Asian long-horned tick distributions in Virginia pastures and evaluating the horn fly as a possible vector of Theileria orientalis Ikeda
| dc.contributor.author | Sharpe, Matthew Payne | en |
| dc.contributor.committeechair | Kuhar, Thomas P. | en |
| dc.contributor.committeemember | Currin, John Franklin | en |
| dc.contributor.committeemember | Eastwood, Gillian | en |
| dc.contributor.department | Entomology | en |
| dc.date.accessioned | 2026-01-06T09:00:11Z | en |
| dc.date.available | 2026-01-06T09:00:11Z | en |
| dc.date.issued | 2026-01-05 | en |
| dc.description.abstract | The Asian longhorned tick (Haemaphysalis longicornis) is an invasive ectoparasite of growing concern in the U.S. due to its role as the primary vector of the emerging cattle parasite, Theileria orientalis Ikeda. To better understand the transmission landscape in Virginia, this study first evaluated the fine-scale environmental drivers of H. longicornis density. Across two field seasons (2023–2024), 25,929 ticks were collected and analyzed using negative binomial generalized linear mixed models. Results indicated that vegetation height was the most consistent predictor of density, with short vegetation supporting significantly fewer ticks than medium-height vegetation. While relative humidity was positively associated with nymphal density, landscape features like distance to trees or water sources were not significant predictors. These findings suggest that fine-scale pasture management may be a viable tool for reducing tick populations. However, because T. orientalis outbreaks have been observed in regions with no or low tick density, investigating alternative transmission pathways is essential. To address this, the second phase of this study evaluated the potential for the horn fly (Haematobia irritans), the most economically significant fly pest of U.S. beef cattle, to act as a vector. A total of 2,365 horn flies (254 pools) were collected from nine Virginia counties and screened using conventional and quantitative PCR. T. orientalis Ikeda DNA was confirmed in flies from four counties (Augusta, Bland, Culpeper, and Nottoway), with remaining samples either negative or below the limit of detection. Collectively, these findings provide a comprehensive look at the ecology of T. orientalis in Virginia. While vegetation management remains a key strategy for controlling the primary tick vector, the detection of Ikeda DNA in horn flies provides the first evidence of this pathogen in a novel arthropod species. This suggests that horn flies may serve as vectors, highlighting a critical need for further experimental studies to determine their epidemiological significance in cattle health management. | en |
| dc.description.abstractgeneral | The Asian longhorned tick is an invasive species that was first detected in the U.S. on livestock in 2017 (retrospectively shown to be in the country since 2010) and has been rapidly spreading since. Although we are only beginning to fully understand the role of this invasive tick in transmitting pathogens to mammals, it has already shown to cause severe problems for livestock, particularly cattle. It is the only known organism to transmit a protozoan pathogen called Theileria orientalis Ikeda to cattle, which can cause them to become anemic, lose weight, become lethargic, and in rare cases cause death. On top of that, the tick can reproduce asexually, meaning one tick can start an entire population by themselves, a factor which has contributed to their rapid spread. Land managers are having a hard time managing these ticks, but this study offers data that may help them. This study collected ALT within cattle pastures in Virginia. Field collections were done several times over the summer of 2023 and 2024. A systematic collection enabled analyses aimed at predicting where in a pasture the ticks would be most likely to congregate according to certain physical and environmental conditions. The analyses showed that environmental variables such as vegetation height and relative humidity at ground level were important for predicting how many ticks would be in that area. In general, the ticks avoided shorter vegetation in favor of taller vegetation. This may seem like common knowledge, but we previously lacked hard data that backed up such assumptions. The presence of ticks was not influenced by proximity to trees or water, which was not expected, as proximity to trees and water are usually associated with higher relative humidity levels, which ticks are known to prefer. The second half of this study investigated the horn fly, a notable cattle pest in the U.S., as a possible alternative vector of T. orientalis. There are cases of T. orientalis Ikeda, where cattle are getting this disease despite no ALT being detected in the pasture. This implies that another organism could be responsible for transmission. Horn flies were chosen to be studied because, like ticks, they also feed on cattle blood, meaning that they could potentially feed on an infected cow and transmit the pathogen to a susceptible cow. This first step aimed to determine if the pathogen is present within horn flies that were feeding on cattle. Horn flies were collected from nine cattle farms in Virginia, some of which had a high rate of T. orientalis Ikeda within the herd. DNA was extracted from collected flies and tested for evidence of T. orientatlis by conventional PCR, and type confirmed via qPCR. Results showed that in four of the nine farms, T. orientalis Ikeda was present in the tested flies. This does not mean that horn flies are actively transmitting the disease, but it does show evidence of infection and lays the groundwork for a future study to examine vector competency. Results from subsequent studies could change the way that horn flies are managed on cattle farms and reveal why pastures without ticks are resulting in cattle contracting the disease. | en |
| dc.description.degree | Master of Science in Life Sciences | en |
| dc.format.medium | ETD | en |
| dc.identifier.other | vt_gsexam:45576 | en |
| dc.identifier.uri | https://hdl.handle.net/10919/140592 | en |
| dc.language.iso | en | en |
| dc.publisher | Virginia Tech | en |
| dc.rights | In Copyright | en |
| dc.rights.uri | http://rightsstatements.org/vocab/InC/1.0/ | en |
| dc.subject | Entomology | en |
| dc.subject | cattle | en |
| dc.subject | pest | en |
| dc.title | Asian long-horned tick distributions in Virginia pastures and evaluating the horn fly as a possible vector of Theileria orientalis Ikeda | en |
| dc.type | Thesis | en |
| thesis.degree.discipline | Entomology | en |
| thesis.degree.grantor | Virginia Polytechnic Institute and State University | en |
| thesis.degree.level | masters | en |
| thesis.degree.name | Master of Science in Life Sciences | en |
Files
Original bundle
1 - 1 of 1