Onchocerca volvulus

SESSION:

ONCHOCERCA VOLVULUS (TISSUE NEMATODE)

Learning Objectives:

• By the end of this session, students are expected to be able to:

The geographical distribution of & Onchocerca volvulus

Phylum Nemathelminthes, Class Nematoda, Order Spirurida, Family Filarioidae, Genus Onchocerca and Species Onchocerca volvulus Onchocerca volvulus occurs mainly in Africa, with additional foci in Latin America and the Middle East.

Occurs most widely along the courses of fast running rivers in the rain forests and savannah areas of the West and Central Africa Also found in South America and Central America Adult worms reside in subcutaneous connective tissue of man Microfilaria is found in skin and nodules

Morphological features or characteristics of Onchocerca volvulus

• Male measures 3 x 0.13 mm with coiled tail while female measures up to 50 x 0.4 mm
• Anterior end is ventrally curved in case of male
• Cuticular oblique and annular thickening is more prominent in female
• Microfilariae of Onchocerca volvulus
• No sheath present; Are unsheathed
• Are non periodic found in skin
• Measured 300 x 6 to µm
• The column of nuclei does not extend up to the tail

The tail is tapered and is sharply angled at the end.

Other nematodes of ocular importance

NEMADOTES

OCULAR DISEASES

TREATMENT

LOA LOA

• Migration of adult worm across the conjuntiva
• Diethylcarbamazine (DEC) OR surgical removal if visible

TOXOCARA CANIS

• Ocular larva migrans causing retinal granuloma and vision loss
• Albendazole plus, corticosteroids

DIROFILARIA REPENS

• Orbital dirofilariasis
• Surgical removal ,antiparasitic drugs may be used in selected cases

BRUGIA MALAYI

• Rare ocular filariasis
• Diethylcarbamazine (DEC)or Ivermectin depending on the cases

ONCHOCERCAL VOLVULUS

• River blindness( onchocerciasis),keratitis,chorioretinitis,optic nerves damage

Ivermectin, sometime Doxycyline to target symbiotic bacteria

The mode of transmission & life cycle of Onchocerca volvulus

Infective larvae are transmitted by infected biting arthropods during a blood meal.

The larvae migrate to the appropriate site of the host's body, where they develop into microfilaria-producing adults.

The adults dwell in various human tissues where they can live for several years.

The agents of lymphatic filariasis reside in lymphatic vessels and lymph nodes; Onchocerca volvulus in nodules in subcutaneous tissues

life cycle cont……

• The female worms produce microfilariae which are found in the skin, and invade the eye.

The microfilariae infect biting arthropods black flies [Simulium] Inside the arthropod, the microfilariae develop in 1 to 2 weeks into infective filariform (third-stage) larvae.

• During a subsequent blood meal by the insect, the larvae infect the vertebrate host.

They migrate to the appropriate site of the host's body, where they develop into adults.

The diseases caused by Onchocerca volvulus

Lymphatic filariasis most often consists of asymptomatic microfilaremia.

Some patients develop lymphatic dysfunction causing lymphedema and elephantiasis (frequently in the lower extremities) Persons who have newly arrived in disease-endemic areas can develop a febrile episode of lymphangitis and lymphadenitis.

Onchocerciasis can cause pruritus, dermatitis, onchocercomata (subcutaneous nodules), and lymphadenopathies.

The most serious manifestation consists of ocular lesions that can progress to blindness.

LABORATORY DIAGNOSIS

Identification of microfilariae by microscopic examination is the most practical diagnostic procedure.

Examination of skin snips will identify microfilariae of Onchocerca volvulus Skin snips can be obtained using a corneal-scleral punch, or more simply a scalpel and needle.

The sample must be allowed to incubate for 30 minutes to 2 hours in saline or culture medium, and then examined for microfilariae that would have migrated from the tissue to the liquid phase of the specimen

PREVENTION AND CONTROL.

It is difficult to control but you can use insecticides by spraying their bushy resting places.

Avoiding Simulium bite by wearing suitable clothing e.g. Long trousers. Sitting settlements, including adequate water supplies away from forest area Destruction of Simulium adult flies larvae by changing the character of breading places where possible. e.g. Clearing vegetation to allow in sunlight to day Using insecticide

Treating infected individuals

KEY POINTS.

• Measures 300 x 6 to 8µ
• The column of nuclei does not extend up to the tail
• Some important characteristics of the microfilariae of this species are shown here:
• No sheath present; the tail is tapered and is sharply angled at the end.

EVALUATION

• Describe morphology of Onchocerca volvulus.

Describe the mode of transmission & life cycle of Onchocerca volvulus