Onchocerciasis : causes, symptoms, diagnosis, treatment, prevention and complications

• Write : Rchp. Khalipha Justice
• Reviewed : Abdulmuminu salisu Ph.D 
• Editor : Victoria solomon (B.A English language)

Overview:

Onchocerciasis, also known as river blindness, is a parasitic infection caused by the nematode Onchocerca volvulus. It is a neglected tropical disease (NTD) that affects around 21 million people worldwide, mainly in sub-Saharan Africa, but also in parts of Latin America and Yemen. The disease can lead to severe itching, skin lesions, and blindness, hence the name "river blindness."

Definition:

Onchocerciasis is a parasitic disease caused by the nematode Onchocerca volvulus, which is transmitted to humans through the bite of infected blackflies. The disease mainly affects the skin and eyes, causing severe itching, skin lesions, and, in some cases, blindness.

Classification:

Onchocerciasis is classified as a filarial disease, a group of parasitic infections caused by nematodes that live in the lymphatic system and subcutaneous tissues.

Causes:

Onchocerciasis is caused by the filarial nematode Onchocerca volvulus, which is transmitted to humans through the bite of infected blackflies of the genus Simulium. When an infected blackfly bites a human, it deposits the infective larvae of the parasite onto the skin, where they migrate into the subcutaneous tissues and mature into adult worms. The adult worms then mate and release millions of microfilariae into the skin and eyes, where they can be ingested by blackflies during a blood meal, completing the life cycle of the parasite.

Causative agent:

The causative agent of onchocerciasis is the nematode Onchocerca volvulus, which is a thread-like worm that can grow up to 50 cm long in the human body. The adult worms live in subcutaneous nodules and can produce millions of microfilariae, which are the stage of the parasite that causes the clinical manifestations of the disease.

Mode of transmission:

Onchocerciasis is transmitted to humans through the bite of infected blackflies of the genus Simulium. The blackflies breed in fast-flowing rivers and streams, and their larvae attach to rocks and other surfaces in the water. When they mature, they emerge from the water as adult flies and seek out a blood meal. If the fly bites a human infected with Onchocerca volvulus, it can become infected and transmit the parasite to other humans during subsequent bites.

Incubation period:

The incubation period for onchocerciasis can vary depending on the number of infective larvae that are deposited by the blackfly and the immune response of the individual. In general, the first clinical signs and symptoms of the disease can appear between six months to two years after infection.

Signs and symptoms:

The signs and symptoms of onchocerciasis can vary depending on the stage of the disease and the individual's immune response. In the early stages of infection, most people develop itching and skin lesions, which can progress to more severe skin changes such as thickening, depigmentation, and scarring. In some cases, the disease can also affect the eyes, leading to inflammation, clouding of the cornea, and ultimately blindness.

Diagnosis and tests:

The diagnosis of onchocerciasis is usually based on clinical signs and symptoms, as well as the individual's history of living in or traveling to an endemic area. The presence of microfilariae in skin snips or onchocercomas (subcutaneous nodules) can also be used to confirm the diagnosis. Serological tests that detect specific antibodies to Onchocerca volvulus can also be used to support the diagnosis.

Management and treatment:

The management and treatment of onchocerciasis typically involves two main approaches: controlling the transmission of the parasite and treating infected individuals.

Controlling the transmission of the parasite involves a combination of measures, including vector control through the use of insecticides and environmental modification to reduce blackfly breeding sites. Mass drug administration (MDA) programs have also been effective in reducing the prevalence of the disease by treating entire communities with ivermectin, a drug that kills the microfilariae and prevents the adult worms from producing more microfilariae.

Treating infected individuals with ivermectin has been shown to reduce the severity of symptoms and prevent blindness. The drug is generally well-tolerated and can be administered annually or biannually for up to 15 years to achieve sustained control of the disease. In some cases, surgery may be necessary to remove subcutaneous nodules that can cause disfigurement and secondary bacterial infections.

Risk factors:

The risk factors for onchocerciasis include living in or traveling to endemic areas, being exposed to blackflies, and poor personal hygiene. Individuals with weakened immune systems, such as those with HIV/AIDS or malnutrition, may be more susceptible to the disease and its complications.

Prevention and control:

Prevention and control of onchocerciasis require a multi-sectoral approach, including health education, vector control, and MDA programs. Health education campaigns can help raise awareness about the disease and promote personal hygiene, such as the use of insect repellents, protective clothing, and avoidance of blackfly breeding areas. Vector control measures such as the use of insecticide-treated bed nets and indoor residual spraying can also help reduce the risk of infection.

MDA programs with ivermectin have been effective in reducing the prevalence of the disease in many endemic areas. The World Health Organization (WHO) has set a target to eliminate onchocerciasis as a public health problem by 2030 through sustained MDA and other interventions.

Complications:

The complications of onchocerciasis can be severe and include blindness, skin disfigurement, and secondary bacterial infections. Blindness can result from inflammation of the optic nerve or cornea, and is a major cause of morbidity and disability in endemic areas. Skin lesions can also lead to disfigurement and social stigmatization, particularly in women and children. Secondary bacterial infections can occur when the skin is compromised and can lead to severe cellulitis, lymphangitis, and sepsis.

Conclusion:

Onchocerciasis, also known as river blindness, is a neglected tropical disease caused by the nematode Onchocerca volvulus. The disease mainly affects the skin and eyes and can lead to severe itching, skin lesions, and blindness. Onchocerciasis is transmitted to humans through the bite of infected blackflies of the genus Simulium, which breed in fast-flowing rivers and streams. The disease can be diagnosed based on clinical signs and symptoms, as well as the presence of microfilariae in skin snips or onchocercomas. Treatment involves controlling the transmission of the parasite through vector control and MDA programs, as well as treating infected individuals with ivermectin. Prevention and control of onchocerciasis require a multi-sectoral approach, including health education, vector control, and MDA programs.