Some epidemiological and economic aspects of a bluetongue-like disease in cattle in South Africa - 1995/96 and 1997

In December 1995 to March 1996 and the early summer of 1997 South Africa experienced above average rainfall which favoured the occurrence of Culicoides transmitted diseases. During this period several outbreaks of an uncommon disease of cattle occurred over a large part of the country. The clinical signs were similar to those of infection with the viruses of bluetongue (BT) and epizootic haemorrhagic disease of deer (EHD). Virus isolation from cattle and Culicoides yielded both viruses. Dual infections occurred on several farms. Typing of BT isolates yielded types 2, 3, 6 and 8. On at least two farms more than one BT virus serotype was involved. On one farm only EHD virus could be isolated from cattle and Culicoides. Serological tests confirmed that on this farm the disease was caused by EHD. In 1932/33, when a similar disease was reported conditions were vastly different. Rainfall figures show that the 1932/33 season was exceptionally dry. Techniques available at that time could not identify EHD and the cause was reported to be BT. The occurrence of BT in a dry season and over a much wider area than the distribution in South Africa of Culicoides imicola, the only proven vector for BT, is a clear indication that other species less dependent on high rainfall are involved. The present isolation of BT virus from three of five pools of parous C. bolitinos is evidence that this species, which breeds in cattle dung, may be an additional vector for BT.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat X Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201

Experimental infection of vaccinated slaughter ostriches with virulent Newcastle disease virus

A virulent Newcastle disease virus (NDV) isolate from an outbreak in commercial poultry, with virulence indices of MDT = 47-48 h; IVPI = 2,17 and ICPI = 1,8; was used to inoculate 10x vaccinated (standard poultry vaccines) as well as 10x unvaccinated slaughter ostriches via intratracheal, ocular and nasal routes, in a controlled environment. All unvaccinated ostriches developed clinical signs (mainly respiratory); two of them died while the other eight recovered. No vaccinated ostriches developed any clinical signs. All remaining (18) ostriches were slaughtered 14 d after the last mortality. Virulent NDV could be re-isolated from the dead birds, but not from organs, muscle (fresh), muscle (24 h chilled) , gastro-instestinal tract, bone-marrow or respiratory system taken from the slaughtered ostriches. It is suggested that it would be extremely unlikely that the international trade in ostrich meat could act as a mechanism for spreading virulent NDV from endemic to non-endemic parts of the world.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat X Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

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 (eDNA) probes (1663 bp and 200 bp res pectively) 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.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201

Laboratory confirmation of African horsesickness in the Western Cape : application of a F(ab')₂-based indirect ELISA

Recently a suspected outbreak of African horsesickness in the Western Cape Province resulted in the deaths of four foals and one adult horse. Spleen samples from these animals were subjected to analysis by an enzyme-linked immunosorbent assay (ELISA) which uses F(ab') ₂ fragments of immunoglobulins to detect African horse sickness virus (AHSV) antigens. The results of the immunoassay were compared with those obtained by isolation followed by serotyping as is currently applied by the Reference Centre at the Veterinary Research Institute, Onderstepoort. Samples of spleen tissue from the four foals contained sufficient antigen to be readily detectable by ELISA. A marginally positive signal was obtained with the tissue from the adult horse. This sample was inoculated onto VERO cells and four days were allowed for viral multiplication. Subsequently, when the cell culture was assayed by F(ab')₂ -ELISA, a much higher absorbance value than that obtained with the original spleen sample resulted, thus confirming the presence of AHSV in the initial specimen. The F(ab')₂-ELISA has potential to be used as an initial diagnostic test to screen for AHSV.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201

The prevalence of different African horsesickness virus serotypes in the Onderstepoort area near Pretoria, during an outbreak of African horsesickness in South Africa in 1995/1996

During 1995/1996 parts of South Africa experienced exceptionally high rainfall. Large numbers of Culicoides midges were seen and an outbreak of African horse sickness (AHS) followed. In the Onderstepoort area, near Pretoria in Gauteng, a number of horses died of suspected AHS. Virus isolation and typing was done from blood and/or organ samples of 21 suspected cases as well as from 5 zebra which were kept in the area. Virus was isolated from 14 of the 21 suspected cases but not from the zebra. The neutralizing antibody response of the zebra to the nine African horsesickness virus (AHSV) serotypes was determined. Results indicated the highest prevalence of serotypes 2 and 4 followed by serotypes 1, 6 and 9. Reverse transcription polymerase chain reaction (RT-PCR) was performed on total RNA extracted from blood samples of the zebra. AHSV RNA was detected in three of five zebra by agarose gel electrophoresis analysis of amplicons and in four of five zebra after Southern blot hybridization using a 32P-labelled probe. RT-PCR can be used together with serological techniques in studies of AHS to further clarify the epizootiology of the disease.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat v.9 was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

An outbreak of encephalomyocarditis-virus infection in free-ranging African elephants in the Kruger National Park

