"The world, said Paul Valery, is equally threatened with two catastrophies: order and disorder. So is virology," __Luaff et al, Cold Spring Harbor Laboratories. Just an interesting little quote regarding the complexities of classifying viruses.

There have been many many attempts to classify viruses into groups. Most of these have failed. Early attempts were based on any one of several properties, and seldom worked in all cases. For example, one such attempt was based on percieved common pathogenic properties (eg causes pox vs. creep, etc). However, this did not work very well if the virus was multi-symptomic, and as we know now, there is not necessarily any genetic, morphological, or evolutionary linkage in cases such as these. Other examples focused on the organ in the body in which the virus most commonly was found, which again had no real basis for classification. Also considered were ecological and transmissional characteristics, such as the carrier, the method of transmission (horizontal or vertical, as will be discussed later), and so on. Finally, the remaining early attempts were based on shared virion properties, such as capsid shape and size, enveloped or non, and so on. But with all of these different methods, there was a lot of confusion as to who was using what, and it was virtually impossible for one to become familiar with all of the methods. This was a serious problem.

This problem was partially rectified by the International Commitee on Taxonomy of Viruses (ICTV). In a nearly annual process they determined a hierarchy of viruses through order, familiy, sub family, genus, and virus. In this classification, an order is defined as a grouping of families that share common characteristics and are distinct from other orders and families. The suffix used is virales, and the only order present in this classification system is Mononegavirales. Families and subfamilies are groupings of genera that share common characteristics different from other member virii of other species. The suffixes here are, respectively, viridae and virinae. A genus is a grouping of species, and has a suffix of virus. A species then is a polythetic class of viruses that constitute a replicating lineage and occupies a particular ecological niche. What does this mean? Well, the main part of the definition is the word "polythetic." Viruses mutate very quickly, so if every single virus with a slightly different genome were grouped as its own species the situation would be very unmanagable. Therefore, by adding polythetic to the definitionsays that there doesn't have to be 100% correlation between two virions to be in the same species. However, it is still open to debate how many characteristics must be shared in order to have a species grouping.

this will be finished later hopefully

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