12 - Enteroviruses that aren't named Poliovirus (w/ Vincent Racaniello!)
12. Enteroviruses that aren't named Poliovirus (w/ Vincent Racaniello!)
The sheer reduction of poliomyelitis-ridden individuals is a testament to how effective the poliovirus vaccines are. Still, related viruses like rhinoviruses, coxsackieviruses, and enteroviruses cause significant burden to public health. What are picornaviruses? Why is there a need for researching viruses like EV-D68 and EV-A71? Let’s learn to be scientifically conversational.
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General Learning Concepts
1) What is a virus? What is an enterovirus?
a. Virus (definition): Viruses are obligate intracellular parasites that are capable of infecting nearby cells. They contain instructions for making more viruses (with either RNA or DNA). It is common (but not entirely correct) to associate viruses with diseases (or symptoms) that they cause: the common cold, flu, warts, fever, paralysis.
b. Enterovirus: Genus of viruses in the picornavirus family (pico, 10-12 , small unit of measurement, RNA, virus). Positive stranded RNA genomes (messenger sense). They are named because of their transmission-route (enteric, or intestinal).
i. Poliovirus: An enterovirus that causes poliomyelitis. Poliomyelitis resulted in tens of thousands of patients a year past 1900, with the often-associated symptom being paralysis. This virus has been in the process of eradication since 1955 (Salk vaccine) and 1961 (Sabin vaccine) but remains in some countries worldwide (Pakistan, Afghanistan, Nigeria).
ii. Rhinovirus: An enterovirus that causes the common cold. Capable of causing respiratory tract infection or related symptoms. While not necessarily traditionally thought of as a dangerous infection for morbidity and mortality, absences from work, school, or events constitute a major cost to organizations.
iii. Coxsackie: An enterovirus that causes hand, foot, and mouth disease. This disease is characterized by a blister-like rash on the hands, feet, and mouth. Infection is generally seen in those under the age of 10. In severe and rare cases, encephalitis (inflammation of the brain) can occur.
iv. Enterovirus D68 and A71: Enteroviruses that are responsible for a variety of different symptoms. They can cause hand, foot, and mouth disease, but have recently been associated with acute flaccid myelitis (AFM, 100+ cases in 2018 in the USA), which is associated with weakness in limbs, facial drooping, slurred speech, and worse. AFM affects the nervous system to cause weakness in muscles and reflexes.
c. How are you infected with an enterovirus? Contact with secretions (saliva, sputum, mucus), feces. Generally fecal-oral transmission is associated with poor hygiene techniques; objects covered in fecal particles invariably end up in someone’s mouth.
2) Why is there such a range of symptoms from enterovirus infection?
a. The viral lifecycle: The virus has to get into the human cell to make more virus. The virus then has to get out of its protein coat (shell) to expose the RNA genome to the cell. Unlike DNA based organisms which use DNA as instructions to make an RNA message, enteroviruses use RNA to make an RNA message (but backwards and opposite). Because humans do not have the capability to turn RNA backwards and opposite, viruses must have a message to make a protein (molecular machine) capable of doing this. This enzyme is known as the RNA-dependent-RNA polymerase. Therefore, the single message that comes in must be used to make protein so that the genome can be multiplied. Then, the genome is replicated many, many times so each virus has instructions to make another virus during their subsequent infection. Those genomes can be used to translate (make protein from the message) more proteins required for packing the viral capsids with the genomes before being released from the human cell. The human cell usually ends up dead or very sick after viral infection.
b. Common symptoms: Over 90% of people infected with enteroviruses show no symptoms or any enterovirus specific symptoms. For those who experience symptoms: runny nose, sneezing, cough, body-and-muscle aches. Poliovirus, for example, is capable of infecting cells that have the proper receptor (think having the right key for a lock) and human cell types. Because polio causes viremia (virus in the blood stream), poliovirus can travel to many different cell types including skeletal muscle cells and different cell types in the brain. Infecting different cell types can be related to different symptoms. [2] [3]
3) What type of public health efforts are there to reduce enterovirus-related symptoms?
a. Specific treatment: With many viruses that have no vaccine or “cure”, treatment generally results in controlling fevers and reducing symptoms. This generally results in trying to maintain inflammation or cold-like symptoms. Prevention often stems from good hygiene; handwashing, caution in what one ingests, and sterilizing common surfaces.
b. Testing: Testing for enterovirus infection is often possible by RT-PCR but does not always have the specificity to be able to delineate exactly which enterovirus has infected an individual.
i. RT-PCR: Reverse transcription polymerase chain reaction: takes RNA (in this case, the foreign viral RNA) and reverse transcribes it back into DNA. However, there is very little DNA from the very little amount of RNA, so polymerase chain reaction is used to amplify the amount of DNA. Having more DNA allows for “reading” the instructions which allows scientists to identify which virus (book) it came from.
c. Research: There are many labs that study picornaviruses and enteroviruses in specific. Some choose to use poliovirus as a model system (episode 4 for definition of model) and some study specific enteroviruses.
4) Questions for Vincent Racaniello:
a. As a graduate student, you worked on influenza virus with Peter Palese. As a post-doctoral fellow, you cloned and sequenced the poliovirus genome with David Baltimore. You continued work on picornaviruses throughout your career but also pursued research with some flaviviruses like Zika. Can you compare and contrast working between different positive stranded RNA viruses and positive and negative strand RNA viruses?
b. What is the importance of patenting ones’ work as a scientist?
c. Do you think that we will ever fully eradicate poliovirus from the planet?
d. Why is it so important to study EV-D68 and EV-A71 now? Why doesn’t the polio vaccine protect individuals from them? How has your work been enabled by a recent crowdfunding experiment?