Microfilariae (juveniles of filarial worms) were first observed on the blood of a native in Celebes Island in the year 1927. Doctors at first thought that the microfilariae (singular: microfilaria) belong to the Wuchereria bancrofti type; not until the 1940 when an adult form of the microfilaria was found in India which is morphologically different from a regular W. bancrofti type. After a year, adult forms of the worm were discovered in an Indonesian community. The filarial worm was named Brugia malayi to differentiate it from W. bancrofti. Note that the species name “malayi” is derived from the word Malay which pertains to the Malayan people living in Celebes, Indonesia, and neighboring islands. Today B. malayi is now found in China, Japan, Korea, India, Sri Lanka, the East Indies, the Philippines, and other parts of Southeast Asia. The worm can also be found in areas where W. bancrofti is found so there is an overlap of distribution between the two. Contrary to W. bancrofti, B. malayi has not spread to the New World and the African continent (Laurence 1989).
B. malayi is morphologically similar to W. bancrofti, but the males of the former are only about half as large as the males of the latter. The two have a little difference in the number of their anal papillae and the left spicule of B. malayi is more intricate than that of W. bancrofti. The difference of B. malayi to W. bancrofti is technically not enough to separate it to a different genus name “Bruglia”, but because a large literature has already accumulated on Malayan filariasis under the genus name “Bruglia”, scientists accepted it as the genus name of the worm. The filarial worm may have been called Wuchereria malayi instead of Bruglia malayi. (King and Freedman 2000)
Morphology of Bruglia malayi
· 13.5 mm to 20.5 mm long
· 70 micrometer to 80 micrometer wide
· tail is curved
· bears 3 or 4 pairs of adanal
· bears 3 or 4 pairs of postanal papillae
· spicules are unequal and dissimilar
· small gubernaculum is present
· 80 mm to 100 mm long
· 240 micrometer to 300 micrometer wide
· its fingerlike tail is covered with tiny cuticular bosses
· its vulva is near the level of the middle of the esophagus
Biology and Pathology of Bruglia malayi
The life cycle of B. malayi is almost similar to W. bancrofti. Mosquitoes belonging to genera Mansonia, Culex, and Aedes are the intermediate hosts of the filarial worm. The worms can be found in mosquitoes’ saliva and readily transmitted every time they feed on human blood. According to King and Freedman (2000), adults of B. malayi live in human lymphatics and cause same disease symptoms as W. bancrofti, though elephantiasis, when it appears, typically does not extend beyond the elbows and knees.
The microfilariae (juveniles) of B. malayi differ from that of W. bancrofti in that they have nuclei in the tail tip. There are strains of B. malayi that exhibits periodicity wherein they are present in peripheral blood vessels at night (accessible to feeding mosquitoes) and at deeper tissues during the day (non feeding time for mosquitoes). There are strains which follow the opposite periodicity: in peripheral blood vessels during the day and at deep tissues during the night. Periodicity may depend on several factors within a geographic area.
The diagnosis and treatment of B. malayi is similar to W. bancrofti. Mosquito eradication is the best control method. The method involves the destruction of containers (filled with water) where the mosquito larvae are found. The larvae usually are found in holes at the stems of herbs; these herbs should be burnt or sprayed with the proper herbicide. (King and Freedman 2000)
King CL, and DO Freedman. 2000. Filariasis. In G.T. Strickland (Ed.), Hunter’s tropical medicine and emerging infectious diseases, 8th Ed. Philadelphia: W.B. Saunders Co.
Laurence BR. 1989. The global dispersal of bancroftian filariasis. Parasitology. Today 5:260-264.
Photo credit: https://commons.wikimedia.org/wiki/File:Brugia_malayi.JPG