Ticks more widespread, more bites and more diseases tied to tick bites
By YALE UNIVERSITY
CREDIT: A. MASTIN/SCIENCE TRANSLATIONAL MEDICINE
Over the past five decades, the U.S. has seen a dramatic rise in
tick-borne diseases, prompting urgent calls for innovative solutions from
scientists at Yale.
Their review highlights the rapid spread of these diseases, attributable to factors like increased deer populations and forest regrowth, and the dominance of the deer tick in transmissions.
Traditional vaccines have had limited success, leading researchers to explore new strategies targeting tick-feeding processes and alert mechanisms. The proposal includes expanding these tactics to wildlife, necessitating a collaborative, multidisciplinary approach similar to the Manhattan Project to effectively combat this public health threat.
The
surge in diseases transmitted by ticks throughout numerous regions of the
United States in the past fifty years poses a significant threat to public
health, necessitating innovative solutions, caution a team of scientists
from Yale. In a review article, they outline why the
stakes are so high and describe some potential solutions.
Possible
solutions include a new class of vaccines for humans, including vaccines being
developed at Yale, and even for the animals that carry the ticks.
The article was recently published in the journal Science Translational Medicine.
The
research team was led by Sukanya Narasimhan, associate professor in Yale’s
Department of Internal Medicine (Infectious Diseases) and Erol Fikrig,
Waldemar Von Zedtwitz Professor of Medicine (Infectious Diseases) and professor
of epidemiology (microbial diseases) and microbial pathogenesis.
Historical Context and Current Scenario
The
public health threat, they say, is escalating rapidly. It wasn’t until 1982
that the threat of tick-borne diseases was recognized after a bacterium
transmitted by ticks caused an outbreak of arthritis-like symptoms in children
in Lyme, Connecticut. And even then, known cases of the disease were extremely
rare.
Today
an estimated 490,000 people in the United States are infected annually by
tick-borne diseases such as Lyme disease, an increase that researchers say has
been fueled by the return of formerly depleted forests and a dramatic increase
in populations of tick-hosting white-tailed deer.
The
threat has also spread from isolated areas near the New England coastline into
the U.S. Midwest and other parts of the country since the cause of Lyme Disease
was identified four decades ago. A single tick species – Ixodes
scapularis, commonly called the black-legged or deer tick — accounts for
97% of tick-borne diseases in the United States.
Challenges and Diverse Pathogens
To
date, most efforts to combat tick-borne diseases have concentrated on
developing vaccines that target Borrelia burgdorferi, the bacterium
that causes Lyme disease. These efforts, however, have had limited success and
do nothing to combat other pathogens that can be transmitted by ticks, the
researchers say.
For
example, deer ticks can also transmit six other human pathogens, including the
Powassan virus — named for a town
where it was first identified in a young boy who eventually died from it —
which kills 10% of infected people and causes permanent neurologic damage in
half of the cases. While still rare, Powassan cases have increased forty-fold
in the last two decades.
In
response to this rapid rise of a host of tick-borne diseases, Fikrig’s lab at
Yale is developing vaccines that combat a variety of infections by thwarting
the ability of ticks to feed and even alert human hosts when they have been
bitten by a tick.
“If
we can keep ticks from feeding, we can control Lyme and other diseases as
well,” said Narasimhan, first author of the new report.
Previous research has shown that multiple exposures to tick bites can increase resistance to tick-borne infections. At Yale, Fikrig’s lab capitalized on this insight.
In a previous study, the lab showed that a vaccine containing a
cocktail of tick salivary proteins can impair tick feeding and even increase
the chances that a person will recognize that they’ve been bitten, which can in
turn prompt rapid tick removal and a reduced likelihood of infection.
Broader Vaccine Strategies
Durland
Fish, professor emeritus of epidemiology (microbial diseases) at Yale School of
Public Health and a co-author of the article, argues that such a vaccine could
also be delivered orally within bait that would be consumed by deer. Ideally,
he said, ticks would then be unable to feed upon the blood of that deer, which
in turn would reduce tick populations and the risk of disease for humans.
“Deer
are the keystone host for deer ticks,” he said. “They do not exist in areas
where there are no deer. I think this should be the Manhattan Project for
tick-borne diseases.”
Similar
strategies have already been carried out to prevent raccoon rabies in the U.S.
and fox rabies in Europe, and also to protect cattle against tick-borne
disease.
“Toward
this goal, we must have a multidisciplinary, One Health approach [an integrated
approach that balances the health of humans, animals, and ecosystems] that will
harness the vision of molecular biologists, entomologists, ecologists,
epidemiologists, physicians, veterinarians, and vaccinologists,” the authors
conclude.
Reference:
“A ticking time bomb hidden in plain sight” by Sukanya Narasimhan, Durland
Fish, Joao H. F. Pedra, Utpal Pal and Erol Fikrig, 18 October 2023, Science
Translational Medicine.
DOI: 10.1126/scitranslmed.adi7829