AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Background

Onchocerciasis is an insidious nonfatal filarial disease that has caused blindness, lifelong human suffering, and grave socioeconomic problems. Onchocerciasis is a cause of clinical and epidemiological burden of skin disease in Africa. An estimated 18-40 million people are afflicted worldwide. Approximately 2 million people are blind because of this disease. About 85.5 million people in 35 countries live in endemic areas. In 1875, O'Neill first reported the presence of filaria in "craw-craw" as onchocerciasis is called in West Africa. In 1919, Robles described in the French literature an anterior uveitis and keratitis associated with acute and chronic skin changes.

Recent advances in prevention and treatment have decreased the prevalence of this disease in localized areas of Africa and Latin America. Most cases are found in Africa, south of the Sahara, in a wide zone that lies along the fifteenth parallel from Senegal to Ethiopia. The endemic area extends from south of the equator to Angola in the west and Tanzania in the east. Localized foci exist in Sudan and Yemen. The geographic distribution of onchocerciasis in Latin America is sporadic, with important foci in Guatemala, Ecuador, Venezuela, Mexico, Colombia, and the state of Amazonas in northern Brazil.

The parasite, Onchocerca volvulus, is a nematode that belongs to the family Filariidae. O volvulus is the only Onchocerca with a human host, although an infected spider monkey and a gorilla have been recorded. Black flies of the genus Simulium are the only vectors of O volvulus. They are tiny ferocious biters. At least 15 different species of blackfly simuliids can transmit onchocerciasis; they vary by terrain and continent (eg, Simulium damnosum in Africa). Their eggs require fast-running rivers for breeding grounds. As a result, the numbers of flies produced fluctuate with the season. The adults emerge after 8-12 days following egg production with the ability to travel hundreds of kilometers in flight on wind currents. Their life span is about 4 weeks.

Pathophysiology

Onchocercal larvae, in the skin of infected individuals, are ingested with a blood meal. They mature to the infective stage within the fly between 6-10 days and are transmitted by the female black flies. Development to the adult stage occurs in humans. The adult worms pair and mate in the human host, and, unlike most nematodes that produce eggs, the female Onchocerca gives birth daily to thousands of microscopic larvae known as microfilariae. These larvae mature to adult worms in about 1 year. The life span of microfilariae is 6-30 months. Those adult worms that complete their life circle may survive a decade during which time they release millions of microfilariae.

The classic lesion of onchocerciasis is the onchocercoma, a firm, painless nodule in the subcutaneous tissue. Onchocercomata are formed predominantly on the head, face, and torso, but they may be found on the pelvic girdle and lower extremities deep-seated against the bones or near the joints. The nodule usually is composed of 2-3 females and daughter microfilariae encapsulated in a fibrous coat. Dead worms may calcify within the nodules. The ocular tissues are involved via migration of the microfilariae from the neighboring tissues, through the bloodstream, or along the nerves. Intraocular organisms are evident early in the disease by direct invasion from the conjunctiva, through the sclera, or through the cornea.

Most microfilariae die as immature worms in the host. Their death causes an intense inflammatory reaction that is responsible for most of the morbidity of onchocerciasis. Antigens of the infective larvae seem to induce cell-mediated and humoral responses. Circulating immune complexes have been identified and implicated in the inflammatory response to infection. Perivascular deposits of immune complexes have been shown in various tissues. Immunoglobulin E (IgE) levels are also very high, thus implicating all of the known mechanisms of pathologic immune destruction. The lymph nodes that drain infected areas show granulomatous inflammation, fibrosis, and atrophy on histologic examination.

Frequency

United States

No current report exists of onchocerciasis due to O volvulus in the United States.

International

Onchocerciasis was considered to be one of the world's most formidable public health problems. Approximately 85.5 million people live in endemic areas. One half of the cases in the world are located in Nigeria. Ocular onchocerciasis has been found in more than 1 million individuals. Variation exists in the blindness rate in different geographical areas, possibly because of distinct strains or biological variants.

Onchocerciasis is more likely to lead to blindness in Africa than in Latin America, and it is 7 times less frequently blinding in the forested areas than in the Savannah (nonforested) areas. More than 90% of certain village populations are infected with this disease, and about 35-50% have ocular onchocerciasis.

