RIVER BLINDNESS -
ONCHOCERSIASIS -
TRANSPORTED BY BLACK FLY
- DISEASE ALSO IN ANIMALS -
With
compliments
to Dr. Marta Botelho and
Dr.
Pedro Faísca
NEW
published
A
case of canine ocular onchocercosis in Portugal
Veterinary
Ophthalmology (2010)
13, 2,
117–121:
included
pictures
canine ocular
onchocercosis in Portugal fulltext
BLACK FLY
laboratorium
photos Oct 08 by
Dr. Pedro
Faísca, dog
Kinky
Lisbon Portugal
pregnant female
onchocerca volvulus
laboratorium
photos Oct 08 by
Dr. Pedro
Faísca,
dog Kinky
Lisbon Portugal
O.volvulus:
females contain eggs and larvae
in different stages of development.
Microfilariae measure between 200 x 6 and 300 x 8 µm
and survive for about 6 months in hosts tissues.
(Section of an adult containing
microfilariae).
*
. * . *
This blind
eye has been taken out - the right eye still sees
MEDICATION used for Kinky 2008 with river blindness disease
:
-
Injection by veterinarian Ivermectine s.c.
NO
metilprednisolon !!! NOT ORAL AND NOT IN THE EYE
-
NOV 08: we start soon the heartworm treatment = 2 injections
see
heartworm and the premedication
-
Nov 08: Flap of the eye, temporarily closed 10 days to heal itself
better
sutured
the 3rd membrane to the upper eyelid
and
go on with the medicines for the eye
-
IN THE EYE p/o veterinarian:
Nov 08: Flap of the eye, temporarily closed 10 days to heal itself
better
and go on with the medicines for the eye
Not
available yet in Portugal Nov08 Cicatrizante ocular
con antibióticos & Visufenicol
So
we use now in The algarve - Portugal
Visine drops
Vit A every 6 hrs quantity : a lot to fill the eye
Cloranfenicol every 8 hrs
one hour (or 2) between each, I give first Visine then
Cloranfenicol then Vit A
Cicatrizante ocular
con antibióticos 3x
a day once
Visufenicol
3x a day
once
Visine every 2
hrs
- - - - -
-
> Cicatrizante ocular con antibióticos
COMPOSICION: Cada 100 ml. contiene:
L-Cistina 0.8 gr., L-Asparginina 0.22 gr., L-Glutamina 0.4 gr.,
Gentamicina S. 0.3 gr., Neomicina S. 0.5 gr., Lidocaína C. 0.005
gr., Vitamina A 90 u/c A.H. p 70000 u/g 0.64 gr., Vitamina D2 66
u/c Sol. 400000 u/g 0.082 gr. Excipientes Vaselinas oftálmicas
purísimas de uso
exclusivo, que a temperatura corporal se disuelve (no actúa como
cuerpo extrano, formando una lente de protección sobre la capa
acuosa de la córnea disponiendo un frente de ataque de sus
componentes activos). c.s.p. 100 gr.
INDICACIONES: Procesos infecciosos Oculares. Ulceras de Córnea.
Queratitis. Heridas en General. Post-Operatorio
DOSIFICACION: 1 aplicación tres veces por día.
- >
Visufenicol
COMPOSICION: Cada 100 ml. contiene:
Cloranfenicol H.S. 1.304 gr., Nafazolina C. 0.065 gr., Lidocaína C.
0.0043 gr., Vitamina A Palmitato 0.0367 gr., Tween80 4.35 gr.,
Vaselina Sólida 41.30., Vaselina Líquida 52.94 gr.
INDICACIONES: Cunjuntivitis, Blefaritis, Queratitis, Epiescleritis,
Iritis, Uveitis, Ulcera de Córnea, Tratamientos
port-quirúrgicos.
DOSIFICACION: 1 aplicación 3 veces por día.
Visine
drops, very often (about every 2 hrs)
-
ORAL (=via mouth) p/o veterinarian:
-
> NO metilprednisolon !!! NOT ORAL AND NOT IN THE
EYE
(Kinky
appeared resistent against Amoxicillina -
Cefradur)
Ciprofloxacina 500mgr (2x a day 250mgr)
!!! Vibramicina 100 mgr (5 days 3x a day 200mgr then 2x a day
200mgr)
Chimar 2x a day 2 tablets
Ulsermin to protect the stomach
Painkiller!!!
