Na-ASP-2 is a protein expressed during the larval stage of the N. americanus hookworm life cycle. In a clinical study in previously hookworm-infected adults in Brazil, this protein induced urticarial reactions (rash) in a subset of volunteers. The clinical trial component of this study involves skin testing for immediate-type hypersensitivity to the Na-ASP-2 Antigen. Both prick-puncture and intradermal tests will be applied.

The clinical testing of the Na-ASP-2 Skin Test Reagent to detect Immediate-type hypersensitivity to the Na-ASP-2 hookworm antigen will be conducted as part of a larger, on-going observational study of the prevalence and intensity of hookworm infection currently underway in Brazil. Eligible adult participants (ages 18-45 years) in this observational study will be invited to undergo the skin testing procedure. Skin testing will only be performed if they agree and sign the supplemental informed consent form for this skin testing procedure.

• Study site: Americaninhas Vaccine Center, Americaninhas, Minas Gerais, Brazil

• Number of participants to be skin tested: approximately 150 adults

• Duration of the skin testing procedures: up to 1 month; each participant will undergo skin testing and a follow-up blood collection 21+/-7 days after skin testing.

• Each participant will have both skin prick-puncture and intradermal skin tests applied on the same study day. The prick-puncture and intradermal tests will be applied sequentially to the volar aspects of the participant's forearms:

  1. Skin prick-puncture: three different concentrations of Na-ASP-2 solution (10, 100, and 1000 μg/mL) will be applied sequentially in duplicate, to the left forearm.
  2. Intradermal: one concentration of Na-ASP-2 (100 μg/mL) will be injected, in duplicate, to the right forearm.
  3. Allergen diluent and histamine solutions will be utilized as the negative and positive controls, respectively, for both the skin prick-puncture and intradermal tests.
  4. Participants will be observed in the study clinic for at least 30 minutes following application of the skin tests, and will be examined 2 and 7 days following skin testing.
  5. Sizes of the wheal and erythema reactions for each application will be recorded and graded in comparison to the histamine positive control reaction.

• Each participant will have blood collected via venipuncture (a maximum of 25 mL) immediately prior to application of the skin tests, and between 2 and 4 weeks after skin testing, in order to measure antibodies (particularly IgG and IgE) to Na-ASP-2 using an ELISA procedure.

Inclusion Criteria:

• Males and females between 6 and 45 years of age, inclusive, at the time of consenting to the parent study.
• Age greater than or equal to 18 years at the time of signing the supplemental informed consent document for the skin test procedure (parent study).
• Willingness to participate in the study as evidenced by signing the informed consent or assent document.

Exclusion Criteria:

• Inability to correctly answer all questions on the informed consent comprehension questionnaire.
• Attends school or works full-time outside of the study area.
• Behavioral, cognitive, or psychiatric disease that in the opinion of the investigator affects the ability of the volunteer to understand and cooperate with the study protocol.
• Other condition that in the opinion of the investigator would jeopardize the safety or rights of a volunteer to participate in the trial or would render the subject unable to comply with the protocol.
• Pregnancy as determined by a positive urine hCG test (if female).
• Use of corticosteroids (excluding topical or nasal) or immunosuppressive drugs within 30 days of planned skin test application.
• Extensive dermatitis precluding skin testing.
• Current use of a beta blocker (oral or topical) or anti-histamine medication. A volunteer may participate in the study if they agree to withhold use of an anti-histamine for at least 5 days prior to application of the skin test.
• Use of a tricyclic anti-depressant within the past month.