Can Lyme disease be transmitted to humans by mosquitoes, horse flies, and deer flies?

Although Borrelia burgdorferi-like organisms have been observed in mosquitoes, horse flies, and deer flies in areas where Lyme disease is endemic, these organisms have not been cultured to verify their identity. Experiments attempting to transmit B. burgdorferi from infected to uninfected laboratory animals by mosquitoes have not been successful (1). Furthermore, epidemiological studies have shown that the date of onset for Lyme disease occurs in June, coincident with the peak abundance of nymphal Ixodes scapularis ticks, and not during August when mosquitoes and other biting files are at peak abundance (2). Despite findings of B. burgdorferi in other tick species such as the American dog tick (Dermacentor variabilis) and the lone star tick (Amblyomma americanum) in the field, laboratory transmission studies have confirmed that these tick species cannot transmit the infection to laboratory animals; thus, they are not competent vectors for Lyme disease (3). Both experimental and epidemiological studies have shown that Ixodes scapularis and Ixodes pacificus are the only tick species in North America that are capable of transmitting B. burgdorferi, the spirochete that causes Lyme disease, to humans. Please consult the Lyme Disease Risk Assessment Map on the home page of the ALDF website ( for specific information on the incidence of Ixodes ticks as well as the numbers of reported cases of Lyme disease for individual States.


1. Magnarelli, LA, and Anderson, JF. J. Clin. Microbiol. 26: 1482-1486, 1988.

2. Falco, R.C., D.F. McKenna, T.J. Daniels, R.B. Nadelman, J. Nowakowski, D. Fish, and G.P. Wormser. Am. J. Epidemiol: 149: 771 -776, 1999.

3. Piesman, J. and Happ, CM. J. Med. Entomol. 34: 451-156, 1997.