesional end-point of papilloma infection. Neither virus particles nor positively staining papillomavirus antigen could be demonstrated in the 2nd giraffe but papillomavirus DNA was detected by real-time PCR which corresponded with BPV-1 and BPV-2.

Molecular epidemiology of human and animal tuberculosis in Ibadan, Southwestern Nigeria

From 2005 to 2007, Mycobacterium tuberculosis complex (MTC) strains were isolated from cattle, goats and pigs samples collected at the Bodija abattoir and from human samples from tuberculosis patients and livestock traders at the Akinyele cattle market in Ibadan, Southwestern Nigeria. Seventy four isolates obtained from humans (24) and livestock (50) were identified as MTC strains. Thirty two isolates were spoligotyped. Nineteen of these 32 isolates were identified as M. tuberculosis whilst 13 were identified as Mycobacterium bovis. M. bovis was isolated from two humans, whereas M. tuberculosis was isolated from a bovine, a pig and a goat. All the M. bovis isolates identified in this study belonged to the Africa 1 clonal complex. Multiple locus VNTR [variable number of tandem repeats] analysis (MLVA) was carried out on the 74 isolates. Three major clusters were defined. Group A consisted of 24 M. tuberculosis isolates (MLVA genotypes 1-18). One strain was isolated from a bovine and one from a pig. Group B consisted of 49 M. bovis strains (MLVA genotypes 19-48), mainly of cattle origin but also included four goat, nine pig and two human isolates. Group C consisted of a single M. tuberculosis isolate (MLVA genotype 49) obtained from a goat. Spoligotyping and MLVA confirmed it as clustering with the East Africa Indian clade found in humans in Sudan and the Republic of Djibouti. The isolation of three M. tuberculosis strains from livestock raises the question of their epidemiological importance as a source of infection for humans.

Evaluation of PCR assays for the detection of Campylobacter fetus in bovine preputial scrapings and the identification of subspecies in South African field isolates

As a result of the high lability and slow growth of Campylobacter fetus subspecies, the laboratory diagnosis of bovine genital campylobacteriosis has always been difficult. This is especially true under South African conditions, where farms are far apart, laboratories are only present in major centres and there are high ambient temperatures. In order to overcome the shortcomings associated with traditional diagnostic methods, the implementation of a molecular assay was sought. This work describes how a previously published PCR assay (MG3F/ MG4R primers) was adapted, optimised and applied in the diagnostic laboratory to test preputial samples directly for the presence of Campylobacter fetus. Field evaluation of the assay revealed an analytical sensitivity and specificity of 85.7% and 99%, respectively. Subsequent genotyping and phenotyping of a diverse collection of South African field isolates revealed that South Africa has an unexpected and previously unreported high incidence of Campylobacter fetus subsp. venerealis biovar intermedius strains. These strains were not identified correctly by the subspecies-specific primer set evaluated. Until such time that cost- effective genotyping methods are available to diagnostic laboratories in South Africa, and other countries with these atypical Campylobacter fetus subsp. venerealis strains, the need for bacterial culture will persist. Identification to subspecies level of isolates at present remains dependent upon a single phenotypic criterion, namely tolerance to 1% glycine.

A potential role for ixodid (hard) tick vectors in the transmission of lumpy skin disease virus in cattle

Lumpy skin disease (LSD) is an economically important cattle disease. The disease is endemic in many African countries, but outbreaks have also been reported in Madagascar and the Middle East. The aim of this study was to investigate the potential role of ixodid (hard) ticks in the transmission of the disease. Cattle were infected with a virulent, South African field isolate of lumpy skin disease virus (LSDV). Three common African tick species (genera Rhipicephalus, Amblyomma and Rhipicephalus (Boophilus)) in different life cycle stages were fed on the infected animals during the viraemic stage and on skin lesions. Post-feeding, the partially fed male ticks were transferred to the skin of non-infected 'recipient' animals, while females were allowed to lay eggs that were then tested using the polymerase chain reaction (PCR) method and virus isolation. Nymphs were allowed to develop for 2-3 weeks after which time they were tested. The non-infected 'recipient' cattle were closely monitored, both skin and blood samples were tested using PCR and virus isolation, and serum samples were tested by the serum neutralization test. This is the first report showing molecular evidence of potential transmission of LSDV by ixodid ticks. The study showed evidence of transstadial and transovarial transmission of LSDV by R. (B.) decoloratus ticks and mechanical or intrastadial transmission by R. appendiculatus and A. hebraeum ticks.

