chapter  20
12 Pages

Fungal Pathogens

Fungi are unicellular or multicellular organisms that are more highly evolved than bacteria (Chapter 17). They are members of the plant kingdom and include molds, mildew, smuts, rusts, and yeasts. They range in size from 3 to 50 µm. With the exception of yeasts, they are usually rod shaped and arranged end-to-end in strands or filaments. Yeasts are usually oval. Fungi reproduce by forming spores. Spores are part of the reproductive cycle and are

not a protective mechanism as used by some bacteria when they are subjected to adverse conditions. Fungal spores can lie dormant, sometimes for decades, waiting for conditions that allow germination. Infections occur when a spore germinates on or in a host. Fungi are relatively easy to grow. Production, isolation, harvesting, and storage of spores are also relatively uncomplicated. Although several notable antipersonnel fungal agents have been investigated as biolo-

gical warfare agents, fungi have primarily been selected because of their ability to attack agriculturally significant crop species such as wheat, corn, or rice. Most antiplant agents are host specific, some are even specific to individual varieties of the host species. There is little potential for antiplant fungi to attack humans or animals. A final group of fungi are those used as simulants to model the release of other, more

hazardous agents. Pathogens employed as biological warfare simulants do not generally pose a significant risk to people, animals, or plants. However, individuals with respiratory illness or suppressed immune systemmay be at risk should they be exposed to an infectious dose of the agent. Fungi can be stored as active cultures or isolated as spores. Spores are easy to disperse.

However, because they are living organisms and can be killed during the dispersal process, there are limitations to the methods that can be used. In most cases, large-scale attacks will be clandestine and only detected through epidemiological analysis of resulting disease patterns. Localized or small-scale attacks may take the form of “anthrax” letters. Even in these cases, without the inclusion of a threat the attack may go unnoticed until the disease appears in exposed individuals (e.g., the initial 2001 anthrax attack at AmericanMedia Inc., which claimed the life of Robert Stevens). Incubation times for diseases resulting from infection vary depending on the specific

pathogen, but are generally on the order of days to weeks. Exposures to extremely high doses of some pathogens may reduce the incubation period to as short as several hours.