VIRAL CLASSES

Tavishi

When I first started liking biology, I enjoyed it in the realm of understanding things. Not knowing the answer to something made me deeply uncomfortable in a way I didn't like. The first time I remember enjoying uncertainty was in my seventh grade biology class, when we were asked to debate whether or not viruses were alive. Although officially viruses aren't considered forms of life, it's still a puzzling question. Viruses are little, evil, infectious, genetic packages that wreak havoc on their hosts, and are divided into six groups based off of what genetic material they carry. DNA viruses tend to lack an envelope studded with glycoproteins around the virus. These glycoproteins are how host cells let the viruses in.

DNA viruses typically reproduce by two cycles- the lytic and lysogenic cycle. The lytic cycle produces new viruses within the host cell, causing lysis of the cell. The lysogenic cycle is arguably more peaceful, with the viral DNA instead being integrated into the cell's own DNA. As a result, the viral DNA replicates alongside the rest, and is passed down into daughter cells during mitosis.

Class I viruses have double stranded DNA. Among the class I viruses are adenoviruses, papillomaviruses, and herpesviruses, most of which lack an external envelopes. The most prominent diseases caused by class I viruses include HPV, herpes, Epstein-Barr virus, and smallpox.

My favorite class I virus is HPV, the primary cause for cervical cancer and the reason why people get pap smears. The most well-known HPV patient in history is Henrietta Lacks. Lacks's cells were the first immortal cell line (HeLa cells), but equally as important was the lack of informed consent in the case of Lacks. Henrietta Lacks didn't know that her cells were collected, and she never consented to the publication of her entire DNA sequence later in life. The treatment of Henrietta Lacks is incredibly unfortunate, and is a significant part of scientific history that is to be learned from. However, HeLa cells have made incredible contributions to science.

Henrietta Lacks

Class II viruses have single stranded DNA, and includes the group of parvoviruses. Parvoviruses aren't nearly as significant in humans as they are in animals. If you have a dog, you've (hopefully) almost certainly gotten them vaccinated for canine parvovirus, as it's one of the core viruses. Parvovirus in dogs generally presents with symptoms of bloody diarrhea, vomiting, and lethargy, and is tested via ELISA tests. (I've actually gotten to do quite a few of the SNAP canine parvovirus tests at the clinic I work at. Pretty cool how they work. Do we want a post for ELISA? Comment below if you think so.)

puppy I once met who survived parvovirus!

Class III viruses have double stranded RNA, including reoviruses. Kind of a boring group, but it does have rotaviruses- diarrhea and gastroenteritis is not very fun. Most likely, you've been vaccinated for rotavirus as an infant.

Class IV viruses have single stranded RNA from which proteins are produced, and include coronaviruses, flaviviruses, togaviruses, and picornaviruses. Funny story- all of the prefixes here are derived from Latin. Everyone is at least vaguely familiar with many of the class IV viruses, especially because it most notably includes Sars-Cov 2 (virus which shut the entire world down for a few years.), but also, because the group includes ebola, Zika, West Nile, yellow fever, and more.

Flaviviruses are especially known for being transmitted by mosquitoes (yellow fever, dengue, West Nile, Zika).

Class V viruses have single stranded RNA from which mRNA is produced. The group of class V viruses includes rhabdoviruses, filoviruses, orthomyxoviruses, and paramyxoviruses, notably including polio, rabies, measles, and mumps. All of which we have some pretty cool vaccinations for- most are core vaccinations throughout a human lifetime. Rabies is the only need-based vaccine- people who handle animals a lot are typically vaccinated for rabies. Pets, on the other hand, receive rabies vaccinations as part of their core vaccination set.

Rabies is not only almost always fatal for the animal, but incredibly deadly for any humans who contract the disease. A most notable sign of rabies is hydrophobia; rabies patients typically panic or fear water. This is because salivation increases exponentially, and the salivary glands are the primary site of rabies virus proliferation. As a result, when someone is bitten by something with rabies, the virus is transmitted.

Class VI viruses have single stranded RNA which is transcribed into DNA. The class VI viruses are colloquially called retroviruses and are very strange. Instead of just arriving as DNA, retroviruses have RNA upon arrival, which undergoes the process of transcription by reverse transcriptase. Then, once the RNA is DNA, the DNA is integrated into the host cell's DNA. Eventually, all the materials to make new viruses are produced from the host, and new viruses peacefully leave the cell via budding.

The most prominent class VI virus is human immunodeficiency virus (HIV), or the virus that later causes the extremely dangerous sexually transmitted disease AIDS.