Dermatologic Manifestations of Onchocerciasis (River Blindness) 

  • Author: Jason F Okulicz, MD; Chief Editor: William D James, MD   more...
 
Updated: Aug 1, 2011
 

Background

Onchocerciasis is a common, chronic, multisystemic disease caused by the nematode Onchocerca volvulus. The disease characteristically includes dermatologic (see the image below), lymphatic, ophthalmologic, and systemic manifestations. Human transmission of the disease is caused by a bite from the intermediate host, the black fly (genus Simulium). Black flies breed along waterways, which can vary from small streams to broad rivers. Affected individuals usually live or work within a few kilometers of these sites. Onchocerciasis has long been associated with a high incidence of detrimental effects on socioeconomic development and public health in endemic areas.

Dermatitis associated with microfilaria. Courtesy Dermatitis associated with microfilaria. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.

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Pathophysiology

In 1875, John O'Neill first observed O volvulus microfilariae in a case of "craw-craw," as onchocerciasis is known in West Africa. Almost 50 years later, Blacklock discovered the vector to be Simulium in Sierra Leone. The main vector in most of Africa is Simulium damnosum; in Ethiopia, Uganda, Tanzania, and the Democratic Republic of the Congo, Simulium neavei is common. In the Americas, the principal vectors are Simulium metallicum, Simulium ochraceum, and Simulium exiguum. Some vectors bite humans rather exclusively, whereas others are zoophilic to varying degrees. Animal reservoirs of O volvulus have not been found.

When a black fly takes a blood meal from an infected human, they also ingest onchocercal microfilariae in the skin. Surviving microfilariae in the black fly burst through the peritrophic membrane formed by the blood meal, invade the midgut, and advance to the thoracic muscles. The differentiation of these microfilariae into L1 larva begins in muscle within 28 hours after the blood meal. The first molt produces L2 larva within 96 hours, followed by the second molt, which produces L3 larva by day 7. The infective L3 larva migrates to the insect's head and mouth for future deposition into human skin during the next blood meal.

After L3 larvae are transmitted to human skin, those that survive molt within 1 week to form L4 larva. Their development into male and female forms is completed by 1-3 months. The adult worms reside in the deep dermis and fascial planes. Thick, fibrous, subcutaneous nodules called onchocercomas are formed as the result of the development of scar tissue around the adult worms. These onchocercomas average 3 cm in diameter, and they typically contain 2-3 female adults and 1-2 male adults. The nodules typically are surrounded by eosinophils and lymphocytes that are ready to attack the newly produced microfilariae.

Adult worms isolated in nodules are not directly harmful to the patient. Their progeny, which are released from the nodules, are responsible for most of the damage related to onchocerciasis. Nonetheless, to control the disease, the identification and removal of these onchocercomas is critical. Ivermectin is the most effective agent against microfilariae (see Medical Care). Currently, available agents that are effective against adult worms are toxic. For this reason, surgical removal of the adult worms is important.

Within 10-12 months after the initial infection, adult female worms start producing microfilariae, which have an average lifespan of 6 months to 2 years. The reproductive life of the adult averages 9-11 years. During this time, female worms may release 1300-1900 microfilariae per day. The maximal production of offspring occurs during the first 5 years of the worm's reproductive life, after which this activity declines in a linear fashion.

The microfilariae released from the nodules easily traverse the skin and connective tissue. The subepidermal lymphatics and the anterior chamber of the eye are the most common migration sites. The microfilariae can also be found in the blood, cerebrospinal fluid, urine, and internal organs. More than 100 million microfilariae may be present in severely affected individuals.

A symbiotic relationship has been demonstrated between Wolbachia bacteria and filarial nematodes, including O volvulus.[1]Wolbachia species are essential for nematode fertility. Embryogenesis in the female worm is disrupted when Wolbachia numbers are depleted. In addition, murine experiments suggest that corneal inflammation secondary to onchocerciasis may be caused by endotoxins produced by Wolbachia. Results from several small trials suggest that clearance of Wolbachia with antibiotic therapy affects transmission and can reduce and prevent onchocerciasis-related blindness.

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Epidemiology

Frequency

United States

Onchocerciasis is rare in the United States. All reported cases result from the immigration of individuals from endemic areas.

International

Onchocerciasis is a major public health problem in many parts of the world. The disease is endemic in 37 countries in Africa, Latin America, and Yemen. In 1995, an estimated 123 million people were at risk of contracting the disease according to the World Health Organization Expert Committee on Onchocerciasis. Another 17-18 million people were estimated to be infected.

