Pathogen transmission in relation to duration of attachment by Ixodes scapularis ticks

Abstract

The blacklegged tick, Ixodes scapularis, is the primary vector to humans in the eastern United States of the deer tick virus lineage of Powassan virus (Powassan virus disease); the protozoan parasite Babesia microti (babesiosis); and multiple bacterial disease agents including Anaplasma phagocytophilum (anaplasmosis), Borrelia burgdorferi and Borrelia mayonii (Lyme disease), Borrelia miyamotoi (relapsing fever-like illness, named Borrelia miyamotoi disease), and Ehrlichia muris eauclairensis (a minor causative agent of ehrlichiosis). With the notable exception of Powassan virus, which can be transmitted within minutes after attachment by an infected tick, there is no doubt that the risk of transmission of other I. scapularis-borne pathogens, including Lyme disease spirochetes, increases with the length of time (number of days) infected ticks are allowed to remain attached. This review summarizes data from experimental transmission studies to reinforce the important disease-prevention message that regular (at least daily) tick checks and prompt tick removal has strong potential to reduce the risk of transmission of I. scapularis-borne bacterial and parasitic pathogens from infected attached ticks. The most likely scenario for human exposure to an I. scapularis-borne pathogen is the bite by a single infected tick. However, recent reviews have failed to make a clear distinction between data based on transmission studies where experimental hosts were fed upon by a single versus multiple infected ticks. A summary of data from experimental studies on transmission of Lyme disease spirochetes (Bo. burgdorferi and Bo. mayonii) by I. scapularis nymphs indicates that the probability of transmission resulting in host infection, at time points from 24 to 72 h after nymphal attachment, is higher when multiple infected ticks feed together as compared to feeding by a single infected tick. In the specific context of risk for human infection, the most relevant experimental studies therefore are those where the probability of pathogen transmission at a given point in time after attachment was determined using a single infected tick. The minimum duration of attachment by single infected I. scapularis nymphs required for transmission to result in host infection is poorly defined for most pathogens, but experimental studies have shown that Powassan virus can be transmitted within 15 min of tick attachment and both A. phagocytophilum and Bo. miyamotoi within the first 24 h of attachment. There is no experimental evidence for transmission of Lyme disease spirochetes by single infected I. scapularis nymphs to result in host infection when ticks are attached for only 24 h (despite exposure of nearly 90 experimental rodent hosts across multiple studies) but the probability of transmission resulting in host infection appears to increase to approximately 10% by 48 h and reach 70% by 72 h for Bo. burgdorferi. Caveats to the results from experimental transmission studies, including specific circumstances (such as re-attachment of previously pa...

The scale affects our view on the identification and distribution of microbial communities in ticks

“…Several contrasting findings can however be observed according to the tick scale we are looking at. With sensitive detection tools, tick co-infections are usually observed in tick-borne pathogen analyses [8,29,39].…”

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

“…Overall, we documented infection, based on detection of B. miyamotoi DNA, in blood from 13 (57%) of 23 mice exposed to a single infected larva and from 5 (83%) of 6 mice exposed to two infected larvae feeding simultaneously. Increased probability of tick feeding to result in host infection after exposure to multiple versus single infected ticks was previously reported for nymphal I. scapularis ticks infected with the Lyme disease spirochetes, B. burgdorferi s.s. and B. mayonii (Eisen, 2018). In this study, all 18 PCR-positive mice also demonstrated seroreactivity to B. miyamotoi .…”

“…The primary vector of B. miyamotoi to humans in the eastern part of the United States is the blacklegged tick, Ixodes scapularis , which also transmits the Lyme disease spirochetes, Borrelia burgdorferi sensu stricto (s.s.) and Borrelia mayonii (Krause et al, 2015; Breuner et al, 2017; Eisen, 2018). For nymphal and adult I. scapularis ticks, local infection prevalence with the relapsing fever spirochete, B. miyamotoi , is commonly 10-fold lower than for the Lyme disease spirochete, B. burgdorferi s.s. (Tsao et al, 2004; Krause et al, 2015; Nelder et al, 2016).…”

Tick-borne pathogens in removed ticks Veneto, northeastern Italy: A cross-sectional investigation

“…A prospective study showed that 8% of people bitten by a B. burgdorferi infected tick acquired the infection [18]. However, it is well known that the risk steadily rises with the increasing duration of the blood meal, reaching 70% if the tick remains attached up to 72 h [19].…”