46 research outputs found
Passive transfer and rate of decay of maternal antibody against African horse sickness virus in South African throughbred foals
REASONS FOR PERFORMING STUDY : African horse sickness is an insect transmitted, non-contagious disease of equids caused by African horse sickness virus (AHSV). Mortality can exceed 90% in fully susceptible horse populations. A live-attenuated (modified-live) cell culture-adapted (MLV) polyvalent AHSV vaccine is widely used to control AHS in endemic areas in southern Africa. Field studies detailing antibody responses of vaccinated horses are lacking. OBJECTIVES : To determine antibody titres to the 9 known serotypes of AHSV in a cohort of brood mares that were regularly vaccinated with the MLV AHSV vaccine, and to measure the passive transfer and rate of decay of maternal antibody to the individual virus serotypes in foals. METHODS : Serum was collected from 15 mares before foaling and from their foals after foaling and monthly thereafter for 6 months. Antibody titres to each of the 9 AHSV serotypes were determined by serum-virus neutralisation assay. RESULTS : There was marked variation in the antibody response of the mares to individual AHSV serotypes even after repeated vaccination, with consistently higher titre responses to some virus serotypes. Similarly, duration of maternally-derived antibodies in foals differed among serotypes. CONCLUSIONS : Data from this study confirm variation of the neutralising antibody response of individual mares to repeated vaccination with polyvalent AHSV vaccine. Virus strains of individual AHSV serotypes included in the vaccine may vary in their inherent immunogenicity. Passivelyacquired maternal antibodies to AHSV vary markedly among foals born to vaccinated mares, with further variation in the duration of passive immunity to individual AHSV serotypes. POTENTIAL RELEVANCE : These data are relevant to the effective utilization of live-attenuated AHSV vaccines in endemic regions, and potentially to the use of vaccines in response to future incursions of AHSV into previously free regions. Further studies involving a larger population will be required to determine the optimal time for vaccinating foals.Racing South Africa and the Equine Research Centre, University of Pretoria.http://www.evj.co.uk/journals/hb2013ab201
African horse sickness in naturally infected, immunised horses
To determine whether subclinical cases, together with clinical cases, of African horse sickness (AHS) occur in immunised horses in field conditions, whole
blood samples were collected and rectal temperatures recorded weekly from 50 Nooitgedacht ponies resident in open camps at the Faculty of Veterinary
Science, University of Pretoria, Onderstepoort, during 2008â2010. The sampleswere tested for the presence of African horse sickness virus (AHSV) RNAby a
recently developed real-time RT-PCR. Itwas shown that 16% of immunised horses in an AHS endemic areawere infected with AHSV over a 2 year period, with
half of these (8%) being subclinically infected. The potential impact of such cases on the epidemiology of AHS warrants further investigation.Equine Research Centre, Faculty of Veterinary Science, University of
Pretoriahttp://onlinelibrary.wiley.com/journal/10.1001/(ISSN)2042-3306hb2014ab201
AlteraçÔes clĂnicas e patolĂłgicas em ovinos infectados naturalmente pelo vĂrus da lĂngua azul no Rio Grande do Sul
Diagnostic applications of molecular and serological assays for bluetongue and African horse sickness
The availability of rapid, highly sensitive and specific molecular and serologic diagnostic assays, such as competitive enzyme-linked immunosorbent assay (cELISA), has expedited the diagnosis of emerging transboundary animal diseases, including bluetongue (BT) and African horse sickness (AHS), and facilitated more thorough characterisation of their epidemiology. The development of assays based on real-time, reverse-transcription polymerase chain reaction (RT-PCR) to detect and identify the numerous serotypes of BT virus (BTV) and AHS virus (AHSV) has aided in-depth studies of the epidemiology of BTV infection in California and AHSV infection in South Africa. The subsequent evaluation of pan-serotype, real-time, RT-PCR-positive samples through the use of serotype-specific RT-PCR assays allows the rapid identification of virus serotypes, reducing the need for expensive and time-consuming conventional methods, such as virus isolation and serotype-specific virus neutralisation assays. These molecular assays and cELISA platforms provide tools that have enhanced epidemiologic surveillance strategies and improved our understanding of potentially altered Culicoides midge behaviour when infected with BTV. They have also supported the detection of subclinical AHSV infection of vaccinated horses in South Africa. Moreover, in conjunction with whole genome sequence analysis, these tests have clarified that the mechanism behind recent outbreaks of AHS in the AHS-controlled area of South Africa was the result of the reversion to virulence and/or genome reassortment of live attenuated vaccine viruses. This review focuses on the use of contemporary molecular diagnostic assays in the context of recent epidemiologic studies and explores their advantages over historic virus isolation and serologic techniques.https://www.woah.org/en/what-we-do/publications/scientific-and-technical-reviewVeterinary Tropical Disease
