Loa loa

Loa loa is a helminth.

Disease / Pathology

Loa loa has a diurnal periodicity.

Location in the Host

Loa loa adults are found in the subcutaneous tissue and have the unusual predilection for migrating over the bridge of the nose and sclera of the eye. Other than the discomfort there is rarely any damage done to the eye. The microfilariae that are produced by the adults can be found in the sputum, spinal fluid, urine, peripheral blood and in the lungs.

Geographic Distribution

Loa loa can be found on the African continent.

Life Cycle

Loa loa is transmitted by the Deerfly (chrysops). The fly obtains the parasites by taking a blood meal from an infected host. An L1 larvae develops and undergoes 3 molts to become the infective L3 larvae stage that migrates to the head and fly proboscis to deliver to another host while taking a blood meal.

Morphology & Diagnosis

Loa loa adults can be obtained when seen migrating on surface of the eye or bridge of nose by surgical removal. The microfilariae can be found in the blood, but is not commonly. When they are found they are approximately 250-300um in length. They are sheathed but the sheath is difficult to see as it is tight, light staining to the point that the sheath may not stain at all. The nuclei are continuous to the tip of the tail which is pointed. The terminal nuclei tend to elongate.


Loa Loa in a tissue prep stained with Geimsa stain
Key identifying characteristics of Loa Loa – Illustration by W. Vientos