Vitamin B complex is also advisable
Multi vitamins
Afterwards treatment needed for the Onchocerca parasite:
Either Injection Ivomec(includes Moxidectine) or heartgard tablet
monthly
* . * . *
ARTICLE IN THE LANCET
*
. * . *
Review several studies :
link
&
A.
Hoerauf
Effects
on ivermectin etc
Model-based
analysis of trial data:
microfilaria and worm-productivity loss after
diethylcarbamazine-albendazole or ivermectin-albendazole
combination therapy against Wuchereria bancrofti.
*
. * . *
!!
plpnemweb.ucdavis.edu/NEMAPLEX/Taxadata/Ovolvulus.HTM
!! :
Filarioidea Onchocercidae
Onchocerca volvulus has, for
many years, been regarded as the causative agent of River
Blindness.
Reports in 2002 indicate that the
bacterium Wolbachia, which is associated with the
nematodes and which may be required for their growth and
reproduction, has a major role in the pathology of the
disease.
Wolbachia incites a severe inflammatory
response, leading to blindness and serious skin disorders.
The immune response of the host is also involved in the disease.
Mice lacking an immune cell receptor molecule called TLR4 showed
fewer signs of eye inflammation when exposed to Wolbachia-laden
worm extract (Hoerauf and Volkmann, 2002).
Management:
Surgical removal of nematode from eye; chemotherapy.
Pinpointing bacteria as the direct factor behind the virulence
suggests new therapies for combating river blindness, especially
since recent studies in infected humans have shown that the
bacteria can be killed by the common antibiotic
doxycycline.
The battle against river
blindness is taking place on two fronts at the moment:
* programs to control the spread of the black fly.
* distribution of an anti-worm medicine,
ivermectin.
Antibiotic treatment of Wolbachia may help reduce the severity of
the symptoms of river blindness in already-infected
individuals.
Targeting Wolbachia could prevent the spread of Onchocerca. Recent
studies have shown that doxycycline treatments in infected humans
kills Wolbachia and also sterilize the nematodes, breaking the life
cycle. In contrast, ivermectin treatments only reduce numbers of
microfilariae for a few months and repeated treatments are
necessary.
* . * . *
commons.wikimedia.org/wiki/Image:Onchocerca_volvulus_LifeCycle.gif
:
Geographic distribution of Onchocerciasis
:
O.volvulus: geographic distribution.
onchocerciasis occurs especially in Tropical Africa,
between the 15° north and the 13° south (high endemicity in B.Faso
and Ghana).
Foci are present in Southern Arabia, Yemen and in America
(Mexico, Guatemala, Colombia, Ecuador, Brazil,
Venezuela).
www.cdfound.to.it/hTML/onc1.htm :
ONCHOCERCA VOLVULUS
:
www.emedicine.com/med/topic1667.htm
:
Causes
* Onchocerciasis is transmitted by the bite of black flies of the
genus Simulium. Black flies breed in well-oxygenated water found in
fast-moving streams and rivers. Females require a blood meal for
ovulation, and they can transmit infective-stage larvae as well as
receive microfilariae during the blood meal. The black fly tends to
stay within 2 km of its breeding site.
* During the blood meal, the black fly can transmit infective-stage
larvae to the host. Fly saliva acts as a chemoattractant for
microfilariae in the surrounding subcutaneous tissues. Large
quantities of microfilariae may be ingested during the blood meal.
Microfilariae then migrate to the fly's flight muscles, where they
emerge as infective-stage larvae after 6-18 days and travel to the
proboscis.
Medical
Care
* The current mainstay of treatment is ivermectin. Mass treatment
campaigns are being run through the World Health Organization.
Merck has made their drug (Mectizan) available without charge for
use in the Onchocerciasis Control Programme (OCP). In 1997, more
than 18 million people in endemic areas received treatment with
ivermectin.
