Retrospective study of 103 presumed cases of tick (Ixodes holocyclus) envenomation in the horse.

This research article retrospectively examines 103 cases of suspected tick envenomation in horses. The study investigates several relevant factors, finding that horses older than 6 months and heavier than 100kg are more likely to die, and that administration of tick antiserum significantly increases survival rates.

Objective and Methodology

• The study retrospectively analyses records of 103 cases of suspected tick envenomation in horses, collected over time across various locations. This method involves looking back at existing data to draw conclusions.
• Various variables were taken into account, such as, breed, age, weight, presence of ticks on the horse, respiratory and gait scores, how long the horse was recumbent, treatment administered, ultimate outcome, and any complications that arose.
• The raw data went through a screening process with univariable tests, and then used in a more complex multivariable logistic regression model for analysis. This complicated statistical analysis is used to understand how the different variables interact and affect the outcome (the survival or death of the horse).

Results

• The horses came from various breeds, their ages ranged from 1 week to 18 years. Heavier and older horses showed higher mortality rates than younger, lighter ones.
• Incidence of cases was geographically spread from North Queensland to the central coast of New South Wales, and cases occurred more frequently in warmer months which is the typical breeding season for ticks.
• The number of ticks on a horse did not influence the survival rate, however, horses with higher respiratory distress were more likely to die.
• Horses that were recumbent, or laying down, for more than 120 hours post-presentation had a higher risk of death. This can be a sign of severe illness, exhaustion, or pain.
• Administration of tick antiserum at a dosage of more than 0.5 mL per kg of horse’s weight significantly improved the odds of survival.
• Overall, 74% of horses survived. The study also pointed out that complications occurred in around 35% of cases, suggesting that managing a recumbent horse poses challenges that could increase the odds of death.

Conclusion

• The researchers concluded that tick envenomation in horses generally follows the regional distribution of the tick species Ixodes holocyclus.
• They also concluded that administering more than 0.5 mL per kg of tick antiserum boosted survival rates. The complications linked with managing a recumbent horse increased the chance of the horse’s death.
• The study highlighted the limitations of their research due to small sample size and suggested that further research is necessary to draw more definitive conclusions.