Brugia malayi

Brugia malayi is found in rural areas of Asia, in addition to isolated pockets in countries extending from the west coast of India to New Guinea, the Philippines and Japan. (Edington and Gilles, 1969)

Brugia malayi is an endoparasite that uses mosquitoes in the genus Mansonia in rural freshwater swamp forests in Southeast Asia as its intermediate host. In open swamp and irrigated fields and hill forests of South and East Asia, B. malayi uses the mosquitoes of the genera Mansonia, Aedes, Anopleles, and Culex. In the intermediate host, B. malayi occupies the stomach, thorax muscles, and the proboscis. When the mosquito bites a human, monkey, domestic cats, or forest carnivores, which are the only definitive hosts it enters the wound where it migrates to the lymphatic system through the blood stream were it remains throughout its adult life. (Anderson, 1992; Despommier, Gwadz, and Hotez, 1995)

Adult Brugia malayi are long and slender with a smooth cuticle, kinked, and has a long cephalic space having a length:width ratio of about 2:1. The head is slightly swollen and has two circles of well-defined papillae. The tail of B. malayi is ventrally curved. Sexual dimorphism exists with the adult female B. malayi being approximately 8 cm long by 0.3 mm wide and the male about 2 cm long and 0.1 mm wide. (Strickland, 1991)

The reproductive cycle of B. malayi begins when a mosquito, the intermediate host which may include species in the genera Mansonia, Aedes, Anopleles, and Culex, acquires the sheathed microfilaria parasite in its blood meal. The microfilariae penetrate the gut wall of the mosquito where they lose their sheath and migrate to the muscles of the thorax. After 10 to 20 days, in which they undergo three molts, they develop into the infective third larval stage. Once the third larval stage is complete the B. malayi migrate to the proboscis of the mosquito. During the mosquito's blood meal the larvae enter the wound of the definitive host, which consist of humans, monkeys, domestic cats, and forest carnivores. The larvae then migrate through the subcutaneous tissue to the lymphatic vessels of the definitive host. Within about a year they develop into mature adults. The sheathed microfilariae produced after copulation, then enter the blood stream allowing the intermediate host to acquire the microfilaria repeating the cycle again.

In general, the worms molt before becoming adults, two molts occurring before they hatch from the eggs. Most all adult structures except certain reproductive parts are found in the young just before hatching. As adults, the worms will not molt, but can grow in size. (Anderson, 1992; Barnes, 1987; Despommier, Gwadz, and Hotez, 1995)

A defining characteristic of B. malayi, as with all nematodes, is that they only have longitudinal muscles, therefore they exhibit an S-shaped motion during locomotion.

There are two forms of B. malayi, the periodic one, in which the microfilariae show a marked nocturnal presence in the blood (10 p.m. - 2 a.m.), and the subperiodic form in which the microfilariae are present throughout the day in the blood of the definitive host. The former is transmitted by species of Mansonia mosquitoes, which bite mainly at night in Southeast Asia, and use humans as the typical reservoir host. The later is found in South and East Asia and is transmitted by species of Mansonia, Aedes, Anopleles, and Culex mosquitoes that feed at any time of the day. (Anderson, 1992; Strickland, 1991)

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

Brugia malayi feeds on blood and lymphatic tissue and fluid of its definitive host. (Anderson, 1992)

These parasites are probably not preyed on directly, but are ingested from host to host. Larval mortality is high as most of the parasites do not reach appropriate hosts.

Intermediate hosts include species in the genera Mansonia, Aedes, Anopleles, and Culex. During the mosquito's blood meal the larvae enter the wound of the definitive host, which consist of humans, monkeys, domestic cats, and forest carnivores.

The economic impact of B. malayi comes in the form of physical and mental disabilities. The physical disabilities come in the form of the inflammation of the lymph nodes, typically located from the waist and below, due to the blockage of the lymphatic circulation. This condition is often called elephantiasis due to the excessive inflammation and enlargment of the appendage. Because of the possible disfigurements, it can affect a person's quality of life and impair their ability to work. The mental disabilities primarily come in the form of depression due to society outcasting them because of their physical deformity. (Rauyajin, Kamthornawachara, and Yablo, 1995)