A cluster of four deaths in late December 1993, marked the onset of an outbreak of disease of African elephants (Loxodonta africana) in the Kruger National Park (KNP) in South Africa, which has an estimated population of 7 500 elephants. Mortalities peaked in January 1994, with 32 deaths, and then declined steadily to reach pre-outbreak levels by September, but sporadic losses continued until November. During the outbreak altogether 64 elephants died, of which 53 (83%) were adult bulls. Archival records revealed that, in addition to the usual losses from known causes such as poaching and intraspecific fighting, sporadic deaths from unexplained causes had, in fact, occurred in widely scattered locations from at least 1987 onwards, and from that time until the perceived outbreak of disease there had been 48 such deaths involving 33 (69%) adult bulls. Carcases had frequently become decomposed or had been scavenged by the time they were found, but seven of eight elephants examined early in 1994 had lesions of cardiac failure suggestive of encephalomyocarditis (EMC)-virus infection, and the virus was isolated from the heart muscles of three fresh carcases. The results of tests for neutralizing antibody on 362 elephant sera collected for unrelated purposes from 1984 onwards and kept frozen, indicated that the virus had been present in the KNP since at least 1987. Antibody prevalences of 62 of 116 (53 %), 18 of 139 (13%) and seven of 33 (21 %) were found in elephants in three different regions of the KNP in 1993 and 1994. Studies had been conducted on myomorph rodents in the KNP for unrelated purposes since 1984, and trapping attempts were increased during the perceived outbreak of disease in elephants. There was a striking temporal correlation between the occurrence of a population explosion (as evidenced by markedly increased catch rates per trap-night) and a surge in prevalence of antibody to EMC virus in rodents, and the occurrence of the outbreak of disease in elephants.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201

Lumpy skin disease of cattle : an emerging problem in the Sultanate of Oman

Lumpy skin disease (LSD) is a highly infectious disease of cattle caused by a virus belonging to the Capripoxvirus genus of the family Poxviridae. The purpose of this study is to place on record the first confirmation of LSD in the Sultanate. The disease was diagnosed and confirmed using polymerase chain reaction, histopathology, transmission electron microscopy and serum neutralization testing. The epizootic occurred in 2009 involving a large number of animals and covering a wide area including Nezwa, Alqabel, Sohar, Saham and Burimi. Morbidity and mortality rates of 29.7 and 26.3 %, and 13.6 and 15.4 % were observed at Nezwa and Sohar, respectively. The clinical signs were much more severe in Holstein–Friesian cattle compared to indigenous breeds and were characterized by multiple skin nodules covering the neck, back, perineum, tail, limbs and genital organs. Affected animals also exhibited lameness, emaciation and cessation of milk production. Oedema of limbs and brisket, and superficial lymph node enlargement were highly prominent. It is not known from where the virus originated, or how it spread to the Sultanate. The disease has become endemic in the country and is liable to extend to other Gulf Cooperation Council Countries and cause a pandemic. It is of major concern to the Omani dairy industry. Due to the widespread presence of screw worm, serious economic losses can follow outbreaks.South African ARChttp://link.springer.com/journal/11250hb201

Indirect enzyme-linked immunosorbent assay for the detection of antibody against Rift Valley fever virus in domestic and wild ruminant sera

An indirect enzyme-linked immunosorbent assay (I-ELISA) for the detection of specific IgG immunoglobulins against Rift Valley fever virus (RVFV) was validated in-house. A total of 3055 sera from sheep (n = 1 159), goats (n = 636), cattle (n = 203), African buffalo (n = 928), and other wild ruminants (n = 129), including eland, kudu, and black wildebeest, was used. Sera from domestic ruminants were collected in West (n = 10), South (n = 1 654) and East Africa (n = 334), and sera from wild ruminants (n = 1 064) were collected in South Africa. In addition, 136 sera from eight experimentally RVFV-infected sheep, taken during a period of 28 days post infection (dpi), were used to study the kinetics of RVFV antibody production. Field sera were tested by the serum neutralization (VN) test and experimental sera by VN and haemagglutination-inhibition (HI) test. Based on VN test results, negative sera were regarded as reference controls from RVFV-free, and positive sera were regarded as reference controls from RVFV-infected subpopulations of animals. ELISA data were expressed as the percentage positivity (PP) of an internal high positive control. The two-graph receiver operating characteristics approach was used for the selection and optimization of I-ELISA cut-offs including the miscIassification costs term and Youden index (J). In addition, cut-off values were determined as the mean plus two-fold standard deviation of the result observed with the RVFV-free subpopulations. Established optimal cut-offs were different for each of the data sets analyzed, and ranged from 1.65 PP (buffalo) to 9.1 PP (goats). At the cut-off giving the highest estimate of combined measure of diagnostic accuracy (highest J value), the I-ELISA test parameters were determined as follows: (1) Diagnostic sensitivity (%): cattle--84.31, buffalo--94.44, sheep--98.91, goats--99.18. (2) Diagnostic specificity (%): cattle--99.34, buffalo--98.28, sheep--99.16, goats--99.23 and other game ruminants--99.26. In the group of RVFV-experimentally infected sheep, seroconversion in all individuals was detected by VN on 4-6 dpi, by HI on 5-7 dpi, and by I-ELISA on 6-7 dpi. All tests showed the same kinetic pattern of immunological response. Antibody levels were low for a very short period before increasing to high titres, after which it was easily detectable by all tests. Compared to traditional tests, the lower sensitivity of I-ELISA in the detection of the earliest stage of immunological response may be practically insignificant, particularly when this assay is used in population-based, disease-surveillance programmes. The high sensitivity and specificity of I-ELISA established in this study, especially for the statistically more representative subpopulations of animals tested, seem to support this prediction. Test parameters determined in this study should, however, be regarded as in-house diagnostic decision limits, for which further updating is recommended, particularly for specimens from other countries, and preferably by applying a standardized method for sampling of new subpopulations of animals to be targeted by the assay.The articles have been scanned with a HP Scanjet 8300; 600dpi, saved in TIFF format. Adobe Acrobat v.9 was used to OCR the text and also for the merging and conversion to the final presentation PDF-format