History of biological warfare
Various types of biological warfare (BW) have been practiced repeatedly throughout history. This has included the use of biological agents (microbes and plants) as well as the biotoxins, including venoms, derived from them.
Before the 20th century, the use of biological agents took three major forms:
- Deliberate contamination of food and water with poisonous or contagious material
- Use of microbes, biological toxins, animals, or plants (living or dead) in a weapon system
- Use of biologically inoculated fabrics and persons
In the 20th century, sophisticated bacteriological and virological techniques allowed the production of significant stockpiles of weaponized bio-agents:
- Bacterial agents: Anthrax, Brucella, Tularemia, etc.
- Viral agents: Smallpox, Viral hemorrhagic fevers, etc.
- Toxins: Botulinum, Ricin, etc.
The earliest documented incident of the intention to use biological weapons is possibly recorded in Hittite texts of 1500–1200 BCE, in which victims of tularemia were driven into enemy lands, causing an epidemic. Although the Assyrians knew of ergot, a parasitic fungus of rye which produces ergotism when ingested, there is no evidence that they poisoned enemy wells with the fungus, as has been claimed.
According to Homer's epic poems about the legendary Trojan War, the Iliad and the Odyssey, spears and arrows were tipped with poison. During the First Sacred War in Greece, in about 590 BCE, Athens and the Amphictionic League poisoned the water supply of the besieged town of Kirrha (near Delphi) with the toxic plant hellebore. According to Herodotus, during the 4th century BC Scythian archers dipped their arrow tips into decomposing cadavers of humans and snakes or in blood mixed with manure, supposedly making them contaminated with dangerous bacterial agents like Clostridium perfringens and Clostridium tetani, and snake venom.
In a naval battle against King Eumenes of Pergamon in 184 BC, Hannibal of Carthage had clay pots filled with venomous snakes and instructed his sailors to throw them onto the decks of enemy ships. The Roman commander Manius Aquillius poisoned the wells of besieged enemy cities in about 130 BC. In about AD 198, the Parthian city of Hatra (near Mosul, Iraq) repulsed the Roman army led by Septimius Severus by hurling clay pots filled with live scorpions at them. Like Scythian archers, Roman soldiers dipped their swords into excrements and cadavers too — victims were commonly infected by tetanus as result.
There are numerous other instances of the use of plant toxins, venoms, and other poisonous substances to create biological weapons in antiquity.
The Mongol Empire established commercial and political connections between the Eastern and Western areas of the world, through the most mobile army ever seen. The armies, composed of the most rapidly moving travelers who had ever moved between the steppes of East Asia (where bubonic plague was and remains endemic among small rodents), managed to keep the chain of infection without a break until they reached, and infected, peoples and rodents who had never encountered it. The ensuing Black Death may have killed up to 25 million total, including China and roughly a third of the population of Europe and in the next decades, changing the course of Asian and European history.
Biologicals were extensively used in many parts of Africa from the sixteenth century AD, most of the time in the form of poisoned arrows, or powder spread on the war front as well as poisoning of horses and water supply of the enemy forces. In Borgu, there were specific mixtures to kill, hypnotize, make the enemy bold, and to act as an antidote against the poison of the enemy as well. The creation of biologicals was reserved for a specific and professional class of medicine-men. In South Sudan, the people of the Koalit Hills kept their country free of Arab invasions by using tsetse flies as a weapon of war. Several accounts can give an idea of the efficiency of the biologicals. For example, Mockley-Ferryman in 1892 commented on the Dahomean invasion of Borgu, stating that "their (Borgawa) poisoned arrows enabled them to hold their own with the forces of Dahomey notwithstanding the latter's muskets." The same scenario happened to Portuguese raiders in Senegambia when they were defeated by Mali's Gambian forces, and to John Hawkins in Sierra Leone where he lost a number of his men to poisoned arrows.
During the Middle Ages, victims of the bubonic plague were used for biological attacks, often by flinging fomites such as infected corpses and excrement over castle walls using catapults. Bodies would be tied along with cannonballs and shot towards the city area. In 1346, during the siege of Caffa (now Feodossia, Crimea) the attacking Tartar Forces (subjugated by the Mongol empire under Genghis Khan more than a century ago), used the bodies of Mongol warriors of the Golden Horde who had died of plague, as weapons. An outbreak of plague followed and the defending forces retreated, followed by the conquest of the city by the Mongols. It has been speculated that this operation may have been responsible for the advent of the Black Death in Europe. At the time, the attackers thought that the stench was enough to kill them, though it was the disease that was deadly.