Comparison of the capillary and agarose electrophoresis based multiple locus VNTR (variable number of tandem repeats) analysis (MLVA) on Mycobacterium bovis isolates

Electrophoretic techniques that can be used for genotyping of bacterial pathogens ranges from manual, low-cost, agarose gels to high-throughput capillary electrophoresis sequencing machines. These two methods are currently employed in the electrophoresis of PCR products used in multiple locus VNTR (variable number of tandem repeats) analysis (MLVA), i.e. the agarose electrophoresis (AE) and the capillary electrophoresis (CE). Some authors have suggested that clusters generated by AE are less reliable than those generated by CE and that the latter is a more sensitive technique than the former when typing Mycobacterium tuberculosis complex (MTC) isolates. Because such a claim could have significant consequences for investigators in this field, a comparison was made on 19 Belgian Mycobacterium bovis strains which had previously been genotyped using CE VNTR analysis. The VNTR profiles of the CE VNTR analysis were compared with those obtained by AE VNTR analysis at 14 VNTR loci. Our results indicated that there were no differences in copy numbers at all loci tested when the copy numbers obtained by the AE VNTR analysis were compared with those obtained by CE VNTR analysis. The use of AE VNTR analysis in mycobacterial genotyping does not alter the sensitivity of the MLVA technique compared with the CE VNTR analysis. The AE VNTR can therefore be regarded as a viable alternative in moderately equipped laboratories that cannot afford the expensive equipment required for CE VNTR analysis and data obtained by AE VNTR analysis can be shared between laboratories which use the CE VNTR method.

Experimental Reproduction of Severe Bluetongue in Sheep

Sheep inoculated with a virulent South African strain of bluetongue (BT) virus serotype 4 developed severe clinical signs and lesions characteristic of fulminant BT, including coronitis, hemorrhage and ulceration of the mucosal lining of the oral cavity and forestomaches, hemorrhage in the wall of the pulmonary artery, and focally extensive necrosis of skeletal muscle, especially of the neck. At necropsy, up to 14 days after infection, the infected sheep exhibited striking pulmonary edema, edema of the subcutaneous tissues and fascial planes of the head and neck, and pleural and pericardial effusion of varying severity. A reliable model for experimental reproduction of fulminant BT in sheep will facilitate future studies to better characterize the pathogenesis of this disease, particularly as it regards the mechanisms responsible for the increased vascular permeability that characterizes BT and related orbiviral diseases such as African horse sickness.

Occurrence of Babesia felis and Babesia leo in various wild felid species and domestic cats in Southern Africa, based on reverse line blot analysis

Reverse line blot (RLB) is a hybridization assay that can be used to detect various blood parasites and differentiate between them. Results, using the RLB, showed that Babesia felis and Babesia leo occurred as single or mixed infections in various felid species, but most frequently in domestic cats and lions, respectively. Prevalence of infection in free-ranging cheetahs in Namibia was low (7, 5%), whereas 50% of free-ranging lions in South Africa and Swaziland were infected. A large number (52, 9%) of samples tested positive only for Babesia, neither B. felis nor B. leo. This could be an indication of at least one further, as yet undescribed, Babesia species in felids.

Comparison of SAT-1 foot-and-mouth disease virus isolates obtained from East Africa between 1971 and 2000 with viruses from the rest of sub-Saharan Africa

Foot-and-mouth disease serotype SAT-1 seems to be endemic in many sub-Saharan African countries. Phylogenetic analysis using the 1D gene of 51 SAT-1 isolates from East, West and southern Africa indicated the presence of at least 6 lineages and 11 genotypes with linkages between various geographical regions of the subcontinent. Differences were observed between countries in East Africa, the main focus of this study, with individual countries suffering outbreaks from isolates belonging to various genotypes, which is evidence of reintroduction of strains and long-term circulation of outbreak viruses. The amount of variation observed has significant implications for disease control on the subcontinent.

Absence of lumpy skin disease virus in semen of vaccinated bulls following vaccination and subsequent experimental infection

Twelve serologically negative bulls were used, six were vaccinated with a modified live LSD vaccine and six unvaccinated. All were then experimentally infected with a virulent field strain of LSDV. No clinical abnormality was detected following vaccination, and mild clinical signs were seen in four vaccinated bulls following challenge. Virus was not found in semen of vaccinated bulls. Two of the unvaccinated bulls developed severe LSD and four showed mild symptoms, all excreted the virus in the semen following challenge. This study confirmed the ability of LSD vaccination to prevent the excretion of LSDV in semen of vaccinated bulls.

