A troubling new coronavirus is generating concern and drawing comparisons to the SARS outbreak of 2003. The MERS coronavirus (MERS-CoV) is the causative agent of MERS, or Middle East Respiratory Syndrome. First isolated from a patient in Saudi Arabia in 2012, MERS-CoV has caused 157 confirmed infections to date and has a mortality rate of 45%. MERS-CoV causes acute respiratory symptoms, such as fever, cough, and shortness of breath.
Patient zero was a male with severe respiratory symptoms treated in Jeddah, Saudi Arabia in 2012. Other cases in the area soon followed. The virus has been shown to spread through close contact with infected individuals, and patient-to-health care provider transmission has been observed. So far, the virus seems to be mainly confined to the Middle East, with the majority of cases seen in Saudi Arabia and fewer in the United Arab Emirates, Jordan, and Qatar. While several cases have been confirmed in Europe, it is thought that these patients contracted the disease through travel to the Middle East. No cases have been reported in North America. Health Canada classes the risk posed by MERS to Canadians as low. In the US, the Centers for Disease Control and Prevention (CDC) has been distributing test kits to state health departments, but has not recommended any travel precautions.
(Right) Transmission electron micrograph of MERS-CoV. False colour added for illustration purposes only. MERS outbreak data current as of Nov 18, 2013. Electron micrograph adapted from the Centers for Disease Control and Prevention (CDC).
Adding to international concern about the virus is the annual Hajj pilgrimage to Mecca, Saudi Arabia, occurring this year from October 13-19. An estimated 2-3 million visitors descend on the area during this time, leading to overcrowded conditions optimal for viral transmission. Despite this, the World Health Organization does not yet endorse entry screening programs or travel restrictions.
Initially thought to be a paramyxovirus, MERS-CoV was soon identified as a novel coronavirus. Analysis showed that its closest relatives are bat viruses isolated from Chinese samples. It is thought that transmission to humans occurred through a livestock intermediate such as camels or goats although this is yet unconfirmed. This information bears significant similarity to the origin of the SARS virus (SARS CoV) which is also closely related to a bat virus and was transmitted to humans through livestock. As well, both viruses show an ability to inhibit the type I IFN response in infected cells. Despite these similarities, there are notable differences between the viruses. MERS CoV uses the receptor dipeptidyl peptidase 4 (DDP4) to enter cells, whereas SARS CoV uses angiotensin converting enzyme 2 (ACE2). As well, MERS-CoV shows a broader host range of cells than does SARS, as well as increased susceptibility to exogenous IFN treatment.
Treatment options for MERS-CoV are being actively investigated. Work in vitro and in infected rhesus macaques indicates that two currently available antiviral agents, interferon alpha 2b and ribavirin, may be effective treatments, although their effectiveness in infected human patients is so far unknown. Efforts to create a vaccine are also well underway. Two US companies, Greffex and Novavax, have already developed nanoparticle vaccine candidates, although they are reportedly at least 5 years from being market-ready.
The emergence of MERS as a global health concern suggests that transmission of dangerous respiratory viruses from animals to humans, as seen in the SARS outbreak, may not be an isolated incident. The ubiquity of frequent international travel compounds the potential for rapid and widespread infection. Greater vigilance, tracking, and preparedness for potential virus outbreaks must become a higher priority for national and international health organizations if more future epidemics are to be avoided.
Kim Lifeso
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- MERS Coronavirus - November 28, 2013
