Dataset Information

Genome Sequences of Three African Swine Fever Viruses of Genotypes I, III, and XXII from South Africa and Zambia, Isolated from Ornithodoros Soft Ticks.

ABSTRACT: Here, we report the draft genome sequences of three African swine fever viruses isolated from Ornithodoros soft ticks. Isolates LIV 5/40 (Zambia), SPEC 57 (South Africa), and RSA/2/2008 (South Africa) belong to genotypes I, III, and XXII, respectively.

SUBMITTER: Ndlovu S

PROVIDER: S-EPMC7171217 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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Genome Sequences of Three African Swine Fever Viruses of Genotypes I, III, and XXII from South Africa and Zambia, Isolated from <i>Ornithodoros</i> Soft Ticks.

Ndlovu S S Williamson A-L AL Malesa R R van Heerden J J Boshoff C I CI Bastos A D S ADS Heath L L Carulei O O

Microbiology resource announcements 20200305 10

Here, we report the draft genome sequences of three African swine fever viruses isolated from <i>Ornithodoros</i> soft ticks. Isolates LIV 5/40 (Zambia), SPEC 57 (South Africa), and RSA/2/2008 (South Africa) belong to genotypes I, III, and XXII, respectively. ...[more]

PMID: 32139555

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Project description:BackgroundSeveral species of soft ticks in genus Ornithodoros are known vectors and reservoirs of African swine fever virus (ASFV). However, the underlying mechanisms of vector competence for ASFV across Ornithodoros species remain to be fully understood. To that end, this study compared ASFV replication and dissemination as well as virus vertical transmission to descendants between Ornithodoros moubata, O. erraticus, and O. verrucosus in relation to what is known about the ability of these soft tick species to transmit ASFV to pigs. To mimic the natural situation, a more realistic model was used where soft ticks were exposed to ASFV by allowing them to engorge on viremic pigs.MethodsOrnithodoros moubata ticks were infected with the ASFV strains Liv13/33 (genotype I) or Georgia2007/1 (genotype II), O. erraticus with OurT88/1 (genotype I) or Georgia2007/1 (genotype II), and O. verrucosus with Ukr12/Zapo (genotype II), resulting in five different tick-virus pairs. Quantitative PCR (qPCR) assays targeting the VP72 ASFV gene was carried out over several months on crushed ticks to study viral replication kinetics. Viral titration assays were also carried out on crushed ticks 2 months post infection to confirm virus survival in soft ticks. Ticks were dissected. and DNA was individually extracted from the following organs to study ASFV dissemination: intestine, salivary glands, and reproductive organs. DNA extracts from each organ were tested by qPCR. Lastly, larval or first nymph-stage progeny emerging from hatching eggs were tested by qPCR to assess ASFV vertical transmission.ResultsComparative analyses revealed higher rates of ASFV replication and dissemination in O. moubata infected with Liv13/33, while the opposite was observed for O. erraticus infected with Georgia2007/1 and for O. verrucosus with Ukr12/Zapo. Intermediate profiles were found for O. moubata infected with Georgia2007/1 and for O. erraticus with OurT88/1. Vertical transmission occurred efficiently in O. moubata infected with Liv13/33, and at very low rates in O. erraticus infected with OurT88/1.ConclusionsThis study provides molecular data indicating that viral replication and dissemination in Ornithodoros ticks are major mechanisms underlying ASFV horizontal and vertical transmission. However, our results indicate that other determinants beyond viral replication also influence ASFV vector competence. Further research is required to fully understand this process in soft ticks.

Project description:African swine fever (ASF) is a lethal hemorrhagic disease in domestic pigs and wild suids caused by African swine fever virus (ASFV), which threatens the swine industry globally. In its native African enzootic foci, ASFV is naturally circulating between soft ticks of the genus Ornithodoros, especially in the O. moubata group, and wild reservoir suids, such as warthogs (Phacochoerus spp.) that are bitten by infected soft ticks inhabiting their burrows. While the ability of some Afrotropical soft ticks to transmit and maintain ASFV is well established, the vector status of Palearctic soft tick species for ASFV strains currently circulating in Eurasia remains largely unknown. For example, the Iberian soft tick O. erraticus is a known vector and reservoir of ASFV, but its ability to transmit different ASFV strains has not been assessed since ASF re-emerged in Europe in 2007. Little is known about vector competence for ASFV in other species, such as O. verrucosus, which occurs in southern parts of Eastern Europe, including Ukraine and parts of Russia, and in the Caucasus. Therefore, we conducted transmission trials with two Palearctic soft tick species, O. erraticus and O. verrucosus, and the Afrotropical species O. moubata. We tested the ability of ticks to transmit virulent ASFV strains, including one of direct African origin (Liv13/33), and three from Eurasia that had been involved in previous (OurT88/1), and the current epizooties (Georgia2007/1 and Ukr12/Zapo). Our experimental results showed that O. moubata was able to transmit the African and Eurasian ASFV strains, whereas O. erraticus and O. verrucosus failed to transmit the Eurasian ASFV strains. However, naïve pigs showed clinical signs of ASF when inoculated with homogenates of crushed O. erraticus and O. verrucosus ticks that fed on viraemic pigs, which proved the infectiousness of ASFV contained in the ticks. These results documented that O. erraticus and O. verrucosus are unlikely to be capable vectors of ASFV strains currently circulating in Eurasia. Additionally, the persistence of infection in soft ticks for several months reaffirms that the infectious status of a given tick species is only part of the data required to assess its vector competence for ASFV.

Dataset Information

Genome Sequences of Three African Swine Fever Viruses of Genotypes I, III, and XXII from South Africa and Zambia, Isolated from Ornithodoros Soft Ticks.

Publications

Genome Sequences of Three African Swine Fever Viruses of Genotypes I, III, and XXII from South Africa and Zambia, Isolated from <i>Ornithodoros</i> Soft Ticks.

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