20,000 leagues under the MERS

This week it was confirmed that there has been a second case of MERS in the Philippines.

Middle East Respiratory Syndrome and the virus causing it, MERS coronavirus, were first identified in Saudi Arabia in 2012, and since then cases have been popping up across the globe; Iran, Jordan, Kuwait, Lebanon, Oman, Qatar, Saudi Arabia, the United Arab Emirates, and Yemen (Middle East); Austria, France, Germany, Greece, Italy, Netherlands, Turkey, and the United Kingdom (Europe); Algeria, Tunisia and Egypt (Africa); China, Malaysia, Republic of Korea, the Philippines and Thailand (Asia); and the United States of America (Americas) all have laboratory-confirmed cases. Since September 2012 there have been 1,365 cases and 487 MERS-related deaths. We still aren’t sure of the reservoir hosts, or the route of transmission from these hosts, or how easily human-to-human transmission occurs. There’s no vaccine and no treatment (other than supportive).

Transmission electron micrograph of Middle Eastern Respiratory Syndrome CoV particles found near the periphery of an infected MRC-5 cell. Credit: NIAID

Transmission electron micrograph of Middle Eastern Respiratory Syndrome CoV particles found near the periphery of an infected MRC-5 cell. Credit: NIAID

Coverage of MERS by the UK media has ranged from trivial to distractingly Eurocentric, numerically irresponsible, fear-mongering, and hilarious (although terrifying in a completely different way).

So how worried do we need to be? How does MERS-CoV compare to other viral infectious diseases?

Fewer confirmed cases: SARS is another coronavirus that causes a respiratory syndrome; in less than a year, SARS caused approximately 8,096 cases and 774 deaths, and has now been eradicated.

Fewer confirmed deaths: In 2012 HIV/AIDS caused approximately 1.5 million deaths, 3000 times more than MERS-CoV in three years.

Less infectious: Measles virus is highly contagious (R0 = 12-18), infecting 90% of non-immune contacts, whereas few infections of MERS-CoV have been passed between humans without close contact (R0 = 2-6.7).

Manageable:  Other viral outbreaks such as Ebola have been tackled with some success; the spread of the virus is now more controlled and numbers of cases are dropping. We have developed rapid diagnostic tests, specialist testing laboratories, a global network of experts and health professionals and made great progress in vaccine development.

Colorized scanning electron micrograph of Middle Eastern Respiratory Syndrome virus particles attached to the surface of an infected VERO E6 cell. Credit NIAID

Colorized scanning electron micrograph of Middle Eastern Respiratory Syndrome virus particles attached to the surface of an infected VERO E6 cell. Credit NIAID

However, the numbers of cases and deaths do not take into account the number of deaths that are, but have not been discovered to be MERS-related. They don’t take into account the number of cases that were symptomatic but not discovered to be MERS-related. And they don’t take into account the number of asymptomatic infections. There may be many more cases of, and deaths due to, MERS-CoV than we know about.

We still don’t know enough about how MERS-CoV is transmitted. It seems fairly certain that it is transmitted through from person-to-person via the infected person’s respiratory secretions, but we don’t know the role of other reservoirs, including bats and camels, and whether direct or indirect contract is required for transmission.

With so many gaps in our understanding of MERS it will be difficult to reduce transmission and develop resources to tackle the outbreak. With so few cases it will be difficult to study the virus or test any potential treatments or vaccines. And with cases in so many countries it will be difficult to coordinate these efforts and eradicate MERS-CoV. Viruses and outbreaks are unpredictable and can change, it will be difficult to anticpate this.

Transmission electron micrograph of Middle East respiratory syndrome coronavirus. Credit: NIAID

Transmission electron micrograph of Middle East respiratory syndrome coronavirus. Credit: NIAID

But, there’s plenty of work ongoing; although we don’t know everything we need to or have perfect health systems in place, we are making progress. We know who the virus is likely to infect, what areas it is more common in, and the symptoms that the virus is likely to cause. We can diagnose previous exposure using ELISA, IFA and microneutralisation, and current infection using rRT-PCR. We know that supportive treatment helps. Whole genome sequences have been published. We know that it may have originated in bats and passed to camels, and that camel-to-human and human-to-human transmission are possible. It has been possible to make sensible recommendations to reduce the risk of infection and prevent spread of the disease.

Perhaps it’s not something to cause panic, but something to fund research into, to understand, treat, prevent and eradicate.

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