Mortality/Morbidity

Microfilariae elicit the onchocerciasis syndrome that includes blindness, lymphadenitis, and dermatitis. O volvulus infection reduces immunity and resistance to other diseases, resulting in a reduction of the life expectancy of infected individuals by approximately 13 years.

Race

• No well-described racial differences in the incidence of onchocerciasis or susceptibility to the disease exist.
• Socioeconomic differences have been clearly identified as a contributing factor.

Sex

• Although no reported differences of exposure exist between men and women, men may be afflicted more often than women because of farm and field occupations.

Age

• As many as 50% of people older than 40 years may be blind in endemic areas.

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

History

• A detailed history and complete ophthalmologic examination should be performed whenever possible.

Physical

• Skin manifestations
• • The earliest skin involvement is mild pruritus and may be followed by papular rash, erosions, and lichenification. In highly endemic communities, the prevalence of itching increased until age 20 years and then plateaued.
  • The classic dermal lesion is referred to as leopard skin, which represents islands of hyperpigmented skin around hair follicles with surrounding depigmentation, most commonly located on the shins. These cutaneous manifestations affect mobility and social acceptability.
• Ocular manifestations
• • By slit lamp biomicroscopy, microfilariae can be seen within the cornea, migrating freely in the anterior chamber and vitreous humor. Although live microfilariae cause minimum reaction, dead microfilariae are associated with a severe inflammatory response.
  • Onchocerciasis-related blindness results from decades of infection and reinfection. Keratitis is one of the most devastating consequences of onchocerciasis. Various epidemiologic studies have found visible corneal or anterior chamber microfilariae (5-45%), punctate keratitis (35%), and sclerosing keratitis (10-15%).
  • Larval death induces an inflammation that results in corneal opacification and neovascularization.
  • • Dead worms are surrounded by inflammatory infiltrates in the superficial stroma. Lymphocytes and eosinophils migrate to the peripheral cornea where the infection is more dense. A sclerosing keratitis follows, which may involve the visual axis over time. Corneal neovascularization and opacification with interstitial keratitis lead to corneal blindness.
    • The development of keratitis is dependent upon the previous immunization and the presence of sensitized T lymphocytes. It is associated with a predominance of T-helper type 2 (Th2) response.
    • Eosinophils are the predominant inflammatory cells in the cornea after injection of the parasite antigen. The severity of keratitis seems to be associated with the number of eosinophils in the cornea.
    • Neutrophils are prominent early in the inflammatory response and mediate keratitis in the absence of eosinophils.
  • Anterior uveitis: Early in the disease, nongranulomatous or granulomatous inflammation may result from invasion of the iris and ciliary body by the microfilariae. The frequency of iritis is about 10-20%. Posterior synechiae may distort the pupil inferiorly giving a classical pear-shaped iris. Seclusio pupillae and iris bombe with secondary angle-closure glaucoma may occur. The common sequelae include occlusio and seclusio pupillae, iris atrophy, iris bombe, inflammatory glaucoma, and cataract.
  • Chorioretinitis is seen in 10-25% of patients with ocular involvement.
  • The choroid is characterized by progressive inflammation associated with loss of pigment, pallor of the vessels from orange to yellow or white, and loss of choriocapillaris.
  • The retinal pigment epithelium is affected in the early stage of infection. Areas of hypopigmentation and hyperpigmentation, mottling, and confluent atrophy characterize it. Dark brown clumps of pigment are seen in a diffusely pale retinal pigment epithelium. Photoreceptors initially are lost, followed by loss of the inner retinal layers.
• In the early stage, chorioretinitis may mimic any other diffuse chorioretinal process, such as histoplasmosis, toxoplasmosis, or retinitis pigmentosa.
• Commonly involving the temporal retina, onchocerciasis tends to spare the macula; as a result, central visual acuity is maintained until late in the disease.
• The pathogenesis of onchocercal chorioretinopathy is not well understood. The following mechanisms have been hypothesized to cause the characteristic chorioretinopathy:
• • Inflammatory reaction to dead microfilariae
  • Deposits of immune complexes
  • Autoimmunity
  • Secretory-excretory products of microfilariae
  • Eosinophil-derived toxic effector molecules
  • Autoimmunity is supported as a mechanism for several reasons. First, the burden of microfilariae is not associated directly with the degree of chorioretinopathy. Second, the chorioretinopathy continues to progress even after effective treatment with reduction of microfilariae and vector control. Finally, retinal disease can persist throughout life unless controlled with anti-inflammatory agents.
  • Evidence favoring the autoreactivity theory for the development of onchocercal chorioretinopathy is derived from the detection of retina-specific autoantibodies in the human-infected sera.
  • • Onchocercal human uveitis is associated with uveitopathogenic peptides, retinal S-antigen, and interphotoreceptor retinoid binding protein (IRBP). This evidence led Vingtain to demonstrate the presence of higher levels of S-antigen antibodies in patients with onchocerciasis who also had involvement of the posterior segment. However, these findings were not replicated.
    • Autoantibodies may have resulted from activation of T and B cells seen in parasitic infections. About 30% of B cells produce antibodies that are able to bind to autoantigens.
    • Hypergammaglobulinemia is a feature of O volvulus infection. Strong evidence exists that the chorioretinopathy is an inflammatory reaction to dead microfilariae because treatment with microfilaricidal induces characteristic retinal pathology. Similar progressive pathology also is seen after antimicrobial therapy of toxocara uveitis in children.
    • Microfilariae load is associated with the presence of new chorioretinal lesions. Even though the incidence of new lesions is reduced after antimicrobial chemotherapy, extension and progression of existing disease is common.
    • This observation suggests that although chorioretinopathy is likely to be initiated by the presence of microfilariae, persistence is a self-perpetuating autoimmune process that does not require the presence of microfilariae.
  • Optic atrophy is seen in 10-25% of patients with ocular manifestation.
  • • Loss of the ganglion cell axons leads to optic nerve head damage.
    • The optic nerve also may be involved by the infectious process or by treatment-induced inflammatory optic neuritis.
    • A heavy load of microfilariae may cause optic neuropathy.

