Anthrax Part I: The bacteria and Toxin

The threat of bioterrorism became clear following the 9/11 attacks on the World Trade Center. Fear propagated about envelopes contaminated with the rod-shaped bacteria Bacillus anthracis, more commonly known as anthrax. Named after the Greek word for “coal,” anthrax was known to infect livestock for over 2 000 years, but human exposure was largely accidental. The American military were well aware of the lethality of anthrax, and they developed it as a biological weapon during World War II. Over 80 strains of the bacteria exist; some strains are more lethal than others.
In soil, air, or contaminated envelopes, anthrax survives as a hardy spore. If anthrax enters the body through a skin lesion or ingestion, the infection causes symptoms in the region of infection, whereas inhalation has much more dangerous consequences. After inhalation, the spores are swallowed by immune cells called macrophages. The macrophages deliver the spores to the lymph nodes where the anthrax multiplies and the macrophage explodes. The freed bacteria circulate throughout the body. When in the lymph nodes, the bacteria can cause chest pain and difficulty in breathing. When the bacteria enters the circulation and secretes their toxins, septic shock follows and massive internal hemorrhaging occurs, and the victim bleeds internally externally through the body orifices.
Anthrax produces three toxins: Edema factor, protective antigen, and lethal factor. Edema factor binds to immune cells called neutrophils and prevents the cells from consuming the bacteria. When the factor enters the cell, it can cause a buidup of fluid at the infection site. Protective antigen binds to cells, changes its form, and binds to the lethal factor. This complex is taken into cells and the lethal factor is released. Lethal factor causes an inflammatory response and the extensive bleeding from blood vessels. It also kills immume cells. The toxin suppresses the immune response in lymph nodes to facilitate release of the bacteria into the circulation.

Coming Up On Monday: A Popular Drink May Prevent Anthrax Infection

Killer Seafood Part II: Shellfish Poisons

In the first part of this post I described some toxins from scalefish: Ciguatoxin from tropical fish and tetrodotoxin from puffer fish. On today’s menu is some shellfish.
Oysters, mussels, and clams contain dinoflagellates that produce saxitoxin. These dinoflagellates are the same ones that create the red tides. Saxitoxin causes paralytic shellfish poisoning.
It is a chemical weapon of the United States military. Consumption of the toxin causes paralytic shellfish poisoning, which begins within minutes of consumption and could lead to death. The paralysis results from blockade of sodium channels that prevent electrical conduction in nerves. Shellfish such as mussels and scallops also contain microscopic diatoms called pseudo -nitzschia. These diatoms contaminate the shellfish with a poison called domoic acid. The toxin causes the usual gastrointestinal problems associated with seafood poisoning. However, domoic acid also causes memory loss, which is termed amnesiac shellfish poisoning. This amnesia is short-term but permanent. The acid can also cause other brain damage and sometimes death. Amnesia results from overstimulation of kainite and AMPA receptors and the consequent cell death. A third toxin, called okadaic acid, targets the epithelial layer of the intestines and causes diarrhetic shellfish poisoning. The severe gastrointestinal symptoms cn last for several days but is rarely fatal. Okadaic acid exerts its effects by inhibiting enzymes called phosphatases, which remove phosphate from proteins.
I didn’t mean for these two posts to be alarmist. Most fish are safe, contamination is rare, and proper preparation and storage prevent just about any poisoning. The topic, like many in toxicology, hooked me, and I couldn’t help but bring it to the surface.

Coming Up On Friday: The Coal Bacteria

Killer Seafood Part I: Scalefish

I dislike most seafood; the texture and taste are very unappealling. Tuna and salmon in sandwiches is okay, but the only way for me to eat most fish is to coat them in batter and thick dollops of ketchup. True, fish is good for you, and I do feel a little bit guilty about my largely fishless diet. Perhaps to help assuage my guilt, I have prepared a menu of some seafood toxins that, in some cases, can cause death,.
Today’s special is scalefish. Poisoning by scalefish is called ichthyosarcotoxism. Some tropical scalefish such as the barracuda, parrotfish, or snapper harbor dangerous dinoflagellates that produce a toxin called ciguatoxin. Poisoning results in ciguatera. Unfortunate victims may suffer gastrointestinal effects such as vomiting, cramps, and diarrhea as well as neurological effects such as hallucinations, dizziness and headache. Symptoms can last for weeks or even years. No treatment exists, but partakers of the poison may receive supportive care for some of the symptoms. Ciguatoxin increases the permeability of cell membranes to sodium, causing excessive nerve stimulation.
The second special is a delicacy in many Asian and Malaysian countries. It is called fugu in Japan and puffer fish or blowfish elsewhere. The fish contain bacteria that secrete a toxin called tetrodotoxin. The toxin concentrates in the liver, gonads, and skin. If the fish is prepared properly, enough toxin should remain in the meal to cause a slight tingling of the tongue and mouth. If not prepared properly, the toxin can cause paralysis and other neurological symptoms and even death from respiratory failure. Some victims of poisoning have been successfully treated with neostigmine, which helps support respiration. Tetrodotoxin blocks proteins called sodium channels on cell membranes. This prevents sodium from entering the cell and thereby inhibits conduction of nerve signals.
Come back in two days for the next set of specials.

Coming Up On Wednesday: More Fishy Poisons