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Ticks are the most harmful ectoparasites of
domestic and wild animals as well as important vectors of disease
agents to humans. In order to develop an effective tick biocontrol
program, we must encourage scientists and policy makers to support
this long neglected field so that it will become an active branch
of research.
The two animals most implicated in the increase of
tick-borne disease are the mouse and the deer. The mice followed
by the chipmunk are the greatest reservoirs for Lyme disease and perhaps
other tick-borne disorders. Therefore, the mouse is the animal most
responsible for transmitting disease. The deer is not responsible
for that since it is not a good reservoir. Larval and
nymphal stages of the tick feed primarilary on small rodents. It
is not uncommon for a mouse to carry over 100 larval ticks, and
transmit disease to them.
The favored host of the adult female tick is the
deer. After becoming engorged with blood at this last meal on the
host animal. It then drops to the ground where it lays
approximately 3,000 eggs. Therefore, the deer is the animal most
responsible for the increasing numbers of ticks.
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There are numerous strategies to
controlling tick populations. These strategies are grouped into
three general catagories:
-
Reducing tick immigration
-
Increasing tick
mortality
-
Reducing tick reproduction
4 POSTER
A topical treatment device to control adult ticks
on deer. The deer come to the device to feed from a bin that
contains corn. In order to feed they must roll their head against a vertical roller,
laced with a "tickacide." Since most
ticks congregate on the ears, head and neck area of the deer, this
drastically cuts down on the next generation of ticks that would
have hatched. This is a carefully controlled and targeted use of a
"tickacide" (selection is one that is not dangerous to
or absorbed systemically by the deer).
BAIT-BOX
A bait box is a topical treatment device to control ticks on
small rodents. The mouse or other small rodent is attracted into
the device to feed and is brushed with a small dose of Fipronil.
Fipronil provides 42 days of control on rodents. CDC trials have
shown amazing success in reducing the tick infestation rate on
mice. This can not only break the cycle of disease, but also the
risk of exposure for the property owner where the devices are
installed. Again this is a carefully controlled and targeted use
of an acaricide.
NEMATODES
Nematodes are microscopic roundworms. Several strains of Steinernema
and strains of Heterorhabditis, are well known to
science and are utilized in attacking insect pests.. They are
harmless to higher vertebrates (humans and livestock, for
instance). In a limited field test by Doloris Hill, Ph.D, U.S.D.A.,
95 -100% of adult engorged females were killed
PHEROMONES
Chemical secreted by ticks that guide behavior
such as assembly, attachment, sex and primer. Scientists are
examining these in order to replicate them and use them to control
tick numbers. Pheromones are species specific so they are
environmentally safe.
FUNGUS
Entomopathic fungi have been widely used for
biological control of agricultural pests. Several of them cause
mortality of ticks.
PARASITOIDS
Tiny sting-less wasps that lay eggs in the body of
ticks. When the bees hatch they kill the ticks.
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The goal is to make Dutchess County a role model
for other communities to follow in drastically reducing Lyme
disease and other tick-borne illnesses. This will be done with
integrated research programs comprised of multifaceted,
environmentally safe tick control programs, and education of
residents to alter their self protection behavior and landscape
management around their homes. Consistent with these goals are the
following projects.
The US Centers for Disease Control has awarded a three year
$300,000 grant to reduce Lyme Disease in Dutchess County.
This is to be accomplished through education, surveys, and tick
reduction intervention. Four areas that have the highest numbers
of individuals with Lyme disease are being carefully
monitored to determine how much of an effect intervention with
"4 - Poster" deer stations and Maxforce Tick Management
System (see '4-Poster' and 'Bait-box' above) will have on the
numbers of ticks and their infection rate. The Dutchess County
Department of Health (DC DOH), the American Lyme Disease
Foundation (ALDF), The Institute of Ecosystem Studies (IES) and a
Community Advisory Board (CAB) are jointly coordinating this
project. (see education below for additional information).
The Dutchess County Legislature formed a Task Force to Study Tick
Control, awarded a research grant to the IES (see below), and
sponsored a conference of scientists to brainstorm about tick
control. The Task force posted signs warning of ticks in areas of
high public visitation. Among other items being studied are deer
intervention modalities, targeted controlled spraying of
recreation areas, the use of other natural predators, etc. Stop
Ticks On People educational web site was an outcrop of the Task
Force (www.StopTicks.org)..
The IES is the primary investigator for the CDC grant. It is also
performing research on naturally occurring environmental fungus
that causes mortality of ticks; with a goal to produce a
commercially available product. Additionally ticks have been
analyzed by the Institute to determine the infection rates of
numerous tick-borne organisms.
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There
is much promising research in the field of tick control by federal
agencies (CDC, USDA, NIH, the Armed Services), state agencies (CT,
TX, CA, etc.), university centers and private institutions.
In spite of this we do not already have solutions that have
reduced human and animal exposure to ticks due to lack of public
awareness, funding, and priorities.
A prime example of neglect of appropriate funding is the situation
in NYS which has the highest number of people infected with Lyme
disease. The NYS DOH Tick Borne Disease Institute (TBDI)
responsible for this kind of research is funded with only
$150,000, while two years in a row $31 million was budgeted for
West Nile Virus. In fact, researchers in New York and elsewhere
were reassigned from the more prevalent debilitating tick-borne
diseases to work on West Nile Virus.
