Transmission of the relapsing fever spirochete, Borrelia miyamotoi, by single transovarially-infected larval Ixodes scapularis ticks

Abstract

The relapsing fever spirochete, Borrelia miyamotoi, is increasingly recognized as a cause of human illness (hard tick-borne relapsing fever) in the United States. We previously demonstrated that single nymphs of the blacklegged tick, Ixodes scapularis, can transmit B. miyamotoi to experimental hosts. However, two recent epidemiological studies from the Northeastern United States indicate that human cases of hard tick-borne relapsing fever peak during late summer, after the spring peak for nymphal tick activity but coincident with the peak seasonal activity period of larval ticks in the Northeast. These epidemiological findings, together with evidence that B. miyamotoi can be passed from infected I. scapularis females to their offspring, suggest that bites by transovarially-infected larval ticks can be an important source of human infection. To demonstrate experimentally that transovarially-infected larval I. scapularis ticks can transmit B. miyamotoi, outbred Mus musculus CD1 mice were exposed to 1 or 2 potentially infected larvae. Individual fed larvae and mouse blood taken 10 d after larvae attached were tested for presence of B. miyamotoi DNA, and mice also were examined for seroreactivity to B. miyamotoi 8 wk after tick feeding. We documented B. miyamotoi DNA in blood from 13 (57%) of 23 mice exposed to a single transovarially-infected larva and in 5 (83%) of 6 mice exposed to two infected larvae feeding simultaneously. All 18 positive mice also demonstrated seroreactivity to B. miyamotoi. Of the 11 remaining mice without detectable B. miyamotoi DNA in their blood 10 d after infected larvae attached, 7 (64%) had evidence of spirochete exposure by serology 8 wk later. Because public health messaging for risk of exposure to Lyme disease spirochetes focuses on nymphal and female I. scapularis ticks, our finding that transovarially-infected larvae effectively transmit B. miyamotoi should lead to refined tick-bite prevention messages.

Immunoproteomic analysis of Borrelia miyamotoi for the identification of serodiagnostic antigens

“…larvae or nymphs) that originated from naturally infected female ticks collected in Minnesota that passed infection to their offspring. The tick feeding protocol was previously described 38 followed by serum collection at 8 or 40 dpi. Serum from two CD-1 mice infested with nymphal B .…”

Isolation of Borrelia miyamotoi and other Borreliae using a modified BSK medium

“…As shown previously for B. burgdorferi, differences in medium composition can significantly affect downstream experiments, due to the loss of plasmids 26 . Towards this end, B. miyamotoi and B. mayonii strains isolated in primary culture, using BSK-R, were used to successfully establish infection in CD1 or SCID mice via subcutaneous infection [27][28][29][30][31][32][33] . Borrelia mayonii infected CD1 mice also supported infection of I. scapularis via feeding 32 .…”

“…Borrelia mayonii infected CD1 mice also supported infection of I. scapularis via feeding 32 . Prior publications referred to BSK-R as either modified BSK or modified BSK-II 11,15,16,[27][28][29][30][31][32][33][34][35][36][37][38][39][40] .…”

Examining Prevalence and Diversity of Tick-Borne Pathogens in Questing Ixodes pacificus Ticks in California

“…B. miyamotoi is known to be vertically transmitted in I. scapularis (18,19), has been observed in I. pacificus larvae (36), and is able to infect small mammals that ticks feed on (18,25,36,37). It is unclear whether infection dynamics in natural populations require amplification by horizontal transmission from the vertebrate hosts.…”