A pilot study on post-evisceration contamination of broiler carcasses and ready-to-sell livers and intestines (mala) with Campylobacter jejuni and Campylobacter coli in a high-throughput South African poultry abattoir

To assess post-evisceration contamination of broiler carcasses, 300 samples were randomly selected during routine slaughter in the winter of 2004. The samples originated from 50 chicken carcasses, taken directly after evisceration, as well as 25 samples from ready-to-sell packages of fresh intestines (mala) and livers. The samples were taken in batches over a period of 4 weeks to allow randomised sampling from different farms of origin. Conventional culture-based detection methods of Campylobacter spp. usually need 4-6 days to produce a result. The polymerase chain reaction (PCR) used for this study took less than 32 hours. The average contamination rates with Campylobacter in both the skin and liver samples were 24%, and 28% for intestines. Chicken and chicken products, especially livers and intestines, form an integral part of the traditional diet of many Black South Africans, as they are cheap and readily available in bulk and un-chilled for direct distribution, mainly through street vending and other informal retail outlets. This sudy showed that Campylobacter spp. are prevalent in poultry in South Africa. The handling of poultry meat and products contaminated with this organism in households and the potential for cross-contamination of other foods presents a high risk of infection to consumers in South Africa. The study also emphasised the need for further research in this field.

Elimination of toxicity and enhanced detection of lumpy skin disease virus on cell culture from experimentally infected bovine semen samples

Lumpy skin disease virus (LSDV), a poxvirus of the genus Capripoxvirus, is shed in the semen of infected bulls. The screening of semen for infectious virus requires a sensitive diagnostic method. The isolation of the virus on cell cultures and/or the polymerase chain reaction (PCR) are sensitive diagnostic tests which may be used to screen semen for LSD viral DNA prior to artificial insemination. Although cell culture detects infectious virus and is a sensitive method, there are major difficulties in using this method due to the toxic effect of semen on the cells. The aim of this study was to find a method that decreases the toxic effect of semen and enhances the isolation of LSDV on cell culture. Semen samples from LSDV sero-negative bulls were collected and infected with a field isolate of LSDV, strain V248/93, with a titre of 6.5 log TCID50. The semen samples were treated with one of four different methods: centrifugation, serial dilution, filtration and chemical treatment with kaolin. The samples subjected to centrifugation, serial dilution and filtration were supplemented with gentamycin. Semen toxicity on cell cultures was eliminated when supernatants of semen samples centrifuged at 2000 rpm for 1, 3 and 5 min and serially diluted were used to inoculate confluent monolayer bovine dermis cells. The toxicity recorded when the pellet fractions of semen samples centrifuged for 5 min at 2000 rpm was comparable to results obtained from serially diluted samples supplemented with gentamycin. Filtration and kaolin treatment of semen samples did not remove the toxic effect.

The detection of lumpy skin disease virus in samples of experimentally infected cattle using different diagnostic techniques

Lumpy skin disease (LSD) is a disease of cattle, primarily in Africa and Madagascar and rarely in the Middle East. It is caused by a capripoxvirus that belongs to the family Poxviridae. The disease is of economic importance in endemic areas. Effective control of LSD requires accurate and rapid laboratory techniques to confirm a tentative clinical diagnosis. Comparative studies on different diagnostic tests used at different stages of the disease have not been done. The aim of this study was to compare several of these tests. Six seronegative bulls, between 11 and 20 months of age, were infected intravenously and kept in an insect-free facility. The course of the infection was monitored. During a 3-month period blood samples and skin biopsies were collected for virus isolation and polymerase chain reaction (PCR). Skin biopsies were also examined using transmission electron microscopy (TEM). The incubation period in infected animals varied from 4-5 days. The length of the viraemic period did not correlate with the severity of clinical disease. Viraemia was detected from 1-12 days using virus isolation and from 4-11 days using the PCR, which is longer than has previously been reported. Virus was isolated from skin biopsies until Day 39 post infection (p.i.) and PCR could demonstrate viral DNA until Day 92 p.i. Transmission electron microscopy of negatively stained skin biopsies detected LSD virus only in one of the four bulls that developed skin lesions until Day 33 p.i. The PCR was a fast and sensitive method to demonstrate viral DNA in blood and skin samples. It could detect viral nucleic acid in skin lesions 53 days longer than virus isolation. Virus isolation from blood and skin samples was sensitive and reliable, but as a single test it may be too time-consuming to use although this depends on how rapidly the diagnosis must be confirmed. In conclusion, this study showed the PCR to be superior in detecting LSD virus from blood and skin samples. However, virus isolation is still required when the infectivity of the LSD virus is to be determined.

