Brugia malayi

Brugia malayi is a filarial roundworm which causes filariasis in humans.^[1] Identified by Lichtenstein and named by Brug in 1927 as distinct from Wuchereria bancrofti, they called it Filaria malayi. In 1958 the separate genus Brugia was proposed by Buckley, and Filaria malayi became known as Brugia malayi.

B. malayi is limited to tropical regions of Asia.

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Life cycle

  Infective larvae are transmitted by infected biting arthropods during a blood meal. The larvae migrate to the appropriate site of the host's body, where they develop into microfilariae-producing adults. The adults dwell in various human tissues where they can live for several years. The agents of lymphatic filariasis reside in lymphatic vessels and lymph nodes. B. malayi dwells particularly in the lymphatics, as with Wuchereria bancrofti. The female worms produce microfilariae which circulate in the blood.

The microfilariae infect mosquitoes. Inside the mosquito, the microfilariae develop in 1 to 2 weeks into infective filariform (third-stage) larvae. During a subsequent blood meal by the insect, the larvae infect the vertebrate host. They migrate to the lymphatics, where they develop into adults, a slow process that can require up to 18 months.

Recently B. malayi was found to contain an endosymbiotic bacterium, Wolbachia, in all life stages.^[2] The genome sequence of this bacterium was determined at New England Biolabs. Experimental results indicate that the Wolbachia can be killed by treatment of the human host with doxycycline. Nematodes cured of the Wolbachia are sterile and have increased morbidity.

Laboratory diagnosis

Identification of microfilariae by microscopic examination is the most practical diagnostic procedure.

Examination of blood samples will allow identification of microfilariae of Brugia malayi. It is important to time the blood collection with the known periodicity of the microfilariae. The blood sample can be a thick smear, stained with Giemsa or hematoxylin and eosin. For increased sensitivity, concentration techniques can be used. These include centrifugation of the blood sample lyzed in 2% formalin (Knott's technique), or filtration through a Nucleopore membrane.

Antigen detection using an immunoassay for circulating filarial antigens constitutes a useful diagnostic approach, because microfilaremia can be low and variable. Molecular diagnosis using polymerase chain reaction is also possible.

Identification of adult worms is possible from tissue samples collected during nodulectomies (onchocerciasis), or during subcutaneous biopsies or worm removal from the eye (loiasis).

Genome deciphered

On September 20, 2007, scientists mapped the genome of Brugia malayi. Figuring out the genes of this organism might lead to development of new drugs and vaccines.^[3]

References

1. ^ Cross JH (1996). Filarial Nematodes. In: Baron's Medical Microbiology (Baron S et al, eds.), 4th ed., Univ of Texas Medical Branch. (via NCBI Bookshelf) ISBN 0-9631172-1-1. 
2. ^ Taylor MJ (2002). "A new insight into the pathogenesis of filarial disease". Curr Mol Med 2 (3): 299-302. PubMed.
3. ^ Reuters, Genome deciphered for elephantiasis-causing worm

• The article is based on the public domain (U.S. Government website) source US Dept. of Health and Human Services / Center for Disease Control: Filariasis

• Brugia malayi worm dance video by R. Rao. Ph.D
• Brugia malayi at UMich