Beware of These 4 Types of Biological Warfare Agents.

Microbiological agents are universally distributed in nature and make up the predominant part of life on earth. They occur in soil and water as well as in plants and animals, but also in the most hostile habitats like hot springs and deep ocean vents. The great majority of microbial agents are harmless and many are beneficial. Some of their properties have been used for fermentation in food processes for centuries, while others are applied in biotechnological processes. However, a few hundred of these agents are pathogenic or toxic, which means they are capable of causing disease in man, plants, or animals. Some of them can to be considered as biological warfare agents.

4.1 What is Special?

Biological agents (B-agents) generally considered as suitable for biological warfare include viruses, bacteria, toxins, and fungi, but only the use of a biological agent in combination with a system for the deliberate dissemination turns the B-agent into a biological weapon (B-weapon) or biological warfare agent (BW-agent).

Not all pathogenic microorganisms and their toxic products are considered as potential biological warfare agents. First, certain properties and characteristics make them attractive for abuse.

Compared to chemical agents or nuclear materials, biological agents are unique in their diversity. For technical and medical B-protection, their classification is important with reference to detection, identification, prophylaxis, and treatment.

4 Types of Biological Agents

B-agents like bacteria, viruses, toxins, and fungi differ significantly in size. While most agents can be identified by microscopic techniques, biological toxins are at the molecular level and well below the resolution of an electron microscope (EM).

1 Bacteria

Bacteria are single-cell microscopic organisms that possess cell walls and cell membranes where the cell wall maintains the shape. Two different types of cell wall in bacteria exist, called Gram-positive and Gram-negative. The names originate from the reaction of cells to the Gram-staining method, a basic test long-employed for the classification of bacterial species. The difference in Gram reaction of these two groups of bacteria is thought to be due to a difference in the structure of their cell walls and explains the distinct susceptibility to antimicrobial agents as well as the different resistance to physical disruption, drying, and sodium azide.

The Gram-positive cell wall consists of thick multilayered peptidoglycan and does not possess a lipid outer membrane. In contrast, Gram-negative cell walls have only one or a few layers of peptidoglycan but also possess an outer membrane consisting of various lipid complexes that confine the perisplasmatic space to the outer milieu.

The difference in cell-wall structure does not refer to the electrical charge of the bacteria. Both Gram-negative and Gram-positive bacteria are negatively charged.

Usually, bacteria have a deoxyribonucleic acid (DNA) genome, transcribe their necessary genes for reproduction and metabolism to ribonucleic acid (RNA), and translate them to proteins. Bacteria are generally much smaller than eukaryotic cells but despite their small size (0.2–5 µm) they are very complex in physiology and cell biology.

Most bacteria replicate by cell division and grow under simple, well-defined conditions. They are either spherical or rod-shaped and occur nearly everywhere in nature. Classical examples of bacteria with potential as BWAs (biological warfare agents) are the species Bacillus anthracis ,Yersinia pestis, and Francisella tularensis, and also Coxiella burnetii and Brucella melitensis. Moreover, some Gram-positive bacteria, like bacilli or clostridia, produce endospores , a kind of highly resistant and permanent mold, others are selective parasites, produce gelatinous slimes or capsules – all features and bacterial characteristics that influence the efficiency of disinfection.

In the electron microscopic picture spores show a thin outer spore coat, thick spore coat, thick spore cortex, and an inner spore membrane surrounding the chromosomal DNA located in the core region. Furthermore, the spore's chromosomal DNA is protected by small acid-soluble spore proteins (SASPs). Spores are generally formed in response to nutritional deprivation and enable, for example, bacilli to survive in an environment without metabolism. In addition, spores are extremely resistant to chemical and physical stress

4.2.2 Viruses

Viruses are non-cellular infectious agents consisting of a nucleic acid containing the genetic information, a strand of DNA or RNA, surrounded by a protein capsule (capsid). At the simplest level the capsid protects the viral genome from physical and chemical damage as well as from enzymatic damage. Moreover, many viruses have viral envelopes covering the protein capsid. These envelopes typically consist of phospholipids and proteins and derive from the host cell membranes; some envelopes also include viral glycoproteins. In general the outer surface of the virus is responsible for the recognition of the host cell, which normally takes place by binding of a specific virus-attachment protein to a cellular receptor.

Viruses are much smaller than bacteria, typically submicroscopic in size and are only visible by EM. Since viruses cannot reproduce independently they are not considered as living. They replicate using the host's metabolic processes and cellular components. In sharp contrast to bacteria, virus structures vary greatly. They come in many shapes that refer to the structure of the viral capsid and taxonomy and classification are in part based on these distinctions: polyhedral, helical, or binal. In addition, classification is based on size, nucleic acid, replication method, and the presence or absence of a viral envelope.

Examples of viruses with potential as biological warfare agent are variola major and variola minor virus, Venezuelan equine encephalitis virus (VEEV), yellow fever virus (YFV), Ebola virus, and hantavirus.

 

4.2.3 Toxins

Toxins of biological origin are not viable and do not reproduce. Therefore, these B-agents are neither infectious nor contagious. Biological toxins are either simple metabolic products from microorganisms or are poisons extracted from plants, marine organisms, snakes, or insects and share many characteristics like the absence of smell, taste, and color with chemical warfare agents. The structure of biological toxins varies from relatively simple to very complex polypeptides or proteins. Toxic substances can be classified according to the physiological effects they have on the human body – many cause stomach pains, diarrhea, and vomiting, and also muscle weakness up to respiratory paralysis.

Classical examples of toxins with potential as BWAs include some of the botulinum toxins produced by the bacteria Clostridium botulinum, ricin derived from castor beans, various staphylococcal enterotoxins from Staphylococcus aureus, and saxitoxin produced by blue green algae. Biotoxins act on the human body as either cyto- or neurotoxin. While the former causes cellular destruction, the latter affects the central nervous system.

 

4.2.4 Fungi

Fungi can be generally divided into microscopic small yeast and molds. While the former are unicellular organisms the latter are filamentous and almost entirely multicellular and produce asexual endospores. Fungi are heterotrophic organisms, which means they derive their energy from another organism, independent of whether the organism is alive or dead. They are typical pathogens that can be weaponized for use against crops to cause diseases and loss of food plants, like rice blast or cereal rust.

An infected leaf has diamond-shaped or elliptical or spindle-shaped spots with gray or white centers and brown margins. The spots may merge and lead to a complete drying of the infected leaf. The infected panicle turns white and dies before being filled with grain.

Fungal pathogens considered of significance as biological agents against humans are Coccidioides immitis and Histoplasma capsulatum. Both fungi are dimorphic and people are infected by inhalation of spores. Infection is characterized by flu-like symptoms and the cognate disease primarily affects the lungs.

 

The valuable contributor of the aboved writing: Andre Richardt

Beware of These 4 Types of Biological Warfare Agents.