|
 
New river blindness therapy may
provide panacea for 18m people
By
Stefanie Petrou-Binder MD
NUERNBERG - A simple combination drug regimen could make a big difference
in the fight against onchocerciasis, or river blindness, in Africa
and other affected areas, according to a report at the annual Congress
of German Ophthalmic Surgeons.
Guido Kluxen MD reported that the eye manifestations of onchocerciasis
result primarily from the inflammatory reaction to the endosymbiotic
bacteria, Wolbachia, which emerges as the microfilariae migrate
through the eye in the later course of the disease.
The reaction intensifies when the microfilariae die causing an intense
host immune reaction.
The gram-negative bacteria have superficial lipopolysaccharides
that are easily recognised and attacked by the immune system.
Mouse studies have shown that keratitis could not be triggered by
the nematode Onchocerca volvulus extracts which lacked the bacteria.
Wolbachia bacteria are passed onto the next generation of worms
through the oocyte, much like an inherited characteristic. The worm
relies on the intracellularly living bacteria for its homeostasis.
The current mainstay of mass treatment programmes is ivermectin,
an antiparasitic agent that inhibits the growth and proliferation
of parasites for several months at a time. The World Health Organisation
distributes the drug to be given once yearly in endemic areas.
But treatment with ivermectin does not cure the disease. Rather,
it targets mature microfilariae, improving several facets of the
disease including river blindness, he explained.
Recently, researchers have investigated the effectiveness of doxycycline
chemotherapy against Wolbachia bacteria.
Doxycycline caused sterility in adult worms and thereby directly
suppressed the embryonic development of the worm.
Another study showed that the combination of ivermectin and doxycycline
significantly enhanced ivermectin-induced suppression of microfiliarae,
effectively blocking disease transmission for as long as 18 months,
possibly irreversibly, he said.
Human beings are the only known important reservoir of Onchocerca
volvulus which causes onchocerciasis. The adult worms are usually
found in subcutaneous nodules and have an average longevity of approximately
10 years.
The adult female worm produces millions of microfilariae. It is
these microfilariae that migrate to the skin and eyes of the human
host.
Microfiliarae enter the eye by direct invasion from the conjunctiva
through the sclera or cornea. They enter the eye after prolonged
disease, when their numbers in the body are at their highest and
space beneath the skin is tight. Blindness therefore tends to occur
in adulthood after many years of infection.
A number of severe immunological reactions occur in the eye that
take a devastating course. They begin with punctate keratitis and
end in a sclerosing keratitis after years of heavy, prolonged infection.
Permanent visual impairment and blindness are among the ocular manifestations
that result from the invasion.
The black fly, Simulium damnosum, is the disease vector and intermediate
host within which the infective larvae develop after a blood meal.
Onchocerciasis affects an estimated 18 million people in central
Africa, parts of the Arabian Peninsula and South America. In Africa,
hyperendemic villages can have infection rates of 100%.
In such areas, 10% of the entire village may be blind, including
up to 50% of those aged 40 years and older.
The World Health Organisation and other health authorities have
large-scale projects in place to eradicate onchocerciasis in endemic
areas of Africa, Latin America and the Middle East.
Top
|
