Richard S. Ostfeld
Institute of Ecosystem Studies

Collaborators: Felicia Keesing (IES and Bard College) and Kathleen LoGiudice (IES and Union College).

Lyme disease is caused by a spirochete bacterium, Borrelia burgdorferi. This bacterium is transmitted to humans during blood meals taken by infected ixodid ticks on human hosts. Several ixodid tick species can transmit the disease; in eastern and central North America the primary vector is the blacklegged tick, Ixodes scapularis. Larval ticks hatch uninfected and are not initially dangerous to humans. If they feed on an infected host during their larval blood meal, they can become infected and later transmit Lyme bacteria to people. Whether a larval tick will acquire an infection and thus molt into an infected nymph depends largely on the species of host on which it feeds. Different species of tick hosts tend to have different probabilities of transmitting an infection to a feeding tick. In eastern and central North America, the host most likely to transmit an infection to a feeding tick is the white-footed mouse (Peromyscus leucopus), which infects between 40% and 90% of feeding larvae. Eastern chipmunks (Tamias striatus) and shrews (Blarina brevicauda and Sorex spp.) tend to be moderately competent reservoirs for B. burgdorferi. Most other mammalian, avian, and reptilian hosts have a considerably lower reservoir competence.