Brown Snake Envenomation

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Background

The brown snake, found in Australia, belongs to the family of Elapidae and contains the following species:

Envenomation by P textilis, P nuchalis, P guttata, and P affinis has been documented, but little information is available about the toxic effects of the other species.

All of these snakes occur mainly in inland floodplains with deeply fissured soils. The snakes are active during cooler parts of the day, such as early morning and late afternoon. They exist in 5 different colors, have a highly flexible head, and can squeeze into narrow places. They feed on small animals but also can grip large prey. They may bite humans above the knee by raising their head from the ground and assuming an "S" shape when striking. Unless provoked, they are thought to be reluctant to attack humans.

Most of the literature describing the brown snake consists of case studies of people accidentally bitten and their clinical course. They have less effective dentition than other elapids and may leave little evidence of a puncture wound; however, their venom is readily diffusible and can rapidly enter the circulation.

These snakes are among the most venomous in the world. The common brown snake produces the second most toxic venom known and is the most common cause of snakebite death in Australia. Common to these species' venom are neurotoxins and hemotoxins.

Pathophysiology

Brown snake envenomations are characterized by disseminated intravascular coagulation (DIC) like hemorrhage and cardiovascular depression. Other, less common, manifestations are conduction defects, thrombocytopenia, renal failure, intracranial hematomas, and paralysis.

The venom-induced consumptive coagulopathy (VICC) is characterized by defibrination, often accompanied by platelet counts within the reference range. The venom has the ability to convert prothrombin to thrombin and to significantly deplete factors V, VII, protein C, and plasminogen within 2 hours of the snakebite.[1] Complete VICC (defined as international normalized ratio >3) occurs in 80% of the victims, while partial VICC occurs in 20% of the victims.[2]

Cardiovascular depression may be caused by intravascular coagulation, or the venom may contain a primary myocardial depressant. The potent neurotoxins cause neurological symptoms soon after envenomation. One example is texilotoxin, a multimumeric polypeptide from the common brown snake. These neurotoxins can cause respiratory paralysis by blocking nicotinic acetylcholine receptors at the postsynaptic motor endplate and/or affect neurotransmitter release at presynaptic motor nerve endings. Convulsions may occur. Little or no myotoxicity is present.

Epidemiology

Frequency

International

Pseudonaja species live mainly in Australia. About 3000 bites occur per year in Australia from all species of snakes, 500 of which require antivenin. The dugite brown snake may be found in the southwestern corner of Australia, in Western Australia and along the South Australian border. The speckled brown snake can be found from central Queensland to the eastern areas of the Northern Territory. Ingram's snake may be found around Barkly Tableland of the Northern Territory, and the ringed snake may be found in the arid regions of all the mainland states. The western snake may be found throughout Australia and the common brown snake in Queensland, New South Wales, and from Victoria to the southeast of South Australia.

Snakebites tend to occur more often in the warmer months reflecting increased snake activity as well as increased human outdoor activity. The predominance of the bites occur in the lower limb.

Mortality/Morbidity

Of all the cases of snakebites in Australia, only 2-3 fatalities occur per year. As many as 60% of fatalities from snake envenomations may be attributed to the brown snake. Early deaths (within hours) are thought to result from the venom's cardiotoxic effect as well as anaphylaxis to the venom. Delayed deaths appear to result from secondary complications, such as intracranial hemorrhage, from the venom's hemotoxins.

Sex

Males are bitten more frequently than females, presumably because of the greater popularity among males of owning and handling snakes as well as greater risk of occupational and recreational exposure.

Age

Young children tend to become critically ill sooner than adults because of their smaller body weight and tendency to receive multiple bites.

History

The bites of Pseudonaja frequently occur on the extremities, mostly on the fingers and feet, because collectors handle them or people accidentally step on them. Unfortunately, unless the patient gives a history of being bitten by a snake, local clues to the evidence of a bite may be subtle or absent because brown snake bites cause little or no local swelling or pain. After giving a history of being bitten by a brown-colored snake, the patient may complain of neurological symptoms within an hour; the symptomatology within a few hours may manifest with a coagulopathy and signs of diaphragmatic paralysis and cardiovascular compromise. The following symptoms may be present:

Physical

Laboratory Studies

Imaging Studies

Other Tests

Prehospital Care

The goals of prehospital treatment include implementing basic and advanced life support algorithms and ensuring an adequate airway. Consider immobilization of the cervical spine if trauma to the cervical spine is suspected.

