Habitat-Host-Vector Interactions of Ornithodoros turicata Dugès (Ixodida: Argasidae) in Texas, USA.

Abstract

Ticks (Class Arachnida: Order Ixodida) are obligatory ectoparasites with diverse vertebrate host groups and vectors of more than 35 human and zoonotic pathogens, which causes untold economic damages. For the past several decades, applications of ecological principles based on tick-host-pathogen interactions have led to the development of effective and efficient tick surveillance and control. However, the progression in tick ecological studies has been largely in Ixodid and not in Argasid ticks. Ornithodoros turicata Dugès (Ixodida: Argasidae) is well established as a vector and reservoir of Borrelia turicatae, the causative agent of Tick-Borne Relapsing Fever. Furthermore, O. turicata is capable of transmitting African swine fever virus, an acute hemorrhagic disease of swine with global implications. Nevertheless, the ecology of O. turicata is poorly understood. The studies conducted in this dissertation determined the O. turicata habitat-host-vector interactions in TX via field observations at the cave environments, immunoassays of O. turicata challenge host sera, and two types of bloodmeal analysis techniques.

The O. turicata habitat studies were conducted in 2015-2016 at the caves of Government Canyon State Natural State Area, TX. The study revealed that O. turicata are active year around with peak activities in the months of June and August. Moreover, the relative humidity and temperature profiles among four O. turicata-active caves in GCSNA remain similar in their values and pattern changes throughout the year. Also, activities of 20 vertebrate animals species, of which only seven were the previously known hosts of O. iii turicata, were noted. There were no correlations among the O. turicata phenology and relative humidity nor animal activities. However, there were significant correlations between O. turicata phenology and temperatures throughout the year.

The enzyme-linked immunosorbent assays of O. turicata challenged domestic pig sera against O. turicata salivary gland extract (SGE) showed a significant increase in the production of immunoglobulin G (IgG) production against SGE as early as three weeks post-challenge. Up to 8,000 fold increase in IgG production in some of the O. turicata challenged pigs were observed. Western blot showed post challenge pig sera began reacting with SGE protein(s), size 25kDa, starting three weeks post-challenge.

The bloodmeal analyses of O. turicata fed on chicken, goat, and swine blood using a qPCR method showed that O. turicata could retain cytochrome b (cytb) genes of hosts beyond 330 days through multiple molting. Also, the qPCR-based bloodmeal analyses could discern ctyb genes of multiple hosts if O. turicata had taken bloodmeals from multiple hosts. The bloodmeal analyses based on stable isotopic ratios of Carbon (δ¹³C) and Nitrogen (δ¹⁵N) in O. turicata generated unique δ¹³C and δ¹⁵N signatures based on the host blood consumed. However, the stable isotope analyses were not able to discern O. turicata which acquired multiple host bloodmeals.