Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.See all posts »
Naturally Occurring Toxins: An Introduction
This is the fifteenth post based upon educational sessions and syllabus material presented at the Wilderness Medical Society Annual Meeting & 25th Anniversary held in Snowmass, Colorado from July 25 to 30, 2008. It includes information from a lecture entitled “Beautiful But Deadly: Naturally Occurring Toxins,” delivered by Edward J. (“Mel”) Otten, MD, FACMT, FAWM, who is Professor Of Emergency Medicine and Pediatrics, as well as Director of the Division of Toxicology in the medical center at the University of Cincinnati. Mel is also a past President of the Wilderness Medical Society.
Toxinology is a branch of toxicology that involves the study of naturally occurring toxins, including those found in microorganisms, plants and animals. These natural toxins are among the most complicated and lethal in existence. Many have been studied for years, but have yet to be thoroughly described. For instance, certain snake venoms may contain fifty or more toxic substances, each of which has a different mechanism of toxicity. Therefore, cumulatively, the clinical outcome of envenomation is frequently difficult to predict or treat.
The best classification of natural toxins involves dividing the groups of toxin-containing organisms into poisonous and venomous.
° Poisonous organisms are those that are assimilated into the host either by ingestion or through the skin. Included are bacteria, fungi, plants, and some animals.
° Venomous organisms are those that have evolved specific toxin delivery systems, which usually include a venom gland and a sting, fang, spine or pore for transporting venom to the host. Venomous animals are found in every class of animals and are distributed throughout the earth's ecosystems. The first venomous member of the class Aves (birds) - the genus Pitohui, from New Guinea - was described in 1992.
As a general rule, venom delivery from the oral pole is designed for food gathering (offensive) and venom delivery from the anal pole is designed for protection (defense). For example, spiders have large fangs and use them for hunting, while bees have modified ovipositors used in defense of the hive. A spider bite is usually painless and neurotoxic, while a single bee sting is quite painful but relatively nontoxic.
The hundreds of microorganisms that cause toxicity in animals and humans in food and water can be divided for simplicity into organisms that form toxins that are pre-formed in food and ingested, and those that produce toxins that cause toxicity upon ingestion.
For example, botulinum toxin, which is produced by the Clostridium botulinum bacteria in improperly preserved foods, is ingested and can cause paralysis. Vibrio bacteria, the agent that causes cholera, may be ingested via food. It then replicates within humans and forms a toxin that produces diarrhea, vomiting, and fever.
There are hundreds of marine toxins that may accidentally be ingested when eating shellfish, seaweed, pufferfish, or other seafood. Four of the more interesting marine toxins that cause poisoning after the ingestion of fish are ciguatera poisoning, scombroid, tetrodotoxin, and “red tide.”
Ciguatera fish poisoning is caused by at least five toxins produced by the dinoflagellate Gambierdiscus toxicus (and others) and is concentrated up the food chain into the larger predators such as barracuda, grouper and snapper. The symptoms are protean and usually include sweating, headache, and a rather unique symptom of hot and cold sensation reversal.
Scombroid fish poisoning is caused when histidine-producing bacteria multiply on and within (typically) dark-fleshed fish such as tuna, mackerel and dolphin (mahimahi) that are not frozen (or otherwise properly preserved) in a timely fashion after being caught. The histidine is then metabolized to histamine and there occurs a severe allergic type reaction.
Tetrodotoxin is a toxin ingested via fish that causes neuromuscular paralysis. More than 100 species of fish, including pufferfish (from which are prepared the Japanese delicacy known as “fugu”), and other animals such as newts, salamanders, frogs, shellfish, and the blue ringed (or spotted) octopus, produce tetrodotoxin.
Shellfish, including crabs, clams snails, oysters, scallops and mussels, may contain a substance known as saxitoxin that is produced by the microcellular organisms that cause red (or other colored) tides. As a general rule, after the ingestion of microorganism-generated toxins by humans, clinical symptoms are usually present within 24 hours and the treatment is usually supportive care. It must be remembered that other toxins not naturally produced may be ingested that cause similar symptoms. For example, heavy metals or organophosphate intoxication, or monosodium glutamate (“Chinese Restaurant syndrome”) ingestion, may resemble the syndromes described above.
To be continued…
photo of scombroid poisoning courtesy of Dermatology Online Journal
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