Download Targeting the tick - Horizon Magazine

HEALTH
Targeting the tick
24 February 2014
by Gary Finnegan
Ticks latch onto your skin as you brush past a tree or shrub. © Shutterstock/D. Kucharski K. Kucharska
Understanding the bloodsucking feeding mechanisms of ticks could result in vaccines against
hard-to-treat diseases like Lyme disease.
A sneeze, a cough, a kiss – even a handshake: diseases such as measles, whooping cough and the
flu are often passed directly from one person to another in tiny droplets of fluid which contain viruses or
bacteria.
However, not all infectious diseases are spread so
directly. Some hijack bloodthirsty insects and
arachnids, taking the opportunity to infect humans
during feeding time.
One such disease risk is the humble tick – an eightlegged parasite often found in Europe’s forests.
If you are bitten by a tick while hill walking this
summer, you will probably feel nothing. The trouble is
that ticks play host to pathogens which cause Lyme
disease, tick-borne encephalitis (TBE), human
babesiosis, and many more besides.
Tick-borne diseases can be very serious, particularly if
timely treatment is not available or if the victim has a
weak immune system. Lyme disease, for example,
See also
Developing-world disease
vaccines being prepared for
human tests
In search of immunity: the
science of vaccines
Searching for a universal flu
vaccine
Vaccination fears lead to
new measles, mumps threat
Life-saving TB vaccines
ready for human tests
1
can cause paralysis if left untreated, while TBE can cause inflammation of the brain and death. Lyme
disease can be treated with antibiotics, however TBE is incurable once the symptoms appear.
Ticks perfer shady and humid woodland or forest clearings, and threaten hillwalkers right across
Europe, from Great Britain in the west to Russia in the east.
Infection can be all too simple. Ticks latch onto your skin as you brush past a tree or shrub. From there
they will find a soft thin area of skin, sink in their proboscis (sucking mouthpart) and begin to feed for
several days. The tick then drools saliva into the wound as it feeds, passing infection on to its human
host.
Why, you might wonder, do ticks not fall off? Why do humans not brush them away when they feel the
bite? Why does the human body’s immune system not block this five-day feeding frenzy?
The answer, said Dr Joppe Hovius, lies in the sophisticated biochemistry of the tick’s saliva.
‘Tick saliva is full of goodies. It has proteins that are like cement and keep it stuck to human skin. It
can inhibit the itch reaction, evade the immune system, and even make blood thinner,’ he said.
Dr Hovius, an infectious diseases consultant at the
Academic Medical Center (AMC) in Amsterdam, is
leading the EU-funded ANTIDotE project which
aims to study the mechanisms of tick feeding, and
use this knowledge to develop new vaccines.
The project is in its early stages, so a wide range of
tick proteins could be in the firing line. One
possibility for vaccine development would be to
develop antibodies against a tick protein that
suppresses the human immune system during
feeding.
Another option would be to neutralise the tick’s
natural anticoagulant – which prevents the host’s
blood from thickening and forming protective scabs.
‘We are focusing on three tick-borne diseases –
Lyme disease, TBE and human babesiosis – but
our work could be extrapolated to others,’ Dr Hovius
said.
The target diseases are caused by a bacterium, a
virus, and a parasite, respectively, but all three
piggyback on the tick’s feeding mechanism.
‘Tick saliva is full of
goodies. It has
proteins that are like
cement and keep it
stuck to human skin.
It can inhibit the itch
reaction, evade the
immune system, and
even make blood
thinner.’
Dr Joppe Hovius,
Infectious Diseases
Consultant, Academic
Medical Center,
Amsterdam
‘We aim for a single vaccine that is capable of
preventing transmission to humans either by
interfering with transmission or by interfering with tick feeding,’ Dr Hovius explained.
2
There are already vaccines against TBE, but the number of
people who opt to be vaccinated is low in most European
countries. The researchers think that if a single vaccine could
protect against a range of diseases at once, uptake rates might
increase.
Ticks need to feed on blood in order to reproduce. A vaccine
which disrupted tick feeding or the reproductive cycle could
bring down the total population of ticks, whereas a vaccine that
allowed feeding but prevented diseases from passing to
humans would only reduce the number of infections.
But a human vaccine is not the only option ANTIDotE is
exploring. It may also be feasible to use a vaccine in wildlife,
delivering it to other animals on which the tick feeds, thereby
reducing numbers. Fewer ticks mean fewer humans will
become victims of tick-borne illnesses.
Dr Joppe Hovius, the coordinator of the
ANTIDotE project, with a tube containing
ticks. © Ivar Pel
A combination of human and animal vaccines is another
possibility – with perhaps a transmission-blocking vaccine in
humans and a tick-feeding vaccine for wildlife – but it will take
several years before the solution emerges. The researchers
plan to bring together a range of experts to discuss the future
exploitation and implementation of anti-tick vaccines in health
systems.
Researchers are also examining other disease carriers such as sand flies which spread leishmaniasis
disease and the chandipura virus, a deadly cousin of rabies, or tsetse flies which spread human African
trypanosomiasis, also known as sleeping sickness.
More info
ANTIDotE
3