Causes

Causes are discussed in Physical.

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Other Problems to be Considered

African trypanosomiasis
Dracunculiasis
Lymphatic filariasis
Schistosomiasis

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Lab Studies

• Skin snips has been the standard diagnostic technique. A scleral punch is the tool of choice to obtain samples of epidermis and dermis. Standardized techniques allow for relatively precise quantification of microfilarial load per milligram of tissue. However, this method is insensitive in low transmission areas and in areas where long-term use of the microfilaricidal ivermectin has resulted in the significant reduction of individual and community microfilariae loads. Also, the procedure is painful and involves a high risk of blood-borne infections (eg, HIV).
• The oncho-dipstick assay is a more reliable and patient friendly alternative to the skin snip technique in establishing a diagnosis of human onchocerciasis. A positive result may indicate active infection by the parasite. In a recent study, the sensitivity of the oncho-dipstick assay was 100% in urine and 92% in tears; its specificity was 100% in both urine and tears.
• Enzyme-linked immunosorbent assay (ELISA) and immunochromatographic test (ICT): ELISA, the ubiquitous biological technique, uses multiple recombinant antigens. ELISA is useful to differentiate O volvulus from its cousins but requires a specialized laboratory. ICT, a rapid format antibody card test, uses an individual antigen.
• • The sensitivity of ELISA and ICT has been estimated as 97% and 86%, respectively.
  • Both ELISA and ICT are more sensitive than the skin snip technique and the patch test using topical diethylcarbamazine (DEC).
  • ICT compares with ELISA and is inexpensive.
• Polymerase chain reaction (PCR): An advanced molecular technique using DNA or RNA probes specific to O volvulus can assay the blackfly vector and human host infection using PCR technology. These probes are sensitive very early in the disease. Although highly specific, PCR requires meticulous laboratory technique to avoid contamination and false-positive results. In addition to requiring specialized skills and being expensive, PCR-based diagnostic methods of onchocerciasis still depend on skin snips.
• Older techniques
• • Nodulectomy: Adult worms can be identified after surgical nodulectomy.
  • Mazzotti test: This test relied on the intense pruritic response induced by microfilariae after treatment with DEC. Used in a minute quantity, it can be associated with untoward effects, ranging from mild discomfort, fever, headaches, and itching to tachypnea, tachycardia, and even pulmonary edema. Antihistamines and corticosteroids pretreatment may lessen the discomfort.
  • Microfilariuria: This test requires a small dose of DEC as it mobilizes the microfilariae into the urine.

