|
||
The vector for Loa
loa filariasis are flies from two species of the genus Chrysops,
C. silacea and C. dimidiata. During a blood meal, an infected
fly (genus Chrysops, day-biting flies) introduces third-stage
filarial larvae onto the skin of the human host, where they penetrate into
the bite wound
. The
larvae develop into adults that commonly reside in subcutaneous tissue
. The
female worms measure 40 to 70 mm in length and 0.5 mm in diameter, while the
males measure 30 to 34 mm in length and 0.35 to 0.43 mm in diameter. Adults
produce microfilariae measuring 250 to 300 μm by 6 to 8 μm, which are
sheathed and have diurnal periodicity. Microfilariae have been recovered
from spinal fluids, urine, and sputum. During the day they are found in
peripheral blood, but during the noncirculation phase, they are found in the
lungs .
The fly ingests microfilariae during a blood meal
. After
ingestion, the microfilariae lose their sheaths and migrate from the fly's
midgut through the hemocoel to the thoracic muscles of the arthropod
. There
the microfilariae develop into first-stage larvae
and
subsequently into third-stage infective larvae
. The
third-stage infective larvae migrate to the fly's proboscis
and can
infect another human when the fly takes a blood meal
.
|