Onchocerciasis, also known as river blindness, is a filarial infection caused by the parasitic worm Onchocerca volvulus, transmitted through bites from infected blackflies. The disease primarily affects the skin and eyes, leading to severe symptoms including blindness and skin lesions, and is prevalent in 31 African countries as well as some regions in Latin America and Yemen. Diagnosis involves clinical evaluation and various tests, and treatment includes ivermectin, while vector control strategies are essential to curb transmission.

1. Onchocerciasis
Group II: presentation

2. PRESENTATION CONTENT
– Description and Classification
– Morphology
– Life cycle
– Pathogenesis and Symptomatology
– Diagnosis (Clinical and Laboratory)
– Treatment
– Epidemiology
– Prevention and Control

3. DESCRIPTION AND
CLASSIFICATION
• Onchocerciasis (also known as River blindness, Robles’
Disease) is a filarial infection which causes blindness
and debilitating skin lesions as caused by parasitic worm
Onchocerca volvulus. It is transmitted to humans through
exposure to repeated bites of infected blackflies of the
genus Simulium.
• The fly breeds in rivers with a prevalence for turbulent
and highly oxygenated waters.
• Both the eyes and the skin are affected by the condition
commonly known as ‘River Blindness’.

4. DESCRIPTION AND
CLASSIFICATION
Taxonomy
• Kingdom - Animalia
• Phylum - Nematoda
• Class - Rhabditea
• Order - Spirurida
• Super Family - Filaroidea
• Family - Onchocercidae
• Genus – Onchocerca
• Specie - volvulus

5. MORPHOLOGY
• Adult worms live mainly in subcutaneous
nodules or are free in the skin.
• The ratio of adult females : males in nodules is
about 3 : 1. The adults are slender white
worms, the male being 2–5 cm × 0.2 mm and
the females 35–70 cm × 0.4 mm.
• The female produces sheath-less microfilariae
measuring 300 × 8 μm with an expanded head
free of nuclei and a sharply pointed tail.
• The tail of the male is curved ventrally.

6. Each adult female worm, thin but
more than 1/2 metre in length,
produces millions of microfilariae
(microscopic larvae) that migrate
throughout the body and give rise to
a variety of symptoms:

7. Onchocerca volvulus
microfilariae from skin snips
A long head space

8. Onchocerca Microfilaria with no sheath.

9. LIFE CYCLE

10. LIFE CYCLE
• During a blood meal, an infected blackfly (genus
Simulium) introduces third-stage filarial larvae onto
the skin of the human host, where they penetrate
into the bite wound.
• Once in the subcutaneous tissues the larvae develop
into adult filariae, which commonly reside in
nodules in subcutaneous connective tissues.
• Adults can live in the nodules for approximately 15
years. Some nodules may contain numerous male
and female worms.
• In the subcutaneous nodule, the female worms are
capable of producing microfilariae for

11. LIFE CYCLE
• Now during blood meal, A blackfly ingests the
microfilariae.
• After ingestion, the microfilariae migrate from the
blackfly's midgut through the hemocoel to the
thoracic muscles.
• There the microfilariae develop into first-stage
larvae and subsequently into third-stage infective
larvae.
• The third-stage infective larvae migrate to the
blackfly's proboscis and can infect another human
when the fly takes a blood meal.

12. PATHOGENESIS
• After inoculation following a bite from an infected fly, the
worm matures (in several months) in subcutaneous tissue
and connective tissues.
• At sites of trauma, over bony prominences and around
joints, fibrosis may form nodules around adult worms which
otherwise causes no direct damage.
• Innumerable microfilariae discharged by the female O.
volvulus move actively in these nodules and in the adjacent
tissues and are widely distributed and may invade the eye.
• Live microfilaria elicit little tissue reaction but dead ones
cause severe allergic inflammation leading to hyaline
necrosis, loss of collagen and elastin.

13. PATHOGENESIS CONTINUING
• The nodule formed is part of interaction
between the human host and the parasite.
• Inside the nodules the worms are actually
safe from the human immune response.
• Death of microfilaria in the eye causes
inflammation and may lead to blindness.

14. SYMPTOMATOLOGY
Main clinical manifestations are the
following;
1.The subcutaneous (or deeper) nodules
(Onchocercoma).
2.Onchocercal Dermatitis.
3.Eye disease.
4.Other Conditions.

15. 1. Onchocercoma/Nodule
formation.
May be visible or palpable but otherwise
asymptomatic. They are composed of
inflammatory cells and fibrotic tissue in
various proportions. Old nodules may
caseate or calsify.

16. 2. Onchocercal Dermatitis.
- Dermal skin changes occur when the microfilaria
undergo destruction in the skin and vary from a few
papules to the extensive pigmentary and chronic
atrophic changes.
• Itching (filarial itch) and rash are the most important
early manifestations of onchocercal dermatitis.
• In the later stages, there may be heavy lichenification
and thickening of the skin (Lizard Skin)
• Hanging groin is a skin manifestation in
Onchocerciasis that is characterized with pendulous
folds following loss of skin elastic fibers.

18. Onchocercal Dermatitis
Continuing;
Leopard Skin - consists of vitiligo-like lesions
with hypopigmented patches containing
perifollicular spots of normally pigmented
skin often affects the shins in a symmetrical
pattern.

19. Onchocercal Dermatitis
Continuing;
• Sowda - is the result of a strong immune
response on the part of the host. It is
characterized by intense itching.