Histologic Findings

O volvulus can be identified using special stains. The adult form is a threadlike, coiled, white worm. The female measures about 50-100 cm, and the male measures 2.5-5.0 cm. The microfilariae are only 0.3 µm in length. The living microfilariae are coiled, whereas the dead worms are straight and opacified. Each living or dead filaria is surrounded by granulation tissue, fibrin, polymorphonuclear neutrophils, eosinophils, plasma cells, and giant cells.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical Care

On the basis of the principle that microfilariae cannot mature in the human host, it was once believed that eradication of the adult worm could potentially cure the infection. Nodulectomy was practiced through a systematic denodulization in most endemic areas of Guatemala. No evidence exists that the prevalence of onchocerciasis was reduced by this mode of treatment.

• Drugs used in the treatment of onchocerciasis
• • DEC is an anthelmintic that was used in the past for the treatment of the microfilarial phase of onchocerciasis. It is administered orally as tablets. It is absorbed rapidly from the gastrointestinal tract, skin, and conjunctiva.
  • • The microfilaricidal activity of DEC is associated with a series of dermal, ocular, and systemic reactions known as the Mazzotti reaction. These reactions may be mild to severe and include itching, rash, headache, joint pain, swollen lymph nodes, fever, tachycardia, vertigo, and hypotension.
    • Mobilization of the microfilariae leads to other serious signs of ocular toxicity, such as punctate keratitis, optic neuritis, and visual field loss. Because of these debilitating manifestations, DEC is no longer recommended for the treatment of onchocerciasis.
  • Suramin (Antrypol) is the only drug in clinical use that is effective against adult worms of onchocerciasis. It is administered by slow intravenous injection, usually as a 10% solution. A total dose of 66.7 mg/kg in 6 incremental weekly doses is recommended.
  • • Severe adverse effects, such as thrombocytopenia, neutropenia, and hemolytic anemia, limit the use of suramin. Ocular toxicity includes photophobia, foreign body sensation, lacrimation, edema, cornea deposits (verticillata), and a high incidence of optic atrophy.
    • Because of the toxic effects, suramin is only considered for treatment of severe hyperreactive onchodermatitis that does not respond to ivermectin for individuals in areas without transmission of onchocerciasis and individuals living in endemic areas.
  • Amocarzine (CGP-6140), an antifilarial anthelmintic drug, is derived from amoscanate. It has the advantage of killing adult worms, but severe systemic adverse effects have prohibited its use.
  • Ivermectin
  • • A semisynthetic macrocyclic lactone, ivermectin (Stromectol, Mectizan), was introduced in 1982 by its producers Merck, Sharp, and Dohme, who offered the drug free of cost for use in developing countries. Isolated from the fermentation products of Streptomyces avermitilis, ivermectin has balanced activity against the spectrum of nematodes and arthropods.
    • Given as a single dose of 150 µg/kg, it reduces the number of microfilariae in the skin to 83.2% after 3 days and 99.5% after 3 months. A reduction greater than 90% is maintained up to 1 year after a single dose. In some patients, an increase of microfilariae in the anterior chamber is noticed at day 3 after treatment, but it reduces greatly after 3 months. Ivermectin is considered to be an excellent tool for the treatment of onchocerciasis and reduction of blindness rates.
    • Because a single dose of 12 mg reduces the microfilariae count to a low level for as long as 2 years, retreatment of the patients at 6- to 18-month intervals is required in endemic areas.
    • Stromectol has no activity against adult O volvulus parasites in the onchocercomata. Therefore, follow-up care and retreatment is required.
    • About 1-5% of patients on ivermectin may experience allergic and inflammatory reactions to dead microfilariae. These reactions may include facial and peripheral edema, headache, myalgia, arthralgia/synovitis, axillary, cervical and inguinal lymph node enlargement, orthostatic hypotension, and tachycardia.
    • Ocular toxicity includes eyelid edema, anterior uveitis, conjunctivitis, limbitis, punctate keratitis, chorioretinitis, or choroiditis.
    • Increased hemoglobin and eosinophilia is seen in 1% of patients.
    • Pretreatment with aspirin and antihistamines usually prevents discomfort. Concomitant community-based treatment has reduced the incidence of new infections.
    • In countries covered under the Onchocerciasis Control Programme (OCP), vector control is combined with large-scale ivermectin distribution. In 1996, more than 2.6 million people were treated with ivermectin within the program area.
    • In Uganda, vector control combined with ivermectin significantly reduced onchocercal dermatitis from 34% (precontrol) to 2.9% (P <0.001), microfilariae carrier rates from 88% to 7.5% (P <0.001), and nodule prevalence from 49% to 19.2% (P <0.001). Because ivermectin in parallel with vector elimination had a greater impact on onchocercal dermatitis and microfilariae carrier rates than ivermectin alone, considering ivermectin supplementation with vector elimination in all isolated foci with Simulium neavei transmission is worthwhile to hasten the elimination of onchocerciasis.
    • The African Programme for Onchocerciasis Control (APOC), which supports onchocerciasis control in endemic African countries outside the OCP, distributes ivermectin to communities in high-risk areas as determined by rapid epidemiological mapping of onchocerciasis (REMO) and geographic information systems (GIS).
    • Yearly or biannually ivermectin prophylaxis is not advisable for everyone. This drug is not safe for pregnant women; lactating mothers; breastfeeding babies; children younger than 5 years; and people with heart, liver, and kidney diseases.
    • Ivermectin treatment improves ocular manifestations. All anterior segment morbidity, including advanced sclerosing keratitis, advanced uveitis, and optic neuropathy, improve, while chorioretinal lesions continue to expand despite treatment.
    • Recent efforts have focused on another chemotherapeutic approach, doxycycline. This agent acts on endosymbiotic bacteria, Wolbachia, in O volvulus. Many filarial nematodes harbor Wolbachia endobacteria, which, as symbionts, are essential for the fertility of their hosts. Doxycycline (100 mg/d PO for 6 wk) targets endosymbiotic bacteria and results in long-term sterility of adult female worms and in a corresponding absence of microfilariae. In Ghana, when ivermectin was given after doxycycline, it resulted in a strong and sustained (18 mo) reduction of microfilariae loads to levels of less than 0.3 mf/mg. This may be a useful adjunctive therapy to ivermectin.
    • Levamisole had little effect on the efficacy of ivermectin when given in combination with this agent. Similarly, the combination of levamisole and albendazole was not efficacious. In fact, the combination of levamisole with ivermectin or albendazole induced unexpected adverse events.

