Clinical Characteristics

Clinical manifestations are variable and are more significant in visitors to an endemic region than in indigenous people. Severity ranges from a mild nuisance as the occasional worm passes beneath the conjunctiva of the eye (Fig. 26.32) to significant CNS invasion and coma in people with a high microfilaremia. The most common and characteristic findings in loiasis are Calabar swellings, which are focal regions of angioedema, usually located in the extremities. These erythematous swellings occur suddenly, range in size from 5 to 15 cm, and resolve gradually over hours to days. The cause is unknown, but they may represent an immune response to antigenic material at a region where the worm has migrated. Calabar swellings generally occur at only one site at a time and may recur sporadically for years, even after a person has left an endemic region. Interestingly, they are more common in visitors to an endemic region than in the local inhabitants. Fatigue and arthralgias also are not uncommon.

A membranous glomerulonephritis, which is probably immune mediated, occurs in many individuals, with hematuria and proteinuria in 22% of patients with loiasis. Loiasis may be one cause of tropical pulmonary eosinophilia. Lymphadenopathy and lymphadenitis are also features of loiasis, but are less prevalent than in other filarial infections. When Loa loa microfilariae are found within lymph nodes, they may be intravascular or within adjacent microabscesses; they also wander throughout the body and have been seen in the spleen, liver, lung, gut, and CNS.

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Fig. 26.32 A-C. Loiasis. A, B Adult nematodes migrating beneath the conjunctiva of the human eye. (Courtesy of R. Noval) C Removal of adult worm (Loa loa) from the conjunctiva of a patient in Cameroon. (Courtesy of Dr. David Cogan; from Marty and Anderson, 1995).