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Table 1 Summary of key literature describing the tested cryopreservation conditions and outcomes for several species of filarial nematodes

From: Cryogenic preservation of Dirofilaria immitis microfilariae, reactivation and completion of the life-cycle in the mosquito and vertebrate hosts

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]
  1. DMSO Dimethyl sulfoxide, HES Hydroxyethyl starch),L3 third-stage larval form, mf microfilariae, PVP olyvinyl pyrolidone
  2. aDi, Dirofilaria immitis; Dr, Dirofilaria repens; Dc, Dirofilaria corynodes; Da, Dirofilaria aethiops; Ll, Loa loa; Og, Onchocerca gutturosa; Oc, Onchocerca cervicalis; Ov, Onchocerca volvulus; Bp, Brugia pahangi.; Bm, Brugia malayi; Wb, Wuchereria bancrofti; Lc, Litomosoides carinii (now L. sigmodontis)