- Is It Contagious?
What is onchocerciasis (river blindness)?
Onchocerciasis is a parasitic disease caused by parasites (nematode) named Onchocerca volvulus. It is transmitted to humans by the bite (blood meal) of the female blackfly (Simulium). The disease is also termed river blindness because the vector, the blackfly, is usually found breeding close to rapidly flowing streams and rivers, and because the most devastating manifestation of the infection is blindness. Although the majority of people infected reside in sub-Saharan Africa (for example, Nigeria), it also occurs in Central and South American countries and Yemen but much less frequently. After trachoma, it is the second-leading cause of infection-caused blindness worldwide. The CDC classifies it in the Neglected Tropical Diseases category: a group of parasitic and bacterial disease that cause substantial illness in more than 1 billion patients.
What causes onchocerciasis?
The cause of onchocerciasis is the transfer of larvae of the parasite Onchocerca volvulus by the female blackfly when the fly gets a blood meal (bites) a human. The larvae enter the subcutaneous tissues and develop into adult male and female worms (filarial nematodes). These reproduce in the human tissue and form microfilariae that migrate to other areas of connective tissue and occasionally to the blood, urine, and sputum. In addition, both the adult worms and the microfilaria are colonized with bacteria termed Wolbachia that help these parasites survive. When the worms die, a host immune response ensues that can destroy optical tissue in the eye. The life cycle of the parasites is continued when a blackfly bites a human and, during its blood meal, ingests microfilariae. The complex life cycle is shown below.
Living in and visiting sub-Sahara Africa and the few other areas where the blackfly is endemic is a major risk factor for developing onchocerciasis. The disease usually occurs after repeated exposures to blackfly bites so short-term travelers through these areas pose little risk; however, missionaries, volunteer health workers, and others who may spend a few months in the areas have an increased risk of infection.
Is onchocerciasis contagious?
Onchocerciasis is not contagious person to person. Transmission of the disease is through the bite of female blackflies (usually occurring during the daytime near rapidly flowing rivers and streams). Multiple bites are usually needed before being infected.
Although the infection with larvae begins immediately, the disease may not become apparent in an individual for months to years. In most individuals, it develops slowly in the skin although some patients may present initially with eye problems.
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What are the symptoms of onchocerciasis?
The symptoms and signs of onchocerciasis are as follows:
- Skin inflammation that is very itchy and forms papules on the skin
- Nodules in the skin (subcutaneous nodules or bumps)
- Scarred, saggy, or drooping areas of skin
- Patchy skin depigmentation (leopard skin)
- Lymph node inflammation (lymphadenitis)
- Eye (ocular) lesions (eye itching, redness, or swelling)
- Visual problems (visual impairment and/or inability to distinguish certain colors, partial or complete blindness)
- Eosinophilia (unusually high levels of eosinophils in the blood)
- "Sowda" is a term used to describe the severe itching and skin discoloration (darkening), that is often confined to one limb, that can be found with onchocerciasis.
Diagnosis of onchocerciasis
Although local clinic doctors, who are often the patient's primary-care provider, usually treat onchocerciasis, specialists may be consulted. Such specialists are infectious-disease, ophthalmologist, dermatologists, and travel-medicine doctors. These specialists can help diagnose and treat patients with onchocerciasis.
Clinical presumptive diagnosis is made if the patient lives or visits areas where the disease is endemic and has characteristic skin or eye changes described above. Definitive diagnosis is simply done by seeing adult worms in excised skin nodules, eye lesions, or by finding microfilariae in skin shavings or punch biopsies of the skin. In addition, an immunological test for antibodies developed against the parasites early in the infection is useful to determine if a person is infected before microfilariae are detectable. This test is available from the CDC. It is important to obtain a definitive diagnosis so that appropriate treatment can be started (see treatment section below). Onchocerciasis is a type of filariasis that does not respond well to some other drugs used to treat other similar filarial diseases. Diethylcarbamazine, a commonly used drug that is a derivative of piperazine, actually has been linked to severe and sometimes fatal patient reactions when used to treat onchocerciasis.
What is the treatment for onchocerciasis?
Treatment is done by giving the patient ivermectin, an antiparasitic drug once or twice per year for about 10-15 years (the life span of adult worms). This antiparasite drug is effective in killing the microfilariae but does not kill the adult worms. The mature worms may remain alive for 10-15 years in the patient. Most clinicians recommend that subcutaneous nodules should be excised, if possible, thereby removing the adult worms that may reproduce more microfilariae over time. Some clinicians recommend that after ivermectin treatment, patients may benefit from a six-week dose of doxycycline antibiotic. Doxycycline damages and kills Wolbachia bacteria that are inside the microfilariae and adult worms, resulting in the death of microfilariae and ineffective microfilariae produced by the surviving adult worms. This may slow or halt further disease development.
