Black Mold Toxin Trichothecene So Dangerous, It Is Used For Biological Warfare
ROBERT W. WANNEMACHER, JR., PH.D.*; AND STANLEY L. WIENER, M.D.†
- HISTORY AND MILITARY SIGNIFICANCE Use in Biological Warfare The Yellow Rain Controversy Weaponization
- DESCRIPTION OF THE AGENT
- Occurrence in Nature Chemical and Physical Properties
- TOXICOLOGY AND TOXICOKINETICS Mechanism of Action Metabolism
- CLINICAL DISEASE Acute Effects Chronic Toxicity
- DIAGNOSIS Battlefield Diagnosis Confirmatory Procedures
- MEDICAL MANAGEMENT Individual and Unit Specific or Supportive Therapy Prophylaxis
*Assistant Chief, Toxinology Division, U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, Frederick, Maryland 21702-5011
†Colonel, Medical Corps, U.S. Army Reserve; Professor of Medicine and Chief, Section of General Internal Medicine, Department of Medicine, University of Illinois College of Medicine, 840 Wood Street, Chicago, Illinois 60612
655 Medical Aspects of Chemical and Biological Warfare
Mycotoxins, by-products of fungal metabolism, have been implicated as causative agents of adverse health effects in humans and animals that have consumed fungus-infected agricultural products.1,2 Consequently, fungi that produce mycotoxins, as well as the mycotoxins themselves, are potential problems from both public health and economic perspectives. The fungi are a vast assemblage of living organisms, but mycotoxin production is most commonly associated with the terrestrial filamentous fungi called the molds.3 Various genera of toxigenic fungi are capable of producing such diverse mycotoxins as the aflatoxins, rubratoxins, ochratoxins, fumonisins, and trichothecenes.1,2
The trichothecenes are a very large family of chemically related toxins produced by various species of Fusarium, Myrotecium, Trichoderma, Cephalosporium, Verticimonosporium, and Stachybotrys.4 They are markedly stable under different environ
mental conditions. The distinguishing chemical feature of trichothecenes is the presence of a trichothecene ring, which contains an olefinic bond at C-9, 10; and an epoxide group at C-12, 12.5 All trichothecenes are mycotoxins, but not all mycotoxins are trichothecenes. This family of mycotoxins causes multiorgan effects including emesis and diarrhea, weight loss, nervous disorders, cardiovascular alterations, immunodepression, hemostatic derangements, skin toxicity, decreased reproductive capacity, and bone marrow damage.4,6
In this chapter, we will concentrate on T-2 mycotoxin, a highly toxic trichothecene that, together with some closely related compounds, has been the causative agent of a number of illnesses in humans and domestic animals.1,2,4 During the 1970s and 1980s, the trichothecene mycotoxins gained some notoriety as putative biological warfare agents when they were implicated in “yellow rain” attacks in Southeast Asia.7–11
History And Military Significance
Fungi that produce trichothecenes are plant pathogens and invade various agricultural products and plants. Since Fusarium and other related fungi infect important foodstuff, they have been associated worldwide with intoxication of humans and animals. Thus, these fungi have potential as biological weapons.
Use in Biological Warfare
From 1974 to 1981, toxic agents were used by the Soviet Union and its client states in such Cold War sites as Afghanistan, Laos, and Kampuchea (Cambodia). Aerosol-and-droplet clouds were produced by delivery systems in the Soviet arsenal such as aircraft spray tanks, aircraft-launched rockets, bombs (exploding cylinders), canisters, a Soviet hand-held weapon (DH-10), and booby traps. Aircraft used for delivery included L-19s, AN-2s, T-28s, T-41s, MiG-21s (in Laos) and Soviet MI-24 helicopters (in Afghanistan and Laos).
Attacks in Laos (1975–1981) were directed against Hmong villagers and resistance forces who opposed the Lao People’s Liberation Army and the North Vietnamese. In Kampuchea, North Vietnamese troops used 60-mm mortar shells; 120-mm shells; 107-mm rockets; M-79 grenade launchers containing chemicals; and chemical rockets, bombs, and
sprays delivered by T-28 aircraft (1979–1981) against Khmer Rouge troops. The chemical munitions were supplied by the Soviets and delivered by North Vietnamese or Laotian pilots. In Afghanistan, the chemical weapons were delivered by Soviet or Afghan pilots against Mujahidin guerrillas (1979– 1981). Lethality of the attacks is documented by a minimum of 6,310 deaths in Laos (from 226 attacks); 981 deaths in Kampuchea (from 124 attacks); and 3,042 deaths in Afghanistan (from 47 attacks).7 Trichothecenes appear to have been used in some of these attacks.
