exposing humans to larval ixodes scapularis to study host response to tickborne diseases and tick bites

Human Exposure to Larval Ticks for Tickborne Disease Research

Hard ticks (Ixodidae: Acari) are obligate blood-feeding ectoparasites that occur worldwide and are capable of transmitting a broad range of pathogens, including bacteria, viruses, and parasites, of major medical and veterinary importance. Ixodid ticks must remain attached to the host for days to complete a blood meal, and they have the capacity to stay attached to the skin while avoiding recognition, preventing local blood coagulation, and facilitating long-term feeding1,2,3. Animal studies have demonstrated that non-permissive hosts acquire resistance to tick bites with repeated tick exposures, which can lead to a decreased ability to transmit a pathogen, while ticks can repeatedly parasitize permissive hosts. Acquired tick resistance is dependent on the nature of the host immune response4,5,6,7.
Tickborne diseases are an increasing threat in the United States (US), with the number of reported cases more than doubling between 2004 and 20168,9. Due to climate change, the geographic ranges of different ticks continue to expand10,11. The leading tickborne diseases in the US include Lyme disease, anaplasmosis, ehrlichiosis, spotted fever rickettsiosis, babesiosis, tularemia, and Powassan virus disease8. Lyme disease, caused by infection with Borrelia burgdorferi sensu lato, is the most common tickborne disease in the US and Europe12. With approximately 476,000 individuals diagnosed with Lyme disease annually in the US, there is both a public health and economic burden to individuals and to society13,14,15.
Ixodes scapularis (the black-legged or deer tick) is the primary vector for Lyme disease, as well as anaplasmosis, babesiosis, Borrelia miyamotoi disease, and Powassan virus disease in the US. Other medically important tick species in the US include Amblyomma americanum (Lone star tick), Dermacentor variabilis (American dog tick), Ixodes pacificus (Western black-legged tick), Dermacentor andersoni (Rocky Mountain wood tick), Ixodes cookei (Groundhog tick), Dermacentor occidentalis (Pacific Coast tick), Rhipicephalus sanguineus (brown dog tick), and Amblyomma maculatum (Gulf Coast tick)16.
Developing a method to expose research volunteers to tick bites supports studies using the natural vector to search for evidence of infection, a procedure known as xenodiagnosis17,18,19,20,21, and to learn more about immunity induced by exposure to ticks, which can contribute to the discovery of an anti-tick vaccine5,6,7. The procedure described here was developed and used in the first human research study using laboratory-reared Ixodes scapularis larva for xenodiagnosis of B. burgdorferi infection after antibiotic therapy (NCT01143558), published in 201419. The system has been successfully used in a phase 2 study investigating whether a positive xenodiagnosis correlated with the persistence of symptoms after antibiotic treatment of Lyme disease (NCT02446626) and in a study exploring the host response to tick bites (NCT05036707).
This procedure protocol describes the process for creating the containment dressing, the tick placement procedure, and the tick removal procedure, as well as the site care needed to maintain the containment dressing. The details regarding the pathogen-free I. scapularis tick colony and tick exposure procedures used for the above-cited studies have been previously described19,22. This methodology offers a flexible research tool that can be adapted to studying different aspects of the human host response to tick bites, the effectiveness of tick prevention medications, as well as Lyme disease and other tickborne illnesses.

Author Spotlight: Controlled Human Exposure Model for Tick Research and Lyme Disease Studies

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 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.

Exposing Humans to Larval Ixodes scapularis to Study Host Response to Tickborne Diseases and Tick Bites

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 xenodiagnosis 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%

Research

JoVE Journal

Immunology and Infection

Tickborne diseases are a significant public health problem in the United States and worldwide. Ticks are obligate blood-feeding arthropods; an ixodid tick ...