METHODS: Mice were intraperitoneally-infected with a mouse-adapted EV-A71 strain and treated with a dose of monoclonal antibody (MAb) daily for 3 days on day 1, 2 and 3 post-infection or for 3 days on 3, 4 and 5 post-infection. Treatment effectiveness was evaluated by signs of infection and survival rate. Histopathology and qPCR analyses were performed on mice sacrificed a day after completing treatment.
RESULTS: In mock-treated mice, CNS infection was established from day 3 post-infection. All mice treated before established CNS infection, survived and recovered completely without CNS infection. All mice treated after established CNS infection survived with mild paralysis, and viral load and antigens/RNA at day 6 post-infection were significantly reduced.
CONCLUSIONS: Passive immunization with our MAb could prevent CNS infection in mice if given early before the establishment of CNS infection. It could also ameliorate established CNS infection if optimal and repeated doses were given.
SIGNIFICANCE: A shotgun proteomic approach adopted in this study revealed the compositional details of the venom of common tiger snake from Australia, Notechis scutatus. The proteomic findings provided additional information on the relative abundances of toxins and the detection of proteins of minor expression unreported previously. The potent lethal effect of the venom was neutralized by bioCSL Sea Snake Antivenom, an anticipated finding due to the fact that the Sea Snake Antivenom is actually bivalent in nature, being raised against a mix of venoms of the beaked sea snake (Hydrophis schistosus) and N. scutatus. However, it is surprising to note that bioCSL Sea Snake Antivenom neutralized N. scutatus venom much more effectively compared to the targeted sea snake venom by a marked difference in potency of approximately 6-fold. This phenomenon may be explained by the main difference in the proteomes of the two venoms, where H. schistosus venom is dominated by short-neurotoxins in high abundance - this is a poorly immunogenic toxin group that has been increasingly recognized in the venoms of a few cobras. Further investigations should be directed toward strategies to improve the neutralization of short-neurotoxins, in line with the envisioned production of an effective pan-regional elapid antivenom.
BIOLOGICAL SIGNIFICANCE: Laticauda colubrina (yellow-lipped sea krait) is a widely distributed, semi-aquatic venomous snake species. The venom proteome at the level of protein family is unsophisticated and consistent with its restricted prey selection. Nonetheless, the subproteomic findings revealed geographical variability of the venom for this widely distributed species. In contrast to two previous reports, the results for the Balinese L. colubrina venom showed that LNTX Neurotoxin a and Neurotoxin b were co-existent while the PLA2 lethal subtype (PLA-II) was undetected by means of LCMS/MS and by in vivo assay. This is an observable trait of L. colubrina considered divergent from specimens previously studied for the Philippines and the Solomon Islands. The stark geographical variation might be reflective of trophic adaptation following evolutionary arms race between the snake and the prey (eels) in different localities. The preferred trait would likely propagate and remain significant within the geographical population, since the strong behaviour of site fidelity in the species would have minimized gene flow between distant populations. Meanwhile, the in vivo neutralization study verified that the efficacy of the heterologous Sea Snake Antivenom (Australian product) is attributable to the cross-neutralization of SNTX and LNTX, two principal lethal toxins that made up the bulk of L. colubrina venom proteins. The findings also implied that L. colubrina, though could be evolutionarily more related to the terrestrial elapids, has evolved a much streamlined, neurotoxin- and PLA2-predominated venom arsenal, with major antigenicity shared among the true sea snakes and the Australo-Papuan elapids. The findings enrich our current understanding of the complexity of L. colubrina venom and the neutralizing spectrum of antivenom against the principal toxins from this unique elapid lineage.