Soft Ticks and Associated Pathogens: Acquiring Knowledge to Advance in Their Control

A special issue of Pathogens (ISSN 2076-0817). This special issue belongs to the section "Ticks".

Deadline for manuscript submissions: closed (31 January 2023) | Viewed by 8025

Special Issue Editors


E-Mail Website1 Website2
Guest Editor
Departamento de Desarrollo Sostenible de Sistemas Agroforestales y Ganaderos IRNASA, CSIC, Salamanca, Spain
Interests: tick physiology; tick-host relationships; tick vaccines
Parasitology Laboratory, Institute of Natural Resources and Agrobiology (IRNASA, CSIC), Cordel de Merinas 40-52, 37008 Salamanca, Spain
Interests: molecular parasitology and omics technologies; host-parasite interactions; vaccine development for tick control

Special Issue Information

Dear Colleagues,

Ticks are classified into two main families, the Argasidae (soft ticks) and Ixodidae (hard ticks), which differ in numerous anatomical, biological, and ecological characteristics. New argasid species have recently been described, but soft ticks show much lower species diversity than hard ticks (∼200 vs. ∼700), while their systematics is less clearly established than that of ixodids and remains a controversial issue.

The typical nidicolous/endophilic lifestyle and short blood feeding duration of soft ticks helps them pass generally unnoticed, such that their impact in public and animal health is generally underestimated. However, they can cause severe direct injury to their hosts and, more notably, are efficient reservoirs and vectors of numerous pathogens including important viruses, such as the African swine fever virus, Borrelia spp. spirochetes that cause human relapsing fever, fowl spirochetosis, and bovine abortion, and an increasing range of pathogenic rickettsiae. In addition to known pathogens, modern molecular tools are discovering new, emerging species, or strains of microbes whose pathogenic potential needs to be investigated.

Successful control of argasids and their transmitted pathogens requires deep knowledge of the ecology and biology of these ticks, from the molecular to the ecosystem level. Accurate knowledge of the distribution and dynamics of argasids is important to define risk areas for argasid-borne diseases and to establish adequate control measures. In this context, tick surveillance emerges as a permanent need, which, in turn, may help the development of predictive distribution models for argasids.

Control of argasid populations with chemical acaricides is inefficient and this has encouraged the development of alternative control methods, among which tick vaccines are considered the most promising. System biology and vacunomics approaches are increasingly being applied to argasids to know the molecules and biological processes involved in tick physiology and tick–host–pathogen relationships, and to identify antigen targets for vaccine development. Additionally, investigation of soft tick microbiomes, which are still unexplored, will reveal the function and influence of such microbial communities on vector biology including vector competence, likely opening new ways to transmission-blocking vaccine development.

The aim of this Special Issue is to update and deepen the knowledge related to soft ticks and their associated pathogens.

Dr. Ricardo Pérez-Sánchez
Dr. Ana Oleaga
Guest Editors

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Keywords

  • eco-epidemiology
  • distribution
  • surveillance
  • life cycle
  • Argasid-host interphase
  • Argasid-borne pathogens
  • African swine fever
  • human relapsing fever
  • microbiome
  • anti-argasid vaccines

Published Papers (3 papers)

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Research

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21 pages, 1932 KiB  
Article
First Data on Ornithodoros moubata Aquaporins: Structural, Phylogenetic and Immunogenic Characterisation as Vaccine Targets
by Ricardo Pérez-Sánchez, Ana Laura Cano-Argüelles, María González-Sánchez and Ana Oleaga
Pathogens 2022, 11(6), 694; https://doi.org/10.3390/pathogens11060694 - 16 Jun 2022
Cited by 2 | Viewed by 2538
Abstract
Ornithodoros moubata transmits African swine fever and human relapsing fever in Africa. The elimination of O. moubata populations from anthropic environments is expected to improve the prevention and control of these diseases. Tick vaccines have emerged as a sustainable method for tick control, [...] Read more.
Ornithodoros moubata transmits African swine fever and human relapsing fever in Africa. The elimination of O. moubata populations from anthropic environments is expected to improve the prevention and control of these diseases. Tick vaccines have emerged as a sustainable method for tick control, and tick aquaporins (AQPs) are promising targets for tick vaccines due to their vital functions, immunogenicity and ease of access by neutralising host antibodies. This study aimed at the systematic identification of the AQPs expressed by O. moubata (OmAQPs) and their characterisation as vaccine targets. Therefore, AQP coding sequences were recovered from available transcriptomic datasets, followed by PCR amplification, cloning, sequence verification and the analysis of the AQP protein structure and epitope exposure. Seven OmAQPs were identified and characterised: six were aquaglyceroporins, and one was a water-specific aquaporin. All of these were expressed in the salivary glands and midgut and only three in the coxal glands. Epitope exposure analysis identified three extracellular domains in each AQP, which concentrate overlapping B and T cell epitopes, making them interesting vaccine targets. Based on these domain sequences, a set of ten antigenic peptides was designed, which showed adequate properties to be produced and tested in pilot vaccine trials. Full article
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Review

