Testosterone Reduces the Resistance of Ticks

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Testosterone Reduces the Resistance of Ticks

• Audrey Cavan
• Biology Department
• Eastern Connecticut State University

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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. 2001.
  Parasitology. 87 49-54.

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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

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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

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Testosterone

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

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Purpose of Study

• To find out
• if testosterone reduced resistance in the host
• if repeated infestations would induce resistance
  to tick feeding

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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

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Mean Testosterone in Mice During Infestation
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Mean Testosterone in Voles During Infestation
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Host Resistance to Tick Feeding

• Percent of engorgement
• Percent of ticks attached (N/S)
• Mean engorged weight (N/S)

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Host Resistance
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Host Resistance
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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

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Conclusions

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

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