Excretion of lumpy skin disease virus in bull semen

This work was done to establish the incidence and duration of excretion of lumpy skin disease virus (LSDV) in semen of experimentally infected susceptible bulls. Six serologically negative bulls 11-20 months of age were experimentally infected with a virulent field isolate (strain V248/93) of LSDV. Animals were observed for the development of clinical signs, blood was collected until day 90 after infection, and semen was collected every second day until day 18, then twice a week till day 63 and twice a month until three consecutive samples were negative when tested for LSDV by polymerase chain reaction (PCR). An aliquot of each sample which tested positive using PCR was inoculated onto cell monolayers for the recovery of virus. Two bulls developed severe lumpy skin disease (LSD), two bulls showed mild signs and two bulls showed a transient fever only. Multiple samples were positive on PCR from both of the severely affected bulls and one of the mildly affected bulls; between days 10 and 159, days 8 and 132, and days 10 and 21 respectively. Only one sample from each of the other three bulls was positive on PCR. Virus was only isolated from two samples from one of the severely affected bulls and from five semen samples from the other. This study confirmed the excretion of LSDV in bovine semen for prolonged periods, even when obvious clinical signs of the disease were no longer apparent.

Molecular epidemiology of serotype O foot-and-mouth disease virus isolated from cattle in Ethiopia between 1979-2001

Partial 1D gene characterization was used to study phylogenetic relationships between 17 serotype O foot-and-mouth disease (FMD) viruses in Ethiopia as well as with other O-type isolates from Eritrea, Kenya, South and West Africa, the Middle East, Asia and South America. A homologous region of 495 bp corresponding to the C-terminus end of the 1D gene was used for phylogenetic analysis. This study described three lineages, viz. African/Middle East-Asia, Cathay and South American. Within lineage I, three topotypes were defined, viz. East and West Africa and the Middle East-Asia together with the South African isolate. The Ethiopian isolates clustered as part of topotype I, the East African topotype. Two clades (based on < 12% nucleotide difference) A and B were identified within the East African isolates, with clade A being further classified into three significant branches, A1 (80 % bootstrap support), A2 (89 % bootstrap support) and A3 (94 % bootstrap support). Clade B consisted of two Kenyan isolates. Within topotype I, the 17 Ethiopian isolates showed genetic heterogeneity between themselves with sequence differences ranging from 4.6-14 %. Lineage 2 and 3 could be equated to two significant topotypes, viz. Cathay and South America. Comparison of amino acid variability at the immunodominant sites between the vaccine strain (ETH/19/77) and other Ethiopian outbreak isolates revealed variations within these sites. These results encourage further work towards the reassessment of the type O vaccine strain currently being used in Ethiopia to provide protection against field variants of the virus.

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 identified 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.

The prevalence of Cowdria ruminantium in free-living adult Amblyomma hebraeum collected at a communal grazing area and in 2 wildlife reserves in South Africa

In order to detect the prevalence of Cowdria ruminantium in the vector tick, Amblyomma hebraeum, free-living, unfed adult ticks were collected with the aid of pheromone/CO2 traps. Ticks were collected at the Rietgat communal grazing area, as well as in the southwestern Kruger National Park and in the Songimvelo Game Reserve, all located in heartwater-endemic areas of South Africa. The presence of C. ruminantium in these ticks was determined by polymerase chain reaction (PCR) analysis. Ticks from the Rietgat communal grazing area were assayed in 2 batches and 4.7% of the one and 11.3% of the other were positive for infection, while 5.7% of the ticks collected in the Kruger National Park and 25% in the Songimvelo Game Reserve were positive. These results support the contention that a vector-wildlife cycle of transmission of C. ruminantium, the cause of heartwater in domestic ruminants, can be maintained in the absence of the latter animals.

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 ID (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.