*
o Because ivermectin is a microfilaricide and does not kill adult
worms, the treatment does not cure the disease. Rather, it
significantly reduces microfilarial burden, which affects several
facets of the disease. Ivermectin treatment decreases transmission
and reduces the prevalence of onchodermatitis, sclerosing
keratitis, and blindness.
o The optimal duration of treatment with ivermectin is not
currently known. In hyperendemic areas, the drug should be
administered every 6 or 12 months for the life span of the adult
worm.
!!! * Newer
therapeutic strategies target bacteria of the Wolbachia species,
known endosymbionts in O volvulus. Doxycycline 100 mg/d
administered for 6-8 weeks has demonstrated efficacy in reducing
microfilarial loads, sterilizing adult worms, and decreasing adult
worm viability. However, the efficiency of using doxycycline in
mass treatment campaigns has been
questioned.
Surgical
Care
Removal of all subcutaneous nodules can be curative; however, many
nodules are difficult to find.
Background
Onchocerciasis is a chronic parasitic disease caused by the
filarial nematode Onchocerca volvulus. Infection affects multiple
organ systems, but the greatest morbidity is due to cutaneous and
ophthalmologic complications. The disease is often called river
blindness because infective microfilariae are acquired at the
breeding site of the Simulium damnosum black fly vector.
Onchocerciasis occurs in 38 countries worldwide, including areas of
Africa, South America, and the Middle East. More than 123 million
people live in endemic areas, and an estimated 18 million people
are currently infected. Of those infected, about 270,000 are blind,
and an additional 500,000 have severe visual impairment.
In 1875, O'Neill first associated the microfilariae of O volvulus
with an irritating papular dermatitis called craw-craw in Ghana.
Eighteen years later, Leuckhart first described the adult worm of
onchocerciasis in subcutaneous nodules. In 1917, Robles published
findings on a new disease from Guatemala with associated
subcutaneous nodules, anterior ocular lesions, dermatitis, and
microfilariae. In Sierra Leone in 1923, Blacklock identified the
black fly, Simulium damnosum, as the disease vector.
Pathophysiology
O volvulus has a 5-stage life cycle, and humans are the only
definitive hosts. Simulium black flies are obligate intermediate
hosts and release infective-stage larvae during a blood meal. In
the human host, the larvae molt twice to become male and female
adult worms. This process occurs in subcutaneous nodules known as
onchocercomata, and a mature female can produce microfilariae after
6-12 months.
Female worm length ranges from 30-80 cm, and more than 1 worm may
be coiled in a subcutaneous nodule. Male adult worms are usually
3-5 cm in length and migrate between various subcutaneous nodules
to inseminate females. Over a life span of up to 14 years, the
female worms produce 700-1900 microfilariae daily.
Microfilariae are usually 220-360 µm in length. When released from
the female, microfilariae can migrate throughout the subcutaneous
tissues and skin; they have a particular affinity for ocular
tissues. When microfilariae are ingested in the blood meal of the
black fly, they pass through 2 molts in a 2- to 3-week period to
become infective-stage larvae.
Microfilariae live for 6-30 months; most die without completing
their life cycle. Symptoms of onchocerciasis are caused by
localized host inflammatory responses to the dead or dying
microfilariae. In persons with heavy infection, as many as 100,000
microfilariae die each day. The predominant immune response is
production of antibodies, but cellular responses, particularly
those of eosinophils, are important.
Frequency
United States
Sporadic cases are observed in immigrants or travelers from endemic
areas.
International
Onchocerciasis predominantly occurs in 30 countries of West and
sub-Saharan Africa. In Africa, hyperendemic villages can have
infection rates of 100%; 10% of the entire village may be blind,
including up to 50% of those aged 40 years and older. Enlarging
foci of infection are located in Central and South America,
particularly in Guatemala, Ecuador, Mexico, Brazil, Venezuela, and
Colombia. The Middle Eastern countries of Saudi Arabia and Yemen
are also endemic for onchocerciasis.
Mortality/Morbidity
Onchocerciasis does not directly cause death, but social and
economic consequences can be devastating.
* Onchodermatitis is the leading cause of morbidity in endemic
areas. Disfigurement resulting from skin lesions and intense
pruritus can cause devastating psychosocial consequences and
isolation.