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28 pages, 5881 KiB  
Review
Mating, Sperm Transfer and Oviposition in Soft Ticks (Acari: Argasidae), a Review
by Julian G. Shepherd
Pathogens 2023, 12(4), 582; https://doi.org/10.3390/pathogens12040582 - 12 Apr 2023
Cited by 2 | Viewed by 1689
Abstract
This review addresses the physiology and behavioral events involved in the reproduction of soft ticks (family Argasidae), with special attention to the events of their adult life: mating, sperm transfer and egg-laying. Many of these aspects are held in common with hard ticks, [...] Read more.
This review addresses the physiology and behavioral events involved in the reproduction of soft ticks (family Argasidae), with special attention to the events of their adult life: mating, sperm transfer and egg-laying. Many of these aspects are held in common with hard ticks, but the repeated short duration of feeding bouts in soft ticks, in contrast to the extended single engorgements of hard ticks, has consequences peculiar to soft tick reproduction. Reviewed are the dramatic external mechanism of sperm transfer, the unusual maturation and unique morphology and motility of the spermatozoa, the mechanism of oogenesis and its hormonal control, the mystery of fertilization, the involvement of pheromones in mating, the control of reproductive arrests and the vertical transmission of symbiotes in reproduction. Jumping-off points for further investigation are discussed throughout. Full article
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22 pages, 1583 KiB  
Review
An Updated Review of Ornithodoros Ticks as Reservoirs of African Swine Fever in Sub-Saharan Africa and Madagascar
by Ferran Jori, Armanda Bastos, Fernando Boinas, Juanita Van Heerden, Livio Heath, Hélène Jourdan-Pineau, Beatriz Martinez-Lopez, Rémi Pereira de Oliveira, Thomas Pollet, Carlos Quembo, Keaton Rea, Edgar Simulundu, Florian Taraveau and Mary-Louise Penrith
Pathogens 2023, 12(3), 469; https://doi.org/10.3390/pathogens12030469 - 16 Mar 2023
Cited by 3 | Viewed by 2909
Abstract
This updated review provides an overview of the available information on Ornithodoros ticks as reservoirs and biological vectors of the ASF virus in Africa and Indian Ocean islands in order to update the current knowledge in this field, inclusive of an overview of [...] Read more.
This updated review provides an overview of the available information on Ornithodoros ticks as reservoirs and biological vectors of the ASF virus in Africa and Indian Ocean islands in order to update the current knowledge in this field, inclusive of an overview of available methods to investigate the presence of ticks in the natural environment and in domestic pig premises. In addition, it highlights the major areas of research that require attention in order to guide future investigations and fill knowledge gaps. The available information suggests that current knowledge is clearly insufficient to develop risk-based control and prevention strategies, which should be based on a sound understanding of genotype distribution and the potential for spillover from the source population. Studies on tick biology in the natural and domestic cycle, including genetics and systematics, represent another important knowledge gap. Considering the rapidly changing dynamics affecting the African continent (demographic growth, agricultural expansion, habitat transformation), anthropogenic factors influencing tick population distribution and ASF virus (ASFV) evolution in Africa are anticipated and have been recorded in southern Africa. This dynamic context, together with the current global trends of ASFV dissemination, highlights the need to prioritize further investigation on the acarological aspects linked with ASF ecology and evolution. Full article
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