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marked in a rat succumbing 34 h postinjection.
11
Thymus hemorrhage and involution
were also observed (Sakai et al., 1990). Within 1 h of i.m. injection of
R. t. tigrinus
venom into rats, fibrinogen was undetectable, PT was prolonged, and fibrin degra-
dation products (FDP) increased (Sakai and Hatsuse, 1995). DIC, hemoglobinuria,
anemia, and thrombocytopenia also developed. The authors suggested that fibrin
thrombus formation accounted for most of the hemostatic abnormalities. Necropsy
detected local and pulmonary hemorrhage/edema and renal tubule necrosis (Sakai
and Hatsuse, 1995). Many of these pathophysiological changes have occurred in
humans envenomated by these species.
4.3.2.5 Conclusion and Assessment of
R. subminiatus
and
R. tigrinus
Both
R. subminiatus
and
R. tigrinus
have inflicted well-documented, carefully reported
life-threatening, and/or fatal bites. Almost all of these have occurred as a consequence
of handling captive specimens. Confusion of these snakes with harmless natricids,
such as some species of
Amphiesma
, has resulted in recurrent concerns (most often
unfounded) regarding the possible accidental presence of either species in the retail pet
trade. Although the posterior maxillary teeth do not show the same extent of adaptation
as in the medically important Dispholidini, the potent venom and potentially fatal con-
sequences of bites inflicted by these species emphasize their medical importance.
Assessment of
R. subminiatus
and
R. tigrinus
based on available evidence:
Hazard Level 1
(see
Table 4.3
).
4.3.3 Comparison of Major Features of Hazard Level 1 Colubrids
(Figure 4.3) (
Dispholidus typus
,
Thelotornis capensis
,
Thelotornis kirtlandii
,
Rhabdophis tigrinus
, and
Rhabdophis
subminiatus
)
l
Serous Duvernoy's glands associated with markedly enlarged noncanaliculated posterior
maxillary teeth. Although these are grooved in
D. typus
(deep grooves that extend over
approximately 50-65% of the tooth surface) and
Thelotornis
spp. (deep grooves that tra-
verse almost the entire tooth surface),
R. tigrinus
and
R. subminiatus
have ungrooved teeth.
Figure 4.3
compares head and dentition profiles of
D. typus
,
T. kirtlandii
, and
R. tigrinus
.
l
All produce potent procoagulant toxins that activate prothrombin, and Factor X, but some
pharmacological studies suggest variability of these activities among different popula-
tions and/or individual snakes. The role of these toxins in the natural history of these taxa
remains unclear and/or unverified.
l
Clinical manifestations of envenoming by any of these snakes results in consumptive coag-
ulopathy, DIC, bleeding, anemia, thrombocytopenia, and other serious hemostatic distur-
bances. Severe cases may result in AKI (see Section 4.6) and death.
l
There are well-documented fatalities from envenomations by
D. typus
,
T. capensis
,
T. kirtlan-
dii
, and
R. tigrinus
, but to date there are no documented fatalities from
R. subminiatus
bites.
11
It is possible that due to some of the delayed effects (e.g., progressive renal tubular necrosis, possible
microthrombi deposition in the splanchnic vasculature, and other evolving pathophysiology) the experi-
mental lethal potencies of these species have been underestimated due to approximations from murine
lethal potency studies conducted with 24-h observation limits.
