Some pathogens are much more dangerous to handle than others, which has led to their classification for laboratory purposes into categories. Category 4, the most dangerous, contains those potentially fatal viruses where no treatment is available, for example Lassa, Ebola, Marburg, smallpox. These call for total isolation and maximum security. Category 3 includes viruses such as hepatitis, HIV, rabies, bacteria like M. tuberculosis, anthrax, and plague, and some fungi and protozoa; these are handled in separate laboratories. The remaining pathogens, treatable or easily prevented by vaccines, are worked on in safety cabinets; these are Category 2. Category 1 are non-pathogens. As a precaution against spread in the populations, most diseases in Categories 2, 3, and 4, and all zoonoses (diseases caught from animals) are notifiable, meaning that a doctor is obliged to report every case to the local health authority, allowing contacts to be traced.