Emergency Department Care

Administer antivenin therapy as soon as possible if any signs of systemic involvement are present because the antivenin may reverse coagulopathy. Skin testing before administration of antivenin is not recommended because it delays treatment of this very toxic venom. Furthermore, larger initial doses should be considered if severe envenomation from multiple bites is evident. The dose of antivenom for children should not be reduced since the amount of venom injected by the snake is independent of the victim's size. The improvement of fibrinogen levels, coagulation parameters, and the patient's condition function as surrogate indicators of venom neutralization. A recent study suggests that 5 ampules will adequately treat two thirds of the patients with severe envenomation, but 10 ampules will adequately treat 89% of these patients.[5]

Before the antivenin is given, premedicate the patient with an antihistamine, and continue the antihistamine for 5 days to prevent anaphylaxis.

Administer corticosteroids if any history of previous serum sickness or allergic reaction to the antivenin is present or for administration of large doses of antivenin.

Pregnancy is not a contraindication to giving antivenin.

Edrophonium, neostigmine, and atropine may be given to temporarily reverse respiratory weakness until antivenin is obtained, but it should not delay necessary intubation.

In the treatment of venom-induced consumptive coagulopathy, administration of FFP and/or cryoprecipitate is controversial; it has been associated with faster resolution of coagulopathy but no change in outcomes.[6]

The most common reasons for antivenom administration were coagulopathy, neurotoxicity, myotoxicity, and nonspecific systemic effects.[7]

Hypersensitivity reaction to antivenom occurred in 25% cases, with nearly half the hypersensitivity cases considered to be anaphylaxis to the antivenom.[7]

Swab the bite for analysis with a CSL Venom Detection Kit, if available.

Consultations

Medication Summary

The antidote for systemic envenomations by the brown snake is the equine-derived antivenin. In a study of 35 patients with severe brown snake envenomation, two thirds of the cases were neutralized with 5 ampules and 89% were neutralized with 10 ampules.[5] As with all equine-derived antivenins, anaphylaxis should be anticipated and treated if any allergic reactions occur. Pretreatment with antihistamines and corticosteroids should be included.

Hypotension should be treated with isotonic crystalloid infusions and vasopressors if blood pressure is refractory to fluids alone.

Tetanus toxoid should be given when indicated.

Cholinesterase inhibitors, such as edrophonium and neostigmine, may be given to palliate the neurological sequelae of the venom but should not replace definitive airway control.

Antivenin

Clinical Context:  According to the Antivenin Index, the monovalent form is not carried in the US but may be found in Australia (Commonwealth Serum Laboratories, Melbourne, Australia). The polyvalent antivenin may be obtained at the Bronx Zoo, but a local zoo may be contacted.

Skin testing before antivenin administration is not recommended because it may sensitize the individual to future antivenin use and will delay the administration of the antivenin. Antihistamines and subcutaneous epinephrine should be administered (if no contraindications are present) before giving the antivenin.

1 U neutralizes 0.01 mg venom in vitro.

Class Summary

Gives passive immunity to the venom and should be administered immediately if any signs of systemic toxicity are present.

Diphenhydramine (Benadryl)

Clinical Context:  For symptomatic relief of symptoms caused by release of histamine in allergic reactions.

Cimetidine (Tagamet)

Clinical Context:  H2 antagonist that, when combined with an H1 type, may be useful in treating itching and flushing in anaphylaxis, pruritus, urticaria, and contact dermatitis that do not respond to H1 antagonists alone. Use this medication in addition to H1 antihistamines.

Chlorpheniramine (Chlor-Trimeton)

Clinical Context:  Competes with histamine or H1-receptor sites on effector cells in blood vessels and respiratory tract.

Class Summary

H1 and H2 blockers should be given to prevent immune mediated responses and may be continued for an additional 5 days or for as long as symptoms persist.

Methylprednisolone (Solu-Medrol)

Clinical Context:  Decreases inflammation by suppressing the migration of polymorphonuclear leukocytes and reversing increased capillary permeability.

Prednisone (Deltasone, Orasone, Sterapred)

Clinical Context:  Used for the treatment of a variety of diseases including serum sickness in the outpatient setting. Prednisone is inactive and must be metabolized to the active metabolite prednisolone. The conversion may be impaired in patients with liver disease.

Class Summary

Should be employed when evidence of an allergy-mediated event is present. However, onset of action is approximately 4-6 h and has limited benefit in the initial acute treatment of the rapidly deteriorating anaphylactic patient. Nonetheless, corticosteroids may benefit patients with persistent bronchospasm or hypotension.