Surgical Care

Nodulectomy was practiced through a systematic denodulization in most endemic areas of Guatemala.

MEDICATION

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

The goals of pharmacotherapy are to reduce morbidity and to prevent complications.

Drug Category: Antiparasitic agents

Parasite biochemical pathways are sufficiently different from the human host to allow selective interference by chemotherapeutic agents in relatively small doses.

In addition to the agents described below, DEC (Hetrazan), a microfilaricidal, was used. It remains the main drug in the management of loiasis due to Loa loa. No longer recommended for treatment of O volvulus. Absorbed from gastrointestinal tract, excreted unchanged in urine in most part, with small amount as N-oxide metabolite. Amocarzine (CGP6140) 4-methyl-4'-(p-nitroanilino) thio-1-piperazinecarboxanilide is an antifilarial anthelmintic isolated from amoscanate. Active against adult worms of O volvulus. Under investigation for oral treatment of onchocerciasis.

Drug Name	Suramin (Antrypol)
Description	Chemical name: The symmetrical 3"-urea of the sodium salt of 8- (3-benzamido-4-methylbenzamido) naphthalene-1,3,5—trisulphonic acid. Administered by slow IV injection as 10% solution. Only drug effective against adult worms of O volvulus. Primarily indicated for severely afflicted, otherwise healthy adults with salvageable vision.
Adult Dose	66.7 mg/kg IV total in 6 incremental weekly doses
Pediatric Dose	Not established
Contraindications	Documented hypersensitivity; severe liver or renal disease; blind patients; moderately infected individuals
Interactions	None reported
Pregnancy	X - Contraindicated in pregnancy
Precautions	Adverse effects include thrombocytopenia, agranulocytosis, anemia, proteinuria, paresthesia, generalized flaccid paralysis, nausea, vomiting, shock, pruritus, urticaria, and erythematous maculopapular rash (eg, erythema multiforme, exfoliative dermatitis, fatal toxic epidermal necrolysis)

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Further Outpatient Care

• Patients should receive follow-up care as needed.