* Vision loss occurs in many areas of Africa and South America.
Persons blinded by onchocerciasis have a life expectancy of 10
years after onset of blindness. Overall life expectancy of an
infected individual in endemic areas is one-third that of an
uninfected individual.
* In Africa, blindness is more commonly reported in the savanna and
woodland areas, whereas depigmented skin disorders are more
frequent in the forests.
Race
All persons in regions of endemicity, regardless of race, are at
risk for infection.
Sex
Onchocerciasis is associated with no known sex predilection.
Age
* Greater morbidity with age is the result of cumulative exposure
in endemic areas.
* Blindness tends to occur in adulthood after many years of
infection.
* Transplacental infection can occur with microfilariae, but
transmission of infective larvae from the black fly is required for
the disease to progress.
CLINICAL
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* Authors and Editors
* Introduction
* Clinical
* Differentials
* Workup
* Treatment
* Medication
* Follow-up
* Acknowledgments
* Multimedia
* References
History
Onchocerciasis is a chronic infection with clinical manifestations
that develop years after initial infection.
* The initial bite of the black fly tends to go unnoticed. A 1- to
2-year latent period is typical as the infective larvae migrate and
develop into adult worms.
* Pruritus is the most common early symptom of infection. Itching
and scratching ranges from mild to severe and from intermittent to
unremitting. The term craw-craw is used in West Africa to describe
chronic onchodermatitis and its associated scratch-induced
excoriations, ulcerations, and secondary infection.
* Lymphadenopathy tends to occur in the inguinal and femoral
regions.
* Subcutaneous nodules (onchocercomata) usually develop over bony
prominences. African Simulium species tend to bite the ribs, hips,
iliac crests and lower limbs, whereas South American Simulium
species prefer the scalp and upper body.
* VisualVisual symptoms range from itching, redness, photophobia,
and blurred vision in early disease to variable degrees of vision
loss and frank blindness later on.
* Weight loss may also occur.
Physical
* Physical findings are diverse and range from early mild
inflammatory lesions to chronic debilitating cutaneous and
ophthalmic lesions.
* Onchodermatitis refers to the various cutaneous findings in
infected individuals, and it has been classified into 6 diseases,
as follows:
*
o Acute papular dermatitis involves numerous small pruritic papules
that may progress to vesicles or pustules. Papules tend to develop
on limbs, shoulders, face, and trunk.
o Chronic papular dermatitis is indicated by larger, pruritic,
flat-topped papules distributed symmetrically over the buttocks,
waist, and shoulders. Affected individuals may also demonstrate
hyperpigmented papules and hyperkeratosis. Sowda is a localized
form of chronic papular dermatitis that is usually confined to one
extremity; characteristic findings also include hyperpigmented
papules, regional lymphadenopathy, and edema.
* Lichenified dermatitis is an intensely pruritic dermatitis with
excoriations and hyperpigmented and hyperkeratotic papules and
plaques.
* Atrophy includes degeneration of elastic fibers and other
structural elements of the skin due to chronic infection. The skin
appears wrinkled and thin, and atrophic changes are most often
noted over the buttocks and limbs.
* Depigmentation is a common finding in advanced onchocerciasis.
The patchy lesions resemble vitiligo and are commonly found on the
shins (also known as leopard skin).
* Lizard skin refers to the chronic ichthyoticlike changes that
occur with longstanding infection.
* Soft tissue disease manifests as the following:
*
o Subcutaneous nodules (onchocercomata), which contain adult worms
and are generally found over bony prominences.
o Lymphadenopathy: "Hanging groin" refers to inguinal
lymphadenopathy accompanied by atrophy of the skin.
* Ocular findings
*
o Microfilariae enter the eye by direct invasion from the
conjunctiva into the sclera or cornea. They may be identified in
ocular tissues early in the disease.
o Ophthalmologic disease is caused by inflammatory responses to
microfilariae as they migrate through the eye. The inflammatory
reaction intensifies when microfilariae die. This intense host
immune reaction can cause the following ocular findings, which are
typically bilateral:
o
+ Punctate keratitis is the initial lesion and is caused by an
immune response to dead microfilariae. It tends to resolve as
inflammation wanes.