Phylogenetic relationships of bluetongue viruses based on gene S7

Previous phylogenetic analyses based on bluetongue virus (BTV) gene segment L3, which encodes the inner core protein, VP3, indicated a geographical distribution of different genotypes. The inner core protein, VP7, of BTV has been identified as a viral attachment protein for insect cell infection. Because the inner core proteins are involved with infectivity of insect cells, we hypothesized that certain VP7 protein sequences are preferred by the insect vector species present in specific geographic locations. We compared the gene segment S7, which encodes VP7, from 39 strains of BTV isolated from Central America, the Caribbean Basin, the United States, South Africa and Australia. For comparison, the S7 sequences from strains of the related orbiviruses, epizootic hemorrhagic disease virus (EHDV) and African horse sickness virus (AHSV) were included. The S7 gene was highly conserved among BTV strains and fairly conserved among the other orbiviruses examined. VP7 sequence alignment suggests that the BTV receptor-binding site in the insect is also conserved. Phylogenetic analyses revealed that the BTV S7 nucleotide sequences do not unequivocally display geographic distribution. The BTV strains can be separated into five clades based on the deduced VP7 amino acid sequence alignment and phylogeny but evidence for preferential selection by available gnat species for a particular VP7 clade is inconclusive. Differences between clades indicate allowable variation of the VP7 binding protein.

Collection of free-living nymphs and adults of Amblyomma hebraeum (Acari: Ixodidae) with pheromone/carbon dioxide traps at 5 different ecological sites in heartwater endemic regions of South Africa

The capture of free-living adults and nymphs of Amblyomma hebraeum, the main vector of heartwater in domestic and wild ruminants in South Africa, by means of attraction-aggregation-attachment-pheromone/carbon dioxide traps at five endemic localities in South Africa is described. Although the traps were used successfully at each of the localities, no determination of their efficiency in relation to the actual abundance of ticks at a particular site was made. This study confirmed that the traps could be used in a variety of ecological areas to locate populations of free-living adult A. hebraeum.

Vector competence of selected South African Culicoides species for the Bryanston serotype of equine encephalosis virus

Equine encephalosis virus (EEV) was recognized and described in the Republic of South Africa in 1967 and subsequent serological studies have shown this orbivirus to be both widespread and prevalent in southern Africa. In the present study it was shown that wild-caught Culicoides (Avaritia) imicola Kieffer (Diptera: Ceratopogonidae) can become infected with and permit the replication of the Bryanston serotype of EEV following membrane-feeding on infective blood containing 5.0 log10 plaque-forming-units (PFU)/ml. The mean prevalence of Bryanston virus infection in C. imicola after 10 days extrinsic incubation at 23.5 degrees C was 22.3% (23/103). The mean infectivity of Bryanston virus in the infected C. imicola increased from 1.3 log10 PFU/midge, in insects assayed immediately after feeding on the blood-virus mixture, to 2.6 log10 PFU/midge in insects assayed after incubation. The virus concentration in individual C. imicola infected with the Bryanston serotype of EEV ranged from 0.7 to 3.6 log10 PFU/midge. Bryanston virus titres higher than 2.5 log10 TCID50, found in individual C. imicola, suggest that this species may be able to transmit this virus to susceptible hosts. Prevalence of virus infection in C. imicola was determined by PFU and microtitration assays on both BHK and Vero cells and confirmation of the Bryanston serotype of EEV was determined by plaque inhibition. No virus replication could be demonstrated in 102 C. nivosus tested after the incubation period, suggesting that not all Culicoides species are equally susceptible to Bryanston virus infection. Other Culicoides species that survived the incubation period and that were negative for the presence of Bryanston virus were C. pycnostictus (42), C. leucostictus (7), C. magnus (2), C. bolitinos (1) and C. bedfordi (1).

Antigenic and genetic analysis of canine parvoviruses in southern Africa

Canine parvovirus (CPV) is a significant pathogen of domestic and free-ranging carnivores all over the world. It suddenly appeared at the end of the 1970s and most likely emerged as a variant of the well known feline panleukopenia virus (FPV). During its adaptation to the new host, the domestic-dog, the virus has changed its antigenic profile twice giving rise to two new antigenic types, CPV-2a and CPV-2b. These new types have replaced the original type CPV-2 in the United States of America, Europe and Japan. However, no data about the prevalence of the new antigenic types on the African continent are available. In this study, 128 recent parvovirus isolates from South Africa and Namibia were antigenically typed with type-specific monoclonal antibodies. No original CPV-2 viruses were found and its complete replacement by the new antigenic types conforms to the situation in other parts of the world. The predominant strain found in southern Africa was CPV-2b (66%), which differs from the situation in Europe and Japan where CPV-2a is the most prevalent type. Analysis of the capsid protein DNA-sequences of four selected African isolates gave no hint of a specific African parvovirus lineage.

