Biology Reference
In-Depth Information
persistent vestibular symptoms could be related to an exacerbation from a provoking
head movement.
Although toxic insult may produce such responses, these would most frequently
be immediate or would occur shortly after exposure (e.g., tetrodotoxin ingestion,
Ahasan et al., 2004; injection of castor bean extract (
Ricinus communis
), Coopman
et al., 2009). Dizziness occasionally associated with bites inflicted by viperids and
elapids occurs within minutes or hours after the envenoming and is probably due to
hypovolemia, pain, and autonomic responses (Warrell, 2004; White and Dart, 2008;
www.toxinology.com
)
. Also, while several snake venom toxins have been character-
ized that produce vestibular disturbances in mice (“gyroxin” or “gyrotoxin”), to date
all of these have been either identified in or isolated from crotaline viperid venoms
[e.g., tiger rattlesnake,
Crotalus tigris
(Minton and Weinstein, 1984; Weinstein and
Smith, 1990), tropical rattlesnake,
C. durissus terrificus
(Alexander et al., 1988),
bushmaster,
Lachesis muta
(da Silva et al., 1989; Magalhaes et al., 1993),
B. asper
(terciopelo, barba amarilla, or cuatro narices; Perez et al., 2008),
B. jararacussu
(jararacuçu; Perez et al., 2007) and others; see
Plates 2.2, 4.73, 4.74A and B, and
4.86
]. Further, these toxins produce distinctive axial gyrations in mice injected
with lethal doses of venom or isolated toxin. Interestingly, gyroxin from
C. d.
terrificus
venom (and others) has been characterized as a thrombin-like enzyme with
fibrinogenase and fibrinase activities (Maruñak et al., 2004). It may appear tempting
to some to speculate that some of the fibrinogenases/proteases characterized from
P. olfersii
Duvernoy's secretion might be similar to gyroxins. However, there have
been no reports of such signs in experimental animals injected with any
Philodryas
spp. Duvernoy's secretion, and there are no reports of thrombin-like activity in
Duvernoy's secretion of any
Philodryas
spp. studied to date (see Section 4.2).
Management of either PVN or BPPV may include antihistamines, such as mecli-
zine or promethazine, and glucocorticoids. Although considered controversial, glu-
cocorticoids (e.g., 100 mg/day for 3 days followed by a 20 mg/day taper) have been
reported to decrease the duration of the episodes associated with vestibular neu-
ronitis and Ménière's syndrome (Cope and Bova, 2008; Fauci et al., 2009; McPhee
and Papadakis, 2009). BBPPV often responds to Epley, Semont, or Brandt-Daroff
maneuvers. Although evidence-based studies are limited, some data suggest that
canalith repositioning maneuvers have greater therapeutic efficacy than medica-
tions (Clinch et al., 2010). Most presentations of either PVN or BPPV resolve in 1-3
weeks (Fauci et al., 2009; Kerber, 2009; Lee et al., 2009; McPhee and Papadakis,
2009). The response to some of these treatments, and the duration of signs/symp-
toms, is compatible with the outcome of the reported case.
The delay between the
P. o. latirostris
bite and the development of the present-
ing symptoms (about 6 days) strongly argues against any specific linkage of the bite
and the episodic vertigo. The possibility of sequestered Duvernoy's secretion causing
a delayed clinical effect may be contemplated. However, this is an extremely remote,
unlikely possibility, as the vast majority of
P. olfersii
bites are medically insignificant,
with some significant bites resulting in only mild-to-moderate local effects (
Table 4.1
;
Section 4.2). Isolated reports of abnormal laboratory tests suggestive of systemic symp-
toms (i.e., coagulopathy; Orduna et al., 1994) require further documentation, as there
