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Lyme disease
is transmitted by the bite of an infective tick.
Ticks go through
four life stages: egg, larva, nymph, and adult. They evolve from
one life stage to another by molting Each of the last three stages
(the "active" life stages) requires a blood meal. If
the tick feeds on an infected host animal, the tick becomes infected.
Ticks that transmit Lyme disease can retain the infection throughout
their life and are able to transmit the infection to subsequent
hosts. This ability to pass the infection on to other hosts makes
the tick "infective". Adult ticks generally do not
pass the spirochete on to the next generation.
Transmitters
of the bacteria in North America include: the Western black-legged
( Ixodes pacificus) tick in the West, and the black-legged
tick ( Ixodes scapularis) in the rest of the country.
The black-legged tick was temporarily known as the "deer"
tick ( Ixodes "dammini"). Research is underway
to determine if the lone star tick ( Amblyomma americanum)
may also transmit the infection.
Other host-specific
ticks may play a minor role in maintaining the infection in nature.
This creates a type of "bi-cycle". One cycle being
animal-tick-animal feeding and the other cycle being animal-tick-human
feeding. The wood rat ( Ixodes neotomae) and the rabbit
tick ( Haemaphysalis leporispalustris) are two examples
of ticks that may maintain the infection in nature, but not transmit
it to humans. These ticks feed almost exclusively on the hosts
mentioned in their common name.
In other parts
of the world, other ticks are responsible for transmitting the
disease to people, such as the sheep tick ( Ixodes ricinus)
in Europe, and the Taiga tick ( Ixodes persulcatus) in
Asia.
These ticks
can be anywhere - in the woods, by the seashore, or even in your
backyard.
While ticks
can bite year-round, peak tick season in the northeast is April
- September, and on the West coast is November - April. Ticks
can survive under a variety of conditions as long as adequate
moisture is available.
An infective
tick with local infection must be attached to the host for a
day or more before transmission of Bb occurs. However,
a systematically infected tick or improper tick removal may cause
transmission of LD much sooner.
Tick infection
rates vary geographically and from one year to another. |