The use of diethylcarbamazine (a treatment used before ivermectin became available) is contraindicated. It may cause severe or fatal patient reactions in individuals with onchocerciasis.
A new drug capable of killing the adult worms of onchocerciasis is under study for use in humans. It's named moxidectin but has not yet been approved for use in humans for treatment of onchocerciasis.
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What is the prognosis for onchocerciasis?
The prognosis (outcome) depends on how quickly the infection is recognized and treated. The prognosis is good if the disease is adequately treated and the patient makes their follow-up appointments and treatments. However, if the diagnosis and treatment is accomplished late in the disease, the prognosis may be fair to poor because the patient may develop complications of significant skin alterations, visual problems, or complete blindness.
Is it possible to prevent onchocerciasis?
Currently, there is no drug or vaccine available that prevents onchocerciasis. However, preventing blackfly bites by avoiding areas where they are endemic can prevent infections. Other measures such as personal protection against blackfly bites and other biting insects (for example, insect repellent, pants tucked in boots, long-sleeved shirts) may reduce the chances of infection. Permethrin, an insect repellent, can be impregnated into cloth (shirts, pants, netting) and offers additional protection against blackfly bites
United States. Centers for Disease Control and Prevention. Cantley, P. "Onchocerciasis (river blindness)." June 24, 2019. <http://wwwnc.cdc.gov/travel/yellowbook/2016/infectious-diseases-related-to-travel/onchocerciasis-river-blindness>.
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BlindnessBlindness is the state of being sightless. Causes of blindness include macular degeneration, stroke, cataract, glaucoma, infection and trauma. Symptoms and signs may include eye pain, eye discharge, or the cornea or pupil turning white. Treatment of blindness depends upon the cause of the blindness.
doxycyclineDoxycycline (Vibramycin, Oracea, Adoxa, Atridox, Acticlate, Acticlate Cap, Doryx, Doxteric, Doxy, Monodox, and others) is a synthetic broad-spectrum antibiotic derived from tetracycline. It is used to treat many different types of infections, including respiratory tract infections due to Hemophilus influenzae, Streptococcus, pneumoniae, or Mycoplasma pneumoniae. It also is used for the treatment of nongonococcal urethritis (due to Ureaplasma), Rocky mountain spotted fever, typhus, chancroid, cholera, brucellosis, anthrax, syphilis, and acne. It is important to be aware of drug interactions, effects on pregnancy and nursing mothers, as well as common side effects on the user.
Itching (Pruritus)Itching can be a common problem. Itches can be localized or generalized. There are many causes of itching including infection (jock itch, vaginal itch), disease (hyperthyroidism, liver or kidney), reactions to drugs, and skin infestations (pubic or body lice). Treatment for itching varies depending on the cause of the itch.
ivermectinIvermectin is an antiworm (anthelmintic) medication used to treat intestinal strongyloidiasis and river blindness (onchocerciasis), types of diseases caused by parasitic roundworm (nematode) infestations. The FDA has not authorized or approved ivermectin for the treatment or prevention of COVID-19. Common side effects of ivermectin include itching, rash, hives (urticaria), skin (swelling) edema, fever, joint pain (arthralgia), inflammation of the synovial membrane on joints (synovitis), enlargement and tenderness of lymph nodes, and eye inflammation. Avoid use or use with caution if pregnant or breastfeeding.
ivermectin (Stromectol)Ivermectin (Stromectol) is a medication prescribed to treat infections caused by Strongyloides stercoralis and for infections caused by the adult form of Onchocerca volvulus. Side effects, drug interactions, dosage, storage, and pregnancy safety information should be reviewed prior to using this medication.
Pink Eye (Conjunctivitis)Pinkeye, also called conjunctivitis, is redness or irritation of the conjunctivae, the membranes on the inner part of the eyelids and the membranes covering the whites of the eyes. These membranes react to a wide range of bacteria, viruses, allergy-provoking agents, irritants, and toxic agents.
Swollen Lymph Nodes (Lymphadenopathy)Lymph nodes help the body's immune system fight infections. Causes of swollen lymph nodes (glands) may include infection (viral, bacterial, fungal, parasites). Symptoms of swollen lymph nodes vary greatly, but may include fever, night sweats, toothache, sore throat, or weight loss. Causes of swollen lymph nodes also vary, but may include cancer, the common cold, mono, chickenox, HIV, and herpes. The treatment of swollen lymph nodes depends upon the cause.