The low infectious dose, its stability in the environment, and its genetic variability enable the virus to cause outbreaks, especially in health care facilities and other similar settings.
Cryptosporidium is a waterborne protozoan parasite, which is problematic for the water industry due to widespread environmental presence, low infectious dose and resistance to chlorine disinfection.
Due to its extreme virulence, ease of dissemination, low infectious dose, and previous weaponization, F. tularensis is considered a potential agent of bioterrorism.
As the actual infectious dose of N. ceranae or IIV that occurs in the field is currently unknown, we chose to utilize a relatively low infectious dose for both pathogens in our experiments.
In addition to infecting humans, B. mallei can cause acute or chronic fatal contagious zoonotic infections in its natural equine host, such as horses, donkeys, and mules, with a very low infectious dose.
The organism has been weaponized and is currently listed as a Category A Select Agent posing a significant threat to humans especially due to its extremely low infectious dose when acquired through the inhalation route [4].
Due to its high virulence, ease of dissemination, low infectious dose, and previous weaponisation, this pathogen has been classified by the Centers for Disease Control and Prevention among the top six 'Category A' biological threat agents [3].
Due to the low infectious dose of F. tularensis for both type A and type B in mice (LD50 <10 CFU for both subspecies) and the acute and rapid onset of infection that results, few studies have used a mouse model to demonstrate tangible virulence differences between F. tularensis strains [1], [4], [14], [15].
The low infectious dose (3 ) exacerbates its potential to cause secondary spread and large outbreaks (4 – 10 ).
The low infectious dose of norovirus readily allows transmission through environmental contamination and aerosols.
