Is it an Emergency?

Inquire

• time of the bite,
• local pain,
• nausea, vomiting, abdominal pain,
• paraesthesias of the extremities and around the mouth,
• muscle pain.

Assess

• state of consciousness.

Measure

• blood pressure/pulse,
• respiratory rate,
• oxygen saturation (pulse oximeter),
• 20WBCT (bedside test).

Observe/investigate

• bite marks,
• extent and intensity of local swelling and beyond,
• enlargement and painfulness of regional lymph nodes,
• swelling in the facial region, including the larynx/pharynx (angio-oedema),
• clinical signs of shock,
• bleeding from bite marks and other injuries,
• subcutaneous bleeding in the region of the swelling,
• gingival bleeding,
• blood-stained sputum, vomit ("coffee ground vomitus"), stools (melaena) or urine,
• acute abdomen (intra-abdominal bleeding!),
• focal neurological deficits, meningismus (intracranial bleeding!),
• cranial nerve deficits, such as ptosis, ophthalmoplegia, dysphagia, dysarthria,
• paralysis of the skeletal musculature including the respiratory musculature (→ respiratory failure),
• myalgia with active and passive movement and upon pressure,
• dark-brown/red urine (differential diagnosis haemoglobinuria; rhabdomyolysis!),
• flank pain and renal bed sensitive to percussion.

There is also large overlap of Crotalus sp. and Bothrops sp. between Central America and Mexico and South America.

Consult also

Clinical Mangment: South America

"Bothrops syndrome” 

"The so-called Bothrops group includes the genera Atropoides, Bothrops, Bothriechis, Bothriopsis, Bothrocophias, and Porthidium, although snakes of the Bothrops genus itself are responsible for more bites than are those of the other genera. Although there is little information about snakebites caused by Agkistrodon, Atropoides, Bothriechis, Bothriopsis, Bothrocophias, and Porthidium,the available data indicate that envenomation by species belonging to any of these genera provoke manifestations similar to those observed in individuals with Bothrops envenomation. Therefore, the term “Bothrops syndrome” will be used to refer to such manifestations, collectively" (Malaque and Gutiérrez 2017).

Malaque and Gutiérrez (2017) compare the characteristics of envenoming across the medically most important Bothrops species in South and Central America (B.asper, B.jararaca, B.atrox, B.jararacussu, and B.moojeni.

Crotalus sp.

"The reported consequences of bites from rattlesnakes of the genus Crotalus in South America are mainly neuromuscular blockade and rhabdomyolysis. Which may cause AKI. In contrast, envenoming by Crotalus in Central America is characterized by effects similar to those of Bothrops envenomation" (Malaque and Gutiérrez 2017).

Local

"Bites from Crotalus simus (found in Mexico and Central America) provoke local changes such as swelling and pain. In severe cases, those changes can affect the entire limb. Bruising and blisters can also be observed. Local necrosis is reported in rare cases" (Malaque and Gutiérrez 2017).

In South America, pain, redness, swelling which are less intense than in Bothrops and Lachesis envenoming. Frequently an absence of further local clinical signs (Malaque and Gutiérrez 2017). Local signs indicating that a significant injection of venom has occurred does not apply to bites from Crotalus durissus sspp. in the southern regions of the distribution area of this species. This represent an important exception to the rule that clinically relevant envenoming can be excluded following bites by Viperidae local swelling is absent. Fatal systemic envenoming may occur in the absence of local signs (Cupo et al. 1988, 1990, Warrell 2004, 2023).

Systemic

“In cases of Crotalus envenomation in Central America, bleeding – including epistaxis, gingival bleeding, hematemesis, and hematuria (macroscopic and microscopic) – has been reported. Victims of Crotalus snakebites in Central America can present with nausea and vomiting, although neuroparalytic manifestations are rare. Coagulopathy with fibrinogen consumption are often observed” (Malaque and Gutiérrez 2017).

"Most of the alterations observed in Crotalus envenomation in South America are systemic. Initial symptoms are blurred vision and a “heavy eyelid” feeling., diplopia, mydriasis, anisocoria, mandibular ptosis, weakness, and tremors. Paralysis of the muscles of the soft palate causes dysphagia. In severe cases, patients progress to weakness and prostration, some developing respiratory failure secondary to paralysis of the respiratory muscles. In addition, there can be signs and symptoms of rhabdomyolysis, such as myalgia and dark urine (due to myoglobinuria). Bruising and bleeding (such as gingival bleeding can occurs, resulting from coagulopathy caused by the procoagulant enzymes of the venom, although those effects are less common." (Malaque and Gutiérrez 2017).

