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Brugia malayi: intravenous injection of microfilariae in ferrets as an experimental method for occult filariasis.
Experimental Parasitology (1985)
  • James P Thompson, University of Florida
  • R. B. Crandall
  • C. A. Crandall
Microfilaremia, immune responses, and pathology were compared in ferrets infected with 100 third-stage larvae of Brugia malayi (subperiodic strain) or injected intravenously with 106 microfilariae. Ferrets (Mustela putorius furo) inoculated with third-stage larvae typically became patent during the third month after infection, with a mean patency of 123 ± 25 (SE) days. Ferrets injected intravenously with microfilariae exhibited a relatively constant microfilaremia for 3–4 weeks and usually cleared microfilariae before the fourth month. Ferrets that cleared microfilariae after intravenous injection of microfilariae or after infection with third-stage larvae failed to become patent or became amicrofilaremic within 3 weeks after a challenge intravenous injection of 106 microfilariae. Clearance of circulating microfilariae was associated with eosinophilia and serum antibody specific for the microfilarial sheath in ferrets injected with microfilariae and in most ferrets infected with third-stage larvae. Ferrets infected with third-stage larvae and necropsied after clearance of microfilariae had tissue inflammatory reactions to microfilariae characteristic of occult filariasis (tropical eosinophilia) in man; these ferrets exhibited immediate cutaneous hypersensitivity and circulating reaginic antibody to antigens of microfilariae. In ferrets necropsied following two intravenous injections of microfilariae, the majority of ferrets examined within 10 days after clearance of microfilariae had visible liver lesions to microfilariae identical to those of the ferrets infected with third-stage larvae; immediate cutaneous hypersensitivity and reaginic antibody were not consistently detected in ferrets injected with microfilariae. Sera from ferrets that had cleared circulating microfilariae were transferred passively into ferrets made microfilaremic by intravenous injection of microfilariae. Sera with microfilarial sheath-reactive IgG antibody titers (⩾1:200) and microfilarial agglutination titers (⩾1:40) rapidly cleared injected microfilariae (<24 hr); this serum also cleared or greatly reduced circulating microfilariae established by an infection with third-stage larvae; only the IgG-containing fraction of the sera was active in immune clearance. Sera that cleared microfilariae of B. malayi did not clear circulating microfilariae of Dirofilaria immitis or prevent recurrence of circulating microfilariae of B. malayi in ferrets infected with adult filariae. Ferrets were examined at 1 and 3 weeks after transfer of sera and injection of microfilariae for lesions on the surface of the liver typical of occult infection. Ferrets that received sera inducing a rapid clearance of microfilariae did not develop liver lesions or eosinophilia. Only certain sera containing reaginic antibody to microfilarial antigens were associated with an accelerated development of liver lesions and eosinophilia. By the third week after injection, ferrets receiving normal sera had liver pathology and eosinophilia comparable to those receiving sera that induced the early development of lesions. There was a significant linear correlation between the numbers of surface liver lesions and the absolute numbers of blood eosinophils in all the ferrets injected with microfilariae.
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Citation Information
James P Thompson, R. B. Crandall and C. A. Crandall. "Brugia malayi: intravenous injection of microfilariae in ferrets as an experimental method for occult filariasis." Experimental Parasitology Vol. 60 Iss. 2 (1985)
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