Idea
Virus are small organisms that infect organisms. They're composed of DNA or RNA (mostly RNA, though not herpes), and encapsulated in some protein shell called a capsid. A single unit of transmissible virus is called a virion.
Virus are random pieces of genetic material, are inhert out of a host, and can only replicate through the cells of the organisms they infect, which leads to usually consider them non living. They infect the cell and use the ribosoms to replicate them, transforming the infected cell into a virus factory.
Virus trigger an immune response when detected by antibodies, which explain some of the symptoms: fever to make the body more hostile, general tiredness, soreness and headaches linked to the diverting of nutriments to antibodies fabrication {TODO: citation needed}.
A certain class of viruses are retroviruses, which are inserting their genetic material in the host's genome. They played an important role in evolution[2], by introducing variability in a species ; approximately 8% of the human genetic sequence is made of viral material[1]. It also causes the virus to reactivate in the infected host. HIV is a retrovirus.
Viruses sometimes have a greasy envelope around their capsid, which is why soap is effective on them: it interferes with the membrane, destroying the capsid, deactivating the virus[3]. Counterintuitively, enveloped viruses tend to be less stable because they need to remain wet to survive. Their transmission vectors are correspondingly aerosol droplets, blood, sex[7].
Virus strains are viruses which underwent mutations conferring it new properties. Viruses mutate with each host, an isolated virus extracted from a host is called an isolate, and by extension this is how the genome of that specific virus is called[4].
Most viruses are causing diseases, (whereas most bacteria dont) [^5]. A virus infection can be productive or non productive. In non productive, most of the time the infection is failing and the virus gets destroyed. Sometimes the virus doesn't reproduce itself but the cell starts dividing uncontrollably, this is the oncogenic transformation which is called cancer[6]. In productive infections, the infection is placed on the spectrum contained between lytic infection (mobilize 100% of cell resource and destroy the cell, called cell lysis) and permanent infection (divert only part of the cell resources and keep it alive).
species
There are millions of virus species, and all are different. However they can be grouped into species, genus, family, and order. They have a few characteristics that confer them similar properties. For example, the type of genetic material (DNA/RNA, segmented or not), the form, the presence or not of a capsid, of a membrane.
Adenoviruses[8] are unenveloped double stranded DNA viruses of medium size. They are very tolerent to low pH and chemicals, and resistant for prolonged periods of time outside of body or water. Primary contamination path is droplets, also fecal oral route. They are used for retrogenotherapy
links
[2]: Viruses are artifacts of Natural Selection. They are both very variable and introduce variability in their hosts' genetic material, they are heavily selected through their transmission mechanisms: viruses need a way to spread, and not to kill their hosts before they can spread. Their variability is a systemic condition of their survival, to be able to infect a host long enough that it can spread before it is killed. There are so many serotypes of the Rhinovirus that it's impossible to build a long lasting immunity, and why it's resilient
References
[1]: Ben L. Callif - The Human Genome Is Full of Virusesref
[3]: Bruce Goldman (Stanford) / What’s a virus, anyway? Part 1: The bare-bones basicsref and Bruce Goldman (Stanford) / What’s a virus, anyway? Part 2: How coronaviruses infect us - and how viruses created us - Scoperef is an intro to how viruses work
[4]: https://www.virology.ws/2020/05/07/there-is-one-and-only-one-strain-of-sars-cov-2/0
[5]: webmd / Bacterial and Viral Infections:
Most bacteria are harmless, and some actually help by digesting food, destroying disease-causing microbes, fighting cancer cells, and providing essential nutrients. Fewer than 1% of bacteria cause diseases in people. [...] In most cases, they reprogram the cells to make new viruses until the cells burst and die. In other cases, they turn normal cells into malignant or cancerous cells. Also unlike bacteria, most viruses do cause disease,
[6]: Professor Dave explains / virus/cell interaction