Almost exactly a year ago I asked the question: could Mers become the next Sars? My answer was that it could, but that we were at least two genetic mutations away from that occurring. So what has happened in the meantime?
Middle East respiratory syndrome (Mers), which causes coughing, fever and sometimes fatal pneumonia, is a coronavirus from the same family as severe acute respiratory syndrome (Sars), which killed about 800 people worldwide after first appearing in China in 2002.
The Mers virus, now formally referred to as Mers-CoV, emerged in September 2012, and has since infected more than 1,300 people around the world and caused some 470 deaths.
Most cases have occurred in Middle Eastern countries but the virus has recently taken hold in Northeast Asia in a big way.
The current outbreak in South Korea is the largest outside the Middle East, with 166 cases confirmed and 24 deaths. Although further global spread of the virus is not a surprise, the numbers and rapidity of the spread in Seoul and its environs is.
A source of particular concern is the fact that the South Korean index (initial) case had no documented history of exposure to camels or healthcare settings while in the Arabian Peninsula. While the exact source of the virus is not entirely clear, it is thought that Mers-CoV is transmitted to humans through contact with infected dromedary camels. Only camels have been found to be infected with a strain of the virus similar to that found in humans.
Transmission of the virus in South Korea has been described as a “super-spreading” event with dozens of diagnosed Mers-CoV cases occurring after exposure to a single patient.
Threshold of suspicion
Much of this rapid spread can be attributed to the initial victim not reporting their recent travel history to the Middle East when they first sought treatment. And because the symptoms of Mers are so like ’flu, the threshold of suspicion among health professionals before the first case is formally confirmed is understandably low.
Another obstacle to Mers diagnosis is the difficulty isolating the virus from swabs taken from the upper respiratory tract. It seems the virus has to take hold in the deeper parts of the respiratory system before it shows up in samples that are more difficult to collect.
Just as cultural factors played a central role in the spread of the Ebola virus in West Africa, cultural issues specific to Korea are at play with Mers. These include “doctor shopping”; because of the accessibility and affordability of healthcare in south Korea, patients frequently consult specialists in several facilities. And it is customary for family members to provide almost constant bedside care, increasing the risk of close exposures in the healthcare setting.
Is there any indication that the make-up of the virus itself has changed? Scientists in the Republic of Korea and China have completed full genome sequencing of coronaviruses from the current outbreak. The preliminary analysis of these findings suggests that the Mers-CoV viruses isolated in Korea are similar to those isolated in the Middle East. However, we now have a situation where sustained human-to-human Mers transmission has occurred for the first time outside the Arabian Peninsula.
With a mortality rate of some 40 per cent and as yet no known treatment or vaccines against Mers available three years after the emergence of the novel infectious agent, the threat remains significant. We must rely on public health measures – infection prevention and control, isolation, contact tracing and quarantine – in order to contain Mers-CoV.
Some subtle changes in the interaction between the virus and humans, leading to increased replication in the upper respiratory tract, giving a much more efficient and deadlier form of transmission, could up the threat level substantially. To paraphrase a famous quote from Northern Irish politics, “it hasn’t gone away, you know”.
mhouston@irishtimes.com muirishouston.com