Vector Blood Meals and Chagas Disease Transmission Potential, United States

Lori Stevens

, Patricia L. Dorn, Julia Hobson, Nicholas M. de la Rua, David E. Lucero, John H. Klotz, Justin O. Schmidt, and Stephen A. Klotz

Author affiliations: University of Vermont, Burlington, Vermont, USA (L. Stevens, J. Hobson, N.M. de la Rua, D.E. Lucero); Loyola University, New Orleans, Louisiana, USA (P. L. Dorn); Southwestern Biological Institute, Tucson, Arizona, USA (J.O. Schmidt); University of California, Riverside, California, USA (J.H. Klotz); University of Arizona, Tucson (S.A. Klotz)

Abstract

A high proportion of triatomine insects, vectors for Trypanosoma cruzi trypanosomes, collected in Arizona and California and examined using a novel assay had fed on humans. Other triatomine insects were positive for T. cruzi parasite infection, which indicates that the potential exists for vector transmission of Chagas disease in the United States.

Chagas disease is a vector-borne disease caused by Trypanosoma cruzi trypanosomes. Although these parasites are rarely transmitted by insects in the United States, there is concern that vector transmission may increase (1). Chagas disease, endemic to most of Latin America, can be transmitted to mammals by >130 species of blood-feeding insect vectors (subfamily Triatominae). In the United States, the most common result of a triatomine bite is allergic reaction, including anaphylaxis, elicited in sensitized persons (2). Despite only 7 cases of vector transmission to humans reported in the United States (3,4), T. cruzi trypanosomes are present in >20 wildlife species. In Latin America, 8–10 million persons are infected with these parasites (5), and an estimated 300,000 of the ≈13 million persons from disease-endemic areas now living in the United States carry the parasite (6). Although vector transmission of T. cruzi trypanosomes is a minimal risk, 9 of the 11 triatomine species in the United States are potential vectors (1,7), and parasite transmission could increase because of climate change (1).
One critical aspect of transmission is parasite reservoirs; hence, the epidemiologic importance of identifying animal sources of the vectors’ blood meals, the likelihood of these vectors also feeding on humans, and their incidence of T. cruzi infection. Blood meals consumed by insect vectors have been detected by using several molecular techniques (8), but assays are challenging because of degradation of the blood in the vector’s gut, PCR inhibition, the often small size of a blood meal, and the difficulty of distinguishing multiple blood meals. We analyzed T. cruzi vectors collected in California and Arizona by using a novel technique— cloning following PCR amplification using universal vertebrate primers—to determine the source of blood meals and indicate the likelihood of parasite transmission to humans.