Varibility of symptoms and degree of envenoming

The symptoms and degree of envenoming depend not only on the amount of venom injected and numerous other variables, but also on the time that has elapsed since the bite. This variable factor must be taken into account when making the following decisions:

• exclusion of envenoming 
• the time interval between clinical examinations
• emergency care (see below)

Bite marks and dry bites

The fact that a patient has been bitten by a known venomous snake and the presence of bite marks do not automatically allow the conclusion that a clinically relevant injection of venom has taken place. 

Autopharmacological signs & symptoms

Bothrops sp. 
Arterial hypotension and shock may occur within minutes of bites (Warrell 2004, 2009, 2023).

Local signs & symptoms

Bothrops sp.

Pain, redness, swelling, ecchymosis, bleeding, blisters. Necrosis (Malaque and Gutiérrez 2017, Warrell 2004). 

Bothrops asper

Intense pain, rapidly expanding oedema, haemorrhage and sometimes muscle necrosis. Damaged musculature regenerates to some extent. However, in many cases regeneration is deficient due to changes in the microcirculation (Gutierrez 1990, Gutierrez and Lomonte 1989, Malaque and Gutiérrez 2017, Warrell 2004).

Crotalus sp. (including former C. durissus durissus: now C. simus) 

Marked local effects with extensive swelling.

Lachesis sp.

Marked local effects with extensive swelling.

Micrurus sp.

Local swelling either does not develop at all or is insignificant. Often complete lack of any local signs at the bite site despite severe envenoming; e.g. in a Micrurus lemniscatus helleri bite. However, with severe pain and paraesthesia in the bitten limb despite morphine and tranquilizers (Manock et al. 2008).

Compartment syndrome

Even extensive swelling of the extremities is not necessarily an indication of compartment syndrome. The decision to perform a fasciotomy must have a rational basis, see Compartment syndrome.

Non-clottable blood and bleeding

Even coagulation disorders that are severe according to laboratory tests may only be clinically apparent to a slight degree, or not at all. There is a threat of spontaneous haemorrhage with extensive loss of blood or focal bleeding (e.g. intracranial) as long as the haemostatic defect exists (untreated, i.e. without antivenom treatment, days to weeks). 

Bothrops sp.

Severe bleeding has been reported, it is, however, rare; ecchymosis distal from bite site (Cardoso et al. 1993, Oliveira et al. 2019, Malaque and Gutiérrez 2017, Warrell 2004).
Intracranial has been reported by Bentes et al. 2024, Martínez-Villota et al. 2022, Mosquera et al. 2003.
Significant haemorrhages are more likely to occur following Bothrops sp. and Lachesis sp. bites than with Crotalus sp. bites. 

Lachesis sp.

Noticeable bleeding may be absent during the initial phase or the entire course of envenoming, even though defibrin(ogen)ation may be present to such a degree that the blood is completely incoagulable.
Significant haemorrhages are more likely to occur following Bothrops sp. and Lachesis sp. bites than with Crotalus sp. 

Thrombotic micro-angiopathy (TMA)

Described in South America and West Indies (see 'Clinical entries: Bothrops sp.') from envenoming by Bothrops atrox (Duarte et al. 2025, Warrell 2009), Bothrops erythromelas (Mota et al. 2020), Bothrops jararaca (Amaral et al. 1985, Bucaretchi et al. 2019, Malaque et al. 2019), Bothrops lanceolatus (Malbranque et al. 2008).

“TMA include disseminated intravascular coagulation, microangiopathic haemolytic anaemia diagnosed by finding schistocytes in peripheral blood films, thrombocytopenia, and acute kidney injury associated with arteriolar and capillary microthrombi. TMA with acute kidney injury is increasingly recognised in patients envenomed by Russell’s vipers and a variety of other species.” (Warrell and Williams 2023).

See also Noutsos et al. (2020, 2022).

Paraesthesias and muscle fasciculation 

Bothrops sp.

Myokymia

“Myokymia, a slower and more regular form of fine contractions than fasciculations that is distinguishable from fasciculations electrophysiologically, is reversible with intravenous calcium chloride. It occurs in envenoming by the common lancehead pit viper (Bothrops atrox) in Trinidad (Warrell and Willimas 2023; cit Lewis and Gutmann 2004).
See also reports: Bothrops atrox (Ramcharan et al. 2016) and Bothrops asper (Delgado and Del Brutto 2012). 