The air attacks in Laos have been described as “yellow rain” and consisted of a shower of sticky, yellow liquid that sounded like rain as it fell from the sky. Other accounts described a yellow cloud of dust or powder, a mist, smoke, or insect spray– like material. Liquid agent rapidly dried to a powder. In Laos, 50% to 81%7 of attacks involved material associated with a yellow pigment. Other attacks were associated with red, green, white, or brown smoke or vapor. More than 80%7 of attacks were delivered by air-to-surface rockets; the remainder, from aircraft spray tanks or bombs. Intelligence information and some of the victims’ descriptions of symptoms raised the possibility that chemical warfare agents such as phosgene, sarin, soman, mustards, CS, phosgene oxime, or BZ may also have been used. These agents may have been used in mixtures or alone, and with or without the trichothecenes.
Unconfirmed reports have implicated the use of trichothecenes in the 1964 Egyptian (or Russian) attacks on Yemeni Royalists in Yemen12 and in combination with mustards during chemical warfare attacks in the Iran–Iraq War (1983–1984).13 According to European sources, Soviet–Cuban forces in Cuba are said to have been equipped with mycotoxins, and a Cuban agent is said to have died of a hemorrhagic syndrome induced by a mycotoxin agent.14
The Yellow Rain Controversy
Actual biological warfare use of trichothecenes in Southeast Asia and Afghanistan is strongly supported by the epidemiological and intelligence assessments and trichothecene assays, although reports in the open literature have discounted this contention. An article written by L. R. Ember,15 published in 1984 in Chemical Engineering News, is the most exhaustive and authoritative account of the controversy surrounding the use of trichothecene mycotoxins in Southeast Asia during the 1970s.
The United States government, its allies, and journalists exhaustively studied the possibility that yellow rain attacks had occurred, based on evidence7,14,15 such as the following:
- interviews of Hmong survivors of and eyewitnesses to lethal yellow rain attacks in Laos, who provided consistent descriptions of the episodes;
- interrogations of a defecting Laotian Air Force officer and North Vietnamese ground troops, who corroborated the descriptions of attacks and admitted using the chemicals;
- interrogations of prisoners of war, who admitted being involved in attacks where unconventional weapons were used (ie, in Afghanistan);
- laboratory confirmations of Soviet use of chemical agents, and
- the presence of Soviet-manufactured chemical agents and Soviet technicians in Laos.
The evidence supports the contention that trichothecene mycotoxins were used as biological warfare agents in Southeast Asia and Afghanistan by the former Soviet Union and its surrogates. The Russians have not recently denied such use but have declined to discuss the subject.
In addition to the evidence stated above, elevated levels and naturally rare mixtures of trichothecene toxins were recovered from the surfaces of plants, fragments of plastic, and rocks in areas attacked9,11,15,16; and were detected in the blood of attack survivors and the tissues of a dead casualty.10,15 Control samples that were taken (a) from an environment that had not been attacked, and during another season of the year,15 and (b) from Hmong who had never been exposed to an attack were consistently negative.
The evidence that trichothecenes were used in Southeast Asia has been challenged: questions have been raised about the interview methodology used by U.S. Army physicians and U.S. State Department personnel in Hmong refugee camps in Thailand to obtain descriptions of the attacks. Some inconsistencies of specific individuals’ stories were demonstrated, but the frequency of unreliable information has not been reported and is unlikely to be large enough to discredit all witnesses.15 Symptom descriptions are generally consistent with known trichothecene effects.
The paucity of positive evidence of the presence of trichothecenes (5 positive environmental and 20 positive biomedical samples) has been used to challenge the belief that biological warfare attacks occurred, since only 10% of samples were positive. However, 32% of samples from victims were positive, a value too high for natural causes (eg, food contamination) to be used as an explanation, since 98% of controls in nonattack areas of Thailand were negative.17 The 2% of samples that were positive could represent either a nonspecific result or low-prevalence food contamination. The paucity and type of control samples have also been questioned.
Some experts18–21 have claimed that yellow rain was not a biological warfare attack at all, but that the yellow residue was caused by showers and deposits of bee feces—the result of massive bee swarming and cleansing–defecation flights over some areas of Southeast Asia. The presence of pollen in bee feces and some samples has not only added confusion18 but is also the supporting evidence used by the skeptics. It is important to remember that persons caught in a shower of bee feces do not get sick and die. Although bee flights have occurred before and since 1982, reports of attacks of yellow rain and death in Asia have not.
Then what explains the symptoms consistent with trichothecene effects in the casualties, and the pollen and bee feces in some of the yellow spots on vegetation in the area? Bee feces do not contain trichothecenes, yet pollen and trichothecenes without mold are found together in some samples from attack areas. The most likely explanation is that during biological warfare attacks, dispersed trichothecenes landed in pollen-containing areas.