The combination of abundance and infection rates of Culicoides sonorensis estimates risk of subsequent bluetongue virus infection of sentinel cattle on California dairy farms
Bluetongue (BT) is an important viral disease of ruminants that is transmitted by
hematophagous Culicoides midges. We examined the seasonal patterns of abundance and
infection of Culicoides sonorensis at four dairy farms in the northern Central Valley of California
to develop estimates of risk for bluetongue virus (BTV) transmission to cattle at each
farm. These four farms were selected because of their similar meteorological conditions
but varying levels of vector abundance and BTV infection of cattle. C. sonorensis midges
were collected weekly at each farm during the seasonal transmission period, using three
different trapping methods: traps baited with either carbon dioxide (CO2) alone or traps
with CO2 and UV light, and by direct aspiration of midges from sentinel cattle. Analysis of
BTV-infected midges using group and serotype-specific quantitative reverse-transcriptase
polymerase chain reaction (RT-qPCR) assays confirmed that BTV serotypes 10, 11, 13 and 17
are all present in the region, but that midge infection rates and the number of BTV serotypes
circulating differed markedly among the individual farms. Furthermore, more serotypes of
BTV were present in midges than in sentinel cattle at individual farms where BTV circulated,
and the virus was detected at each farm in midges prior to detection in cattle. BTV
infection rates were remarkably lower among female C. sonorensis midges collected by CO2
traps with UV light than among midges collected by either animal-baited aspirations or
in CO2 traps without light. A subsample of female midges examined from each collection
method showed no overall differences in the proportion of female midges that had previously
fed on a host. Findings from this study confirm the importance of using sensitive
surveillance methods for both midge collection and virus detection in epidemiological studies
of BTV infection, which is especially critical if the data are to be used for development
of mathematical models to predict the occurrence of BTV infection of livestock.The Center for Food Animal Health at the University of California-Davis,
the U.S. Department of Agriculture and the Bernice Barbour Foundation.http://www.elsevier.com/locate/vetpa
Development of three triplex real-time reverse transcription PCR assays for the qualitative molecular typing of the nine serotypes of African horse sickness virus
Blood samples collected as part of routine diagnostic investigations from South African horses with clinical signs suggestive of African horse sickness (AHS) were subjected to analysis with an AHS virus (AHSV) group specific reverse transcription quantitative polymerase chain reaction (AHSV RT-qPCR) assay and virus isolation (VI) with subsequent serotyping by plaque inhibition (PI) assays using AHSV serotype-specific antisera. Blood samples that tested positive by AHSV RT-qPCR were then selected for analysis using AHSV type specific RT-qPCR (AHSV TS RT-qPCR) assays. The TS RT-qPCR assays were evaluated using both historic stocks of the South African reference strains of each of the 9 AHSV serotypes, as well as recently derived stocks of these same viruses. Of the 503 horse blood samples tested, 156 were positive by both AHSV RT-qPCR and VI assays, whereas 135 samples that were VI negative were positive by AHSV RT-qPCR assay. The virus isolates made from the various blood samples included all 9 AHSV serotypes, and there was 100% agreement between the results of conventional serotyping of individual virus isolates by PI assay and AHSV TS RT-qPCR typing results. Results of the current study confirm that the AHSV TS RT-qPCR assays for the identification of individual AHSV serotypes are applicable and practicable and therefore are potentially highly useful and appropriate for virus typing in AHS outbreak situations in endemic or sporadic incursion areas, which can be crucial in determining appropriate and timely vaccination and control strategies.Racing South Africa (Pty) Ltd, the Mary Slack and Daughters Foundation and Thoroughbred Racing Trust of South Africa.http://www.elsevier.com/locate/jviromet2016-10-31hb2016Equine Research CentreVeterinary Tropical Disease