English Longbowmen usually did not draw their arrows from a quiver; rather, they stuck their arrows into the ground in front of them. This allowed them to nock the arrows faster and the dirt and soil was likely to stick to the arrowheads, thus making the wounds much more likely to become infected.
17th and 18th century
The last known incident of using plague corpses for biological warfare occurred in 1710, when Russian forces attacked the Swedes by flinging plague-infected corpses over the city walls of Reval (Tallinn). However, during the 1785 siege of La Calle, Tunisian forces flung diseased clothing into the city.
The British Army attempted use of smallpox against Native Americans during the Siege of Fort Pitt in June 1763. During a parley in midst of the siege on June 24, 1763, Captain Simeon Ecuyer gave representatives of the besieging Delawares two blankets and a handkerchief enclosed in small metal boxes that had been exposed to smallpox, in an attempt to spread the disease to the Natives in order to end the siege. William Trent, the trader turned militia commander who had come up with the plan, sent a bill to the British Army indicating that the purpose of giving the blankets was "to Convey the Smallpox to the Indians." The invoice's approval confirms that the British command endorsed Trent's actions. A reported outbreak that began the spring before left as many as one hundred Native Americans dead in Ohio Country from 1763 to 1764. It is not clear, however, whether the smallpox was a result of the Fort Pitt incident or the virus was already present among the Delaware people as outbreaks happened on their own every dozen or so years and the delegates were met again later and they seemingly hadn't contracted smallpox. Trade and combat also provided ample opportunity for transmission of the disease.
A month later British commander Lord Jeffery Amherst and Swiss-British officer Colonel Henry Bouquet discussed the topic of using blankets to spread smallpox amongst Natives. Four letters are cited from June 29, July 13, 16 and 26th, 1763. Excerpts: Amherst wrote on July 16, 1763, "P.S. You will Do well to try to Inocculate the Indians by means of Blankets, as well as to try Every other method that can serve to Extirpate this Execrable Race. I should be very glad your Scheme for Hunting them Down by Dogs could take Effect,..." Bouquet replied on July 26, 1763, "I received yesterday your Excellency's letters of 16th with their Inclosures. The signal for Indian Messengers, and all your directions will be observed." Smallpox was highly contagious among the Native Americans, and — together with measles, influenza, chicken pox, and other Old World diseases — was a major cause of death since the arrival of Europeans and their animals.
New South Wales
Australian aborigines (Kooris) have always maintained that the British deliberately spread smallpox in 1789, but this possibility has only been raised by historians from the 1980s when Dr Noel Butlin suggested; “there are some possibilities that ... disease could have been used deliberately as an exterminating agent”.
In 1997, David Day claimed there “remains considerable circumstantial evidence to suggest that officers other than Phillip, or perhaps convicts or soldiers … deliberately spread smallpox among aborigines” and in 2000 Dr John Lambert argued that “strong circumstantial evidence suggests the smallpox epidemic which ravaged Aborigines in 1789, may have resulted from deliberate infection”.
Judy Campbell argued in 2002 that it is highly improbable that the First Fleet was the source of the epidemic as "smallpox had not occurred in any members of the First Fleet"; the only possible source of infection from the Fleet being exposure to variolous matter imported for the purposes of inoculation against smallpox. Campbell argued that, while there has been considerable speculation about a hypothetical exposure to the First Fleet's variolous matter, there was no evidence that Aboriginal people were ever actually exposed to it. She pointed to regular contact between fishing fleets from the Indonesia archipelago, where smallpox was always present, and Aboriginal people in Australia's North as a more likely source for the introduction of smallpox. She notes that while these fishermen are generally referred to as ‘Macassans’, referring to the port of Macassar on the island of Sulawesi from which most of the fishermen originated, “some travelled from islands as distant as New Guinea”. She noted that there is little disagreement that the smallpox epidemic of the 1860s was contracted from Macassan fishermen and spread through the Aboriginal population by Aborigines fleeing outbreaks and also via their traditional social, kinship and trading networks. She argued that the 1789–90 epidemic followed the same pattern.
