Common North American ticks that infest horses have preferred attachment sites, a study in Oklahoma has found.
Kellee Sundstrom and her fellow researchers at Oklahoma State University said ticks are common on horses, but noted that recent publications describing equine tick infestations in North America are lacking.
To further understand attachment site preferences, the study team enrolled 88 horses from eight farms in the northeast of the state. The horses, comprising 26 males and 62 females, ranged in age from 1 to 23 years.
They were evaluated twice a month over a one-year period. Each horse was systematically inspected, from head to tail.
Attachment sites of ticks were recorded and all ticks were collected for identification of the species and stage.
A total of 2731 ticks were collected during the study.
In all, 84.1% of the horses — 74 of the 88 animals — were infested at one or more examinations. The median number of ticks found during examinations was three.
Five tick species were identified, including Amblyomma americanum (78.2% of all ticks), Ixodes scapularis (18.2%), Dermacentor albipictus brown variant (2.6%), Dermacentor variabilis (0.7%), and Amblyomma maculatum (0.3%).
Most ticks were adults (83.6%), but immature A. americanum, D. albipictus, and A. maculatum were occasionally recovered.
A. americanum were most often attached to the inguinal area (the underbelly), while I. scapularis and D. albipictus were most commonly found on the chest and axillary region (the area between a horse’s foreleg and chest).
Ticks were found on horses in every month of the year, with the largest number (638 ticks, or 23.4%) collected in May.
A. americanum, primarily immature, was the only tick recovered in September, while I. scapularis and D. albipictus predominated October through February, and both A. americanum and I. scapularis were common in March.
In the warmer months, April through August, A. americanum was the most common tick, followed by D. variabilis and A. maculatum.
“This research confirms that ticks common on horses in North America have attachment site preferences and that ticks infest horses in Oklahoma throughout the year, including during the winter,” the study team concluded.
The authors said that habitat may also have influenced the findings: Both A. americanum and I. scapularis prefer wooded habitat with dense understory, whereas D. variabilis and A. maculatum are more commonly found in open areas, overgrown fields, or meadows.
Tick control practices were not recorded for the horses in the study and likely varied between premises, but ticks were still commonly found, the authors noted.
“Although attachment site preferences for the species considered are broadly applicable, additional research is warranted to fully appreciate the risk all tick species in North America pose to equine health.
“As with small animals, horses may benefit from year-round tick control. Unfortunately, available options for equine tick control are limited, require frequent re-application, and may have safety concerns, suggesting tick infestations will continue to be a challenge for horse owners.”
The study team comprised Sundstrom, Megan Lineberry, Amber Grant, Kathryn Duncan, Michelle Ientile and Susan Little.
Sundstrom, K.D., Lineberry, M.W., Grant, A.N. et al. Equine attachment site preferences and seasonality of common North American ticks: Amblyomma americanum, Dermacentor albipictus, and Ixodes scapularis. Parasites Vectors 14, 404 (2021). https://doi.org/10.1186/s13071-021-04927-8