River
Blindness – An Eye Disorder
Merlin N.J.* and Arya
Ezhuthachan College of Pharmaceutical
Sciences, Marayamuttom, Neyyattinkara,
Thiruvananthapuram, Kerala
ABSTRACT:
Onchocerciasis,
also known as river blindness and Robles' Disease, is a parasitic
disease caused by infection by Onchocerca volvulus. Doxycycline
and Ivermycetin are used to treat this disease.
KEYWORDS:
INTRODUCTION:
The visual system detects, transmits and
interprets photic stimuli. Photic
stimuli are electromagnetic waves with wavelengths between 400 and 725 nm. This
is visible light or the adequate (effective) stimulus for the eye.
According to WHO estimates,
the most common causes of blindness around the world in 2002 were: cataracts
(47.9%), glaucoma (12.3%), age-related macular degeneration (8.7%), corneal
opacity (5.1%), diabetic retinopathy (4.8%), childhood
blindness (3.9%), Trachoma and onchocerciasis (0.8%).1
In terms of the worldwide prevalence of
blindness, the vastly greater number of people in the developing world and the
greater likelihood of their being affected mean that the causes of blindness in
those areas are numerically more important. Cataract is responsible for more
than 22 million cases of blindness and glaucoma 6 million, while leprosy and
onchocerciasis each blind approximately 1 million individuals worldwide. The
number of individuals blind from trachoma has dropped dramatically in the past
10 years from 6 million to 1.3 million, putting it in seventh place on the list
of causes of blindness worldwide. Xerophthalmia is
estimated to affect 5 million children each year; 500,000 develop active
corneal involvement, and half of these go blind. Central corneal ulceration is
also a significant cause of monocular blindness worldwide, accounting for an
estimated 850,000 cases of corneal blindness every year in the Indian
subcontinent alone. As a result, corneal scarring from all causes now is the
fourth greatest cause of global blindness.
In developed countries where parasitic
diseases are less common and cataract surgery is more available, age-related
macular degeneration, glaucoma, and diabetic retinopathy are usually the
leading causes of blindness.2 Childhood blindness can be caused by
conditions related to pregnancy, such as congenital rubella syndrome and
retinopathy of prematurity. Abnormalities
and injuries Eye injuries, most often occurring in people under 30, are
the leading cause of monocular blindness (vision loss in one eye) throughout
the United States. Injuries and cataracts affect the eye itself, while
abnormalities such as optic nerve hypoplasia affect
the nerve bundle that sends signals from the eye to the back of the brain,
which can lead to decreased visual acuity. People with injuries to the
occipital lobe of the brain can, despite having undamaged eyes and optic
nerves, still be legally or totally blind.
People with albinism often have vision loss to the
extent that many are legally blind, though few of them actually cannot see. Leber's congenital amaurosis can
cause total blindness or severe sight loss from birth or early childhood.
Recent advances in mapping of the human genome have identified other genetic
causes of low vision or blindness. One such example is Bardet-Biedl
syndrome.
Poisoning:
Rarely, blindness is caused by the intake
of certain chemicals. A well-known example is methanol, which is only mildly
toxic and minimally intoxicating, but when not competing with ethanol for
metabolism, methanol breaks down into the substances formaldehyde and formic
acid which in turn can cause blindness, an array of other health complications,
and death.3 Methanol is commonly found in methylated
spirits, denatured ethyl alcohol, to avoid paying taxes on selling ethanol intended
for human consumption. Methylated spirits are
sometimes used by alcoholics as a desperate and cheap substitute for regular
ethanol alcoholic beverages.
RIVER
BLINDNESS:
Onchocerciasis, also known as river blindness and Robles'
Disease, is a parasitic disease caused by infection by Onchocerca
volvulus, a nematode (roundworm). Onchocerciasis
is the world's second-leading infectious cause of blindness.4
It is not the nematode but its endosymbiont, Wolbachia
pipientis, that causes the severe inflammatory response that leaves
many blind.5
The parasite is transmitted to humans through the bite of a blackfly
of the genus Simulium. The larval nematodes
spread throughout the body. When the worms die their Wolbachia symbionts are released, triggering a host immune system
response that causes intense itching and can destroy nearby tissue, such as the
eye.6
Fig1.2: Diagram
of Onchocerca volvulus
Onchocerciasis may be divided into the
following phases or types7:
Erisipela
de la costa:
An acute phase characterized by swelling of the face with erythema and itching: Onchocerciasis causes
different kinds of skin changes and these changes vary in different geographic
regions. This skin change, erisípela de la costa, of acute onchocerciasis is most commonly seen among
victims in Central and South America.8
Mal morando:
A cutaneous condition characterized by
inflammation that is accompanied by hyperpigmentation.