These claims are controversial as it is argued that any smallpox virus brought to New South Wales probably would have been sterilised by heat and humidity encountered during the voyage of the First Fleet from England and incapable of biological warfare. However, in 2007, Christopher Warren demonstrated that the British smallpox may have been still viable. Since then some scholars have argued that the British committed biological warfare in 1789 near their new convict settlement at Port Jackson.
In 2013 Warren reviewed the issue and argued that smallpox did not spread across Australia before 1824 and showed that there was no smallpox at Macassar that could have caused the outbreak at Sydney. Warren, however, did not address the issue of persons who joined the Macassan fleet from other islands and from parts of Sulawesi other than the port of Macassar. Warren concluded that the British were "the most likely candidates to have released smallpox" near Sydney Cove in 1789. Warren proposed that the British had no choice as they were confronted with dire circumstances when, among other factors, they ran out of ammunition for their muskets. Warren also uses native oral tradition and the archaeology of native graves to analyse the cause and effect of the spread of smallpox in 1789.
Prior to the publication of Warren's article (2013), a professor of physiology John Carmody argued that the epidemic was an outbreak of chickenpox which took a drastic toll on an Aboriginal population without immunological resistance. With regard to how smallpox might have reached the Sydney region, Dr Carmody said: "There is absolutely no evidence to support any of the theories and some of them are fanciful and far-fetched.." Warren argued against the chickenpox theory at endnote 3 of Smallpox at Sydney Cove – Who, When, Why?. However, in a 2014 joint paper on historic Aboriginal demography, Carmody and the Australian National University's Boyd Hunter argued that the recorded behavior of the epidemic ruled out smallpox and indicated chickenpox.
By the turn of the 20th century, advances in microbiology had made thinking about "germ warfare" part of the zeitgeist. Jack London, in his short story '"Yah! Yah! Yah!"' (1909), described a punitive European expedition to a South Pacific island deliberately exposing the Polynesian population to measles, of which many of them died. London wrote another science fiction tale the following year, "The Unparalleled Invasion" (1910), in which the Western nations wipe out all of China with a biological attack.
First World War
During the First World War (1914–1918), the Empire of Germany made some early attempts at anti-agriculture biological warfare. Those attempts were made by special sabotage group headed by Rudolf Nadolny. Using diplomatic pouches and couriers, the German General Staff supplied small teams of saboteurs in the Russian Duchy of Finland, and in the then-neutral countries of Romania, the United States, and Argentina. In Finland, saboteurs mounted on reindeer placed ampoules of anthrax in stables of Russian horses in 1916. Anthrax was also supplied to the German military attaché in Bucharest, as was glanders, which was employed against livestock destined for Allied service. German intelligence officer and US citizen Dr. Anton Casimir Dilger established a secret lab in the basement of his sister's home in Chevy Chase, Maryland, that produced glanders which was used to infect livestock in ports and inland collection points including, at least, Newport News, Norfolk, Baltimore, and New York City, and probably St. Louis and Covington, Kentucky. In Argentina, German agents also employed glanders in the port of Buenos Aires and also tried to ruin wheat harvests with a destructive fungus. Also, Germany itself became a victim of similar attacks — horses bound for Germany were infected with Burkholderia by French operatives in Switzerland.
The Geneva Protocol of 1925 prohibited the use of chemical weapons and biological weapons, but said nothing about experimentation, production, storage, or transfer; later treaties did cover these aspects. Twentieth-century advances in microbiology enabled the first pure-culture biological agents to be developed by World War II.
Interwar period and WWII
In the interwar period, little research was done in biological warfare in both Britain and the United States at first. In the United Kingdom the preoccupation was mainly in withstanding the anticipated conventional bombing attacks that would be unleashed in the event of war with Germany. As tensions increased, Sir Frederick Banting began lobbying the British government to establish a research program into the research and development of biological weapons to effectively deter the Germans from launching a biological attack. Banting proposed a number of innovative schemes for the dissemination of pathogens, including aerial-spray attacks and germs distributed through the mail system.
With the onset of hostilities, the Ministry of Supply finally established a biological weapons programme at Porton Down, headed by the microbiologist Paul Fildes. The research was championed by Winston Churchill and soon tularemia, anthrax, brucellosis, and botulism toxins had been effectively weaponized. In particular, Gruinard Island in Scotland, during a series of extensive tests, was contaminated with anthrax for the next 48 years. Although Britain never offensively used the biological weapons it developed, its program was the first to successfully weaponize a variety of deadly pathogens and bring them into industrial production. Other nations, notably France and Japan, had begun their own biological-weapons programs.
