http://jme.oxfordjournals.org/content/early/2016/07/19/jme.tjw103
Abstract
In the 1980s, the blacklegged tick, Ixodes scapularis Say, and rodents were recognized as the principal vector and reservoir hosts of the Lyme disease spirochete Borrelia burgdorferi in the eastern United States, and deer were incriminated as principal hosts for I. scapularis adults. These realizations led to pioneering studies aiming to reduce the risk for transmission of B. burgdorferi
to humans by attacking host-seeking ticks with acaricides, interrupting
the enzootic transmission cycle by killing immatures infesting rodent
reservoirs by means of acaricide-treated nesting material, or reducing
deer abundance to suppress tick numbers. We review the progress over the
past three decades in the fields of: 1) prevention of human–tick
contact with repellents and permethrin-treated clothing, and 2)
suppression of I. scapularis and disruption of enzootic B. burgdorferi
transmission with environmentally based control methods. Personal
protective measures include synthetic and natural product-based
repellents that can be applied to skin and clothing, permethrin sprays
for clothing and gear, and permethrin-treated clothing. A wide variety
of approaches and products to suppress I. scapularis or disrupt enzootic B. burgdorferi
transmission have emerged and been evaluated in field trials.
Application of synthetic chemical acaricides is a robust method to
suppress host-seeking I. scapularis ticks within a treated area
for at least 6–8 wk. Natural product-based acaricides or
entomopathogenic fungi have emerged as alternatives to kill host-seeking
ticks for homeowners who are unwilling to use synthetic chemical
acaricides. However, as compared with synthetic chemical acaricides,
these approaches appear less robust in terms of both their killing
efficacy and persistence. Use of rodent-targeted topical acaricides
represents an alternative for homeowners opposed to open distribution of
acaricides to the ground and vegetation on their properties. This
host-targeted approach also provides the benefit of the intervention
impacting the entire rodent home range. Rodent-targeted oral vaccines
against B. burgdorferi and a rodent-targeted antibiotic bait
have been evaluated in laboratory and field trials but are not yet
commercially available. Targeting of deer—via deer reduction or
treatment of deer with topical acaricides—can provide area-wide
suppression of host-seeking I. scapularis. These two
deer-targeted approaches combine great potential for protection that
impacts the entire landscape with severe problems relating to public
acceptance or implementation logistics. Integrated use of two or more
methods has unfortunately been evaluated in very few published studies,
but additional field evaluations of integrated tick and pathogen
strategies are underway.
- Borrelia burgdorferi
- Ixodes scapularis
- blacklegged tick
- Lyme disease
- risk management
In the early 1980s, the blacklegged tick, Ixodes scapularis Say (including the junior synonym Ixodes dammini
Spielman, Clifford, Piesman & Corwin), was implicated as a vector
to humans in the eastern United States of the Lyme disease spirochete Borrelia burgdorferi (Burgdorfer et al. 1982; Spielman et al. 1985; Piesman et al. 1987a,b). Rodents, particularly the white-footed mouse, Peromyscus leucopus (Rafinesque), were recognized as primary enzootic spirochete reservoirs (Levine et al. 1985, Donahue et al. 1987, Mather et al. 1989) and the white-tailed deer, Odocoileus virginianus (Zimmerman), was shown to be the principal host for the adult stage of I. scapularis (Piesman et al. 1979, Main et al. 1981). These findings led to pioneering field studies aiming to reduce the risk for transmission of B. burgdorferi to humans by directly attacking host-seeking ticks with acaricide applied to the ground substrate and vegetation (Schulze et al. 1987),
interrupting the enzootic transmission cycle by killing immatures
infesting rodent reservoirs by means of acaricide-treated nesting
material (Mather et al. 1987a), or reducing the abundance of white-tailed deer to suppress tick numbers (Wilson et al. 1988).
Nearly three decades later, a wide array of approaches to avoid contact
with ticks through personal protective measures, suppress host-seeking I. scapularis, or disrupt enzootic B. burgdorferi transmission through environmentally based control methods have emerged.
We review the evidence for personal protective measures to reduce human contact with I. scapularis and for environmentally based control methods to suppress host-seeking nymphs and B. burgdorferi
infection in nymphs and rodent reservoirs. Published literature was
queried by searching the Scopus database, last done in December 2015.
The search spanned the years 1960 to present and used the following key
words: 1) “Ixodes scapularis” and 2) “Ixodes dammini”.
Additional searches using the same key words were conducted in PubMed
and the Armed Forces Pest Management Board’s Literature Retrieval
System. The snowball technique, which identifies additional publications
based on referenced materials, was then employed to identify additional
publications of interest. Because most human infections with B. burgdorferi in the eastern United States are considered to result from bites by infected I. scapularis nymphs (Spielman et al. 1985; Piesman 1987a; Falco et al. 1996, 1999; Mead 2015),
we focus primarily on the impact of personal protective measures
against nymphal tick bites, and the impact of environmentally based
interventions on the abundance of host-seeking nymphs, infection rates
of host-seeking nymphs with B. burgdorferi, and the abundance
of infected nymphs. As used in this paper, data for abundance or density
of host-seeking ticks (e.g., <0.1 nymphs/100 m2)
generated by drag or flag sampling should be interpreted as relative
abundance and relative density rather than as absolute estimates of the
nymphal population present. Prospects for current personal protective
measures and environmentally based tick and pathogen suppression methods
to reduce Lyme disease will be discussed in a separate forthcoming
paper.
