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Early symptoms of systemic envenomation include goose bumps, sweating, tingling around the mouth and tongue, twitching (initially facial and intercostal), salivation, watery eyes, elevated heart rate and elevated blood pressure. As systemic envenomation progresses symptoms include nausea, vomiting, shortness of breath (caused by airway obstruction), agitation, confusion, writhing, grimacing, muscle spasms, pulmonary oedema (of neurogenic or hypertensive origin), metabolic acidosis and extreme hypertension. The final stages of severe envenomation include dilation of the pupils (often fixed), uncontrolled generalised muscle twitching, unconsciousness, elevated intracranial pressure and death. When death occurs it is generally as a result of progressive hypotension or possibly elevated intracranial pressure consequent on cerebral oedema.
The onset of severe envenomation can be rapid. In one prospective study, the median time to onset of envenomation was 28 minutes, with only two cases having onset after 2 hours (both had pressure immobilisation bandages applied). Death may occur within a period ranging from 15 minutes (this occurred when a small child was bitten) to three days.