An outbreak of dictyocauliasis among a captive herd of black-tailed deer fawns (Odocoileus hemionus columbianus) occurred in January, 1971. A transient decrease in output of Dictyocaulus viviparus larvae in feces occurred after treatment with levamisole hydrochloride given as a drench at the rate of 16 mg/kg of body weight.

Lungworm larvae were not recovered in feces 6 days after cambendazole, 2-(4-thiazolyl)-5-isopropoxycarbonylaminobenzimidazole, was given as a drench at 40 and 50 mg/kg of body weight. Larvae were again recovered in feces from these fawns between post-treatment days 15 and 23. Output of larvae in feces increased when fawns were confined on a contaminated grass pasture that was intensively grazed. Deteriorating physical condition of the fawns necessitated additional treatment with cambendazole and movement to a woodlot where reinfection by ingestion of larvae was probably minimized.

A noninfected deer was placed on the contaminated pasture 75 days after the infected herd was removed. After 55 days, lungworm larvae were recovered in feces from this deer. Then 29 days later, 20 fawns were placed on this pasture. Four of six of these fawns that were subsequently necropsied harbored light burdens of D. viviparus. Small numbers of lungworm larvae were recovered in feces from five of eight remaining fawns.