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Loiasis is
infection by the filarial nematode, Loa loa, the African
“eyeworm” or “loa” worm.
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Filariasis
;
Onchocerciasis
;
Dirofilariasis
It prevails in the rain forests of central
and West Africa.
Humans and baboons are definitive hosts and infection
is transmitted by mango flies (Chrysops species).
The adult L. loa migrates in the skin and occasionally crosses the eye beneath the
conjunctiva, making the patient acutely aware of his infection.
Gravid
worms discharge microfilariae that circulate in the blood stream
during the day but reside in capillaries of the skin, lungs, and other
organs at night.
Most
infections are asymptomatic but persist for years.
Some patients have pruritic, red, subcutaneous, “Calabar” swellings, which may be a
reaction to migrating adult worms or to microfilaria in capillaries of
the dermis.
Ocular symptoms include swelling of lids, congestion,
itching, and pain.
Female worms, and rarely male worms, may be
extracted during their migration beneath the conjunctiva.
Systemic
reactions include fever, pain, itching, urticaria, and eosinophilia.
Dead worms in or near major nerves may cause paresthesias and focal
paralyses.
Some patients have a regional lymphadenopathy,
characterized by follicular atrophy, histiocytic hyperplasia, and
eosinophilia.
Treatment with microfilariacides may cause massive death
of microfilariae and provoke fever, meningoencephalitis, nephritis,
coma and death.
Migrating worms cause no inflammation, but static
worms are surrounded by plasma cells, lymphocytes, eosinophils,
neutrophils, fibrin, and a foreign body giant cell reaction.
At autopsy
patients with acute generalized loiasis have obstructive fibrin
thrombi, which contain degenerating, microfilaria, in small vessels of
most organs.
When the brain is involved, obstruction
of vessels by filarial thrombi kills the patient through sudden and
diffuse cerebral ischemia.
Diagnosis is
made by identifying microfilariae in blood films taken during the day,
by removal of adult worms from the conjunctiva or by identifying
microfilariae or adult worms in biopsy specimens.
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