Characterization of Anaplasma isolates from eland (Taurotragus oryx). Pathogenicity in cattle and sheep and DNA profiles analysis

Two eland Anaplasma isolates, AnapE1, from Kenya, and AnapE2, from South Africa were characterised. Their characterization was based on their pathogenicity to intact and splenectomized cattle and sheep and also their DNA profiles. Their DNA profiles were analysed and compared to Anaplasma marginale, A. ovis and A. centrale after endonuclease restrictions and probing with Anaplasma DNA probes, AC5-12 and AC-1. The results of the pathogenicity trials showed AnapE1 to be similar to A. ovis and AnapE2 an isolate of A. marginale. On DNA profiles, AnapE1 was close to A. ovis, with differences that occur even in same Anaplasma species isolates from different locations. On the other hand, AnapE2, resembled one of the A. marginale isolates known to occur in South Africa. The DNA profiles correlated well with the pathogenicity results. It is concluded that elands are carriers of both A. marginale and A. ovis parasites and are therefore important reservoirs that need attention in epidemiology of anaplasmosis.

The effect of activation of the lactoperoxidase system and souring on certain potential human pathogens in cows' milk

Conventional methods of ensuring the safety and soundness of cows' milk for human consumption, such as pasteurisation, are not always practical in poor socioeconomic conditions or in rural communities that lack modern amenities. Activation of lactoperoxidase (LP) system and souring of milk were investigated as potential alternative methods to sustain the safety of milk by inhibiting certain microorganisms with known pathogenic potential. The activation of the LP-system inhibited the growth of Staphylococcus aureus and Escherichia coli by the order of 2 log values. The inhibition of Brucella abortus was negligible. The replication of Coxiella burnetti in milk was not disturbed even after 17 h of LP-system activation at 20 degrees C, but the outcome of the LP-system treatment on Mycobacterium bovis could not be determined as the conventional culturing technique used to grow this organism did not allow full recovery. Souring inhibited the growth of S. aureus and E. coli also by the order of 2 log values. From the results obtained in this investigation are concluded that the activation of the LP-system and souring can be used to inhibit the growth of S. aureus and E. coli in cows' milk, thereby increasing its safety.

Detection of bluetongue virus and African horsesickness virus in co-infected cell cultures with NS1 gene probes

The serogroup specificity of the bluetongue virus (BTV) NS1 and VP3 gene probes was confirmed by means of northern blot hybridization. Under high-stringency conditions both probes hybridized to 22 BTV serotypes (18 South African serotypes, BTV3 from Cyprus and BTV16 from Pakistan) but not to serotypes that originate from Australia and India. Furthermore, NS1 gene probes of BTV and African horsesickness virus (AHSV) were used in a dot-spot in situ hybridization procedure to differentiate between BTV and AHSV in co-infected cell cultures. The method detects viral RNA directly i glutaraldehyde-fixed infected cell cultures without prior nucleic-acid extraction or purification. AHSV could be detected in cells infected with AHSV at a multiplicity of infection of 10(-4) PFU/cell in the presence of a hundred excess of co-infecting BTV. The method may have an application in epidemiological surveys to detect different orbiviruses in the same Culicoides population.

Detection of human papillomavirus DNA with in situ hybridisation in oral squamous carcinoma in a rural black population

Intra-oral carcinoma is the third most common malignancy among men in developing countries, and carries a high mortality rate, particularly in Africa, where patients often present initially with lesions at an advanced stage. The present study was undertaken to determine the prevalence of human papillomavirus (HPV) DNA in oral squamous carcinoma in the west of the Northern Transvaal, an area where a large number of new cases has been diagnosed over the past few years. Paraffin blocks from 66 cases (51 men, 15 women; mean age 58.7 years) of oral squamous carcinoma were randomly selected. Blocks contained samples of both tumour and adjacent normal epithelium. The presence of HPV antigen was established by means of immunocytochemistry and HPV DNA by in situ hybridisation with radiolabelled probes for HPV-6, 11, 16 and 18. Immunocytochemistry for viral antigen was negative in all the specimens. HPV-18 was detected in normal epithelium adjacent to the tumour in one case only. It appears from our study that HPV is of limited importance in oral squamous cell carcinogenesis in the population studied.

