A biological attack is the deliberate release of viruses, bacteria, fungi, or their toxins to cause illness or death in people, livestock, or food crops. Unlike a bombing or chemical attack, the effects of a biological attack may not be visible for days or even weeks, making it one of the hardest security threats to detect and contain. These attacks can target civilian populations directly or aim to create widespread panic and disrupt governments.
How Biological Agents Are Used as Weapons
To be effective as a weapon, a microorganism needs to reliably cause disease or death at low concentrations. The agents used in biological attacks fall into two broad categories: living pathogens (bacteria, viruses, fungi) that can infect and multiply inside a host, and toxins, which are poisonous substances produced by organisms. Anthrax spores, for example, are bacterial. Botulinum toxin, one of the most potent poisons known, is a toxin produced by bacteria but does not spread from person to person.
The CDC classifies biological threat agents into three priority tiers. Category A agents pose the greatest risk to national security because they spread easily, cause high mortality, or could trigger public panic. This tier includes anthrax, smallpox, plague, botulism, and Ebola. Category B and C agents are considered lower priority but still dangerous, including organisms that contaminate food or water or emerging pathogens that could be engineered for mass spread.
How These Agents Reach People
The most dangerous delivery method is aerosolization: dispersing microscopic particles into the air. Particles between 0.3 and 5.0 micrometers in diameter are small enough to travel deep into the lungs when inhaled. Aerosols can be released from generators mounted on vehicles, boats, or planes equipped with spray nozzles, or pushed into building ventilation systems. The 2001 anthrax attacks in the United States used an even simpler method: letters containing powdered spores sent through the postal system. That attack killed five Americans and sickened 17 others, making it the worst biological attack in U.S. history.
Food and water contamination is another viable route, though it tends to work on a more local scale. In 1984, members of the Rajneeshee cult contaminated salad bars in Oregon with salmonella, causing over 750 cases of food poisoning. Suicide attacks, where an infected individual deliberately moves through crowded spaces, have also been identified as a potential method for spreading contagious diseases like smallpox.
Why Biological Attacks Are Hard to Detect
Most biological agents are invisible, odorless, and tasteless. Symptoms may not appear for days after exposure, and early signs often mimic common illnesses like the flu. By the time hospitals notice an unusual pattern, the agent may have already spread widely. This delayed effect is what makes biological attacks fundamentally different from explosions or chemical releases, where the damage is immediate and obvious.
Epidemiologists look for specific red flags that distinguish a deliberate release from a natural outbreak. These include an unusual geographic cluster of illness (many patients who attended the same event), diseases appearing in unexpected age groups (such as a chickenpox-like illness suddenly affecting adults, which could indicate smallpox), or a sudden wave of otherwise healthy people showing up with severe pneumonia, sepsis, or muscle paralysis. A large number of cases of sudden, unexplained paralysis, for instance, would strongly suggest a release of botulinum toxin.
Detection Systems and Response Times
The United States operates BioWatch, an early warning network that continuously samples air in major cities for DNA from specific threat pathogens. Air is pulled through filters, and those filters are collected and analyzed in laboratories using genomic testing. With current technology, results take 10 to 34 hours after sample collection. Filter recovery and transport alone can take up to four hours, and lab screening adds another six. The program is working toward reducing this window to four to six hours total.
Once an attack is confirmed, the Strategic National Stockpile holds emergency medical supplies, including vaccines for smallpox, antitoxins for botulism, and treatments for anthrax exposure. The system was designed to deliver supplies to any point in the United States or its territories within 12 hours of a decision to deploy. Over time, the stockpile has expanded to include antiviral medications, protective equipment like face masks, and even psychotropic medications for managing mass psychological trauma.
The Threat From Synthetic Biology
Advances in genetic engineering have changed the risk profile of biological attacks. In 2002, researchers demonstrated that a dangerous human virus, poliovirus, could be built from scratch in a laboratory using publicly available genetic sequences. Since then, several other viruses have been recreated in labs without access to natural samples. The genomes of more than 2,500 viruses are currently available in public databases, and in theory, any of them could be used as a blueprint, including smallpox.
Companies that sell synthetic DNA have developed screening protocols, automatically scanning customer orders against databases of dangerous pathogen sequences. This provides one layer of control. Still, the underlying capability is widespread: researchers can now order custom DNA sequences electronically from vendors around the world. So-called “gain-of-function” research, which deliberately enhances a pathogen’s ability to cause disease or spread between hosts, adds another layer of concern. While engineering a more dangerous virus is generally difficult because genetic changes often reduce a pathogen’s ability to survive in nature, it is not impossible, and the tools to attempt it are more accessible than ever.
International Prohibitions
The Biological Weapons Convention, which prohibits the development, production, and stockpiling of biological weapons, currently has 189 member states. It has been in force since 1975 and remains the primary international legal framework against biological warfare. However, the treaty lacks a formal verification mechanism, meaning there is no independent inspection system to confirm that countries are complying. This gap has been a persistent point of criticism and negotiation for decades.
What Makes Certain Agents Especially Dangerous
Anthrax is often considered the most practical bioweapon because its spores are hardy, easy to produce, and can be dispersed as a fine powder. Inhaled anthrax is fatal 85 to 90 percent of the time if untreated, and roughly half of respiratory cases develop into meningitis. Critically, anthrax does not spread from person to person, which means an attacker can target a specific area without risking uncontrolled contagion.
Smallpox sits at the other end of the spectrum. It spreads through respiratory droplets and would be devastating in a population with virtually no remaining immunity, since routine vaccination ended decades ago. Plague, caused by bacteria, is another Category A threat. Pneumonic plague, the form most likely to be weaponized, spreads through respiratory droplets and requires only 100 to 500 bacteria to cause infection. Person-to-person transmission is possible, though risk is low during the first 20 to 24 hours of illness.
Botulinum toxin is extraordinarily potent but does not spread between people. Exposure requires inhaling or ingesting the toxin itself. Its value as a weapon lies in its lethality at microscopic doses and the severe paralysis it causes, which can overwhelm hospital intensive care capacity in a mass-casualty event.