- Biological cycle
- Signs and symptoms of onchocerciasis
- How to diagnose
- How the treatment is done
- Prevention of Onchocerciasis
Onchocerciasis, popularly known as river blindness or gold digger disease, is a parasitosis caused by the parasite Onchocerca volvulus. This disease is transmitted by the bite of the fly of the genus Simulium spp. , also known as the black fly or rubber mosquito, due to its similarity to mosquitoes, which can usually be found on riverside.
The main clinical manifestation of this disease is the presence of the parasite in the eyes, causing progressive loss of vision, which is why onchocerciasis is also known as river blindness. However, onchocerciasis can remain asymptomatic for years, which makes its diagnosis difficult.
Biological cycle
The biological cycle of Onchocerca volvulus happens in both the fly and the man. The cycle in man begins when the insect feeds on the blood, releasing infective larvae into the bloodstream. These larvae undergo a maturation process, reproduce and release microfilariae, which spread through the blood and reach various organs, where they develop, give rise to symptoms and start a new life cycle.
Flies can become infectious when biting a person who has microfilariae in their blood, because at the time of feeding they end up ingesting the microfilariae, which in the intestine becomes infectious and goes to the salivary glands, being possible the infection of other people during blood feeding.
The release of microfilariae by adult larvae takes about 1 year, that is, the symptoms of onchocerciasis only begin to appear after 1 year of infection and the severity of symptoms depends on the amount of microfilariae. In addition, adult larvae are able to survive in the body between 10 and 12 years, with the female capable of releasing approximately 1000 microfilariae a day, whose lifespan is around 2 years.
Signs and symptoms of onchocerciasis
The main symptom of onchocerciasis is the progressive loss of vision due to the presence of microfilariae in the eyes, which if left untreated can lead to blindness. Other clinical manifestations characteristic of the disease are:
- Onchocercoma, which corresponds to the formation of subcutaneous and mobile nodules that contain adult worms. These nodules can appear in the pelvic area, chest and head, for example, and are painless while the worms are alive, when they die they cause an intense inflammatory process, becoming quite painful; Oncodermatitis, also called oncocercosal dermatitis, which is characterized by loss of skin elasticity, atrophy and fold formation that occurs due to the death of the microfilariae that are present in the connective tissue of the skin; Eye injuries, which are irreversible injuries caused by the presence of microfilariae in the eyes that can result in complete blindness.
In addition, there may be lymphatic lesions, in which the microfilariae can reach the lymph nodes near the skin lesions and cause damage.
How to diagnose
Early diagnosis of onchocerciasis is difficult, as the disease can be asymptomatic for years. The diagnosis is made through the symptoms presented by the person, in addition to tests requested by the doctor that help confirm the diagnosis, such as eye exams and blood tests in which microfilariae are sought among the red blood cells. In addition, the doctor may request ultrasound, to check the formation of nodules by the parasite, and molecular tests, such as PCR to identify Onchocerca volvulus .
In addition to these tests, the doctor may request a histopathological examination, in which a biopsy of a small skin fragment is performed to identify the microfilariae and exclude the occurrence of other diseases, such as adenopathies, lipomas and sebaceous cysts, for example.
How the treatment is done
The treatment of onchocerciasis is done with the use of the anti-parasitic Ivermectin, which is very effective against microfilaria, as it is capable of causing its death without causing very serious side effects. Learn how to take Ivermectin.
Despite being very effective against microfilariae, Ivermectin has no effect on adult larvae, and it is necessary to surgically remove the nodules containing the adult larvae.
Prevention of Onchocerciasis
The best way to prevent infection by Onchocerca volvulus is to use repellents and appropriate clothing, especially in regions where the insect is more prevalent and in river beds, in addition to measures to combat the mosquito, such as the use of biodegradable larvicides and insecticides, for example.
In addition, it is recommended that inhabitants of endemic regions or that people who have been in those regions be treated with Ivermectin annually or semi-annually as a way to prevent onchocerciasis.
