The transmission and development of Cosmocephalus obvelatus (Nematoda: Acuarioidea) of gulls (Laridae)

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Abstract
C. obvelatus, found in the esophagus of ring-billed gulls (Larus delawarensis), from Lake Ontario [Canada] developed to the infective stage in the hemocoel of the amphipods Crangonyx laurentianus, Hyalella azteca and Gammarus fasciatus. At 20.degree. C, The 1st molt occurred at 10 days and the 2nd 18 days postinfection Infective larvae given to laboratory-reared herring (Larus argentatus) and ring-billed gulls entered the proventriculus of the birds and molted 3.5 days postinfection. Five days postinfection, 4th-stage larvae were found attached to the posterior 3rd of the esophagus. The 4th molt occurred 11 days postinfection and worms were found throughout the esophagus. Females were gravid 27 days postinfection. Various developmental stages are described. Infective larvae became encapsulated on the mesentery of experimentally infected goldfish (Carassius auratus) and a shiner (Notropis sp.). Infective larvae were found in various fish collected in waters adjacent to the gull colony. Regular examination of adult gulls indicated birds acquired infections soon after arriving from the wintering grounds. There was little evidence that transmission occurred in the latter regions. Young-of-the-year birds acquired infections by regurgitation of 4th-stage larvae and adult worms along with food during feeding by parents and from infective larvae contained in the fish given to them by the parents. Prevalence in 28-day-old birds had reached 100%. Intensity (including all stages) in fledglings 35-42 days old on July 3 was 15.7 (6-38).

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