When the United States entered the war, mounting British pressure for the creation of a similar research program for an Allied pooling of resources led to the creation of a large industrial complex at Fort Detrick, Maryland in 1942 under the direction of George W. Merck. The biological and chemical weapons developed during that period were tested at the Dugway Proving Grounds in Utah. Soon there were facilities for the mass production of anthrax spores, brucellosis, and botulism toxins, although the war was over before these weapons could be of much operational use.
However, the most notorious program of the period was run by the secret Imperial Japanese Army Unit 731 during the war, based at Pingfan in Manchuria and commanded by Lieutenant General Shirō Ishii. This unit did research on BW, conducted often fatal human experiments on prisoners, and produced biological weapons for combat use. Although the Japanese effort lacked the technological sophistication of the American or British programs, it far outstripped them in its widespread application and indiscriminate brutality. Biological weapons were used against both Chinese soldiers and civilians in several military campaigns. Three veterans of Unit 731 testified in a 1989 interview to the Asahi Shimbun that they contaminated the Horustein river with typhoid near the Soviet troops during the Battle of Khalkhin Gol. In 1940, the Imperial Japanese Army Air Force bombed Ningbo with ceramic bombs full of fleas carrying the bubonic plague. A film showing this operation was seen by the imperial princes Tsuneyoshi Takeda and Takahito Mikasa during a screening made by mastermind Shiro Ishii. During the Khabarovsk War Crime Trials the accused, such as Major General Kiyashi Kawashima, testified that as early as 1941 some 40 members of Unit 731 air-dropped plague-contaminated fleas on Changde. These operations caused epidemic plague outbreaks.
Ban Shigeo, a technician at the Japanese Army's 9th Technical Research Institute, left an account of the activities at the Institute which was published in "The Truth About the Army Nororito Institute". Ban included an account of his trip to Nanking in 1941 to participate in the testing of poisons on Chinese prisoners. His testimony tied the Noborito Institute to the infamous Unit 731, which participated in biomedical research.
During the final months of World War II, Japan planned to utilize plague as a biological weapon against U.S. civilians in San Diego, California, during Operation Cherry Blossoms at Night. They hope that it would kill tens of thousands of U.S. civilians and thereby dissuading America from attacking Japan. The plan was set to launch on September 22, 1945, at night, but it never came into fruition due to Japan's surrender on August 15, 1945.
When the war ended, the US Army quietly enlisted certain members of Noborito in its efforts against the communist camp in the early years of the Cold War. The head of Unit 731, Shiro Ishii, was granted immunity from war crimes prosecution in exchange for providing information to the United States on the Unit's activities. Allegations were made that a "chemical section" of a US clandestine unit hidden within Yokosuka naval base was operational during the Korean War, and then worked on unspecified projects inside the United States from 1955 to 1959, before returning to Japan to enter the private sector.
Some of the Unit 731 personnel were imprisoned by the Soviets, and may have been a potential source of information on Japanese weaponization.
Considerable research into BW was undertaken throughout the Cold War era by the US, UK and USSR, and probably other major nations as well, although it is generally believed that such weapons were never used.
In Britain, the 1950s saw the weaponization of plague, brucellosis, tularemia and later equine encephalomyelitis and vaccinia viruses. Trial tests at sea were carried out including Operation Cauldron off Stornoway in 1952. The programme was cancelled in 1956, when the British government unilaterally renounced the use of biological and chemical weapons.
The United States initiated its weaponization efforts with disease vectors in 1953, focused on Plague-fleas, EEE-mosquitoes, and yellow fever – mosquitoes (OJ-AP). However, US medical scientists in occupied Japan undertook extensive research on insect vectors, with the assistance of former Unit 731 staff, as early as 1946.
The United States Army Chemical Corps then initiated a crash program to weaponize anthrax (N) in the E61 1/2-lb hour-glass bomblet. Though the program was successful in meeting its development goals, the lack of validation on the infectivity of anthrax stalled standardization. The United States Air Force was also unsatisfied with the operational qualities of the M114/US bursting bomblet and labeled it an interim item until the Chemical Corps could deliver a superior weapon.
