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.

Evaluation of Vector Competence of Ixodes Ticks for Kemerovo Virus

“…aegypti [ 20 ]. A comparative study of vector competence of different Ornithodoros species ( O. moubata , O. erraticus and O. verrucosus ) using several strains of ASFV showed variable infection rates depending on the tick–virus pairs assessed [ 21 ].…”

Disinfectants against African Swine Fever: An Updated Review

“…Regarding the variety of ASFV strains used to test the virucidal activity of chemical compounds, it emerged that these are limited to the use of genotype I and Vero-adapted ASFV strains such as the BA71V and Lisbon 60 strains. Few studies tested field ASFV strains [24,26,27,30,33,35] belonging to genotype I and II and only one study used a field ASFV belonging to genotype VIII [40]. Regarding the virulence and hemadsorption characteristics of the ASFV tested, no data is available.…”

Early Transcriptional Changes in the Midgut of Ornithodoros moubata after Feeding and Infection with Borrelia duttonii

“…In this context it is interesting to mention that Pereira De Oliveira et al observed higher susceptibility for ASFV infection in a long-time lab-reared colony of O. moubata compared to field collected Ornithodoros sp. [ 58 ]. They hypothesized that lab-reared ticks are highly inbred with fixed alleles and have a poor microbiome, resulting in a poorly stimulated or even immunologically naïve immune system compared to ticks collected from the field; (iii) represent non-coding RNA (ncRNA) sequences.…”