Onchocerca volvulus and Loa loa are parasitic worms responsible for river blindness and loiasis, respectively, affecting humans in tropical regions. Their life cycles involve transmission through black flies and mango flies, leading to various clinical signs including severe eye damage and skin swelling. Diagnosis typically includes identifying microfilariae through specific tests, with treatments encompassing surgical removal and the use of diethylcarbamazine.

1. Onchocerca volvulus
• Kingdom: Animalia
• Phylum: Nematoda
• Class: Secernentea
• Order: Spirurida
• Family: Onchocercidae
• Genus: Onchocerca
• Species: Onchocerca volvulus

2. Onchocerca volvulus
(The convoluted filaria)
• It is common in parts of tropical Africa and Central
America.
• Habitat: nodules in the subcutaneous tissue of
man.

3. Morphology
• Adult worms are white, opalescent and
transparent with transverse striations on the
cuticle.
• Male measures 1.9-4.2 cm in length and has
coiled tail.
• The female is much longer,
measuring 33.5-50 cm in
length.
O. volvulus microfilaria: unsheathed with no nuclei
in the end of long pointed tail.

4. Life cycle
• Definitive host: Man.
• Intermediate host: Black fly (Simulium).
• Humans become infected by bite of black fly,
which possesses in its mouth the infective 3rd
stage larvae.
• The larvae enter the skin through the punctured
wound and migrate to subcutaneous tissue in
which they moult twice and develop into adult
worms.

5. • The adult worms live in deep fascia or in the
subcutaneous tissue.
• The females release actively motile, unsheathed
microfilariae which migrate to the skin and eyes of
infected subjects.
• When a black fly again bites diseased human, the
microfilariae migrate into thoracic muscles, they
moult twice and develop into infective larvae.
• The larvae migrate to the mouth parts of black fly
where they transmitted to humans at next blood
meal.

6. Life cycle

7. Pathogenesis and clinical signs
• The disease is known as river
blindness (association of vector with
rivers) due to invasion of the eye
lead to loss of vision, corneal and
retinal lesions.
• Skin itching because the
microfilariae live in superficial layers
of skin.

8. Diagnosis
• Demonstration of the adult worms inside
nodules.
• Demonstration of microfilariae in skin snips.
• Serological tests: PCR.

9. Treatment
• Surgical removable of detectable
nodules (nodulectomy).
• Suramin is the first successful drug for treatment
of onchocerciasis.
• Diethylcarbamazine is effective microfilaricidal
drug.

10. Loa loa
• Kingdom: Animalia
• Phylum: Nematoda
• Class: Chromadorea
• Order: Spirurida
• Superfamily: Filarioidea
• Family: Onchocercidae
• Genus: Loa
• Species: Loa loa

11. Loa Loa
(Africa eye worm)
• Disease: loiasis, Calabar swelling.
• It is restricted in distribution West and Central
Africa.
• Habitat: in subcutaneous connective tissues of
man.

12. Morphology
• Adult worms are thin, whitish and
taper towards cephalic end.
• Male measures 30-34 mm x 0.35-
0.43 mm with ventrally curved
caudal end and narrow alae.
• The female, 40-70 mm x 0.5 mm
with vulva opens in cervical
region.
• Loa loa microfilaria: sheathed
with nuclei in extending to the
end of the tail.

13. Life cycle
• Definitive host: Man.
• Intermediate host: Mango fly (Chrysops
dimidiata, C. silacea).
• Man infects by bite of infected female, the larvae
enter through punctured wound on the skin to
subcutaneous tissue, moult and develop to
mature adult worms (takes 6-12 months).
• The females produce microfilariae which reach
peripheral blood during the day time and
ingested by female Chrysops during blood meal,

14. • They penetrate stomach wall and reach thoracic
muscles where they develop into infective
larvae.
• The infective larvae migrate to mouth parts of
Chrysops for transmission to human.

15. Life cycle

16. Pathogenesis and clinical signs
• Eye lesions: pain, impaired vision,
granuloma and oedema of eyelid.
• The worm live in subcutaneous connective
tissue and causing painless, oedematous
swelling known as fugitive or Calabar swelling
(measure 5-10 cm in diameter).

17. Diagnosis
• Identification of microfilariae in peripheral blood
during day time.
• Detection or removal of adults from eye or
Calabar swelling.

18. Treatment
• Surgical removal of adult worms.
• Diethylcarbamazine is the drug of choice.