We are now 25 years into Lyme disease and we have not progressed
very far although millions have been spent in research for testing
and cures. In these twenty five years tick numbers have
grown like wildfire and the number of diseases identified to be
caused by them have been increasing as well. Thus, many more
people are coming into contact with ticks, and are being infected
with more than one disease which only complicates the already
difficult problems of diagnosis, treatment and cure. One
would have to wonder if a fraction of this money had been spent on
tick reduction if there would even be a tick-borne disease
problem today?
The 1999 Annual Review of Entomology, "Pathogens and
Predators of Ticks and Their Potential in Biological
Controls," says it best: "We must encourage scientists
and policy makers to turn this long neglected, important field
into an active branch of research..." This is necessary to
develop an effective tick biocontrol program.
When a three year old child has 23 ticks removed during her bath
after a visit to a rural park in Dutchess County, you know it's
time to do something. Additionally, the myth that people do not
die from Lyme disease needs to be dispelled, although rare, they
do, from complications directly caused by Lyme, and from other
tick-borne diseases which can be fatal.
What is needed is public action. You and others are needed to
start demanding your local, state, and federal
representatives to redirect future funding priorities where it can
have the most dramatic effect, tick control, to reduce human and
animal exposure to these blood sucking disease ridden parasites!
Check the following web sites to find your representatives:
Federal:
United
States Senate
House
of Representatives
NY State:
New
York State Senate
New
York State Assembly
UPDATE
ON RESEARCH INITIATIVES
Stephen
Wikel, Ph.D.
Anti-tick
Vaccine Research
Significant
progress is being made in characterizing host responses to tick
infestation and tick countermeasures to those responses. The
spectrum of tick modulation of host immune defenses is extensive
and increasingly important links being made between those events
and tick transmission of infectious agents. A recent example is
the finding that Ixodes
scapularis, a vector of Lyme disease, babesiosis and
granulocytic anaplasmosis, and Dermacentor
andersoni, a vector of Rocky Mountain spotted fever, both
down regulate adhesion molecules that are essential for cells of
the immune response to leave the circulation, cross endothelial
cells of blood vessels and enter tissues. These changes in
adhesion molecule expression differ for each tick species and
they correlate with changes that would impair the ability of the
host to mount an effective immune response to both tick and
infectious agents transmitted by those species.
Extensive
analyses are being conducted of gene and protein expression in
tick salivary glands. Rapid progress is being made in linking
genes and their products to specific functions, such as inducing
or modulating host defenses. A few comments can be made about
emerging findings. During the course of feeding by Ixodes
scapularis the protein composition of the saliva changes
with new proteins being expressed at different times and with
other proteins no longer expressed. The magnitude of those
changes appears to be much greater than previously recognized.
In addition, ticks appear to generate slightly different copies
of molecules that are essential for successful blood feeding.
Those molecules appear to be highly conserved at their active
sites, but the remainder of the molecule can be structurally
very different. This “variant redundancy” is likely a away
to avoid host immune responses that could target key molecules
for tick survival.
A recent
study correlated human skin reactivity to repeated tick bites
with heightened resistance to infection with Borrelia
burgdorferi. Studies are underway to identify the spectrum
of human immune responses to tick bite and their possible
correlation with resistance to tick transmitted infections. Due
to research on genes and proteins expressed by tick salivary
glands, and the forthcoming data from the Ixodes
scapularis genome project, the molecules responsible for
those responses will ultimately be identified.
The
overarching goal of all this research is to identify molecules
that can be incorporated into vaccines that block transmission
of tick-borne infectious agents.
Ixodes
scapularis Genome Project
The Ixodes
scapularis genome is the first tick genome to be sequenced
and information obtained will provide an unprecedented resource
for the study of tick biology and tick-host-pathogen
interactions. The Microbial Sequencing Centers (http://www.niaid.nih.gov/dmid/genomes/mscs/)
of the National Institute of Allergy and Infectious Diseases,
National Institutes of Health were established with a
significant commitment to sequencing the genomes of
microorganisms considered to be possible bioterrorism threats,
emerging and re-emerging infectious diseases, and arthropod
vectors of human disease. The Ixodes
scapularis genome project is a collaborative effort of an
international community of tick researchers, the National
Institutes of Health and the Microbial Sequencing Centers. The
project co-directors are Dr. Catherine Hill, Department of
Entomology, Purdue University, West Lafayette, IN 47907 and Dr.
Stephen Wikel, Center for Microbial Pathogenesis, School of
Medicine, University of Connecticut Health Center, Farmington,
CT 06030.
The
project is underway and the white paper describing the genome
project can be viewed in its entirety at http://www.entm.purdue.edu/ig/overview.html.
The first phase of the project involves (1) massive sequence
analysis of cDNA libraries, 100,000 clones, composed of all
tissues from all developmental stages; and, (2) complete end to
end sequencing of approximately 40 randomly chosen large-insert
bacterial artificial chromosome, BAC, clones containing I.
scapularis genomic DNA. This phase provides information
about the genes, their density, repetitive elements and the
degree of polymorphism in the sequenced tick tissues. The second
phase is whole-genome random shotgun sequencing to provide
sufficient information for assembly and annotation of large
sections of the genome. The size of the Ixodes
scapularis genome is approximately two-thirds the size of
the human genome. The Ixodes
scapularis genome is approximately seven times larger than
that of the malaria vector mosquito, Anopheles
gambiae. A small tick has a very large genome and abundant
information to reveal.
All sequence data generated will be provided rapidly and
in an unrestricted manner through public databases. The
information obtained will be an unparalleled resource for the
tick research community and will provide the basis for rapid
advances, particularly in those areas that have been previously
difficult to study.
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