Assessment of the Geographic Distribution of Ornithodoros turicata (Argasidae): Climate Variation and Host Diversity

Abstract

Background: Ornithodoros turicata is a veterinary and medically important argasid tick that is recognized as a vector of the relapsing fever spirochete Borrelia turicatae and African swine fever virus. Historic collections of O. turicata have been recorded from Latin America to the southern United States. However, the geographic distribution of this vector is poorly understood in relation to environmental variables, their hosts, and consequently the pathogens they transmit.

Methodology: Localities of O. turicata were generated by performing literature searches, evaluating records from the United States National Tick Collection and the Symbiota Collections of Arthropods Network, and by conducting field studies. Maximum entropy species distribution modeling (Maxent) was used to predict the current distribution of O. turicata. Vertebrate host diversity and GIS analyses of their distributions were used to ascertain the area of shared occupancy of both the hosts and vector.

Conclusions and significance: Our results predicted previously unrecognized regions of the United States with habitat that may maintain O. turicata and could guide future surveillance efforts for a tick capable of transmitting high-consequence pathogens to human and animal populations.

Fig 1. Ornithodoros turicata localities generated from USNTC and SCAN reports, literature reviews, and field studies.

Localities in which a collection date was not recorded are represented by black circles. Blue, yellow, and red circles represent localities that were collected from 1800–1950, 1950–2000, and 2000-present, respectively.

Fig 2. Model predictions for the distribution of O. turicata based on current climate conditions: A) precipitation model, B) temperature model, C) full model, and D) top-five environmental variables model.

Probability of O. turicata classified into 5 categories: very high probability (red), high probability (orange), moderate probability (yellow), low probability (green), and very low probability (white).

Fig 3. Known (asterisk) and suspected (no mark) hosts of O. turicata ranked by the percentage of their distribution overlap with the estimated range (full model, > 20% probability range = 1,752,272 km²) of O. turicata.

Blue bars correspond to mammalian hosts, yellow bars to reptilian hosts, and the red bars to the single suspected avian host (burrowing owl, Athene cunicularia) whose range varies depending on their nesting phenology. Only hosts that had 5% or more overlap are included in this figure. Abbreviation code as in S3 Table where the complete list of hosts is included.

Fig 4. Environmental variables that may explain the gap between populations of O. turicata in Florida and Texas.

Shown are mean temperature of the wettest quarter (BIO8) (A), mean temperature of driest quarter (BIO9) (B), and precipitation of the driest quarter (BIO17) (C). The gradient of red to blue represents high to low temperatures (°C) (A–B). For the precipitation variable, a gradient of green to dark brown represents the amount of high to low precipitation (mm) (C).

Fig 5. Three response curves with only corresponding variables in the O. turicata model: A) mean temperature of the wettest quarter (BIO8), B) mean temperature of the driest quarter (BIO9), and C) precipitation of the driest quarter (BIO17).

Mean response of 10 Maxent runs (red) and the mean ± 1 standard deviation (yellow).