DEVELOPMENT OF BRUGIA MALA YI IN MONGOLIAN GERBILS PREVIOUSLY EXPOSED TO WUCHERERIA BANCROFT! JOHN H. CRoss* and MEI-YUAN Hsu U.S. Naval Medical Research Unit No. 2, Manila, Philippines. INTRODUCTION in the NAMRU-2 laboratory in Taipei, Taiwan, for several years. Laboratory raised In the past we reported on studies carried Aedes togoi (Formosan strain) were permitted out with lymphatic filarid species which to feed on a human volunteer with W. included reports on the development of bancrofti microfilaremia on the island of Wuchereria bancrofti in monkeys (Cross eta/., Kinmen, and the mosquitoes transported by 1979), the developmem of W. bancrofti, air to Taipei. Aedes togoi also were fed on Brugia malayi and B. pahangi in Toxorhyn­ B. malayi infected gerbils in the laboratory to chites sp. (Cross et al., 1980), the development obtain infective stage larvae. Methods of of W. bancrofti in Mongolian gerbils (Cross infecting the mosquitoes, obtaining the third­ et al., 1981), and hybridization experiments stage larvae and infecting and necropsing the between B. malayi and B. pahangi (Cross animals were similar to methods used in et a/., 1984). During the course of these earlier studies (Cross et al., 1979; 1981). studies we also carried out a preliminary The Mongolian gerbils ( Meriones unguicu­ experiment to determine whether previous latus) were from a colony maintained at the exposure to infection of W. bancrofti would NAMRU-2 laboratory in Taipei, Taiwan. influence the development of a challenging infection of B.malayi in the same animals. Only adult males were used" The paper presents the results of this study. Each of 12 animals was given 100 third­ stage larvae of W. bancr£?fti in saline by syringe MATERIALS AND METHODS inoculation subcutaneously into the groin. Approximately one month later the animals The strain of W. bancroftiwas fromKinmen, were given a challenging infection of 100 China, and the strain of B. malayi was from a third-stage larvae of B. malayi by the same cat collected during a field trip to South route. Four gerbils served as controls for Kalimantan (Borneo), Indonesia. The strain the challenging B. malayi infection. The had been maintained in Mongolian gerbils blood or the animals were examined for *Present address: Uniformed Services University of microfilariae at 3 months post-infection, and the Health Sciences, Bethesda, Maryland 20814, all were killed and examined for parasites 6 U.S.A. This study was supported through funds provided months after infection. by the Naval Medical Research and Development Command, Navy Department for Work Unit MR041. 09.01-0145. RESULTS AND DISCUSSION The opinions and assertions contained herein are those of the authors and are not to be construed as Eleven of the 12 B. malayi-challenged official or reflecting the views of the U.S. Navy Department or the Naval Service at large. animals and the 4 controls survived the Reprint requests to Publications Office, U.S.Naval experiments, and were necropsied at 6 months Medical Research Unit No.2, P.O. Box SC:fl:410, post-infection. Eight of the challenging Sta. Cruz, Manila or APO San Francisco, California 96528. infections produced microfilariae as well as Vol. 18 No. 2 June 1987 183 SoUTHEAST AsiAN J. TRoP. MEn. PuB. HLTH. Table I Development of Brugia malayi in Mongolian gerbils previously infected with 100 third-stage larvae of Wuchereria bancrofti. Number of worms recovered, sex and location No. gerbils Total infected Range Male Female Testes Pelt/Carcass Viscera No. Experimental 11 2-33 169 72 97 116 2 51 (Av. 15) Control 4 24-50 152 72 90 102 2 48 (Av. 38) the 4 control animals. The microfilariae­ The results of this preliminary study suggest negative experimental animals were found that a previous infection with W. bancrofti to harbor single sex infections at necropsy. has influence on the development of a chal­ No W. bancrofti microfilariae were found, lenging infection of B. malayi in Mongolian and at necropsy one fourth-stage larvae was gerbils. Only 15% of the B. malayi given to recovered from one of the experimental previously W. bancrofti ·infected