20. 3. Eye Disease.
Many changes in both anterior and posterior segments can
occur in the eyes of infected individuals. The more serious
lesions may progress to blindness. Manifest in 2 ways;
• Anterior Segment Lesions - Punctate keratitis (snowflake
opacities) occurs as an acute inflammatory reaction around
microfilariae. These lesions are reversible. In sclerosing
keratitis, vascular infiltrates begin at the limbus and pass
inwards, resulting in a cellular organization and excessive
scarring of the cornea, which causes blindness.
• Posterior Segment Lesions - Both optic nerve atrophy and
choroidoretinitis of the posterior segment may result in
blindness.

22. 4. Other Conditions.
Onchocerciasis has been associated with weight loss
and musculoskeletal pain. Several reports have
indicated a higher than normal frequency of epilepsy in
onchocerciasis hyperendemic areas.
Onchocerciasis has also been associated with a
syndrome of growth arrest and delayed sexual
development (the Nakalanga syndrome) seen in Uganda
and Burundi.

27. DIAGNOSIS
Diagnosis of Onchocerciasis is possible through a variety of
methods;
1.Clinical diagnosis.
2.Ultrasonography - has proved capable of detecting
onchocercal nodules in the tissues of patients. This technique
may be especially useful for detecting deep non-palpable
nodules, and for assessing drug effects on adult worms.
3.Mazotti test - Done when skin snip is negative in which a Pt is
given low single dose of oral 50mg
Diethylcarbamazine(DEC) and observe intense pruritic skin
rash after 1-24hrs. Can precipitate the condition , not
recommended.

28. DIAGNOSIS CONTINUING;
4. Parasitological diagnosis.
Skin snips is the most common method described. A tool is used to scrape
a razor thin piece of skin from an individual's arm. This primitive biopsy is
combined with saline and examined under a microscope to view
microfilariae. This method needs to be done on individuals that have been
infected for years or the microfilariae will not be present near the epidermis.
5. Immunodiagnosis. They are of limited practical use because of low of low
specificity and sensitivity of the tests. It has cross reactivity with other
nematode infection as well as cannot distinguish between past and current
infection.
6. PCR based diagnosis.
7. Slit lamp can be used to visualize microfilaria in individuals with eye
involvement.
8. OTHERS - DEC patch test, ELISA, Rapid-Format antibody card tests.

30. TREATMENT
Pharmacological;
Ivermectin in a single oral dose of 150 μg/kg body weight causes
a rapid elimination of microfilariae from the skin.
NOTE; DEC is no longer recommended for the treatment of
onchocerciasis.
Moxidectin was approved for Onchocerciasis in 2018 for people
over the age of 11 in the united states, Safety of multiple doses is
unclear.
Non Pharmacological;
Nodulectomy has only limited use because many worms are
present outside the nodules and some nodules are not palpable.
Head nodules should be excised because their presence
increases the risk of eye disease and blindness.

31. EPIDEMIOLOGY
More than 99% of infected people live in 31 African countries. The disease
also exists in some foci in Latin America and Yemen. (WHO)
The Global Burden of Disease Study estimated in 2017 that there were 20.9
million prevalent O. volvulus infections worldwide: 14.6 million of the
infected people had skin disease and 1.15 million had vision loss. (WHO)
O. volvulus is transmitted between humans and the vectors. The infection is not a
zoonosis.
• Onchocercal infections are found in tropical climates.
• The main burden is in 30 countries in sub-Saharan Africa, though the parasite
is found in limited areas in the Americas and in Yemen in the Middle East
• The people most at risk for acquiring onchocerciasis are those who live near
streams or rivers where there are Simulium blackflies

32. EPIDEMIOLOGY CONTINUING
• In the Americas, transmission of onchocerciasis has been
interrupted in 11 of the 13 foci.
• Interventions to limit transmission stopped in Colombia in 2008,
in Ecuador in 2010, in Mexico in 2012, and in Guatemala in 2012
• Transmission and interventions to limit transmission continue in
one area in Venezuela and one area in Brazil.
East and central Africa
The most important vectors in East and Central Africa belong
to the S. damnosum complex, but vectors of the S. neavei
group also transmit onchocerciasis in Ethiopia, Tanzania,
Malawi, Uganda and parts of Zaire.

33. CONTROL - VECTOR
• The principal method for controlling
onchocerciasis has been to break the cycle of
transmission by eliminating the back fly.
• Simulium larvae are destroyed by application of
selected insecticides through aerial spraying of
breeding sites in fast-flowing rivers.
• Once the cycle of river blindness has been
interrupted for 14 years the reservoir of adult
worms dies out in the human population, thus
eliminating the source of the disease

34. CONTROL – IVERMECTIN
TREATMENT
• To complement vector control activities, the
drug ivermectin is distributed where needed
through a community directed approach.
• Ivermectin kills the larval worms that cause
blindness and other onchocercal
manifestations and acts to decrease
transmission as well. Ivermectin became
available in 1987 to complement blackfly
control activities.

35. CONTROL - BLACKFLIES
• Control of adults by insecticides not feasible, they
bite outdoors and are highly scattered in the bush;
would need to spray large areas in the bush that
would be extremely expensive.
• Larval control ideal, larvae remain in their breeding
sites. Most useful in Africa, employ biodegradable
insecticides such as temefos (Abate) in low
concentrations, sprayed once weekly. Bacillus
thuringiensis H-14, a biological insecticide suspension
can also be used at a dose 2.5 times higher than
temefos.

36. African Program For
Onchocerciasis Control (APOC)
• WHO is the executing agent of APOC.
• In four areas of Uganda, the United Republic of
Tanzania, and Equatorial Guinea, African
Programme for Onchocerciasis Control’s
(APOC) strategy of community-directed
treatment with ivermectin has been
supplemented by activities to eliminate the
black-fly vector. Vector control is not considered
feasible or cost-effective in the remaining
APOC countries.

37. References
• Manson’s Tropical Diseases , 22nd
Edition.
• WHO.
• Articles.
• CDC.