Around 1950 the Chemical Corps also initiated a program to weaponize tularemia (UL). Shortly after the E61/N failed to make standardization, tularemia was standardized in the 3.4" M143 bursting spherical bomblet. This was intended for delivery by the MGM-29 Sergeant missile warhead and could produce 50% infection over a 7-square-mile (18 km2) area. Although tularemia is treatable by antibiotics, treatment does not shorten the course of the disease. US conscientious objectors were used as consenting test subjects for tularemia in a program known as Operation Whitecoat. There were also many unpublicized tests carried out in public places with bio-agent simulants during the Cold War.
In addition to the use of bursting bomblets for creating biological aerosols, the Chemical Corps started investigating aerosol-generating bomblets in the 1950s. The E99 was the first workable design, but was too complex to be manufactured. By the late 1950s the 4.5" E120 spraying spherical bomblet was developed; a B-47 bomber with a SUU-24/A dispenser could infect 50% or more of the population of a 16-square-mile (41 km2) area with tularemia with the E120. The E120 was later superseded by dry-type agents.
Dry-type biologicals resemble talcum powder, and can be disseminated as aerosols using gas expulsion devices instead of a burster or complex sprayer. The Chemical Corps developed Flettner rotor bomblets and later triangular bomblets for wider coverage due to improved glide angles over Magnus-lift spherical bomblets. Weapons of this type were in advanced development by the time the program ended.
From January 1962, Rocky Mountain Arsenal “grew, purified and biodemilitarized” plant pathogen Wheat Stem Rust (Agent TX), Puccinia graminis, var. tritici, for the Air Force biological anti-crop program. TX-treated grain was grown at the Arsenal from 1962–1968 in Sections 23–26. Unprocessed TX was also transported from Beale AFB for purification, storage, and disposal. Trichothecenes Mycotoxin is a toxin that can be extracted from Wheat Stem Rust and Rice Blast and can kill or incapacitate depending on the concentration used. The “red mold disease” of wheat and barley in Japan is prevalent in the region that faces the Pacific Ocean. Toxic trichothecenes, including nivalenol, deoxynivalenol, and monoace tylnivalenol (fusarenon- X) from Fusarium nivale, can be isolated from moldy grains. In the suburbs of Tokyo, an illness similar to “red mold disease” was described in an outbreak of a food borne disease, as a result of the consumption of Fusarium- infected rice. Ingestion of moldy grains that are contaminated with trichothecenes has been associated with mycotoxicosis.
Although there is no evidence that biological weapons were used by the United States, China and North Korea accused the US of large-scale field testing of BW against them during the Korean War (1950–1953). At the time of the Korean War the United States had only weaponized one agent, brucellosis ("Agent US"), which is caused by Brucella suis. The original weaponized form used the M114 bursting bomblet in M33 cluster bombs. While the specific form of the biological bomb was classified until some years after the Korean War, in the various exhibits of biological weapons that Korea alleged were dropped on their country nothing resembled an M114 bomblet. There were ceramic containers that had some similarity to Japanese weapons used against the Chinese in World War II, developed by Unit 731.
During the 1948 1947–1949 Palestine war, International Red Cross reports raised suspicion that the Israeli Haganah militia had released Salmonella typhi bacteria into the water supply for the city of Acre, causing an outbreak of typhoid among the inhabitants. Egyptian troops later claimed to have captured disguised Haganah soldiers near wells in Gaza, whom they executed for allegedly attempting another attack. Israel denies these allegations.
Biological and Toxin Weapons Convention
In mid-1969, the UK and the Warsaw Pact, separately, introduced proposals to the UN to ban biological weapons, which would lead to the signing of the Biological and Toxin Weapons Convention in 1972. United States President Richard Nixon signed an executive order on November 1969, which stopped production of biological weapons in the United States and allowed only scientific research of lethal biological agents and defensive measures such as immunization and biosafety. The biological munition stockpiles were destroyed, and approximately 2,200 researchers became redundant.
Special munitions for the United States Special Forces and the CIA and the Big Five Weapons for the military were destroyed in accordance with Nixon's executive order to end the offensive program. The CIA maintained its collection of biologicals well into 1975 when it became the subject of the senate Church Committee.
