Is the patient envenomed?
Is it likely that poisoning caused by a poisonous animal is present?
Patient history: consumption of a meal containing potentially poisonous animal foodstuffs in the last few hours? (see Biomedical database entries)
Gastrointestinal symptoms: nausea, vomiting, diarrhoea, abdominal pain within hours after such a meal
Systemic signs and symptoms consistent with poisoning caused by a poisonous animal.
The following forms of poisoning due to poisonous animals are described:
- Ciguatera, scombroid and tetrodotoxin poisoning and the 4 different forms of shellfish poisoning,
- paralytic shellfish poisoning = PSP,
- neurotoxic shellfish poisoning = NSP,
- the central nervous form of shellfish poisoning (amnesic shellfish poisoning) = ASP,
- the gastrointestinal form of shellfish poisoning (diarrhoetic shellfish poisoning) = DSP;
- allergic reactions to fish, shellfish and crabs.
All other forms of poisoning due to poisonous animals are dealt with in the relevant Biomedical database entries.
From a differential diagnostic perspective with regard to poisoning due to poisonous animals, only scombroid (histamine) poisoning and ciguatera need to be positively identified. All other forms of poisoning caused by poisonous animals are treated solely symptomatically.
The following complaints, which can also be caused by the consumption of seafood, including those animals that are poisonous, need to be delineated for the purposes of differential diagnosis (Eastaugh and Shepherd 1989, Liston 1990, Noble 1990, Scoging 1991):
1. Infectious gastroenteritis
Norwalk virus (Norovirus): source of infection: shellfish, incubation period 24–48 h. Symptoms: nausea, vomiting, cramping abdominal pain, diarrhoea, (headache, myalgia, weakness), duration 1–2 days (Benenson 1990, Morse et al. 1986).
Vibrio sp. (Vibrio cholerae, V. parahaemolyticus among others): source of infection: usually shellfish and crabs, incubation period a few hours–5 days. Signs and symptoms: large loss of plasma isotonic fluid (secretory enteritis) with rapid dehydration, acidosis and circulatory failure, occasionally vomiting, generally no fever (Benenson 1990).
Type E botulism (Clostridium botulinum): source of infection: incorrectly processed fish and fish eggs, incubation period: 12–36 h. Symptoms: nausea and vomiting with neurological symptoms (cerebral nerve deficits, descending paralysis) that occur concurrently or after a delay of some days (Schaffner 1990, Telzak et al. 1990).
Other bacteria: Campylobacter, Salmonella, Shigella, E. coli: in rare cases carried by seafood.
Hepatitis A, helminthiasis: due to the long incubation period alone, these conditions do not represent a differential diagnostic problem with regard to poisoning due to poisonous animals.
Other food allergies need to be distinguished from toxin-induced fish and shellfish poisoning (ciguatera, scombroid poisoning, PSP, NSP etc.) and fish, shellfish and crab allergies (Taylor and Bush 1988). They can either be caused by food that is eaten at the same time as seafood (peanuts, walnuts, eggs etc.) or by additives to seafood or other foods consumed together with seafood (monosodium glutamate, preservatives such as sulfites, food colouring such as tartrazine) (Cochran and Cochran 1984, Settipane 1986, Twarog and Leung 1982, Vitoria et al. 1982). An essential characteristic that distinguishes these food allergies from toxin-induced fish and shellfish poisoning is the fact that the latter nearly always affect several people at the same time, whereas allergies only affect individuals with the relevant predisposition.
3. Other contaminants
Contamination of foodstuffs by organophosphates (insecticides) produces gastrointestinal-neurological symptoms that are similar to those of fish and shellfish poisoning. Moreover, this type of poisoning also occurs in the form of small epidemics.
4. Psychogenic hyperventilation
When coinciding with gastrointestinal symptoms, the acroparaesthesias and perioral paraesthesias caused by this condition can mimic the clinical picture of fish or shellfish toxin-induced poisoning.