Onchocerciasis

Background

Onchocerciasis is a devastating infection by a nematode (helminth). It is a major public health problem in Africa and Latin America. The bite of the black fly causes transmits the infective larvae into the skin where they develop into subcutaneous nodules. In patients of the Americas, these nodules are usually on the upper body while in African patients, these nodules are on the lower trunk. Migration of these microfilariae lead to lesions in various tissues, including the eye, leading to blindness. These organisms concentrate in the dermis and epidermis and trigger an inflammatory response leading to intense itching (pruritis). Over time, the skin changes become thickened, wrinkled, and atrophic and post-inflammatory pigmentary alteration may occur.

OUTLINE

Epidemiology

Disease Associations

Pathogenesis

Laboratory/Radiologic/
Other Diagnostic Testing

Gross Appearance and Clinical Variants

Histopathological Features and Variants

Special Stains/
Immunohistochemistry/
Electron Microscopy

Differential Diagnosis

Prognosis

Treatment

Commonly Used Terms

Internet Links

EPIDEMIOLOGY CHARACTERIZATION

SYNONYMS River blindness

INCIDENCE
Third leading cause of blindness in Africa

Approximately one million people are significantly sight impaired or blind and approximately 40,000 new cases of blindness occur each year in Africa

It is estimated that a minimum of 15 million people are currently heavily infected with onchocerciasis and over 100 million people remain at risk of infection

GEOGRAPHY
Latin American
Africa

PATHOGENESIS CHARACTERIZATION

Onchocerca volvolus Nematode

Transmission
Infective larvae transmitted by bite of black fly Simulium

Larvae develops into adults and aggregate to form painless subcutaneous nodules located over bony prominences

GROSS APPEARANCE/
CLINICAL VARIANTS CHARACTERIZATION

General

VARIANTS

Chronic lymphatic obstruction May lead to hanging groin or elephantiasis of the genitalia

HISTOLOGICAL TYPES CHARACTERIZATION

General A snip of skin examined with normal saline may reveal the organism

VARIANTS

SKIN

Mixed inflammatory cell infiltrate with large number of eosinophils
Microfilariae are present between the slits of collagen bundles
Epidermis may show secondary hyperplastic features

Older lesions may show fibrosis and calcifications

PROGNOSIS AND TREATMENT CHARACTERIZATION

Treatment
Ivermectin p.o.

Preventive measures to avoid contact with the black fly

Int J Dermatol 1997;36:23-28.
Macpherson and Pincus. Clinical Diagnosis and Management by Laboratory Methods. Twentyfirst Edition. WB Saunders. 2006.
Rosai J. Ackerman's Surgical Pathology. Ninth Edition. Mosby 2004.
Sternberg S. Diagnostic Surgical Pathology. Fourth Edition. Lipincott Williams and Wilkins 2004.
Robbins Pathologic Basis of Disease. Seventh Edition. WB Saunders 2005.
DeMay RM. The Art and Science of Cytopathology. Volume 1 and 2. ASCP Press. 1996.
Weedon D. Weedon's Skin Pathology Second Edition. Churchill Livingstone. 2002
Fitzpatrick's Dermatology in General Medicine. 6th Edition. McGraw-Hill. 2003.
Weiss SW and Goldblum JR. Enzinger and Weiss's Soft Tissue Tumors. Fourth Edition. Mosby 2001.

Commonly Used Terms

Basic Principles of Disease
Learn the basic disease classifications of cancers, infections, and inflammation

Commonly Used Terms
This is a glossary of terms often found in a pathology report.

Diagnostic Process
Learn how a pathologist makes a diagnosis using a microscope

Surgical Pathology Report
Examine an actual biopsy report to understand what each section means

Special Stains
Understand the tools the pathologist utilizes to aid in the diagnosis

How Accurate is My Report?
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Got Path?
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Last Updated 1/5/2004

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Epidemiology
Disease Associations
Pathogenesis
Laboratory/Radiologic/ Other Diagnostic Testing
Gross Appearance and Clinical Variants
Histopathological Features and Variants
Special Stains/ Immunohistochemistry/ Electron Microscopy
Differential Diagnosis
Prognosis
Treatment
Commonly Used Terms
Internet Links

EPIDEMIOLOGY	CHARACTERIZATION
SYNONYMS	River blindness
INCIDENCE	Third leading cause of blindness in Africa Approximately one million people are significantly sight impaired or blind and approximately 40,000 new cases of blindness occur each year in Africa It is estimated that a minimum of 15 million people are currently heavily infected with onchocerciasis and over 100 million people remain at risk of infection
GEOGRAPHY	Latin American Africa

GROSS APPEARANCE/ CLINICAL VARIANTS	CHARACTERIZATION
General
VARIANTS
Chronic lymphatic obstruction	May lead to hanging groin or elephantiasis of the genitalia

HISTOLOGICAL TYPES	CHARACTERIZATION
General	A snip of skin examined with normal saline may reveal the organism
VARIANTS
SKIN	Mixed inflammatory cell infiltrate with large number of eosinophils Microfilariae are present between the slits of collagen bundles Epidermis may show secondary hyperplastic features Older lesions may show fibrosis and calcifications