Medical Fun Facts Podcast

MFF0079: Enteroviral infections II

It’s Monday 14 August 2017.

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Last week I did part I of enteroviral infections. I’m recording parts I and II on the same day because I’m going to be busy on the weekend 13 and 14 August. So, to recap, enteroviral infections are caused by enteroviruses, or viruses in the genus Enterovirus. These are very small RNA viruses in the family Picornavirdidae (pico=small so small RNA viruses). There were traditionally four major groups with polioviruses being in a single group, but now each enterovirus serotype is given a number, e.g., EV71. Apart from the polioviruses you may have heard about coxsackieviruses, echovirsues, and rhinoviruses. Within the genus Enterovirus there are 12 species, viz., Enterovirus A to Enterovirus J and Rhinovirus A to Rhinovirus C. The polioviruses PV1, PV2 and PV3 are found in Enterovirus C. Common clinical syndromes caused by enteroviruses include: Poliomyelitis Polio-like disease Aseptic meningitis Nonspecific febrile illness Hand foot and mouth disease Pericarditis and/or myocarditis Acute conjunctivitis Herpangina Encephalitis Diabetes Mellitus type 1

Last week I briefly described hand, foot and mouth disease. Tonight I want to describe aseptic meningitis. Aseptic meningitis is an old fashioned term used before we really knew a lot about the causes of meningitis and when most serious meningitis was caused by bacteria like pneumococci, meningococci, Hæmophilus influenzæ and Streptococcus agalactiæ. With the advent of HIV infection and AIDS, fungal meningitis also became more common and better described.

The term aseptic effectively means bacteria-free rather than microorganism-free. Unlike the bacterial causes of meningitis mentioned before, viral and fungal meningitis is mostly subacute as well. By that, I mean, rather than fulminating in less than 24 hours, aseptic meningitides tend to take longer than 24 hours to develop. Patients tend to feel unwell with a fever and a slowly worsening headache. They may also take longer to develop the signs of inflammation of the meninges, such as neck stiffness or nuchal rigidity and pain when looking into the light or photophobia.

The other reason why the term aseptic is used is because traditional bacterial culture methods will not reveal the ætiological agent. Even in 2017, viral culture is not commonly performed. My clinical virology friends like to point out that they pioneered molecular microbiology well before simple bacteriologists like me thought about using genetic techniques let alone whole genome sequencing.

So the most common cause of viral or what we used to call aseptic meningitis are enteroviruses. The clinical illness progresses over a few days to a really severe headache and body aches and pains. You’ll want to keep the doors and windows covered to prevent sunlight hurting your eyes and you will not want to make any sharp movements because your head and body feels so delicate. So long as you rest and keep your fluids up, most of the time you will recover with no sequelæ. Unfortunately, some patients will progress to more severe meningitis and even to encephalitis or inflammation of the brain.

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