Differential vector competence of Ornithodoros soft ticks for African swine fever virus: What if it involves more than just crossing organic barriers in ticks?

Abstract Background Several 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 Ornithodorosmoubata, 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. Methods Ornithodoros 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. Results Comparative 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. Conclusions This 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.

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The first genotype II African swine fever virus isolated in Africa provides insight into the current Eurasian pandemic

Scientific Reports ◽

10.1038/s41598-021-92593-2 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Emma P. Njau ◽

Jean-Baka Domelevo Entfellner ◽

Eunice M. Machuka ◽

Edwina N. Bochere ◽

Sarah Cleaveland ◽

...

Keyword(s):

Complete Genome ◽

African Swine Fever Virus ◽

African Swine Fever ◽

Gene Families ◽

Fever Virus ◽

Eastern Africa ◽

Chinese Isolate ◽

Genome Sequences ◽

Genotype I ◽

Genotype Ii

AbstractAfrican swine fever (ASF) caused by the African swine fever virus (ASFV) is ranked by OIE as the most important source of mortality in domestic pigs globally and is indigenous to African wild suids and soft ticks. Despite two ASFV genotypes causing economically devastating epidemics outside the continent since 1961, there have been no genome-level analyses of virus evolution in Africa. The virus was recently transported from south-eastern Africa to Georgia in 2007 and has subsequently spread to Russia, eastern Europe, China, and south-east Asia with devastating socioeconomic consequences. To date, two of the 24 currently described ASFV genotypes defined by sequencing of the p72 gene, namely genotype I and II, have been reported outside Africa, with genotype II being responsible for the ongoing pig pandemic. Multiple complete genotype II genome sequences have been reported from European, Russian and Chinese virus isolates but no complete genome sequences have yet been reported from Africa. We report herein the complete genome of a Tanzanian genotype II isolate, Tanzania/Rukwa/2017/1, collected in 2017 and determined using an Illumina short read strategy. The Tanzania/Rukwa/2017/1 sequence is 183,186 bp in length (in a single contig) and contains 188 open reading frames. Considering only un-gapped sites in the pairwise alignments, the new sequence has 99.961% identity with the updated Georgia 2007/1 reference isolate (FR682468.2), 99.960% identity with Polish isolate Pol16_29413_o23 (MG939586) and 99.957% identity with Chinese isolate ASFV-wbBS01 (MK645909.1). This represents 73 single nucleotide polymorphisms (SNPs) relative to the Polish isolate and 78 SNPs with the Chinese genome. Phylogenetic analysis indicated that Tanzania/Rukwa/2017/1 clusters most closely with Georgia 2007/1. The majority of the differences between Tanzania/Rukwa/2017/1 and Georgia 2007/1 genotype II genomes are insertions/deletions (indels) as is typical for ASFV. The indels included differences in the length and copy number of the terminal multicopy gene families, MGF 360 and 110. The Rukwa2017/1 sequence is the first complete genotype II genome from a precisely mapped locality in Africa, since the exact origin of Georgia2007/1 is unknown. It therefore provides baseline information for future analyses of the diversity and phylogeography of this globally important genetic sub-group of ASF viruses.

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Live Attenuated African Swine Fever Viruses as Ideal Tools to Dissect the Mechanisms Involved in Cross-Protection

Viruses ◽

10.3390/v12121474 ◽

2020 ◽

Vol 12 (12) ◽

pp. 1474

Author(s):

Elisabeth Lopez ◽

Juanita van Heerden ◽

Laia Bosch-Camós ◽

Francesc Accensi ◽

Maria Jesus Navas ◽

...

Keyword(s):