Deterrence/Prevention

• Identification of endemic areas, education of the populace, training of local health care officials, procurement of antifilarial drugs, and vector control create a coordinated effort to eliminate onchocerciasis. Improved socioeconomic status with economic advancement also contributes to disease eradication.
• OCP
• • Onchocerciasis is a chronic disease that affects rural populations. Accepted as inevitable by those who live in impoverished endemic areas, it is a striking example of how a disease can compromise the human potential for economic growth.
  • Onchocerciasis has produced economically blind communities. In some villages in Burkina Faso, the prevalence of blindness has reached 35% of the population, reducing the agricultural productivity below their survival level. An estimated average of 22 years of productivity was lost for every blind person. The disease has led to the abandonment of some of the most fertile valleys in tropical Africa.
  • Burdened by the adverse health and socioeconomic impact of this disease and encouraged by the prospects of effective control, several West African countries expressed interest in an action against the disease. A joint technical meeting of the Agency for International Development of the United States of America, Organization de Coordination et de Cooperation pour la Lutte Contre les Grandes Endemies, and the World Health Organization (WHO) was held in Tunis, Tunisia, in July 1968 to discuss the feasibility of onchocerciasis control. The implementation of a large-scale intercountry program in West Africa was recommended.
  • The United Nations Development Programme (UNDP), Food and Agricultural Organization of the United Nations (FAO), World Bank, and WHO cosponsored a mission to 7 West African countries. The OCP began operations in 1974. The insecticides used were B T (Eriochrome black T), H-14, Abate (Temophos), pyraclofos, phoxim, permethrin, carbosulfan, and vectron. These were used on a rotation basis depending on the sensitivity of the Simulium complex. The rotation of the insecticides also deterred the emergence of resistant strains of the blackfly in the 1980s.
  • Today, the number of people infected within the program area is nil because the vector almost has been eradicated. This astonishing result was achieved by a weekly aerial application of insecticides to the breeding sites of blackfly larvae in the rivers over a period of 14 years.
• Fourteen years of intensive public health efforts leading to vector control have led to the elimination of onchocerciasis as a significant public health hazard in 11 participating countries. The OCP established multinational collaboration as a keystone for onchocerciasis eradication. This remarkable public health accomplishment is of particular importance in that onchocerciasis eradication promoted significant socioeconomic development. Vector control continues through the year 2002 in the extension areas, where larviciding started much later. The success of the OCP must be maintained after the end of the program.
• Devolution, already in progress, is a challenge for the involved countries. They have assumed the responsibility of detecting and controlling the disease at the low level achieved by the OCP. Continuous collaboration between the countries is crucial because the blackfly does not recognize borders and can readily convey the infection from country to country.
• The Global 2000 River Blindness Program (GRBP) of the Carter Center has played and continues to play a substantial role in controlling this disease. In fact, the Carter Center, in collaboration with the Lions Clubs Sight First program (LCSF), provided 69% of the treatments in 1998 in Nigeria. Approximately 6 million people were treated with ivermectin in the sub-Sahara region in 1998, with Nigeria benefiting the most (3,912,476 persons).
• • The GRBP increased the treatment in Sudan 200% from the previous year despite the civil war of more than a decade.
  • Of the 1 million Ugandans treated with ivermectin in 1998, 78% were treated under the GRBP. This was considered to be 98% of the annual treatment objectives of the GRBP for that year.
  • The GRBP-assisted program in Cameroon achieved a 92% increase relative to the previous year with a total of 407,281 treatments in 1998.
• The World Bank's APOC trust fund has greatly supported the GRBP efforts. The strategy of the APOC is to achieve a complete community based program, called Community Directed Treatment with Ivermectin (CDTI). Under CDTI directions, the GRBP will try to increase community support so that village members will be encouraged and involved in the distribution of ivermectin even after the end of the OCP.
• With the theme "Elimination through sustainability of Mectizan treatment" by President Carter, the Onchocerciasis Elimination Program for the Americas (OEPA) treated 270,622 people in the Americas in 1998. This was 75% of the annual treatment objectives for that year.
• • Continuous efforts are being made to identify endemic areas in Venezuela, the most endemic country for river blindness in the Americas, so that ivermectin treatment can be implemented.
  • Training of cadres of national experts, who would assume responsibility, is very important.
• The prospect for the development of a vaccine against onchocerciasis is hindered by the fact that antigens of O volvulus are complex and show extensive cross-reactivity with other filaria parasites of humans and animals. Challenges to development of the vaccine include development of field-usable immunodiagnostic tests to enable quantification of worm burdens in infected patients and research using immunology and molecular biology to develop a vaccine against O volvulus.