+ Sclerosing keratitis results from years of heavy prolonged
infection; corneal opacities accumulate, causing irreversible
visual impairment or blindness.
+ Anterior uveitis is caused by microfilariae invading the iris and
ciliary body, which results in both granulomatous and
nongranulomatous inflammation. This can lead to iris atrophy,
inflammatory glaucoma, and cataracts.
+ Posterior segment lesions are also due to inflammatory responses
to microfilarial death. This causes disturbances of the retinal
pigment epithelium and can lead to chorioretinitis, chorioretinal
atrophy, and subretinal fibrosis. Only 5% of patients have active
retinitis.
+ Active optic neuritis may be due to infection or may develop
after systemic treatment. Both optic neuritis and optic atrophy can
cause blindness in up to 10% of some populations with
onchocerciasis.
Causes
* Onchocerciasis is transmitted by the bite of black flies of the
genus Simulium. Black flies breed in well-oxygenated water found in
fast-moving streams and rivers. Females require a blood meal for
ovulation, and they can transmit infective-stage larvae as well as
receive microfilariae during the blood meal. The black fly tends to
stay within 2 km of its breeding site.
* During the blood meal, the black fly can transmit infective-stage
larvae to the host. Fly saliva acts as a chemoattractant for
microfilariae in the surrounding subcutaneous tissues. Large
quantities of microfilariae may be ingested during the blood meal.
Microfilariae then migrate to the fly's flight muscles, where they
emerge as infective-stage larvae after 6-18 days and travel to the
proboscis.
Drug Category: Antiparasitics
Inhibit growth and proliferation of parasites.
Drug Name Ivermectin (Mectizan, Stromectol)
Description Selectively binds glutamate-gated chloride ion channels
in invertebrate nerve and muscle cells, causing cell death.
Half-life is 16 h. Metabolized in the liver. DOC for treating
onchocerciasis.
Adult Dose 150 mcg/kg/d PO as single dose q6-12mo
Pediatric Dose <5 years: Not established
>5 years: Administer as in adults
Contraindications Documented hypersensitivity.
Interactions May interact with other ligand-gated chloride
channels, such as those gated by GABA
Pregnancy C - Safety for use during pregnancy has not been
established.
Precautions Caution in pregnancy, breastfeeding women with infants
<3 mo, and in elderly persons with serious medical problems;
immunocompromised patients may require repeated courses of therapy;
adverse effects typically occur within first 48 h after first dose
and include edema, pruritus, arthralgias, and postural hypotension;
may be associated with nausea, vomiting, mild CNS depression, and
drowsiness; caution in regions where onchocerciasis and Loa Loa
(another filarial disease) are both endemic; patients with high
microfilarial loads of Loa Loa are susceptible to encephalopathy
upon treatment with ivermectin
Drug Name Suramin (Metaret)
Description Only available macrofilaricidal agent. Extremely toxic;
each dose requires several days of hospitalization. WHO only
recommends use in selected individuals in nonendemic areas for
curative treatment of severe hyperreactive onchodermatitis
uncontrolled by repeated ivermectin treatment. Granted orphan drug
status and available from the CDC under brand names Antrypol, Bayer
205, Belganyl, Fourneau 309, Germanin, Moranyl, and
Naphuride.
Adult Dose <60 kg: Not established
Parenteral/IV:>60 kg: 0.2 g week 1; 0.4 g week 2; 0.6 g week 3;
0.8 g week 4; 1 g week 5 and 6; total dose 4 g
Pediatric Dose Not established
Contraindications Documented hypersensitivity
Interactions None reported
Pregnancy X - Contraindicated in pregnancy
Precautions Consult WHO prior to treatment; contraindicated in
pregnant women with onchocerciasis, but may be used in African
trypanosomiasis; may cause vision loss
Drug Name Diethylcarbamazine (Hetrazan)
Description Piperazine derivative microfilaricidal agent that can
cause frequent unacceptable reactions ranging from urticaria and
angioedema to death. Only used for Mazzotti test and not for
treatment.