Vaccine Development ◽

African Swine Fever Virus ◽

Virulent Strain ◽

Sequence Similarity ◽

Clinical Signs ◽

African Swine Fever ◽

Cross Protection ◽

Sub Saharan Africa ◽

Genotype I ◽

Genotype Ii

African swine fever (ASF) has become the major threat for the global swine industry. Furthermore, the epidemiological situation of African swine fever virus (ASFV) in some endemic regions of Sub-Saharan Africa is worse than ever, with multiple virus strains and genotypes currently circulating in a given area. Despite the recent advances on ASF vaccine development, there are no commercial vaccines yet, and most of the promising vaccine prototypes available today have been specifically designed to fight the genotype II strains currently circulating in Europe, Asia, and Oceania. Previous results from our laboratory have demonstrated the ability of BA71∆CD2, a recombinant LAV lacking CD2v, to confer protection against homologous (BA71) and heterologous genotype I (E75) and genotype II (Georgia2007/01) ASFV strains, both belonging to same clade (clade C). Here, we extend these results using BA71∆CD2 as a tool trying to understand ASFV cross-protection, using phylogenetically distant ASFV strains. We first observed that five out of six (83.3%) of the pigs immunized once with 106 PFU of BA71∆CD2 survived the tick-bite challenge using Ornithodoros sp. soft ticks naturally infected with RSA/11/2017 strain (genotype XIX, clade D). Second, only two out of six (33.3%) survived the challenge with Ken06.Bus (genotype IX, clade A), which is phylogenetically more distant to BA71∆CD2 than the RSA/11/2017 strain. On the other hand, homologous prime-boosting with BA71∆CD2 only improved the survival rate to 50% after Ken06.Bus challenge, all suffering mild ASF-compatible clinical signs, while 100% of the pigs immunized with BA71∆CD2 and boosted with the parental BA71 virulent strain survived the lethal challenge with Ken06.Bus, without almost no clinical signs of the disease. Our results confirm that cross-protection is a multifactorial phenomenon that not only depends on sequence similarity. We believe that understanding this complex phenomenon will be useful for designing future vaccines for ASF-endemic areas.

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BA71ΔCD2: a New Recombinant Live Attenuated African Swine Fever Virus with Cross-Protective Capabilities

Journal of Virology ◽

10.1128/jvi.01058-17 ◽

2017 ◽

Vol 91 (21) ◽

Cited By ~ 51

Author(s):

Paula L. Monteagudo ◽

Anna Lacasta ◽

Elisabeth López ◽

Laia Bosch ◽

Javier Collado ◽

...

Keyword(s):

African Swine Fever Virus ◽

African Swine Fever ◽

Fever Virus ◽

Sub Saharan Africa ◽

Swine Industry ◽

Lethal Challenge ◽

Major Threat ◽

Attenuated Viruses ◽

Genotype Ii

ABSTRACT African swine fever is a highly contagious viral disease of mandatory declaration to the World Organization for Animal Health (OIE). The lack of available vaccines makes its control difficult; thus, African swine fever virus (ASFV) represents a major threat to the swine industry. Inactivated vaccines do not confer solid protection against ASFV. Conversely, live attenuated viruses (LAV), either naturally isolated or obtained by genetic manipulation, have demonstrated reliable protection against homologous ASFV strains, although little or no protection has been demonstrated against heterologous viruses. Safety concerns are a major issue for the use of ASFV attenuated vaccine candidates and have hampered their implementation in the field so far. While trying to develop safer and efficient ASFV vaccines, we found that the deletion of the viral CD2v (EP402R) gene highly attenuated the virulent BA71 strain in vivo. Inoculation of pigs with the deletion mutant virus BA71ΔCD2 conferred protection not only against lethal challenge with the parental BA71 but also against the heterologous E75 (both genotype I strains). The protection induced was dose dependent, and the cross-protection observed in vivo correlated with the ability of BA71ΔCD2 to induce specific CD8+ T cells capable of recognizing both BA71 and E75 viruses in vitro. Interestingly, 100% of the pigs immunized with BA71ΔCD2 also survived lethal challenge with Georgia 2007/1, the genotype II strain of ASFV currently circulating in continental Europe. These results open new avenues to design ASFV cross-protective vaccines, essential to fight ASFV in areas where the virus is endemic and where multiple viruses are circulating. IMPORTANCE African swine fever virus (ASFV) remains enzootic in most countries of Sub-Saharan Africa, today representing a major threat for the development of their swine industry. The uncontrolled presence of ASFV has favored its periodic exportation to other countries, the last event being in Georgia in 2007. Since then, ASFV has spread toward neighboring countries, reaching the European Union's east border in 2014. The lack of available vaccines against ASFV makes its control difficult; so far, only live attenuated viruses have demonstrated solid protection against homologous experimental challenges, but they have failed at inducing solid cross-protective immunity against heterologous viruses. Here we describe a new LAV candidate with unique cross-protective abilities: BA71ΔCD2. Inoculation of BA71ΔCD2 protected pigs not only against experimental challenge with BA71, the virulent parental strain, but also against heterologous viruses, including Georgia 2007/1, the genotype II strain of ASFV currently circulating in Eastern Europe.

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Biological characterization of African swine fever virus genotype II strains from north-eastern Estonia in European wild boar

Transboundary and Emerging Diseases ◽

10.1111/tbed.12614 ◽

2017 ◽

Vol 64 (6) ◽

pp. 2034-2041 ◽

Cited By ~ 41

Author(s):

I. Nurmoja ◽

A. Petrov ◽

C. Breidenstein ◽

L. Zani ◽

J. H. Forth ◽

...

