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Dermatologic Manifestations of Onchocerciasis (River Blindness) Workup

  • Author: Jason F Okulicz, MD, FACP, FIDSA; Chief Editor: William D James, MD  more...
 
Updated: Oct 06, 2015
 

Laboratory Studies

The traditional standard diagnosis of onchocerciasis is based on the acquisition of 3- to 5-mg skin snips from an affected area. These snips are immediately immersed in sodium chloride solution and placed under a microscope. The emerging microfilariae are then counted. This method is specific, and it has been the most accurate. However, the use of skin snips is not sensitive for detecting early or mild infections, and this method is becoming increasingly unacceptable to people in endemic communities because of its invasiveness.

The Mazzotti test, now seldom used, involves the administration of 6 mg of diethylcarbamazine (DEC). DEC inhibits neuromuscular transmission in nematodes. Within 2 hours, a positive result produces pruritus and, sometimes, intense inflammation in the areas of dying microfilariae. Other possible effects such as vomiting, conjunctivitis, albuminuria, hypotension, and sudden death (rare) limit its usefulness. Oral DEC was formerly used in treatment of the disease.

The DEC patch test (ie, Mazzotti patch test) involves a topical application of DEC, which produces a local reaction to dying microfilariae at the patch site.[5, 6]  This noninvasive test is specific, but it is less sensitive than the skin-snip test. In the future, this test may be more valuable in detecting the recrudescence of infection in onchocerciasis-free zones than in diagnosing the disease.

Enzyme-linked immunosorbent assays (ELISAs), which require only a finger-stick sample, are more sensitive and less invasive than skin-snip tests. This test is used to recognize specific microfilarial antigens. However, ELISA results cannot be used to distinguish past and current infections, a considerable problem in endemic areas.

The polymerase chain reaction (PCR) amplifies repetitive parasite DNA sequences in skin-snip specimens.[7]  Compared with skin-snip tests, this method has greater sensitivity in patients with low-level infections. The return of microfilariae to the skin after drug treatment can also be identified earlier with this test. The major disadvantages of PCR are its high cost and invasiveness. A minimally invasive and painless alternative to the use of skin snips is the collection of skin scratches. The superficial layer of the epidermis is removed by carefully scraping the skin with the blunt edge of a disposable lancet. PCR studies of skin scratches, instead of skin snips, have yielded similar results and may be used more often in the future.

Rapid-format antibody card tests are being developed to diagnose onchocerciasis.[8, 9]  In these tests, serum samples can be used to detect antibodies, such as immunoglobulin G4 (IgG4) antibodies to recombinant O volvulus antigen Ov16. Tests for additional antibodies are currently under development. Initial studies show good sensitivity and specificity in small numbers of samples and controls using various methods. Some tests can be modified to permit the use of blood samples obtained from less invasive finger sticks. This modification increases the utility of the test for field use. Additional studies are needed to determine the value of these tests in the diagnosis of onchocerciasis.

Microfilariae can often be directly observed by means of slit lamp examination of the cornea and anterior chamber of the eye.

An oncho-C27 antigen detection dipstick assay using urine and tears has been developed. The test can be completed in as short as 3 hours, and the strips maintain reactivity when kept at room temperature for up to 8 months. Sensitivity and specificity were good in an initial study.[10]

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Histologic Findings

In early untreated cases, tissue biopsy samples may show a mild chronic inflammatory infiltration; eosinophils, lymphocytes, and histiocytes may surround the microfilariae. Microfilariae are often present without a surrounding cellular reaction. Later cases show hyperkeratosis, parakeratosis, tortuous dermal vessels, dilated lymphatics, and pigment incontinence. An increased number of dermal fibroblasts leads to perivascular fibrosis. In more advanced cases, hyalinized scar tissue replaces the collagen and elastic fibers in the dermis.

The microfilariae have pointed tails, elongated posterior nuclei, paired anterior nuclei, and large spaces between the tip or tail and the first nuclei. They lack sheaths.

Onchocercomas are made up of an outer vascular fibrous stroma embedded with groups of perivascular leukocytes. The inner layer is composed of hyaline connective tissue intermingled with coiled adult worms. A dense cellular infiltrate composed of eosinophils, lymphocytes, macrophages, and giant cells surrounds the worm. The coiled appearance of the worm, the presence of microfilaria in gravid females, and the presence of a gut help in identifying the worm. See the images below.

Photomicrograph of a skin biopsy specimen from a p 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 (hematox 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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Contributor Information and Disclosures
Author

Jason F Okulicz, MD, FACP, FIDSA Director, HIV Medical Evaluation Unit, Infectious Disease Service, San Antonio Military Medical Center; Associate Professor of Medicine, F Edward Hebert School of Medicine, Uniformed Services University of the Health Sciences; Clinical Associate Professor of Medicine, University of Texas Health Science Center at San Antonio; Adjunct Clinical Instructor, Feik School of Pharmacy, University of the Incarnate Word

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

Disclosure: Nothing to disclose.

Coauthor(s)

Robert A Schwartz, MD, MPH Professor and Head of Dermatology, Professor of Pathology, Pediatrics, Medicine, and Preventive Medicine and Community Health, Rutgers New Jersey Medical School; Visiting Professor, Rutgers University School of Public Affairs and Administration

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

Disclosure: Nothing to disclose.

Dirk M Elston, MD Professor and Chairman, Department of Dermatology and Dermatologic Surgery, Medical University of South Carolina College of Medicine

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

Disclosure: Nothing to disclose.

Specialty Editor Board

David F Butler, MD Section Chief of Dermatology, Central Texas Veterans Healthcare System; Professor of Dermatology, Texas A&M University College of Medicine; Founding Chair, Department of Dermatology, Scott and White Clinic

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

Disclosure: Nothing to disclose.

Jeffrey Meffert, MD Associate 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, Texas Dermatological Society

Disclosure: Nothing to disclose.

Chief Editor

William D James, MD Paul R Gross Professor of Dermatology, Vice-Chairman, Residency Program Director, Department of Dermatology, University of Pennsylvania School of Medicine

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

Disclosure: Nothing to disclose.

Additional Contributors

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: New York County Medical Society, Noah Worcester Dermatological Society, Phi Beta Kappa, American Contact Dermatitis Society, Dermatology Foundation, Dermatologic Society of Greater New York, Alpha Omega Alpha, American Academy of Dermatology

Disclosure: Nothing to disclose.

References
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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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