Adult Dose 6 mg PO once (Mazzotti test)
Pediatric Dose Not established
Contraindications Documented hypersensitivity
Interactions None reported
Pregnancy C - Safety for use during pregnancy has not been
established.
Precautions Contact a physician if itching and facial swelling
(especially eyes), skin rash, fever, and painful or tender glands
(armpits, groin, neck) occur; not known to cause birth defects, but
do not treat during pregnancy; safety in breastfeeding unknown;
prolonged use is associated with vision loss, night blindness, and
tunnel vision
- - - - - - - -
From
Wikipedia, the free encyclopedia
The life cycle of O. volvulus
(Illustration: Giovanni Maki)
Adult Black Fly (Simulium yahense) with
parasite (Onchocerca volvulus) emerging from
the insect's antenna. Magnified 100x.
Onchocerciasis
Classification and external resources
ICD-10 B73.
ICD-9 125.3
DiseasesDB 9218
eMedicine med/1667 oph/709
MeSH D009855
Onchocerca volvulus
O. volvulus, the causative agent of river blindness.
Scientific classification
Kingdom: Animalia
Phylum: Nematoda
Class: Secernentea
Order: Spirurida
Family: Onchocercidae
Genus: Onchocerca
Species: O. volvulus
Binomial name
Onchocerca volvulus
Bickel 1982
Onchocerciasis (pronounced /ˈɒnkoʊsɝːˈsaɪəsɨs/
or /ˈɒnkoʊsɝːˈkaɪəsɨs/),[1] also known as river blindness, is the
world's second leading infectious cause of blindness. It is caused
by Onchocerca volvulus, a nematode that can live for up to fifteen
years in the human body.[2] It is transmitted to people through the
bite of a black fly. The worms spread throughout the body, and when
they die, they cause intense itching and a strong immune system
response that can destroy nearby tissue, such as the eye.[3]
The primary treatment is a drug, ivermectin. For best effect,
entire communities are treated at the same time. A single dose may
kill first-stage larvae (microfilariae) in infected people and
prevent transmission for many months in the remaining
population.[4]
About 18 million people are currently infected with this parasite;
approximately 300,000 have been irreversibly blinded by
it.[5]
* . * . *
In/Out Patient Meds:
* Ivermectin 150 mcg/kg PO once every 6-12 months
* . * . *
www.soton.ac.uk/~ceb/Diagnosis/Vol10.htm
:
Microfilaria worms found in tissue and skin
The main species of microfilariae found in the skin and tissue are
Onchocerca volvulus and Mansonella streptocerca. Microfilariae of
Onchocerca volvulus and less often, Mansonella streptocerca migrate
through the dermis causing itching and skin texture changes and
occasionally arrive in the eye where they cause blindness.
Detection of these microfilariae is from skin snips or nodule
biopsies. When high numbers of microfilariae are present, they can
occasionally be found in the blood and urine.
Onchocerca volvulus
Introduction
Onchocerca volvulus is mainly found in West Africa and Central and
South America. Onchocerciasis, also known as river blindness, is a
major public health problem, especially in West Africa, there an
eradication program has been established. It is one of the world’s
most distressing diseases of helminth origin, often resulting in
blindness. Onchocerca volvulus is transmitted by the species
Simulium or black fly whose breeding habitat is by fast flowing
rivers or streams, therefore there is a patchy distribution of the
disease as it is specified to where water courses are. The adult
worms are found in nodules or onchodermata in superficial sites,
but may invade other tissues.
It is estimated that there are 18 million cases worldwide with 17.5
million being found in Africa. Nigeria is the most infected region.
The rate of morbidity is high in relation to those with an
infection.
Life cycle
Figure 11. Diagram showing the life cycle of Onchocerca volvulus, a
filarial nematode which causes onchocerciasis, or River blindness.
It is known as river blindness due to the vector, Simulium
damnosum, breeding in fast flowing rivers.
The life cycle is similar to W. bancrofti, except that the
intermediate hosts are various species from the genus Simulium
(Black flies), the most important species is Simulium damnosum.
(Fig. 11)
The microfilariae are ingested by a Black fly during a blood meal,
from where they are carried to the midgut where they penetrate the
epithelium and migrate, via the haemocoele, to the indirect flight
muscles. Here they undergo two moults, L1 – L3 and develop into
infective L3 larvae which move to the mouth parts. Development is
completed in 6 – 9 days.