Keyword(s):

Wild Boar ◽

African Swine Fever Virus ◽

African Swine Fever ◽

Fever Virus ◽

Biological Characterization ◽

Virus Genotype ◽

European Wild Boar ◽

North Eastern ◽

Genotype Ii

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Newly emerged African swine fever virus strain Belgium/Etalle/wb/2018: Complete genomic sequence and comparative analysis with reference p72 genotype II strains

Transboundary and Emerging Diseases ◽

10.1111/tbed.13302 ◽

2019 ◽

Vol 66 (6) ◽

pp. 2566-2591 ◽

Cited By ~ 7

Author(s):

Gautier Gilliaux ◽

Mutien Garigliany ◽

Alain Licoppe ◽

Julien Paternostre ◽

Christophe Lesenfants ◽

...

Keyword(s):

Comparative Analysis ◽

Virus Strain ◽

Genomic Sequence ◽

African Swine Fever Virus ◽

African Swine Fever ◽

Fever Virus ◽

Complete Genomic Sequence ◽

Genotype Ii ◽

Complete Genomic

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In vitro inhibition of African swine fever virus-topoisomerase II disrupts viral replication

Antiviral Research ◽

10.1016/j.antiviral.2016.08.021 ◽

2016 ◽

Vol 134 ◽

pp. 34-41 ◽

Cited By ~ 16

Author(s):

Ferdinando B. Freitas ◽

Gonçalo Frouco ◽

Carlos Martins ◽

Alexandre Leitão ◽

Fernando Ferreira

Keyword(s):

Viral Replication ◽

Topoisomerase Ii ◽

African Swine Fever Virus ◽

African Swine Fever ◽

Fever Virus ◽

In Vitro Inhibition

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Subunit Vaccine Approaches for African Swine Fever Virus

Vaccines ◽

10.3390/vaccines7020056 ◽

2019 ◽

Vol 7 (2) ◽

pp. 56 ◽

Cited By ~ 13

Author(s):

Natasha N. Gaudreault ◽

Juergen A. Richt

Keyword(s):

Western Europe ◽

African Swine Fever Virus ◽

African Swine Fever ◽

Fever Virus ◽

Swine Industry ◽

Fatal Disease ◽

The Caucasus ◽

Caucasus Region ◽

Highly Virulent ◽

Genotype Ii

African swine fever virus (ASFV) is the cause of a highly fatal disease in swine, for which there is no available vaccine. The disease is highly contagious and poses a serious threat to the swine industry worldwide. Since its introduction to the Caucasus region in 2007, a highly virulent, genotype II strain of ASFV has continued to circulate and spread into Eastern Europe and Russia, and most recently into Western Europe, China, and various countries of Southeast Asia. This review summarizes various ASFV vaccine strategies that have been investigated, with focus on antigen-, DNA-, and virus vector-based vaccines. Known ASFV antigens and the determinants of protection against ASFV versus immunopathological enhancement of infection and disease are also discussed.

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Identification and Isolation of Two Different Subpopulations Within African Swine Fever Virus Arm/07 Stock

Vaccines ◽

10.3390/vaccines8040625 ◽

2020 ◽

Vol 8 (4) ◽

pp. 625

Author(s):

Daniel Pérez-Núñez ◽

Eva Castillo-Rosa ◽

Gonzalo Vigara-Astillero ◽

Raquel García-Belmonte ◽

Carmina Gallardo ◽

...

Keyword(s):

Vaccine Development ◽

African Swine Fever Virus ◽

African Swine Fever ◽

Fever Virus ◽

Single Mutation ◽

High Sequence Identity ◽

Genotype I ◽

High Coverage ◽

Purification Method

No efficient vaccines exist against African swine fever virus (ASFV), which causes a serious disease in wild boars and domestic pigs that produces great industrial and ecological concerns worldwide. An extensive genetic characterization of the original ASFV stocks used to produce live attenuated vaccine (LAV) prototypes is needed for vaccine biosecurity and control. Here, we sequenced for the first time the Arm/07 stock which was obtained from an infected pig during the Armenia outbreak in 2007, using an improved viral dsDNA purification method together with high coverage analysis. There was unexpected viral heterogeneity within the stock, with two genetically distinct ASFV subpopulations. The first, represented by the Arm/07/CBM/c2 clone, displayed high sequence identity to the updated genotype II Georgia 2007/1, whereas the second (exemplified by clone Arm/07/CBM/c4) displayed a hemadsorbing phenotype and grouped within genotype I based on a central region conserved among all members of this group. Intriguingly, Arm/07/CBM/c4 contained a unique EP402R sequence, produced by a single mutation in the N-terminal region. Importantly, Arm/07/CBM/c4 showed in vitro features of attenuated strains regarding innate immune response pathway. Both Arm/07/CBM/c2 and c4 represent well-characterized viral clones, useful for different molecular and virus-host interaction studies, including virulence studies and vaccine development.

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