A recent rise in the number of cases of Middle East respiratory syndrome coronavirus (MERS-CoV) has officials with the World Health Organization (WHO) concerned lately, especially since there are still so many uncertainties about exactly where the virus comes from and how it's spread from person to person.

Since the MERS coronavirus was first discovered, in April 2012, it's taken until March 26 of this year for the official WHO number of cases, worldwide, to top 200, including 85 that were fatal. In just shy of a month since then, the official number of cases that WHO is reporting (as of April 24) has jumped to 254, with a total of 93 deaths.

However, since WHO depends on nations supplying them with official numbers, their totals often lag behind what's actually happening. This is especially true in this case, as Saudi Arabia — where the first cases of MERS showed up and the most cases have been reported — has shown a persistent reluctance to cooperate with requests for reports.

As of Tuesday, April 22, The European Centre for Disease Prevention and Control has reported a total of 333 cases, with 107 deaths, but this very likely doesn't include the latest WHO additions to their numbers from Wednesday and Thursday. Adding up all reports from all affected countries apparently puts the totals at 360 cases, including 109 deaths.

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It's this recent surge in numbers that's causing the concern. Over 160 cases in just one month, compared to 200 or so cases in the 23 months before that, implies that something's going on. According to Science magazine, it's possible that there's a problem with contaminated samples, so that cases are being over-reported. WHO is stating that it could be due to inadequate prevention and control measures in health care centres (where most of the new cases are popping up). Other possibilities they mention are that mild cases have been missed up until now, but are being caught in further screening, and perhaps more ominously, there's also a chance that the virus has mutated into a form that's easier to transmit, similar to its 'cousin' SARS — Severe Acute Respiratory Syndrome.

However, Ziad Memish, the deputy minister of Saudi Arabia's Health Ministry said that it's simply because more people are requesting to be tested.

"In the last 2 years we tested 20,000 people," he said, according to Science. "Just in the last weeks, we tested 5,000 people."

A press release from WHO is urging nations to be vigilant about potential cases, as 75 per cent of those recently reported are from human-to-human transmission, which is a bit more than usual. The majority of cases have been in health care workers and those visiting health care facilities, most of which show little or no symptoms. It's still not known exactly how it's being transmitted between people.

Although MERS is certainly a more lethal relative of SARS — killing 30 per cent of those infected so far, compared to the 10 per cent of infected that SARS killed in 2003-2004 — there's at least one key difference between the two that will limit the ability of MERS to become a pandemic.

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Jason Tetro, over at Popular Science, has an excellent article explaining this, but basically, SARS spread so easily in 2003-2004 because it has two stages of infection. Early in the first stage, which can last for several days, the infected person shows no symptoms at all while the virus incubates inside their body. As stage one progresses, they start to show symptoms, but they can still move about and interact with others, they just feel like they have a bad cold or the flu. They're most certainly contagious at this point, although they may be before that as well, and any cough or sneeze can spread the virus, which can live for up to six hours outside the body. It's only when stage two of the infection sets in that the person needs to be hospitalized. So, that gives a lot of time for the infected person to come into contact with many other people.

MERS, on the other hand, has only one stage of infection. When a person becomes infected, they need immediate medical attention, so there's far less opportunity for the virus to be transmitted.

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