Testosterone Reduces the Resistance of Ticks Audrey Cavan Biology Department Eastern Connecticut State University

Testosterone Depresses Innate and Acquired Resistance to Ticks in Natural Rodent Hosts: A Force for Aggregated Distributions of Parasites Hughes, V. L. and S. E. Randolph Parasitology. 87:

Background Information Tick-borne diseases are common vector-borne illnesses in the U.S. –Lyme disease –Ehrlichioses –Babesioses How do ticks transmit diseases? Find host Attaches to host Saliva is passed to host –Pathogen is contained in saliva –Several hours for pathogen transmission –Enzymes

Ticks saliva provokes immune response in mice and voles Response caused by: Exchange of saliva –Host acquires resistance –Degree of resistance depends on exposure to tick feeding –Ticks respond by: Reduced feeding and /or reduced survival to next stage in development

Testosterone Mature males have high testosterone –Mice naturally have higher testosterone than voles Male hosts carry more ticks –Greater home range –High testosterone

Purpose of Study To find out: – if testosterone reduced resistance in the host –if repeated infestations would induce resistance to tick feeding

Testosterone manipulation Male rodents were castrated Implants of testosterone and oil were inserted 40 tick larvae Series of three infestations Measure host resistance to the ticks –Engorgement of the feeding ticks Testosterone levels measured

Mean Testosterone in Mice During Infestation

Mean Testosterone in Voles During Infestation

Host Resistance to Tick Feeding Percent of engorgement Percent of ticks attached (N/S) Mean engorged weight (N/S)

Host Resistance

Results: Testosterone – reduces resistance to tick feeding Ticks are more abundant on and more aggregated on mature male mice Ticks on sexually active males enjoy high feeding success and survival

Conclusions: Ticks enjoy feeding on hosts with high testosterone Repeated infestations induces a resistance against tick feeding