Sowda:
A cutaneous
condition, a localized type of onchocerciasis.
Additionally, the various skin changes
associated with onchocerciasis may be described as follows:
Leopard skin:
A term referring to the spotted depigmentation of the skin that may occur with
onchocerciasis.
Elephant skin:
A term used to describe the thickening of human skin that may be
associated with onchocerciasis.
Lizard skin:
A term used to describe the thickened, wrinkled skin changes that
may result with onchocerciasis.
There are various control programs that aim
to stop onchocerciasis from being a public health problem. The first was the
Onchocerciasis Control Programme (OCP), which was
launched in 1974 and at its peak covered 30 million people in eleven countries.
Through the use of larvicide spraying of fast flowing
rivers to control black fly populations and, from 1988 onwards, the use of ivermectin to treat infected people, the OCP eliminated
onchocerciasis as a public health problem. The OCP, a joint effort of the World
Health Organisation, the World Bank, the United
Nations Development Programme and the UN Food and
Agriculture Organization, was considered to be a success and came to an end in
2002. Continued monitoring ensures that onchocerciasis cannot reinvade the area
of the OCP.[9]
In 1992 the Onchocerciasis Elimination Programme for
the Americas (OEPA) was launched. The OEPA also relies on ivermectin.10
In 1995 the African Programme
for Onchocerciasis Control (APOC) began covering another nineteen countries and
mainly relying upon the use of ivermectin. Its goal is
to set up a community-directed supply of ivermectin
for those who are infected. In these ways, transmission has declined.11
For the treatment of individuals, doxycycline
is used to kill the Wolbachia bacteria that lives in
adult worms. This adjunct therapy has been shown to significantly lower microfilarial loads in the host, and may have activity
against the adult worms, due to the symbiotic relationship between Wolbachia
and the worm.12 In four separate trials over ten years with various dosing
regimes of doxycycline for individualized treatment,
doxycycline was found to be effective in sterilizing the female worms and
reducing their numbers over a period of four to six weeks. Research on other
antibiotics such as rifampicin has shown it to been effective in animal models
at reducing Wolbachia both as an alternative and as an adjunct to doxycycline13
However, doxycycline treatment requires daily dosing for at least four to six
weeks, making it more difficult to administer in the affected areas.14
Ivermectin is a broad-spectrum antiparasitic
agent. It is traditionally used against worms. It is mainly used in humans in
the treatment of onchocerciasis, but is also effective against other worm
infestations (such as strongyloidiasis, ascariasis, trichuriasis, filariasis and enterobiasis).
Ivermectin, under the brand name Mectizan,
is currently being used to help eliminate river blindness (onchocerciasis) in
the Americas and stop transmission of lymphatic filariasis
and onchocerciasis around the world.15 .Currently, large amounts of ivermectin are donated by Merck to fight river blindness in
countries that are unable to afford the drug. The disease is endemic in 30
African countries, 6 Latin American countries and Yemen, according to studies
conducted by the World Health Organization.
CONCLUSION:
Eye being a very sensitive organ, is easily
prone to infections. Let us take care and protect our eyes.
References:
1.
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Archived from the original on February 20,
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Rea PA, Zhang V, Baras YS (2010). "Ivermectin and RiverBlindness". American Scientist
98 (4): 294–303. http://www.americanscientist.org/issues/feature/2010/4/ivermectin-and-river-blindness.
15.
The Carter
Center. ""River Blindness (Onchocerciasis) Program"". http://www.cartercenter.org/health/river_blindness/index.html. Retrieved 2008-07-17
Received on 04.06.2011 Accepted
on 12.06.2011
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Asian J. Res. Pharm. Sci. 1(2): April-June 2011; Page 39-41