A Continuing Exploration of Tick-Virus Interactions Using Various Experimental Viral Infections of Hard Ticks

Potential mechanisms implied in tick infection by arboviruses and their transmission to vertebrate hosts

Ticks can transmit many pathogens, including arboviruses, to their vertebrate hosts. Arboviruses must overcome or evade defense mechanisms during their passage from the tick gut to the hemolymph, salivary glands, and the feeding site in the host skin. This review summarizes current knowledge of defense mechanisms in specific tick tissues and at the feeding site in the host skin. We discuss the possible roles of these defense mechanisms in viral infection and transmission. The responses of tick salivary proteins to arbovirus infection are also discussed. This review provides information that may help accelerate research on virus-tick interactions.

Ixodid Tick Dissection and Tick Ex Vivo Organ Cultures for Tick-Borne Virus Research

Tick-borne viruses cause thousands of cases of disease worldwide every year. Specific countermeasures to many tick-borne viruses are not commercially available. Very little is known regarding tick-virus interactions and increasing this knowledge can lead to potential targets for countermeasure development. Virus infection of ex vivo organ cultures from ticks can provide an approach to identify susceptible cell types of tissue to infection. Additionally, these organ cultures can be used for functional genomic studies to pinpoint tick-specific genes involved in the virus lifecycle. Provided here are step-by-step procedures to set up basic tick organ cultures in combination with virus infection and/or functional genomic studies. These procedures can be adapted for future use to characterize other tick-borne pathogen infections as well as tick-specific biological processes. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Loading 96-well plates with gelfoam substrate Basic Protocol 2: Step-by-step aseptic dissection of unfed female/male Ixodes scapularis ticks for multiple organs Basic Protocol 3: Step-by-step aseptic dissection of fed female Ixodes scapularis ticks to remove salivary glands Basic Protocol 4: Metabolic viability analyses of tick organ cultures Basic Protocol 5: Virus infection of tick organ cultures Basic Protocol 6: Functional RNA interference analyses using tick organ cultures.

The antiviral immunity of ticks against transmitted viral pathogens

Ticks, being obligate hematophagous arthropods, are exposed to various blood-borne pathogens, including arboviruses. Consequently, their feeding behavior can readily transmit economically important viral pathogens to humans and animals. With this tightly knit vector and pathogen interaction, the replication and transmission of tick-borne viruses (TBVs) must be highly regulated by their respective tick vectors to avoid any adverse effect on the ticks' biological development and viability. Knowledge about the tick-virus interface, although gaining relevant advances in recent years, is advancing at a slower pace than the scientific developments related to mosquito-virus interactions. The unique and complicated feeding behavior of ticks, compared to that of other blood-feeding arthropods, also limits the studies that would further elaborate the antiviral immunity of ticks against TBVs. Hence, knowledge of molecular and cellular immune mechanisms at the tick-virus interface, will further elucidate the successful viral replication of TBVs in ticks and their effective transmission to human and animal hosts.

De novo transcriptome sequencing and comparative profiling of the ovary in partially engorged and fully engorged Haemaphysalis flava ticks

Haemaphysalis flava is the vector of several pathogens and has medical and veterinary importance. Transcriptome information of the ovary of H. flava is unavailable and limits understanding of its molecular basis of reproduction. We studied the ovary transcriptome of partially engorged and fully engorged H. flava using high-throughput RNA sequencing technology. A total of 53,025,360 and 57,942,890 clean reads were obtained with 7.95 GB and 8.69 GB clean bases in partially engorged ticks (PETs) and fully engorged ticks (FETs), respectively. The clean reads were assembled into 138,711 unigenes. A total of 72,043 unigenes (51.93%) were annotated and 66,668 unigenes (48.07%) were unknown. A total of 38,487 differentially expressed genes (DEGs) were found between PET and FET with 19,031 upregulated genes and 19,456 downregulated genes. The RNA-seq results were validated by qRT-PCR, including six upregulated genes and three downregulated genes. Some unigenes coding for nutrient transporters, proteases, and protease inhibitors were found and analyzed. This study was the first time to perform the transcriptome sequences of the ovary of partially engorged and fully engorged H. flava. The results can benefit the understanding of the molecular basis of ovary maturation and oogenesis of the H. flava and boost the development of the strategies for control of H. flava.

Applications of artificial membrane feeding for ixodid ticks

Ticks are obligatory hematophagous ectoparasites that feed on a large variety of vertebrates. In the laboratory, animals (mainly mice and rabbits) are used to maintain tick colonies. However, the use of animals to rear ticks can be expensive and requires dedicated animal facilities. In addition, research institutions are committed to the principle of 3Rs (Replacement, Reduction and Refinement), which encourages the use of alternatives to animals when possible. The development of artificial membrane systems has provided an alternative to animals, at least for some tick species. Over the years, different modifications in artificial feeding systems have led to new applications, including acaricide testing, tick-pathogen interaction, and novel approaches to study tick physiology. Although artificial membrane feeding still has some limitations, the method can provide numerous advantages, including the standardization of acaricide treatments under controlled conditions, an alternative to animals for tick rearing, and reduction of cost associated with animals and animal housing facilities. In this review, we summarized the evolution of tick feeding membranes and their applications over time, explaining the modifications incorporated to study tick physiology, tick-pathogen interactions, and acaricide testing.