Human papillomavirus DNA in aerodigestive squamous carcinomas demonstrated by means of in situ hybridisation

A series of 10 oesophageal and 10 laryngeal squamous carcinomas was examined by means of immunocytochemistry and in situ DNA hybridisation to demonstrate human papillomavirus (HPV) infection. Changes in the epithelium adjacent to the carcinoma were found in 5 of 10 oesophageal and 7 of 10 laryngeal carcinomas. Viral antigens could not be detected with immunocytochemistry in any of the specimens. HPV 6, 11 and 16 were detected in 3 oesophageal specimens. In one of these, HPV 16 was detected in normal as well as malignant cells. HPV 7 was detected for the first time in a laryngeal carcinoma. Our results confirm previous reports of possible HPV involvement in the pathogenesis of aerodigestive carcinomas.

Detection of human papillomavirus DNA in an ameloblastoma using the in situ hybridization technique

HPV type 18 DNA was identified in an intrabony ameloblastoma using radiolabelled in situ hybridization. The viral DNA was found in a verrucous lesion in a cystic area of the tumor. The absence of HPV DNA in other epithelial areas of the ameloblastoma is suggestive of a secondary infection. HPV is not considered to be an etiological factor in the pathogenesis of this ameloblastoma.

Detection of bluetongue virus RNA in cell cultures and in the central nervous system of experimentally infected mice using in situ hybridization

Two radiolabelled complementary DNA (cDNA) probes (1663 bp and 200 bp respectively) were prepared from the genome segment that encodes the non-structural protein 1 (NS1) of bluetongue virus serotype 4 (BTV4). The probes were used to optimize the in situ hybridization (ISH) method on baby hamster kidney-21 (BHK-21) cells and to investigate the use of the technique as a diagnostic procedure. Cells were infected with BTV4 at a multiplicity of infection of 0.5 PFU/cell. An intense cytoplasmic hybridization signal could be detected from 3 hours post-infection onwards, reaching a peak at 17 hours. The ISH procedure has potential use as a diagnostic technique, but will probably find a wider application in pathogenesis studies. An in situ hybridization method was also developed for the detection of BTV RNA in the central nervous system of newborn mice after intracranial inoculation with BTV10. Viral RNA-positive cells were detected from Day 3 onwards, predominantly in areas where the virus caused necrotic encephalitis.

Congress: Opening address

No abstract available.

A comparison of different genomic probes in the detection of virus-specified RNA in Orbivirus-infected cells

Different 32P-labelled genomic probes of bluetongue virus (BTV), epizootic haemorrhagic disease virus (EHDV) and equine encephalosis virus (EEV) were compared with respect to the detection of virus-specified RNA in infected cells. The probe derived from the genome segment that encodes nonstructural protein NS1 was found to be the most sensitive, detecting virus-specified RNA in glutaraldehyde-fixed cells as early as 2-3 h p.i. This comparison was based on the observation that the NS1 gene probe required a smaller number of infected cells to produce a positive hybridization signal than the other nucleic acid probes. The only exception was the EHDV NS2 gene probe which appeared to be as sensitive as the NS1 gene probe. The advantage of using the NS1 gene probe was particularly evident in the analysis of cells infected at very low multiplicities of infection. At a multiplicity of infection of 1 x 10(-5) plaque forming units/cell, virus-specified RNA could be detected 48 h after infection. The greater sensitivity of the NS1 gene-specific probe is ascribed to the fact that its target, the NS1 mRNA, is transcribed more frequently than the other target viral mRNAs. The major application of the cell-hybridization method is the rapid detection of small quantities of infectious virus particles.

Nosocomial rotavirus infections in a South African hospital nursery for white infants

Rotavirus infections in a nursery ward for newborn white infants in South Africa do not apparently differ from those encountered in other temperate countries. Neonates began to excrete rotavirus as early as 2 days after birth; a peak incidence of excretion occurred during the winter months. After a period of 4 years the incidence of excretion remained virtually unchanged. Rotaviruses also colonized and spread very rapidly in a newly commissioned nursery ward, possibly via respiratory infections. Passively acquired antibodies had no influence on the prevention of infections but may play a role in the suppression of clinical symptoms since none of the newborn population studied developed gastro-enteritis. The immunosorbent electron microscopy technique used to detect rotaviruses in this study yielded results that compared well with results obtained previously by other techniques.