title: Cryopreservation of Dictyocaulus viviparus third-stage larvae and Trichinella spiralis muscle larvae.
abstract: In cryopreservation studies with third-stage larvae of Dictyocaulus viviparus, best results were achieved by incubating larvae in 0.05% NaOCl at 37 degrees C to remove the sheath, followed by cooling at a rate of 1 degree C min per min down to about 0 degree C. After an equilibration time of 10 min at +4 degrees C with or without 4% polyethylene glycol-400 as cryoprotectant, samples were frozen at the same cooling rate to an intermediate temperature of -20 degrees C, maintained at this temperature for 10 min and finally plunged into liquid nitrogen for storage. Three groups of 3 calves were infected with the following batches of third-stage larvae: (a) fresh, sheated; (b) fresh, exsheathed; (c) exsheathed, cryopreserved for 13 weeks in liquid nitrogen and subsequently thawed. Although 62% of group (c) were regarded as viable in vitro, their infectivity to calves was low and only an average of 0.08% of the inoculated larvae (3000 per animal) developed into adult lungworms (= infectivity rate). Average infectivity rates of fresh, sheathed (a) and fresh, exsheathed (b) larvae were much higher (38.3% and 29.7%) and not significantly different from each other. Two of the calves inoculated with previously frozen larvae and all of the calves infected with fresh larvae excreted first-stage larvae in their faeces, but the latter groups in higher quantities. The results show that cryopreservation of exsheathed third-stage larvae of D. viviparus is possible, but for strain maintenance infection doses greater than 3000 larvae should be used for inoculation of calves.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000469:parasitology; D004021:Dictyocaulus / Q000254:growth & development* / Q000472:pathogenicity; D004022:Dictyocaulus Infections / Q000469:parasitology; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005615:Freezing; D007814:Larva / Q000254:growth & development; D011309:Preservation, Biological; D051381:Rats; D014234:Trichinella / Q000254:growth & development* / Q000472:pathogenicity; D014235:Trichinellosis / Q000469:parasitology / Q000662:veterinary; D014251:Trichostrongyloidea / Q000254:growth & development*