The host-parasite relationship is an important and complex ecological interaction. Parasite load affects disease transfer and can influence host fitness. The specific objective of this research was to determine if the number of immature Dermacentor variabilis (American dog tick) is associated with gender, body size or habitat of its host Peromyscus leucopus (white-footed mouse).  Mice were live trapped in three night trapping sessions conducted on two permanent grids every other month from August 2006 to October 2007.  Grids were established in an old field and an early successional forest each with 104 sampling points. Mice were anesthetized, weighed, sexed and right hindfoot and tail length recorded.  Ticks were collected from mice, stored in ethanol, and identified to species. 
Results/Conclusions

Data were analyzed using a negative binomial regression. Gender and body size both had significant effects on tick load (P =0.012 and P =0.029, respectively). However, body size and gender were not significantly related with one another (P = 0.234).  Males were found to have higher mean number of immature D. variabilis  compared with females. This sex difference could be a result of a larger home range size or sex hormone production. Regardless of sex, body size has a positive effect on tick burden, possibly due to the increased surface area providing a greater attachment probability or greater metabolic demands causing the mouse to forage more extensively.