Loa loa

Loa loa inhabits rainforests in West Africa and equatorial Sudan. (Roberts and Janovy, 2000; Thompson, et al., 2000)

Loa loa live in areas with hot, wet climates, such as rainforests and swamps. They are transfered by tabinid flies to their human hosts, where they live in subcutaneous tissues, although they have been known to migrate deeper into the body. (Gardon, et al., 1997; Roberts and Janovy, 2000)

Loa loa is cylindrical, has a cuticle with three main outer layers made of collagen and other compounds. The outer layers are non-cellular and are secreted by the epidermis. The cuticle layer protects the nematodes so they can invade the digestive tracts of animals. The worms molt four times, the first two before hatching, and then before their adult stage.

Nematodes have longitudinal muscles along the body wall. The muscles are obliquely arranged in bands. Dorsal, ventral and longitudinal nerve cords are connected to the main body of the muscle.

Loa loa adults are small, thin worms ranging in length from 20-70 mm long and 350-430 micrometers wide. Females are typically larger than males. The head of Loa loa is simple and lacks lips. The tail is blunt. Loa loa juveniles look similar to adults, but are much smaller. (Barnes, 1987; Brusca and Brusca, 2003; Roberts and Janovy, 2000)

After mating, female Loa loa give birth to microfilariae. The microfilariae migrate into the blood stream. At this stage, they can be ingested by any number of deer fly species that feed on the infected host. In the fly, the microfilariae develop in the fat body until reaching the juvenile stage. The infective juvenile Loa loa move to the mouthparts of the fly so that when it slices open a human to feed, the Loa loa may again invade a human host. After a year of development in their definitive host, the Loa loa are adults that may begin the cycle anew. (Roberts and Janovy, 2000)

Females may produce a phermomone to attract males. The male coils around a female with his curved area over the female genital pore. The gubernaculum, made of cuticle tissue, guides spicules which extend through the cloaca and anus. Males use spicules to hold the female during copulation. Nematode sperm are amoeboid-like and lack flagella. (Barnes, 1987; Brusca and Brusca, 2003; Roberts and Janovy, 2000)

Adults may live up to 15 years or more. (Roberts and Janovy, 2000)

Adult worms migrate throughout the subcutaneous tissues of their host at all times of the day. When they linger in one area long enough, a swelling in the shape of the worm can be seen on the skin. Microfilariae live the bloodstream during daylight hours when the host is most likely to be bitten by flies. At night, they retreat into the lungs. In their fly intermediate host, Loa loa microfilariae live in the fat body, while the infective juveniles inhabit the mouthparts of the fly. (Roberts and Janovy, 2000)

Nematodes within the Secernentea have phasmids, which are unicellular glands. Phasmids likely function as chemoreceptors. Females may produce pheromones to attract males.

Nematodes in general have papillae, setae and amphids as the main sense organs. Setae detect motion (mechanoreceptors), while amphids detect chemicals (chemoreceptors). (Barnes, 1987; Brusca and Brusca, 2003; Roberts and Janovy, 2000)

Loa loa is an obligate endoparasite, feeding on fluids in the tissues of humans. Pharyngeal glands and intestinal epithelium produce digestive enzymes to feed on the hosts’ body fluids. Extracellular digestion begins within the lumen and is finished intracellularly. Tabanid flies serve as intermediate hosts. (Barnes, 1987; Brusca and Brusca, 2003; Roberts and Janovy, 2000)

These parasites are usually not preyed on directly, but are ingested. Larval mortality is high as most of the parasites do not reach appropriate hosts. (Barnes, 1987; Brusca and Brusca, 2003; Roberts and Janovy, 2000)

Loa loa is an obligate endoparasite, feeding on fluids in the tissues of humans. Tabanid flies serve as intermediate hosts. (Roberts and Janovy, 2000)

Loa loa is a serious parasite of humans in rural areas of West Africa. When Loa loa migrate into deeper tissues of a host, they can cause encephalitis, sometimes leading to death. Other pathogenic effects include joint pain caused by swelling when a worm stays near a joint for a period of time and damage to the eyes as the worm crawls through the cornea and conjunctive tissues. (Blum, et al., 2000; Chippaux, et al., 1996; Gardon, et al., 1997; Roberts and Janovy, 2000)