Pathophysiology

The toxins responsible for the signs and symptoms of marine food-borne illnesses are primarily produced in microorganisms such as dinoflagellates, diatoms, and marine bacteria and are bioaccumulated by shellfish or fish, which are then ingested by humans and result in toxicity. Most of these toxins modulate neuronal and muscle sodium channels. Scombroid is not caused by a preformed toxin but rather by breakdown of histidine into histamine in inadequately stored dark-meat fish. Table 142.1 lists the common marine food-borne poisonings, causative toxins, and typical sources of such poisonings.⁸

Presenting Signs and Symptoms

Table 142.1 lists the typical onset and common symptoms associated with marine food-borne poisonings. Typically, a history of seafood ingestion can be obtained. In most cases the symptoms are manifested within minutes to hours and include a mixture of gastroenteritis (nausea, vomiting, and diarrhea) and often dramatic neurologic findings.

Differential Diagnosis and Medical Decision Making

The differential diagnosis for marine food-borne poisoning includes disease processes that cause acute neurologic symptoms with or without gastrointestinal symptoms. Botulism, myasthenia gravis, poliomyelitis, and tick paralysis should be considered. In cases in which the neurologic symptoms are not as obvious, the more common bacterial causes of food-borne poisoning would also need to be considered. The diagnosis of marine food-borne poisoning must be made on a clinical basis because testing for the specific toxins is not readily available.

Treatment

Treatment of marine food-borne poisoning is entirely supportive (see Table 142.1). Attention should be paid to fluid resuscitation and control of nausea and vomiting with antiemetics (ondansetron, 4 to 8 mg intravenously as needed). Although scombroid can be treated with antihistamine therapy, no antidotes are available for any other seafood toxin–mediated poisonings.

Pathophysiology

Envenomation can occur from both marine invertebrates and vertebrates. Members of the Cnidaria phylum, which includes the box jellyfish, true jellyfish, Portuguese man-o-war, and sea anemone, have nematocysts with hollow venomous barbs that deliver venom hypodermically. Stingrays have a serrated spine connected to a venom gland located on the tail that can be impaled into unsuspecting victims, whereas the Scorpaenidae family of fish (stonefish, lionfish, scorpion fish) have venomous spines on their fins (Fig. 142.1). Table 142.2 lists the most medically important offending marine organisms and their toxicity.^5,9-15

Fig. 142.1 Lionfish—a member of the Scorpaenidae family of fish.

Presenting Signs and Symptoms

The signs and symptoms of marine envenomation depend on the offending organism. Local pain and irritation are the most common symptoms, especially when nematocysts and spines are involved (Fig. 142.2). However, certain marine organisms can cause severe systemic symptoms and even death. The Australian box jellyfish (Chironex fleckeri) can cause sudden cardiopulmonary collapse.⁵ The Irukandji jellyfish (Carukia barnesi) can cause Irukandji syndrome, a condition characterized by severe whole-body pain and spasms, tachycardia, and severe hypertension, and it has caused deaths.¹² The blue-ringed octopus has tetrodotoxin in its venom, which can cause paralysis and respiratory failure.¹³ The cone snail’s venom is a complex mixture of peptides that can lead to rapid paralysis and death.¹⁴ Stonefish envenomation can result in cardiovascular instability and death, although severe local effects are more common.¹⁰ Sea snake venom has both a neurotoxic component, which leads to ascending paralysis, and a myotoxic component, which causes muscle breakdown.¹⁵ Table 142.2 summarizes the signs and symptoms of the more significant marine envenomations.

Fig. 142.2 Skin lesions after envenomation by jellyfish species.

Differential Diagnosis and Medical Decision Making

Frequently, the identity of the offending marine organism will not be known. The geographic location can be a useful predictor, and physicians should be aware of the venomous marine organisms in their local area. It can be helpful to look for physical clues, such as retained jellyfish tentacles and puncture marks. The presence of severe local pain often indicates a Cnidaria or fish envenomation, whereas significant neurologic symptoms, such as weakness, should raise suspicion for cone snail or other neurotoxic organisms.

Treatment

Treatment of marine envenomation begins with addressing the patient’s airway, breathing, and circulation status. Typically, good supportive care and pain control are all that is needed. Hot water immersion is recommended to control the pain caused by Cnidaria, Scorpaenidae fish, and stingray envenomation and is efficacious because of the heat-labile properties of the neurotoxic component of the venom responsible for the pain. This is typically achieved by immersing the affected body part in water heated to approximately 42° C to 45° C for 20 minutes.^16,17 Acetic acid may have a role in inactivating the nematocysts of the box jellyfish and Irukandji jellyfish but should not be used on other types of jellyfish because it may worsen these envenomations.¹⁸ Recently, topical lidocaine was shown to help in alleviating the pain and inactivating nematocysts from several different species of Cnidaria, including the Portuguese man-o-war.¹⁹ Antivenom therapy is available to treat poisoning by the Australian box jellyfish, the stonefish, and the sea snake.²⁰ Evaluation for a retained foreign body should also be considered, especially with stingray and sea urchin envenomation^21,22 (Fig. 142.3). Table 142.2 summarizes the recommended treatments.

Fig. 142.3 Retained stingray barb (arrow) in the foot.

Pathophysiology

Traumatic marine injuries are most often caused by the simple action of scraping against the rock-hard and sometimes razor-sharp exoskeletons of sponges, corals, and other sessile marine organisms. Bites from sharks and fish cause trauma directly related to the size of the animal, force of the bite, and cutting nature of the teeth. The severity of direct injuries from stingray barbs depends on the location where the victim was impaled.

Differential Diagnosis and Medical Decision Making

The offending organisms may or may not be known to the victim, and concomitant envenomation should be considered. Radiographic evaluation may be needed. The most important medical decision to be made is whether the injury is severe enough to warrant specialist care by a trauma, vascular, or orthopedic surgeon.

Treatment

After initially addressing the airway, breathing, and circulation, direct wound care is usually sufficient to treat most traumatic marine injuries. Control of bleeding and wound irrigation are important. Because infections can complicate these injuries, prophylactic antibiotics should be considered.²³ Injuries to tendons, ligaments, and other vital structures should be evaluated and addressed.

Follow-Up, Next Steps in Care, and Patient Education

All the marine food-borne illnesses are self-limited, although amnestic shellfish poisoning has been linked to long-term neurologic sequelae.²⁴ Patients with suspected tetrodotoxin poisoning should be admitted to the hospital for observation. Most other patients who are asymptomatic after treatment can be discharged. Those with ongoing or severe symptoms should be admitted. The local public health department should be informed of suspected cases of marine food-borne poisoning.

The vast majority of marine envenomations will be self-limited and resolve with simple supportive care. Infection from sea urchin spines, fish spines, and stingray barbs is well documented, and prophylactic treatment with antibiotics effective against pathogens such as Vibrio species should be considered.^21,22,25 Patients with persistent or severe pain may need to be admitted, as will any patient with envenomation by a potentially neurotoxic organism.

Serious injuries may need treatment by a trauma or orthopedic surgeon, either on an emergency basis or as an outpatient. Otherwise, good wound care measures should be explained to the patient and return precautions focusing on signs and symptoms of infection stressed.