Effects of doxycycline on prepatent and patent infections of Brugia pahangi in dogs and observations on the growth and survival of L3 in jirds and dogs.

The effects of doxycycyline administered orally at 10 mg/kg twice daily for 30-day periods in 20 Beagles with SC-induced infections of Brugia pahangi and the effects of treatment on in vivo development of L3 fed on blood from these dogs was studied. Doxycycline was administered on Days 0-29, 40-69 or 65-94, with an untreated control. No worms were recovered from dogs treated on Days 0-29, while all dogs treated on Days 40-69 and 65-94 had some live, stunted worms at necropsy on 218-22 days PI. All control dogs had normal worms. Mosquitoes were fed blood from dogs to assess the ability of L3 to develop in jirds and dogs. L3 from treated and untreated groups were injected IP into jirds. Worm recovery for the treated group at Day 35 PI was somewhat lower than for controls, while recovery for the treated group at Day 60 PI was significantly lower. When L3 from treated and control groups were injected SC into dogs, none of the dogs in the treated group had Mf or live adult worms at necropsy on Day 88 PI, while all control dogs were microfilaremic and had live worms. In conclusion, doxycycline treatment of dogs infected with B. pahangi killed all developing larvae, most immature adults, and some mature adults and disrupted embryogenesis. L3 from mosquitoes fed on dogs treated with doxycycline were unable to complete development when injected into dogs, and IP inoculation into jirds revealed short-term growth, stunting and gradual reduction in survival of the worms.