Onchocerciasis is a river blindness disease caused by the filarial nematode parasite Onchocerca volvulus.

1. ONCHOCERCIASIS, NIGERIAN
PERSPECTIVE
B Y
UWAMOSE,
Martin Nelson Osaigbokan

2. Onchocerciasis a River Blindness disease is a chronic parasitic
multi systemic disease caused by the filarial nematode
Onchocerca volvulus.
The parasite causes blindness and severe skin diseases in tropical
regions of the world.
Approximately 18–44 million individuals in the world have
Onchocerciasis infection. It is the second-leading infectious cause
of preventable blindness in the world after Trachoma (WHO
2012).
Man is the only definitive host of this parasite and acquire
infection through the bite of black fly (genus Simulium).
The damage caused by this disease is irreversible. When someone
is blinded by the parasite there is no cure; you can only kill the
parasites.

3.  Nigeria is the most endemic country in the world for
Onchocerciasis.
 First reported in northern Nigeria in 1908 (Budden 1956).
 Endemic areas extend from the North, Southwest & Southeastern
part of the country with highest prevalence in Zamfara, Kwara -
NW Nigeria and Enugu, Imo, Ebonyi - SE Nigeria (Meredith 2012)
 The provisional estimates had suggested that 7–10 million Nigerians
are infected with Onchocerca volvulus, approximately 40 million
are at risk of the disease and 120,000 cases of onchocerciasis-related
blindness (WHO 2010).
 The disease is lower in individuals between the age of 0–10 years
but increases with a peak in individuals between the age of 20-30
years (Uttah 2010).

4. Presence
Absence
Lakes
States boundaries
Fig. 1: Map showing the presences of Onchocerciasis in Nigeria
Source:WHO 2010

5. The only known vectors of O. volvulus are the female
black flies of the genus Simulium.
The fly bites during daylight hours.
Eggs require fast-running rivers which have well-oxygenated
water for breeding grounds. This is
important because larvae of O. volvulus have an
obligatory aquatic stage during which they require a high
oxygen tension.
Adults emerge after 8-12 days following egg production.
The adult fly has the ability to travel hundreds of
kilometres in flight on wind currents.
Their life span is about 4 weeks.

6. Fig. 2: Female black fly of the genus Simulium
Source:WHO 2010.

7. MORPHOLOGY OF THE
PARASITE
Adult worms are white, opalescent and transparent.
They are slender and blunt at both ends.
They are usually found knotted together in pairs or
groups in subcutaneous tissues.
Males measures 1.9-4.2cm in length and has a coiled tail.
The females are much longer, measuring 33.5-50cm in
length.
Adult worms live long; the female has an average life
span of 8 years.

8. Fig. 3: Onchocerca volvulus adult worms
Source: Google images.

9. ETIOLOGY: study of the cause of
diseases
Microfilaria invade the midgut of the fly, advance to
the thoracic muscles where they undergo
differentiation into L1 larva within 28 hours after the
blood meal.
They moth twice producing L2 and L3 larva (infective
larva) within 06 hours and 7 days respectively.
Infective L3 larva migrates to the proboscis for future
deposition into human skin during the next blood
meal.
When the Fly bites another person, Infective L3 larvae
are transmitted to human skin.

10. ETIOLOGY (CONT.)
The larvae move under the skin and form nodules where
they develop into adult worms in 12 to 18 months. Adult
worms pair and mate in the human host.
Female Onchocerca gives birth daily to thousands of
microscopic larvae (microfilaria)
Microfilaria released from the nodules traverse the skin
and connective tissue easily.
The most common migration sites are subepidermal
lymphatics and the anterior chamber of the eye.

11. LIFE CYCLE OVERVIEW
Onchocerciasis is transmitted
person to person through the
bites of Simulium black fly
The black flies breed in fast
flowing water and streams.
When a Black fly bites an infected
person, microfilariae are transferred
from the person to the fly.
Between 1-3 weeks the microfilariae
develop in the fly and become infective
larvae.
These are passed to the human host
and the larvae migrate to
subcutaneous tissue, form nodules
and slowly mature into adult worms
vectors.

12. Fig. 4: Life cycle of Onchocercia volvulus
Source: Google images.

13. Fig. 5: Life cycle of Onchocercia volvulus
Source: CDC images.

14. PATHOGENESIS
The adult worms and the microfilariae contribute to the
pathogenesis of Onchocerciasis. Adult worms isolated in nodules
are not directly harmful to the patient, their progeny
(Microfilaria) are responsible for the damage related to
Onchocerciasis.
In some infected persons, 100,000 or more microfilariae die each
day.
Live microfilariae found in the eye do little, but when they die is
the problem. Most microfilariae die as immature worms in the
host.
Inflammatory and immune reaction to dead or dying
microfilariae are responsible for the clinical manifestation.
This causes the most important reason of blindness, which is
sclerosing (scarring) keratitis, a hardening inflammation of the

15. SIGNS AND SYMPTOMS
The symptoms include:
 Preventable blindness
 Skin rashes
 Lesions
 Itching
 Skin depigmentation

16. Fig. 4: Depigmentation over the skin in later onchocerciasis (Leopard skin).
Source: Google images.

17. Fig. 5: Eye lesions in Onchocerciasis
Source: Google images.

18. Fig. 6: Preventive blindness in Onchocerciasis
Source: Google images.

19. DIAGNOSIS
 The best method for diagnosis is identification of microfilariae in
bloodless skin snips.
 Buttocks and legs are often most heavily infected and are most
likely to yield microfilariae.
 A small piece of skin is raise with a needle and clipped with
a razor or scissors.

20. DIAGNOSIS CONT.
In heavily infected individuals, microfilariae can even be found in
the blood, sputum and urine.
Fig. 7: Living microfilariae of Onchocerca volvulus on urine
sample
Source: Google images
Fig. 8: Living microfilariae of Onchocerca volvulus in blood
sample
Source: Google images

21. TREATMENT
 The treatment is with a single of Ivermectin (150
microglkg).
 It kills the microfilaria rapidly,
 Reduces production of microfilaria from adult worm for
several month.
 After treatment, microfilaria disappears from the skin
within 1 week and from eye within 3 months.
NOTE: There is no cure; once someone is blind by the
parasite, you can only kill the parasites
21

22. PREVENTION AND CONTROL
 Primary means of preventing Onchocerciasis in Nigeria
include:
1. Vector control – applications of environmentally-safe
insecticides to the black fly's breeding areas
(fast-flowing rivers) during the rainy season.
2. Mass treatment with Ivermectin.
22

23. CONCLUSION
Onchocerciasis is one of the neglected tropical diseases
of public health concern in Nigeria. It is common in rural
area where black flies have favourable environment to
habit and reproduce as the outbreak and spread of this
disease rely on the activities and survival of black fly.
The high prevalence of microfilariae in Nigeria
underscore the need for renewed awareness campaign to
bring the attention of individuals in endemic areas to the
importance of personal protective measures against the
infective bites of the black fly vector. This is also a
wake-up call to health authorities to embark on massive
community treatment with Ivermectin. 23

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