Biology Reference
In-Depth Information
defibrinating activity. Fibrinogen was undetectable within 10 min after i.v. injection of
a gland extract into rats (Kornalik and Taborska, 1978). The afibrinogenemia persisted
for 24 h with restored fibrinogen levels noted after about 72 h.
In vivo
hemolytic activ-
ity was also reported (Kornalik and Taborska, 1978).
Figure 4.1
summarizes the essen-
tial features of human coagulation, and the mechanisms of coagulopathy induced by
toxins currently known from venoms of the dispholidines,
D. typus
,
Thelotornis
spp.,
and the natricids,
R. tigrinus
and
R. subminiatus
(see later).
The action of these procoagulants must be considered in combination with strong pro-
teolytic activities (suggesting the presence of possible rhexic hemorrhagins) detected in
these venoms (Grasset and Schaafsma, 1940; Hiestand and Hiestand, 1979; Kamiguti
et al., 2000; Robertson and Delpierre, 1969; Weinstein and Smith, 1993). Some of
these, such as the metalloproteases that exhibit disintegrin-like domains (likely that
of P-III/P-IV metalloproteases) as noted in the 65-kDa species characterized from
D.
typus
venom by Kamiguti et al. (2000), in combination with the Factor II and X activa-
tors, likely account for most of the life-threatening sequelae from bites of these snakes.
Section 4.6 considers the possibility of direct and indirect intrarenal
7
as well as procoagu-
lant-related prerenal
8
pathology contributing to the concerning nephrotoxicity associated
with envenoming from the medically important Dispholidini and
Rhabdophis
spp.
A recent study of the transcriptomes and Duvernoy's gland and venom gland mor-
phology of representative colubroid genera included
T. jacksoni
(Fry et al., 2008).
This study reported that the transcriptome of
T. jacksoni
contained toxin transcripts
(particularly, P-III-type metalloproteases and a disintegrin-metalloprotease) closely
similar to those of
D. typus
. On this basis, the authors warned of a possible medical
risk from this species (Fry et al., 2008).
4.3.1.3
Dispholidus typus
: A Colubrid Important in Veterinary Medicine
There are very few data regarding the veterinary importance of non-front-fanged
colubroid species.
Boiga irregularis
is known to actively prey on domestic animals
(see Section 4.4.1), but there is little information regarding specific cases of dogs
or cats bitten by this species. However, there are several well-documented cases of
serious
D. typus
envenoming in dogs (Hoole and Goddard, 2007; Leisewitz et al.,
2004; Vaughan and Lobetti, 1995), and a case of persistent bleeding (from the pre-
sumed bite wound) in a dog after it was bitten by a
T. capensis
(Otto and Blaylock,
2003). Dogs with clinically significant
D. typus
envenomation exhibit consumptive
coagulopathy, often with profuse hemorrhage (Hoole and Goddard, 2007; Vaughan
and Lobetti, 1995). Animals seriously envenomated by
D. typus
respond rapidly to
monospecific
D. typus
antivenom. As reported in humans treated with this antivenom
(Section 4.6), dogs treated with monospecific anti-
D. typus
antivenom may develop
early anaphylaxis that is responsive to i.v. cortisone (we recommend epinephrine)
7
This refers to toxin effects within the kidney.
8
Any process or substance that reduces blood flow to the kidney has prerenal effects. This may include
toxins, nonsteroidal anti-inflammatory medications (NSAIDS), loss of blood volume (hypovolemia), and
many others.
