Ticks were once described as
“..disgusting parasitic
animals..” (Aristotle) but now
they are considered “supreme
pharmacologists.” This change of
attitude has arisen from a
greater understanding of how
ticks feed on the blood of their
hosts, and how the
pharmacological properties of
tick saliva promote the
transmission of tick-borne
pathogens. Ixodid ticks in
particular face one of the
greatest challenges of all
parasites. To survive, they must
attach and remain feeding on a
host for several days or weeks.
The physical and chemical
processes of feeding, and long
duration of attachment, provoke
host haemostatic, inflammatory
and immune responses. Ticks
counterattack with
anti-haemostatic,
anti-inflammatory and
immunomodulatory substances
secreted in their saliva.
Included in this armoury are
proteins that bind
immunoglobulins, histamine, and
serotonin, and various cytokine
regulators that affect the
production or activity of
several cytokines, including
interferons. As a result of the
pharmacological activities of
this rich cocktail of bioactive
saliva molecules, the feeding
pool within the skin becomes an
immunologically privileged site.
Any pathogens (viruses,
bacteria, protozoa) transmitted
by infected ticks into the
feeding pool, or that are
acquired by feeding ticks from
infected hosts, will benefit
from a supportive ecological
niche created by the tick. Such
a phenomenon, often referred to
as ‘saliva-activated
transmission,’ has been reported
for several tick-borne
pathogens. The challenge now is
to determine whether this
immunologically privileged
feeding site can be destroyed,
and pathogen transmission
prevented.
Index terms:
ticks, blood-feeding,
immunomodulation, vector-borne
pathogen transmission.
Copyright:
The copyrights of this
original work belong to the
author (see right-most box
of the title table). This
document also appears in the
Plenury Lectures: ABSTRACT
BOOK I – XXI-International
Congress of Entomology,
Brazil, August 20-26, 2000.