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112 CHAPTER 4

Surgical extraction of the organisms from the eyes and feeds on the human host, the only host known for Loa
head as they appear and treatment is available. Diethylcar- loa, and ingests microfilariae. Development takes place
bamazine is effective at killing the microfilariae, but side in the thoracic muscles of the insect and in less than
effects are considerable in heavy infections. two weeks, the infective larvae appear in the mouth
parts of the fly, which are then injected into another
human host.
LOA LOA

Loa loa is the African eyeworm that is a species of filaria Disease Transmission
that resides in the subcutaneous tissues and conjunc-
tiva (tissues around the eye). Approximately 3 million No environmental conditions give rise to the causative
residents in Central Africa suffer from this condition, in organism. The vectors (flies) must have access to infected
which adult worms migrate through deeper tissues and hosts in order to transmit the organisms to others. Infective
into the conjunctiva of the eyes. larvae are transferred to the human host by the Chrysops fly,
and require 6 months or more for maturation. The worms
move undetected through the subcutaneous layers of skin,
Morphology
and are seldom noticed in areas where the disease is en-
Adult male worms average a range of 20 to 35 millime- demic. Sometimes the first clue that a person is infected
ters in length and 0.5 millimeters in diameter. The female occurs when the larvae cause visual disturbances as they
adults are slightly longer in average size, and measure pass through the conjunctiva of the eye.
from 50 to 70 millimeters in length. Microfilariae are
sheath-covered and are approximately 250 to 300 μm Laboratory Diagnosis
in length.
The microscopic study of blood samples is the sim-
plest and most practical way of diagnosing Loa loa.
Symptoms
Blood samples should be collected between 10 am
Localized inflammatory responses appear to be related and 2 pm due to the diurnal cycle of the appearance
to the host response to either the worm or its wastes of microfilaria in circulation. Thick and thin smears
from metabolic functions. Swollen areas as responses to prepared and stained with Giemsa and sometimes
the organism or its wastes are called Calabar swellings. concentration procedures are preferred. A sample
These areas of edema may appear on any region of the of blood with 2 percent formalin as a fixative can be
body but are found mostly on the extremities. Localized centrifuged and organisms will be concentrated into a
lesions develop quickly and cause itching for several small area. One basic feature of this species lies in the
days. Lymphadenitis and moderate eosinophilia are also fact that nuclei will be visible to the tip of the tail, a
common. One important clinical sign is that of extreme characteristic valuable in differentiating between spe-
eosinophilia, where 50 to 70 percent of the leukocytes cies of microfilariae.
of this type is common, with an average percentage for
healthy individuals of only 5 to 7 percent. Treatment and Prevention

Life Cycle Treatment includes surgical removal of the adult worm
if seen in the conjunctiva of the eye or where it migrates
The vector for the disease organism is the Chrysops near the skin’s surface. Diethylcarbamazine is a thera-
genus, known as mango or deer flies. The female bites peutic drug that kills both the adult worm and the filar-
the host and the infective larvae are injected into the ial form. Drugs to combat inflammation are often used.
wound site. After maturing, both the male and female Destroying or avoiding the vector is an effective way of
adult worms migrate through subcutaneous and deep preventing infections. Insecticides and protective cloth-
connective tissues. The microfilariae enter the vascu- ing and clearing and draining of moist areas where the
lar system and are found in the bloodstream predomi- flies breed will accomplish a great deal in preventing
nantly at noon. The vector becomes infected when it infections.