Onchocerciasis (River blindness)

Onchocerciasis (River Blindness)

Onchocerciasis, also known as river blindness, is a chronic parasitic disease caused by the nematode worm Onchocerca volvulus. 

It is characterized by severe itching, skin lesions, and, in advanced cases, blindness. The disease is primarily found in sub-Saharan Africa, with smaller outbreaks in Central and South America.

Transmission:

Vector: The disease is transmitted through the bite of infected blackflies (genus Simulium) that live near fast-flowing rivers and streams, hence the name \”river blindness.\”

Lifecycle:

In the Vector (Blackfly):

1. The female blackfly ingests microfilariae (larval worms) from an infected human during a blood meal.
2. Inside the blackfly, microfilariae develop into infective larvae.
3. After approximately 1 to 2 weeks, the larvae mature and migrate to the mouthparts of the blackfly.

In Humans:

1. An infected blackfly bites a human, injecting the infective larvae into the subcutaneous tissue.
2. Larvae migrate to the skin, where they mature into adult worms within 1 to 2 years.
3. Adult worms reside in nodules (onchocercomas) beneath the skin and produce microfilariae.
4. Microfilariae travel throughout the body, especially to the eyes, skin, and lymph nodes.
5. The cycle continues as blackflies ingest microfilariae from infected humans.

Clinical Features:

Skin Lesions:

• Papular, itchy skin lesions (onchocercal dermatitis).
• Hyperpigmented or depigmented skin patches.
• Severe itching, leading to secondary bacterial infections.
• \”Elephantine\” skin thickening, especially on the legs and scrotum.

Eye Involvement:

• Microfilariae migrate to the eyes, causing inflammation (onchocercal keratitis).
• Loss of vision, including blindness, due to corneal scarring, optic atrophy, and retinal detachment.
• Severe itching and burning in the eyes.

Onchocercomas:

• Firm, subcutaneous nodules that contain adult worms.
• Located in various parts of the body, including the head, neck, limbs, and buttocks.
• Often painful and can cause pressure on nearby nerves or organs.

Lymphatic Involvement:

• Swelling of lymph nodes and lymphedema.
• Chronic inflammation of the lymph system.

General Symptoms:

• Fever
• Headache
• Fatigue
• Joint pain
• Loss of appetite
• Weight loss

Diagnosis and Investigations:

• Skin Biopsy: Examination of skin samples for microfilariae under a microscope.
• Slit-lamp Examination: Examination of the eyes to detect microfilariae and eye damage.
• Nodule Biopsy: Biopsy of onchocercomas to confirm the presence of adult worms.
• ELISA (Enzyme-Linked Immunosorbent Assay): Blood test to detect antibodies against Onchocerca volvulus.

Prevention:

Vector Control:

• Reducing blackfly populations through insecticides and larvicides.
• Using insect repellents and protective clothing.
• Avoiding areas with high blackfly density.

Mass Drug Administration (MDA):

• Regular administration of antiparasitic drugs (ivermectin) to kill microfilariae.
• Typically given every 6 months to all individuals in endemic areas.
• Ivermectin 150 micrograms/kg once yearly for 10-14 years 

Management:

Aims of Management:

• To eliminate microfilariae and reduce the number of adult worms.
• To prevent further transmission of the disease.
• To manage complications and improve quality of life.

 

Medical Management:

• Antibiotics: For treating secondary bacterial infections.
• Doxycycline 100 mg twice a day for 6 weeks followed by;
• Antiparasitic Drugs:
• Ivermectin: Kills microfilariae but does not eliminate adult worms.

• • Ivermectin 150 micrograms/kg single dose.

• Anti-Inflammatory Medications: For managing eye inflammation and other inflammatory conditions.

Surgical Management:

• Excision of Onchocercomas: Surgical removal of nodules can be considered for symptomatic nodules or those causing pressure on nearby structures.

Nursing Care:

Symptom Management:

• Provide comfort measures for itching and pain.
• Administer medications as prescribed.
• Monitor for side effects of medications.

Eye Care:

• Teach patients proper eye hygiene and care.
• Monitor for signs of eye infection and vision loss.

Skin Care:

• Provide soothing baths and lotions for itching.
• Encourage the use of insect repellents.

Education:

• Educate patients about the disease, transmission, and prevention.
• Encourage adherence to treatment and follow-up appointments.