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Lyme disease is an zoonotic infection caused by the spirochete Borrelia burgdorferi. Spirochetes are bacteria with
a spiral or corkscrew type shape. They are extremely small and difficult to detect in microscopy. Darkfield microscopy
with immunofluorescence have demonstrated spirochetes. B.burgdorferi express a number of lipoproteins on the outer
surface called Osp (outer surface proteins) which are linked to survival mechanism and immunity. Outer surface
proteins can be expressed differently depending on the stage of tick infection.
Borrelia burgorferi involves are complex cycle involving ticks, mice and deer. The primary reservoir of B. burgorferi
is rodents, mainly the white-footed mouse. Infection is transmitted by the deer tick (black legged tick) Ixodes
scapularis. Other Ixodes species are responsible for transmission as well in various parts of the United States,
Europe and Asia. The tick has a three stage life cycle, it passes from larva to nymph to adult. People aquire Lyme
disease mainly from the nymph (which survive on mice and other rodents) because they are active during the time
of year when people are in there ecosystem such as walking through brush or tall grass. Because the nymph is the
size of a small freckle, it often is not detected and remains attached from 36-48 hours, the period that is required
to transmit infection. As the tick feeds, spirochetes escape from the salivary gland of the insect into the skin
of the human host.
The deer and other large mammals are the primary host for the adult tick and are essential to the mating and survival
of the tick. The female tick can lay around 2,000 eggs or more where larvae starts the beginning of the life cycle.
Birds can be a host for Ixodes scapularis and have been implicated in long distance dispersion. Lyme disease is
characterized by fatigue, muscle and joint pain, rash, headache, fever, chills and stiff neck. Later stage implications
can occur with neurological, cardiovascular and neuropsychiatric complications. Symptoms may occur within days
to weeks. Later stages can be months to years after infection.
Co-infections or other tick-borne illnesses with Lyme disease can result in more severe disease as well as complications
in treatment. Ixodes scapularis can also transmit the casual agent of two other diseases: Human babesiosis and
ehrlichiosis. Basbesiosis is a malaria-like illness that is caused by Babesia microti in the northeast and mid-west
of United States. Babesia microti is a parasite of the white-footed mouse (transmitted by I.scapularis). Human
granulocytic ehrlichiosis (HGE) is caused by the bacteria Anaplasma phagocytophilum and invades certain white blood
cells. Symptoms include fever, headache, nausea, vomiting, muscle pain and fatigue. |
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