gerbils de­ veloped, compared to 38 %in control gerbils animals. not previously infected with W. bancrofti. Adult B. malayi were recovered from all Although measurements were not made, the experimental and control animals (Table 1). B. malayi recovered from the experimental The recovery rates ranged from 2 % to 33 % animals were noticeably smaller than those (average 15 %) for those gerbils previously from the control animals. There was little infected with W. bancrofti, and ranged from difference in the recovery rates by sex of the 24% to 50% (average 38 %) in the control worms and in the location of development in animals only given B. malayi infections. the animals. Most of the worms in both Forty-three percent of the worms recovered groups of animals were found in the testes from the experimental animals were males and followed by the heart, liver, lung, intestines, carcass and pelt. 57% females; most (69%) were found in testes, while 30% were recovered from the One wonders whether this cross resistance heart, lungs, and intestine. Two worms were also occurs in nature. In some areas of Asia, found in the carcass. In the single sex infec­ both B. malayi and W. bancrofti are known to tions involving females, most of the worms be endemic with microfilariae of both species were in the viscera, and in one animal two found in the peripheral blood of humans. male worms were in the testes. A total of 152 In gerbils, B. malayi was able to complete worms were recovered from the control development in animals first infected with gerbils. Forty-seven percent were males and W. bancrofti, and while microfilariae of B. 58% females. Sixty-seven percent were found malayi were produced, the number of adult in the testes, 32% in the viscera and one worm worms recovered were less than the number each in the pelt and carcass. of worms recovered from the controls. It 184 Vol. 18 No. 2 June 1987 DEVELOPMENT OF Brugia ma/ayi in W. bancrofti INFECTED GERBILS seems tenable that similar results could occur experimental animals also appeared to be in humans. It would be difficult to determine smaller. This study suggests that gerbils are this in man, however. Unfortunately, the able to develop partial resistance to Brugia effect of B. malayi on the development of malayi following a previous infection with W. bancrofti cannot be tested in gerbils since Wuchereria bancrofti. it is only on rare occasions that W. bancroftt will complete development in this host (Cross REFERENCES et a!., 1981). On the other hand, this too could possibly happen in nature. CRoss, J.H., PARTONo, F., Hsu, M-Y. K., AsH, L.R. and OEMIJATI, S., (1979). SUMMARY Experimental transmission of Wuchereria bancroftitomonkeys. Amer. J. Trop. Med. Twelve Mongolian gerbils, Meriones un­ Hyg., 28 : 56. guiculatus, were infected with 100 third­ CRoss, J.H., SHu, M-Y. K. and LIEN, J.C., stage larvae of Wuchereria bancro.fti. One (1980). Preliminary observation on the month later these animals, along with 4 con­ development of larval filariae in Toxor­ trol animals, were given 100 third-stage larvae hynchites species. Amer. J. Trop. Med. of Brugia malayi. Eleven of the 12 experimen­ Hyg., 29 : 46. tal animals and the 4 controls survived, and 8 of the experimental animals and all of the CRoss, J.H., PARTONO, F., Hsu, M-Y. K., controls demonstrated microfilaremia after AsH, L.R. and OEMIJATI, S., (1981). 3 months. The animals were killed at 6- Further studies on the development of months post-infection and examined for Wuchereria bancrofti in laboratory ani­ parasites. One W. bancrofti larva was found mals. Southeast Asian J. Trop. Med. in one of the experimental animals, and 15% Pub!. Hlth .. 12 : 114. of the B. malayi given were recovered as CRoss, J.H., Hsu, M-Y. K. and Lu, S.K., adults from the testes, viscera, and carcass. (1984). Hybridization between Brugia Thirty-eight percent of the worms given to malayi and Brugia pahangi from South the controls were recovered from the testes, Kalimantan, Indonesia. Southeast Asian viscera, and pelt. The worms from the J. Trop. Med. Pub!. Hlth., 15: 190. Vol. 18 No. 2 June 1987 185 .