Epinephrine (Adrenalin, EpiPen)

Clinical Context:  DOC for treating anaphylactoid reactions. The alpha-agonist effects of epinephrine increase peripheral vascular resistance and reverse peripheral vasodilatation, vascular permeability, and systemic hypotension. Conversely, the beta-agonist effects produce bronchodilatation, positive inotropic and chronotropic cardiac activity, and result in an increased production of intracellular cAMP.

Albuterol (Ventolin, Proventil)

Clinical Context:  Beta-agonist useful in the treatment of bronchospasm that is refractory to epinephrine. Relaxes bronchial smooth muscle by action on beta 2-receptors and has little effect on cardiac muscle contractility

Theophylline (Aminophylline, Theo-Dur, Slo-bid)

Clinical Context:  Potentiates exogenous catecholamines. Stimulates endogenous catecholamine release and diaphragmatic muscular relaxation, which in turn stimulates bronchodilation.

For bronchodilation, near toxic (>20 mg/dL) levels are usually required.

Ipratropium (Atrovent)

Clinical Context:  Chemically related to atropine. Has antisecretory properties and, when applied locally, inhibits secretions from serous and seromucous glands lining the nasal mucosa.

Class Summary

These agents have combined alpha- and beta-adrenergic agonist action and are the agents of first choice in the treatment of anaphylaxis.

An additional option in the management of persistent bronchospasm may be anticholinergic agents. These agents block the action of acetylcholine at parasympathetic sites in bronchial smooth muscle.

Edrophonium (Enlon, Reversol, Tensilon)

Clinical Context:  Short active cholinesterase inhibitor that inhibits the destruction of acetylcholine by acetylcholinesterase and may palliate weakness. Facilitates transmission of impulses across myoneural junction and results in increased cholinergic responses (eg, miosis, increased tonus of intestinal and skeletal muscles, bronchial and ureteral constriction, bradycardia, and increased salivary and sweat gland secretions).

Usually administered IV, but, if this is not possible, IM/SC route may be used.

Neostigmine (Prostigmin)

Clinical Context:  Longer acting cholinesterase inhibitor that can be used when edrophonium is ineffective. Inhibits destruction of acetylcholine by acetylcholinesterase, which facilitates transmission of impulses across myoneural junction.

Class Summary

May be useful in reversing neurological complications of the venom; however, they should not be a substitute for airway management.

Tetanus immune globulin (TIG)

Clinical Context:  Used for passive immunization of any person with a wound that might be contaminated with tetanus spores.

Class Summary

Consists of administration of immunoglobulin pooled from serum of immunized subjects.

Further Inpatient Care

Further Outpatient Care

Transfer

Deterrence/Prevention

Complications

Prognosis

Author

David Cheng, MD, Associate Professor of Emergency Medicine, Education Director, Associate Emergency Medicine Residency Director, Case Medical Center

Disclosure: Nothing to disclose.

Specialty Editors

Daniel J Dire, MD, FACEP, FAAP, FAAEM, Clinical Professor, Department of Emergency Medicine, University of Texas Medical School at Houston; Clinical Professor, Department of Pediatrics, University of Texas Health Sciences Center San Antonio

Disclosure: Nothing to disclose.

John T VanDeVoort, PharmD, Regional Director of Pharmacy, Sacred Heart and St Joseph's Hospitals

Disclosure: Nothing to disclose.

David Eitel, MD, MBA, Associate Professor, Department of Emergency Medicine, York Hospital; Physician Advisor for Case Management, Wellspan Health System, York

Disclosure: Nothing to disclose.

John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center

Disclosure: Nothing to disclose.

Chief Editor

Joe Alcock, MD, MS, Associate Professor, Department of Emergency Medicine, University of New Mexico Health Sciences Center; Chief, Emergency Medicine Service, New Mexico Veterans Affairs Health Care System

Disclosure: Nothing to disclose.

Additional Contributors

The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous author, Shaun J Chun, MD, to the development and writing of this article.

References

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Pseudonaja guttata (speckled brown snake).

Pseudonaja textilis (eastern brown snake).

Pseudonaja nuchalis (western brown snake).

Pseudonaja modesta (ringed brown snake).

Pseudonaja guttata (speckled brown snake).

Pseudonaja textilis (eastern brown snake).

Pseudonaja modesta (ringed brown snake).

Pseudonaja nuchalis (western brown snake).