Approximately 95% of all infected people live in Africa. The disease is most severe along the major rivers in 30 countries across the northern and central areas of the continent. Nigeria, Ethiopia, Cameroon, Uganda, and the Democratic Republic of the Congo have the largest number of infected people.

In Latin America, onchocerciasis can be found in Brazil, Venezuela, Colombia, Ecuador, and Guatemala, as well as in the southern mountainous states of Chiapas and Oaxaca in Mexico.[2]

Mortality/Morbidity

  • In 1995, an estimated 270,000 people were blinded and another 500,000 had severe visual impairment as a result of the disease.
  • A multicountry study showed that more than 30% of the population in endemic areas have onchocercal dermatitis.
  • In a survey of skin disease in 7 endemic sites in 5 African countries, 40-50% of adults reported troublesome itching. Blindness is not associated with excess mortality. However, increasing microfilarial load is associated with mortality in both males and females.

Race

To the author's knowledge, no current well-described studies have been performed to determine the frequency of onchocerciasis in specific races.

Sex

  • The disease generally affects more men than women, although sex-related differences may not be apparent until the patient reaches a certain age.
  • Sex-related differences are more pronounced in high-transmission areas, particularly the savanna.
  • The overall trend is partially attributed to increased exposures in men, which are related to the occupational risk in farmers, fishermen, and other workers.

Age

The prevalence of onchocerciasis is lowest in individuals aged 0-10 years. Afterward, the prevalence sharply increases, with a peak in individuals aged 20-30 years.

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Contributor Information and Disclosures
Author

Jason F Okulicz, MD  Assistant Professor of Medicine, Uniformed Services University of the Health Sciences; Staff, Infectious Disease Service, Brooke Army Medical Center

Jason F Okulicz, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians-American Society of Internal Medicine, and Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Coauthor(s)

Dirk M Elston, MD  Director, Ackerman Academy of Dermatopathology, New York

Dirk M Elston, MD is a member of the following medical societies: American Academy of Dermatology

Disclosure: Nothing to disclose.

Robert A Schwartz, MD, MPH  Professor and Head, Dermatology, Professor of Pathology, Pediatrics, Medicine, and Preventive Medicine and Community Health, University of Medicine and Dentistry of New Jersey-New Jersey Medical School

Robert A Schwartz, MD, MPH is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American College of Physicians, and Sigma Xi

Disclosure: Nothing to disclose.

Specialty Editor Board

Donald Belsito, MD  Professor of Clinical Dermatology, Department of Dermatology, Columbia University Medical Center

Donald Belsito, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Contact Dermatitis Society, Dermatology Foundation, New York County Medical Society, New York Dermatological Society, Noah Worcester Dermatological Society, and Phi Beta Kappa

Disclosure: Nothing to disclose.

David F Butler, MD  Professor of Dermatology, Texas A&M University College of Medicine; Chair, Department of Dermatology, Director, Dermatology Residency Training Program, Scott and White Clinic, Northside Clinic

David F Butler, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Medical Association, American Society for Dermatologic Surgery, American Society for MOHS Surgery, Association of Military Dermatologists, and Phi Beta Kappa

Disclosure: Nothing to disclose.

Jeffrey Meffert, MD  Assistant Clinical Professor of Dermatology, University of Texas School of Medicine at San Antonio

Jeffrey Meffert, MD is a member of the following medical societies: American Academy of Dermatology, American Medical Association, Association of Military Dermatologists, and Texas Dermatological Society

Disclosure: Nothing to disclose.

Catherine M Quirk, MD  Clinical Assistant Professor, Department of Dermatology, University of Pennsylvania

Catherine M Quirk, MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Dermatology

Disclosure: Nothing to disclose.

Chief Editor

William D James, MD  Paul R Gross Professor of Dermatology, University of Pennsylvania School of Medicine; Vice-Chair, Program Director, Department of Dermatology, University of Pennsylvania Health System

William D James, MD is a member of the following medical societies: American Academy of Dermatology and Society for Investigative Dermatology

Disclosure: Elsevier Royalty Other

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Leopard-spot pattern of depigmentation on the shins. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
Dermatitis associated with microfilaria. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
Hanging groin sign. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
Hanging groin sign. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
Onchocercoma. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
Onchocercoma. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
Photomicrograph of a skin biopsy specimen from a patient with onchocerciasis. A worm is shown in cross-section. Courtesy of Brooke Army Medical Center teaching file. All images are in the public domain.
Photomicrograph from a gravid female worm (hematoxylin and eosin]). Courtesy of Brooke Army Medical Center. All images are in the public domain.
 
 
 
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