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The Babesia microti
life cycle involves two hosts, which includes a rodent, primarily the
white-footed mouse, Peromyscus leucopus. During a blood meal, a
Babesia-infected tick introduces sporozoites into the mouse host
.
Sporozoites enter erythrocytes and undergo asexual reproduction (budding)
. In the
blood, some parasites differentiate into male and female gametes although
these cannot be distinguished at the light microscope level
. The
definitive host is a tick, in this case the deer tick, Ixodes dammini
(I. scapularis). Once ingested by an appropriate tick
, gametes
unite and undergo a sporogonic cycle resulting in sporozoites
.
Transovarial transmission (also known as vertical, or hereditary,
transmission) has been documented for “large” Babesia spp. but not
for the “small” babesiae, such as B. microti
.
Humans enter the cycle when bitten by
infected ticks. During a blood meal, a Babesia-infected tick
introduces sporozoites into the human host .
Sporozoites enter erythrocytes
and
undergo asexual replication (budding)
.
Multiplication of the blood stage parasites is responsible for the clinical
manifestations of the disease. Humans are, for all practical purposes,
dead-end hosts and there is probably little, if any, subsequent transmission
that occurs from ticks feeding on infected persons. However, human to human
transmission is well recognized to occur through blood transfusions
.
Note: Deer are the hosts
upon which the adult ticks feed and are indirectly part of the Babesia
cycle as they influence the tick population. When deer populations
increase, the tick population also increases, thus heightening the potential
for transmission. |
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