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Blood (Intracellular) and Other Tissue Protozoa 111

inches per day to prevent breaking apart of the worm. But the most serious sign of the disease is visual
This treatment is quite effective and is suitable for the damage, which is dependent upon the severity of the in-
geographic regions where the disease is endemic and liv- fections. Lesions occur in a part of the eye as migrating
ing conditions are quite primitive. Medications such as larvae invade the tissues there. When the dying microfi-
metronidazole are effective in relieving symptoms but are laria produce an acute inflammatory reaction, the sclera
not known to destroy the worm. of the eye becomes opaque. Lymphadenopathy in both
Prevention of the condition is possible by con- the inguinal and femoral areas may occur, leaving the vic-
structing facilities where safe drinking water and water tims at increased potential for hernias in the inguinal and
for personal use can be obtained. This water may then femoral regions of the body.
be treated by chemicals and filtration to accomplish the
goal of clean water. Water that may be contaminated with Life Cycle
infected copecods should be boiled, filtered, or chemi-
cally treated. Global efforts by governmental agencies The infective larvae are transferred to a human host from
and private organizations have the potential of eventually a bite by one of the species of flies of the genus Simu-
eradicating the organism. lium. During a period ranging from a half-year to 3 years
following infection of a host, the female worms begin to
produce microfilariae in nodules produced in the body,
ONCHOCERCA VOLVULUS mostly in the dermis or subcutaneous tissues.
Onchocerciasis is caused by the filarial nematode called
Onchocerca volvulus which infects millions worldwide. Disease Transmission
The common name for onchocerciasis is “river blind-
ness” based on the likelihood for blindness in those who The disease is rampant and often devastating in the en-
are infected with O. volvulus. The condition is second demic areas populated mostly by agricultural settlements
only to trachoma, which is a disease resulting from an in- that are found on some of the most fertile farmland in the
fection by Chlamydia trachomatis, in causing blindness world, but the lands are sometimes abandoned due to
on a worldwide basis. Those at risk for contracting on- the rate of infection of these residents. The organism is
chocerciasis number into the tens of millions in 37 dif- spread by the bite of the blackfly or the buffalo gnat of
ferent countries spanning the continents and regions of the genus Simulium, a vector that breeds in quickly flow-
Africa, Latin America, and the Saudi peninsula. ing rivers and smaller streams.

Morphology Laboratory Diagnosis

The female worm may reach a length of 50 centimeters Skin snips are used to determine the diagnosis of on-
and measure one-half centimeter in diameter. The adult chocerciasis from the skin biopsies. Tissue samples are
male is only about 5 centimeters in length and also is placed in saline and the organisms are removed by use
roughly one-half centimeter in diameter. of microbiological needles in order to provide good visu-
alization of the filarial. Microfilaria from this species are
Symptoms unsheathed and the nuclei do not extend to the tip of the
tail as occurs in other species of microfilariae.
Clinical signs of the disease are pruritis (itching) and a
rash. The skin may become swollen and painful, even Treatment and Prevention
increasing in temperature in the infected areas. Victims
of the disease appear to be much older chronologically Ivermectin is a highly active antimicrofilarial drug and is
as the skin undergoes changes similar to aging. Loss of furnished by the manufacturer at no cost in poor areas of
elasticity of the skin leaves a condition of thickened and the world. The medication does not actually kill the female
wrinkled appearance. Sometimes pigmentation of the worm but reduces the fertility of the female worms. Pred-
skin changes in response to the infection, particularly in nisone, a steroidal preparation, is used in the eyes to re-
the extremities. duce the inflammatory reaction to the dying microfilariae.