A Model for Experimental Exposure of Humans to Larval Ixodes scapularis Ticks

This protocol offers an effective method for a controlled exposure of humans to ticks. For research, the protocol can be used to study the human immune response to tick bites, as well as the development of diagnostics and preventions against tick-borne diseases. There were no published procedures for placing ticks on human research volunteers.

The challenge was to develop a system that allowed the ticks to feed for days while also being comfortable for the participants. This model contains the ticks for the duration of the feeding and allow the research participants to proceed with their daily activities with minor lifestyle adjustments. To begin, photocopy the three by three inch hydrocolloid containment dressing along the side of the measurement lines to create a measurement template.

Cut the photocopied template along the one inch line, and then the two inch line to create a two inch circle with a one inch center. Use this template to cut the non-adhesive foam dressing, creating a two inch circle with a one inch center. Use the same template to cut a two inch circle in the center of the four by four inch extra-thin hydrocolloid dressing.

Cut the hydrocolloid layer of the three by three inch containment dressing at the one and a half inch line. Pull back the paper liner of the hydrocolloid layer of the containment dressing to expose the adhesive. Place the cut foam dressing within the two inch circle of the adhesive.

To begin, create a visible field by placing a white sheet around the placement area. Use a four by four inch gauze pad dampened with clean water or saline to clean the skin of the placement site. Pat dry the site with clean gauze.

Take the prepared containment dressing and remove the adhesive liner from the hydrocolloid side. Affix the dressing to the skin at the placement site. Break the wooden swab in half to expose jagged ends.

Now, open the vial of ticks carefully. Use the jagged end of the wooden swab to transfer active ticks from the vial to the skin within the containment dressing. Then remove the adhesive liner from the mesh layer of the containment dressing, and close the mesh layer over the opening, ensuring the adhesive is securely attached.

Apply the prepared four by four inch extra-thin hydrocolloid dressing over the containment dressing for additional security. Provide a water barrier cover and two inch hypoallergenic tape to the research participant. Periodically check the adhesion of the dressing's edges to the skin.

Apply additional tape to reinforce the edges as needed. Puncture holes in the vial cap using a 20 gauge needle, if preservation of live ticks is necessary. Use nylon or polyester mesh and the cap to seal the vial.

Label the tick collection vials with the required identifiers. To maintain humidity, place the tick vial in a sealable bag with a moist sponge. Arrange white sheets around the bandage site.

Using alcohol wipes, carefully remove the bandage from the skin. Place the removed bandage in the collection basin and examine it for the presence of detached ticks. Assess the skin at the placement site for attached ticks.

Use fine-tip forceps to remove the attached ticks. In the first Human Xeno Diagnosis Study, a total of 43 procedures were conducted. When compared to the number of ticks placed the mean percentage of attached ticks recovery was approximately 45%