The Biological and Toxin Weapons Convention was signed by the US, UK, USSR and other nations, as a ban on "development, production and stockpiling of microbes or their poisonous products except in amounts necessary for protective and peaceful research" in 1972. The convention bound its signatories to a far more stringent set of regulations than had been envisioned by the 1925 Geneva Protocols. By 1996, 137 countries had signed the treaty; however it is believed that since the signing of the Convention the number of countries capable of producing such weapons has increased.
The Soviet Union continued research and production of offensive biological weapons in a program called Biopreparat, despite having signed the convention. The United States had no solid proof of this program until Dr. Vladimir Pasechnik defected in 1989, and Dr. Kanatjan Alibekov, the first deputy director of Biopreparat defected in 1992. Pathogens developed by the organization would be used in open-air trials. It is known that Vozrozhdeniye Island, located in the Aral Sea, was used as a testing site. In 1971, such testing led to the accidental aerosol release of smallpox over the Aral Sea and a subsequent smallpox epidemic.
During the closing stages of the Rhodesian Bush War, the Rhodesian government resorted to use chemical and biological warfare agents. Watercourses at several sites inside the Mozambique border were deliberately contaminated with cholera. These biological attacks had little impact on the fighting capability of ZANLA, but caused considerable distress to the local population. The Rhodesians also experimented with several other pathogens and toxins for use in their counterinsurgency.
After the 1991 Persian Gulf War, Iraq admitted to the United Nations inspection team to having produced 19,000 liters of concentrated botulinum toxin, of which approximately 10,000 L were loaded into military weapons; the 19,000 liters have never been fully accounted for. This is approximately three times the amount needed to kill the entire current human population by inhalation, although in practice it would be impossible to distribute it so efficiently, and, unless it is protected from oxygen, it deteriorates in storage.
According to the U.S. Congress Office of Technology Assessment 8 countries were generally reported as having undeclared offensive biological warfare programs in 1995: China, Iran, Iraq, Israel, Libya, North Korea, Syria and Taiwan. Five countries had admitted to having had offensive weapon or development programs in the past: United States, Russia, France, the United Kingdom, and Canada. Offensive BW programs in Iraq were dismantled by Coalition Forces and the UN after the first Gulf War (1990–91), although an Iraqi military BW program was covertly maintained in defiance of international agreements until it was apparently abandoned during 1995 and 1996.
On September 18, 2001, and for a few days thereafter, several letters were received by members of the U.S. Congress and American media outlets which contained intentionally prepared anthrax spores; the attack sickened at least 22 people of whom five died. The identity of the bioterrorist remained unknown until 2008, when an official suspect, who had committed suicide, was named. (See 2001 anthrax attacks.)
Suspicions of an ongoing Iraqi biological warfare program were not substantiated in the wake of the March 2003 invasion of that country. Later that year, however, Muammar Gaddafi was persuaded to terminate Libya's biological warfare program. In 2008, according to a U.S. Congressional Research Service report, China, Cuba, Egypt, Iran, Israel, North Korea, Russia, Syria and Taiwan are considered, with varying degrees of certainty, to have some BW capability. By 2011, 165 countries had officially joined the BWC and pledged to disavow biological weapons.
List of historical Biological Weapons programs by country
- United States biological weapons program
- United Kingdom and weapons of mass destruction#Biological weapons
- Soviet biological weapons program
- Japanese special research units
- Iraqi biological weapons program (see also Iraq and weapons of mass destruction)
- South Africa and weapons of mass destruction#Biological and chemical weapons
- Rhodesia and weapons of mass destruction
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However, in the light of contemporary knowledge, it remains doubtful whether his hopes were fulfilled, given the fact that the transmission of smallpox through this kind of vector is much less efficient than respiratory transmission, and that Native Americans had been in contact with smallpox >200 years before Ecuyer’s trickery, notably during Pizarro’s conquest of South America in the 16th century. As a whole, the analysis of the various ‘pre-micro- biological” attempts at BW illustrate the difficulty of differentiating attempted biological attack from naturally occurring epidemics.
- Medical Aspects of Biological Warfare. Government Printing Office. 2007. p. 3. ISBN 978-0-16-087238-9.
In retrospect, it is difficult to evaluate the tactical success of Captain Ecuyer's biological attack because smallpox may have been transmitted after other contacts with colonists, as had previously happened in New England and the South. Although scabs from smallpox patients are thought to be of low infectivity as a result of binding of the virus in fibrin metric, and transmission by fomites has been considered inefficient compared with respiratory droplet transmission.
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