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Brugia malayi

By Kensey Amaya

Geographic Range

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)

Habitat

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, et al., 1995)

Physical Description

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)

  • Sexual Dimorphism
  • female larger
  • Range length
    2 to 8 cm
    0.79 to 3.15 in

Development

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, et al., 1995)

Reproduction

Nematode 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)

There is no parental investment beyond egg-laying.

  • Parental Investment
  • pre-fertilization
    • provisioning

Behavior

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)

Communication and Perception

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

Food Habits

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

  • Animal Foods
  • blood
  • body fluids

Predation

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.

Ecosystem Roles

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.

Species Used as Host

Economic Importance for Humans: Negative

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, et al., 1995)

Contributors

Renee Sherman Mulcrone (editor).

Kensey Amaya (author), University of Michigan-Ann Arbor, Teresa Friedrich (editor), University of Michigan-Ann Arbor.

Glossary

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

chemical

uses smells or other chemicals to communicate

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

marsh

marshes are wetland areas often dominated by grasses and reeds.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

suburban

living in residential areas on the outskirts of large cities or towns.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

References

Anderson, R. 1992. Nematode Parasites of Vertebrates Their Development and Transmission. Oxon, UK: C.A.B. International.

Barnes, R. 1987. Invertebrate Zoology. Orlando Florida: Dryden Press.

Brusca, R., G. Brusca. 2003. Invertebrates. Sunderland, Massachusetts: Sinauer Associates, Inc..

Despommier, D., R. Gwadz, P. Hotez. 1995. Parasitic Diseases. Spriner-Verlag.

Edington, G., H. Gilles. 1969. Pathology in the Tropics. London, UK: Edward Arnold LTD.

Rauyajin, O., B. Kamthornawachara, P. Yablo. 1995. Socio-cultural and Behavioral Aspects of Mosquito-Borne Lymphatic Filariasis in Thailand: A qualitative Analysis. Soc. Sci. Med, 41: 1705-1713.

Strickland, T. 1991. Hunter’s Tropical Medicine. Philidelphia, PA: W.B. Saunders Company.

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