When the infected fly takes another blood meal the infective larvae
are once again transmitted into another host (definitive host). The
microfilariae are released from the mouth parts and transmitted
directly into the hosts bloodstream. Moulting takes place form L3 -
L4 within 2 - 5 days and the larvae then migrate widely through the
body under the skin and between muscles, ligaments and tendons. The
final moult to L5 occurs at 1.5 – 2.5 months after transmission.
Male worms are known to mature in about 4 months later. Female
worms initiate the formation of the nodules and the males may join
later. The sexually mature female worms release microfilariae which
migrate out from the nodules into the skin and other tissues, most
significantly into the eye.
Morphology
The whitish adult worm lies coiled within capsules in the fibrous
tissue. The female can measure up to 50cm while the males are
shorter measuring up to 5 cm. The microfilariae of O. volvulus are
unsheathed and are usually found in the dermis. They measure
between 221 - 287mm long. (Fig. 12 & Table 2)
Figure 12. Onchocerca volvulus microfilariae after being released
by the adult female worm. They escape to the subcutaneous tissues
and the eye and can be recovered with blood-free skin snips. (Wet
mount preparation) (www.cdfound.to.it)
Clinical Disease
Clinical manifestations are due to microfilarie in the epidermis.
(Table 4)
Light infections may be asymptomatic or cause pruritis. This leads
to scratching which can result in infection. Lyphadenopathy may
also be a feature of early infection. After months or years,
onchodermatitis results in secondary stage of thickening due to
intradermal oedema and pachydermis. There is a loss of elastic
fibres resulting in hanging groin, hernias and elephantiasis of the
scrotum. There is finally atrophy of the skin resulting in loss of
elasticity. There is mottled depigmentation of the skin.
Ocular lesions are related to the intensity of the microfilariae in
the skin. Ocular lesions include sclerosing keratitis, secondary
glaucoma and cataract, coroidoretinitis and fluffy corneal
opacities. The major complication of onchocerciasis is the
development of lesions in the eye which may result in blindness or
other distressing ocular diseases.
Laboratory diagnosis
1. Analysis of Skin Snips
Small amounts of skin are collected by using a needle to raise the
skin and then to slice about 1 mg of skin to a depth of 0.5mm.
Snips are collected from several sites, usually the shoulders or
the buttocks and sometimes the chest and calves. The snips are
placed immediately in 0.5ml normal saline in a microtitre plate and
left for 4 hours to allow the microfilariae to migrate out of the
tissues. After 4 hours, the wells are examined using an inversion
microscope. The microfilariae should still be moving and can be
identified from the table below. The microfilariae can also be
collected by filtration or centrifugation and the deposit
containing microfilariae can be stained with Giemsa at pH
6.8.
2. Analysis of Biopsies
Biopsies of tissue nodules can be dabbed on to a slide to produce
impression smears and then stained with Giemsa stain at pH 6.8 for
the presence of microfilariae.
Recent advances in diagnostic methods includes and ELISA-based
antibody detection assay which utilises a cocktail of recombinant
antigens. The advantages of using this test is that it is highly
sensitive (almost 100% in onchocerciasis foci). It is also highly
specific (100%), it also uses finger prick blood. Therefore,
reducing the painful procedure of gaining a skin snip.
The disadvantages is that it requires advanced ELISA apparatus and
reagents and cannot distinguish between past and present infections
due to it detecting antibodies which stay present in the body for a
long time after the infection. Another modern detection method is
for Parasite DNA detection, which is based on the amplification of
specific DNA sequences form microfilariae using molecular biology
technology. The advantages of this technique is its exquisite
sensitivity and detects active infections only. The disadvantages
are that it requires specialised equipment and expensive reagents.
Also it still require a skin snip but a urine assay is a
possibility for the future.
Thick microfilaria. Does not have a sheath. Head often spatulate.
Nuclei do not extend to tip of tail. Found only in skin.
* . * . *
With compliments to Dr. Marta Botelho and Dr. Pedro Faísca
