Table 1 Summary of key literature describing the tested cryopreservation conditions and outcomes for several species of filarial nematodes
Speciesa | Experimental conditions | Summary of outcomes | Reference | |||
|---|---|---|---|---|---|---|
Additives | Freezing conditions | |||||
Rate (°C/min) | Duration (days) | Final temperature (°C) | ||||
Di, Wb, Lc | None | No control | 1–69 | − 15 and − 70 | Based on post-thaw motility, mf survival was low for Wb, 60–95% survival of Di, 38–54% survival of Lc | [17] |
Ll, Wb, Bm, Di, Dr,Da, Lc | Glycerol with serum | No control | Not stated | − 79 | 50–80% survived and were motile, but phase contrast and ultraviolet microscopy showed morphological changes | [18] |
Di | None | No control | 660 | − 68 | Thawed mf successfully developed to L3s in mosquito, but with low rate of recovery compared to unfrozen control | [19] |
Oc, Og, Ov | 5% Methanol 5% DMSO 5% Ethanediol 5% Glycerol | 1 | Not stated | − 196 | Thawed mf were successfully isolated from mammalian host following injection. Viable L3s were isolated from competent insect vectors following injection. 5% Methanol as cryoprotectant showed improved recovery rates compared to other cryoprotectants tested | [20] |
Di, Dr, Og, Bp | 16% HES | 1.3 to > 200 | Not stated | − 196 | Viable L3s were isolated from insect vector after feeding. Cooling rate of 1.3 C/min showed best recovery of viable L3s. HES does not require washing after thaw and thawed blood can be fed directly to insect vector | [21] |
Di—mf and L3 | mf—5% DMSO with 20% newborn calf serum L3—as above, with or without 16% HES | 1 | Not stated | − 196 | Motility and rate of L3 recovery was lower for thawed mf compared to fresh mf following fluid enema of mf into mosquito. L3 survival after thawing was similar to unfrozen controls, but rate of molting to L4 was very low | [22] |
Dc, Bm, Wb | Dc—6% DMSO with 4 mM PVP Bm—9% DMSO | 0.5–10 | 4–540 | − 196 | Dc, Bm and Wb L3 successfully developed to L3 in insect vector after feeding. Resulting Bm L3s injected into primate host, and life-cycle was successfully completed | [9] |
Bm | 6% DMSO with 15% newborn calf serum | 0.5–1.0 | 6–375 | − 196 | Post-thaw survival of mf was 94–98%. Motility and L3 development in insect vector after feeding were similar to those of unfrozen control | [23] |
Di, Bm, Wb | 6% DMSO with 4 mM PVP | 1 | 30 | − 196 | Post-thaw motility of mf, and L3 recovery from insect vector after feeding was comparable to that of unfrozen controls | [24] |