The most frequent coronaviruses we encounter are those that cause common colds, although other, more severe viruses occur within this family including the virus that causes SARS.
The current newsmaker, MERS-CoV, is a newly described coronavirus noteworthy for its high mortality (approximately 50% of patients diagnosed with the virus have died). Aside from high mortality, the name of the virus (MERS-CoV stands for Middle East Respiratory System Coronavirus) has drawn controversy because of its identity with the ‘Middle East’. Beyond that, this provides an opportune time to describe and discuss the coronavirus family in terms of structure and other characteristics, which might be a good place to begin.
The Coronavirus Family
Coronaviruses are a group of viruses with a plasma membrane envelope surrounding a helical nucleocapsid, which, in turn, surrounds the genetic material – in this case a positive strand RNA.
Coronavirus genomes an extraordinarily large positive strand RNAs encoding a spike protein (S), and Envelope protein (E), a membrane protein (M) and a nucleocapsid protein (N). Additionally, the virus also encodes an RNA polymerase required for the copying of its RNA genome (a function unlike any naturally occurring in the host cell and therefore requiring a specialized viral protein).
The Envelope is derived from the intracellular membrane of previously infected cells that is taken during the process of viral ‘budding’. Coronaviruses are named for the corona-like appearance (by electron microscopy) of these envelopes and the distinctive viral proteins (E and S) radiating out from the surface. These proteins are essential for the virus’ ability to bind to, and enter, uninfected cells through specific protein:protein interactions.
Within the envelope is the nucleocapsid, a helical structure that self-assembles from capsid proteins in the host cell’s cytoplasm. As this structure assembles, it binds and takes up a viral genome that contains all the genetic information to infect and reproduce in subsequent host cells.
MERS-CoV by the numbers
So far, of the 55 cases the CDC recognizes as testing positively for the virus, 31 have died. That’s 56% of infected persons dying of the disease. The majority of these cases remain in the middle east, however a small number have also appeared in western Europe, but with identifiable ties to the middle east. Compare this to the 2.5% mortality rate from the devastating 1918 swine flue epidemic.
Although the name has accepted been adopted (as well as ‘Saudi SARS’), it goes against a tradition opposing the use of locations in the name of the virus. There are two reasons for this convention – first, it may easily become inaccurate as the virus spreads and second, it can lead to stereotyping and persecution of a group of people. A previous example of this sort of mistake occurred when a new autoimmune disease was becoming prevalent amongst homosexual men in the US. Instead of using a more generically descriptive name, this virus was initially referred to as GRID (gay-related immunodeficiency virus). The virus, itself, had no idea it was supposed to stick to the gay population and before long it was discovered that everyone was potentially vulnerable. The name was then switched (or, more accurately, it finally got an official name, ‘HIV’, for human immunodeficiency virus). However, the damage was already done and many people adopted the belief that the virus only affected gay men, so straight people were not as likely to practice ‘safe sex’, and practitioners of hate speech added another arrow to their quiver: ‘Gay plague was sent by God, who was upset at homosexuals.’
Last week Novavax, Inc. announced the production of a nanoparticle vaccine candidate using the spike protein of MERS-CoV, a strategy that the company previously used in making a SARS vaccine.
Regardless of the method (vaccination, quarantine, etc.) it remains a vital priority to establish a protocol for maintaining public health prior to the Hajj, which is expected to fall between October 13-18, 2013. In 2011 the hajj saw An estimated 2.5 million pilgrims gathered in Mecca, most traveling from (and then returning to) countries outside the Arabian peninsula.