Autonomous syndrome

Lachesis sp.

“Bushmaster (Lachesis spp) envenoming causes a distinctive autonomic syndrome of sweating, repeated bilious vomiting, severe abdominal colic, profuse diarrhoea, hypotension, sinus bradycardia, and shock that can develop as early as 15 min after the bite.” (Warrell and Williams 2023, cit. Bolaños et al. 1982, Jorge et al. 1997).

“A review of reports of 20 cases of bites in humans reliably attributed to this snake in Costa Rica, French Guiana, Brazil, Colombia and Venezuela confirms a syndrome of nausea, vomiting, abdominal colic, diarrhoea, sweating, hypotension, bradycardia and shock, possibly autopharmacological or autonomic in origin, not seen in victims of other American crotaline snakes” (Jorge et al. 1997).

Descending paralysis / Respiratory failure

Micrurus sp.

Typical neurological effects of envenoming have been observed developing with a lack period of 14 hrs after the bite (Manock et al. 2008). The reported onset of respiratory muscle paralysis ranges from a few hours to 60 hrs (need of oxygen) to 72 hours (need of intubation and mechanical ventilation) with recurring respiratory distress for 38 hrs (Micrurus lemniscatus helleri; Manock et al. 2008).

In 20 clearly identified Micrurus fulvius (described as M. fulvius fulvius) bites in 14 of 15 patients, the average time between the bite and appearance of the first symptoms of envenoming was 140 min (30–780 min). In one case the delay between the bite and the onset of severe envenoming (complete paralysis including respiratory muscles) was delayed for 13 hours after the bite with a, then, precipitous onset (Kitchens and Van Mierop 1987).

Neurological effects include autonomous nervous system activity (profuse sweating, urinary incontinence) (Warrell 2004; Manock et al. 2008).

Muscles pain (active and passive); secondary effects of rhabdomyolysis

Micrurus sp.

In human envenoming muscular effect have been described in bites by Micrurus lemniscatus (modest increase in serum creatine kinase activity, from 256 to 749 U/l) (Manock et al 2008), by Micrurus fulvius (generalised myalgia with evidence of gross rhabdomyolysis with serum creatine kinase levels of up to 18 000 U/l) (Kitchens and Van Mierop, 1987), and, also mild, in a patient bitten by Micrurus laticollaris (CK 1,392 U/l (normal 8–132 U/l); LDH 945 U/l (normal 83–200 U/l)) (Pettigrew & Glass 1985).
Observed very raely in coral snake envenoming.

Acute kidney injury (AKI) and chronic kidney disease

Envenoming by many snake species occasionally results in acute kidney injury. Direct venom nephrotoxicity, renal ischaemia secondary to shock, disseminated intravascular coagulation with thrombotic microangiopathy (TMA), haemoglobinuria, myoglobinuria, and hyperkalaemia contribute to acute tubular necrosis (Malaque and Gutiérrez 2017; Pinho et al. 2008, Sitprija 2006; Warrell 2004, 2023; Warrell and Williams 2023).

The risk of progression from acute kidney injury to chronic kidney disease has been underestimated because of inadequate follow-up. 

Bothrops sp.

Acute renal failure is also a commonly observed complication following Bothrops sp. bites. In most cases acute renal failure occurs as a consequence of acute tubular necrosis. The prognosis is good, as long as there is adequate medical care (dialysis, fluid and electrolyte balance). 

Monitoring for signs and symptoms that would indicate systemic envenoming for at least 24 h.

At least hourly

• state of consciousness,
• ptosis,
• heart rate and rhythm,
• blood pressure,
• respiratory rate,
• bleeding,
• local swelling,
• other newly appearing signs and symptoms.

6-hourly (or more frequently if there is cause for suspicion)

• 20WBCT (bedside test),
• laboratory-based clotting tests (see above),
• urine output.

The absence of signs of envenoming in the first hours after the bite does not exclude the possibility that a relevant injection of venom has taken place. There may be a long delay before systemic signs of envenoming develop. Moreover, the continued absorption of venom from the region around the site of the bite can lead to renewed symptoms of systemic envenoming even after successful administration of antivenom (e.g correction of the haemostatic defect).

Following Micrurus sp. bites the problem of assessing the risk of a clinically relevant envenoming is even greater. Minimal or no local signs of envenoming are the rule, and systemic signs of envenoming only develop after a long delay.