Complications

• See Mortality/Morbidity.

Prognosis

• Vector control has been effectively applied through the OCP in West Africa with remarkable results, interrupting transmission in most parts of the original program area.
• • Treatment with ivermectin has been effective in controlling onchocerciasis in all endemic areas. Community-based studies have shown that ivermectin, when administered at 6-month intervals, can maintain low levels of microfilariae in the skin. This treatment clearly has the potential for interrupting transmission in hypoendemic and mesoendemic areas.
  • According to the final report of the conference on the eradicability of onchocerciasis, programs in the Americas and other carefully selected sites should aim for complete interruption of transmission.
• Currently, onchocerciasis in Africa cannot be eradicated; nevertheless, continuous efforts will preserve those areas in West Africa made free of onchocerciasis transmission through the OCP. Indefinitely, the distribution of ivermectin was recommended to keep onchocerciasis controlled in the hyperendemic and mesoendemic foci in Africa to a point where it is no longer a public health problem.

Patient Education

• Training of cadres of national experts, who would assume responsibility for human and vector population surveillance, is very important.

MISCELLANEOUS

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical/Legal Pitfalls

• Fortunately, tort reform, risk management, and litigation legislation are not major issues in the developing countries where onchocerciasis is endemic. No important legal issues or lawsuits have been associated with implementing potential prevention programs and blindness treatments to these unfortunate locations.

Special Concerns

• See Medication.

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

• Awadzi K, Edwards G, Opoku NO, et al. The safety, tolerability and pharmacokinetics of levamisole alone, levamisole plus ivermectin, and levamisole plus albendazole, and their efficacy against Onchocerca volvulus. Ann Trop Med Parasitol. Sep 2004;98(6):595-614. [Medline].
• Ayong LS, Tume CB, Wembe FE, et al. Development and evaluation of an antigen detection dipstick assay for the diagnosis of human onchocerciasis. Trop Med Int Health. Mar 2005;10(3):228-33. [Medline].
• Cooper PJ, Guderian RH, Proano R, Taylor DW. Absence of cellular responses to a putative autoantigen in onchocercal chorioretinopathy. Cellular autoimmunity in onchocercal chorioretinopathy. Invest Ophthalmol Vis Sci. Feb 1996;37(2):405-12. [Medline].
• Dadzie Y, Neira M, Hopkins D, et al. Final report of the Conference on the eradicability of Onchocerciasis. Filaria J. Feb 7 2003;2(1):2. [Medline].
• Ndyomugyenyi R, Tukesiga E, Buttner DW, et al. The impact of ivermectin treatment alone and when in parallel with Simulium neavei elimination on onchocerciasis in Uganda. Trop Med Int Health. Aug 2004;9(8):882-6. [Medline].
• Nguyen JC, Murphy ME, Nutman TB, et al. Cutaneous onchocerciasis in an American traveler. Int J Dermatol. Feb 2005;44(2):125-8. [Medline].
• Pearlman E, Hall LR, Higgins AW, et al. The role of eosinophils and neutrophils in helminth-induced keratitis. Invest Ophthalmol Vis Sci. Jun 1998;39(7):1176-82. [Medline].
• Rowe SG, Durand M. Blackflies and whitewater: onchocerciasis and the eye. Int Ophthalmol Clin. Winter 1998;38(1):231-40. [Medline].
• The Carter Center. The global 2000 river blindness. Vol 11. River Blindness News;1999: 1-8.
• World Health Organization/OCP. West Africa without onchocerciasis. World Health Organization/OCP;1997.

Article Last Updated: Sep 25, 2006