Survival and temporal change in the viability of <i>Ascaridia galli</i> eggs exposed to refrigeration or freezing temperatures in the presence of a cryoprotectant

Preserving viable infective stages of chicken ascarids under laboratory conditions facilitates the maintenance of characterized nematode strains for research purposes. We investigated the survivability of <i>Ascaridia galli</i> eggs exposed to low temperatures and the cryoprotectant dimethyl sulfoxide (DMSO). Two egg developmental stages (unembryonated or fully embryonated) were stored at 4°C, -20°, or -80°C in sterile water or with 5% and 10% DMSO for 1, 2, 4, or 8 weeks. Egg survival was assessed by morphology following post-storage incubation in 0.1 N H₂SO₄ at 26°C for unembryonated eggs or with a viability dye exclusion test of hatched larvae for the embryonated eggs. The results revealed that neither DMSO nor the hardy chitinous eggshell protected eggs from freezing damage, and not a single egg survived even for 1 week of storage at -20° or -80°C. DMSO at 10% significantly reduced (P < 0.0001) overall egg survival and embryonation capacity with increasing storage time at 4°C compared to water alone. For both egg developmental stages, egg survival was maintained in 5% DMSO at a rate similar to that in water alone. Unembryonated <i>A. galli</i> eggs survived refrigeration better than embryonated eggs with larval viability declining linearly at almost a double rate in the latter (9.75%/week) compared to the former (5.64 %/week). We conclude that DMSO is unlikely to provide cryoprotection for <i>A. galli</i> eggs and also causes concentration-dependent toxicity with increasing exposure time. Furthermore, survival during refrigeration is better for unembryonated than embryonated eggs.