French scientists have reported the simultaneous synthesis of three trichothecene toxins by Fusarium growing on corn, but actual production of these toxins by Fusarium species in Southeast Asia has not been demonstrated, presumably because of high environmental temperature (ie, toxin production usually increases at low temperatures). Whether or not Fusarium toxin is produced in the high-mountain temperate regions of Laos inhabited by the Hmong remains unanswered. The presence of toxin on leaves without accompanying mold also is unexplained by critics of the trichothecene weapon hypothesis. In vivo studies have demonstrated that F semitectum var semitectum will grow on leaves in Southeast Asia, but have not shown that it will produce toxin in vivo.15
In support of the weapon hypothesis are the positive trichothecene analyses performed by two leading researchers9,10 in the detection of trichothecenes; the Defense Research Establishment, Ottawa, Canada11,22; and the U.S. Army Chemical Research and Development Center, Edgewood, Maryland.23 Negative results of analyses of biomedical and environmental samples from Southeast Asia have come from Porton Down Laboratory in England,17,24 but according to the British, such results do not exclude sampling problems, including delay in sample collection after an attack, as a cause of the negative results.15
Proponents have been accused of analyzing samples that were purposely contaminated with toxin, either after collection or during the analysis. Other methodological criticisms include poor recovery (< 10% of one sample spiked with T-2 toxin); low precision of quantitative data when analyzing two portions of the same leaf; and lack of well-documented, confirming, replicate analyses in Mirocha’s or a similarly equipped second laboratory.15 The presence of polyethylene glycol in the sample analyzed by Rosen9 also indicates that the trichothecene mixture detected was manufactured, not natural.
Many experts in the intelligence community,16 academia,8,9 the U.S. Department of State,7 and the authors of this chapter believe that trichothecenes were used as biological weapons in Southeast Asia and Afghanistan. However, a weapon containing trichothecenes was not found in South
east Asia, and the Soviets have not declared any stockpiles of trichothecenes among their chemical or biological weapons. Thus, it has not been possible for the United States to prove unequivocally that trichothecene mycotoxins were used as biological weapons.
Trichothecene mycotoxins can be delivered as dusts, droplets, aerosols, or smoke from aircraft, rockets, missiles, artillery, mines, or portable sprayers. Because of their antipersonnel properties, ease of large-scale production, and apparent proven delivery by various aerial dispersal systems, the trichothecene mycotoxins (especially T-2 toxin) have an excellent potential for weaponization.
When delivered at low doses, trichothecene mycotoxins cause skin, eye, and gastrointestinal problems. In nanogram amounts,4,25 they (T-2 toxin, in particular) cause severe skin irritation (erythema, edema, and necrosis).4,6 Skin vesication has been observed in a number of humans exposed to yellow rain attacks.4,14,15 T-2 toxin is about 400-fold more potent (50 ng vs 20 μg) than mustard in producing skin injury.26 Lower-microgram quantities of trichothecene mycotoxins cause severe eye irritation, corneal damage, and impaired vision.4,16,26,27 Emesis and diarrhea have been observed at amounts that are one fifth to one tenth the lethal doses of trichothecene mycotoxins.26
Depending on the species of experimental animal tested and the exposure procedure,28,29 the lethality of T-2 toxin by aerosol exposure can be 10to 50-fold greater than when injected parenterally.30 With larger doses in humans, aerosolized trichothecenes may produce death within minutes to hours..7,14,15
The term LCt50 (the concentration • time that is lethal to 50% of the exposed population) is used to describe exposure to vapors and aerosols; milligrams • minutes per cubic meter is the conventional unit of measurement. LCt50 and its relation to LD50 (the dose that is lethal to 50% of the exposed population) are discussed in detail in Chapter 5, Nerve Agents, and will not be further explicated here.
The toxicity of T-2 toxin by the inhalational route of exposure (LCt50 range: 200–5,800 mg•min/m3)28–30 is similar to that observed for mustards or Lewisite (LCt50 range: 1,500–1,800 mg•min/m3).31 However, the lethality of T-2 toxin by the dermal route (LD50 range: 2–12 mg/kg6) is higher than that for liquid Lewisite (LD50: approximately 30 mg/kg31(p39)) or liquid mustards (LD50: approximately 100 mg/kg31(p32)). Therefore, the trichothecene mycotoxins are considered to be primarily blister agents that, at lower exposure concentrations, can cause severe skin and eye irritation, and at larger doses can produce considerable incapacitation and death within minutes to hours.
By solid substrate fermentation, T-2 toxin can be produced at approximately 9 g/kg of substrate, with a yield of 2 to 3 g of crystalline product.32 Several of the trichothecene mycotoxins have been produced in liquid culture at medium yields and large volumes of culture for extraction.33 Thus, using existing state-of-the-art fermentation processes that were developed for brewing and antibiotics, it would be fairly simple to produce ton quantities of a number of the trichothecene mycotoxins.
In Southeast Asia, most of the yellow rain attacks were delivered by aircraft or helicopter spray, bombs, and air-to-surface rockets. The attacks were described as a shower of sticky liquid, a yellow cloud of dust or powder, or a mist (like an insect spray).7,15 The delivery of the trichothecene mycotoxins was similar in many aspects to the spraying of pesticides on agricultural crops. This would result in a very low-efficiency respiratory aerosol (1–5 μm particles)34 but a highly effective droplet aerosol that could cause severe skin and eye irritation.