Mers: most people never even knew they had it

A study in Saudi Arabia of the Middle East Respiratory Syndrome reveals that about 40,000 people have probably been infected with Mers.

Tourists at Gyeongbok Palace, Seoul, South Korea, take precautions against the Mers virus. The government announced yesterday that it was strengthening measures to stem the spread of the disease, and public fear. Lee Jin-man / AP PhotoShow less

A study in Saudi Arabia of the Middle East Respiratory Syndrome reveals that about 40,000 people have probably been infected with it. Many were not aware they had it, but they are now immune to further exposure.

As South Korea desperately tries to stem a Mers outbreak that has so far killed five people and infected 64, a new study reveals that 40,000 people in Saudi Arabia have probably contracted the virus in the past decade.

Yet most of these people will never even know they had it, or that they now have antibodies making them immune to further exposure to Middle East Respiratory Syndrome.

This is the first large-scale population study, as scientists continue to assess whether Mers could follow other coronaviruses (a species of virus) such as Severe Acute Respiratory Syndrome, or Sars, which killed 8,000 between 2002 and 2003.

It is three years since the first case of Mers was reported and the World Health Organisation still describes it as: “A newly emerging disease that remains poorly understood.”

While the death toll, at about 450, remains low compared with that of Sars, to scientists “poorly understood” translates as potentially very dangerous.

“The resolution of the picture we have is still quite coarse,” says Prof Christian Drosten, one of the authors of the study Presence of Mers Coronavirus Antibodies in Saudi Arabia: a Nationwide, Cross-sectional, Serological Study, published in The Lancet. “We don’t have the very clear picture about the number of mild or asymptomatic cases in the community.”

Prof Drosten, the director of the Institute of Virology at the University of Bonn, examined more than 10,000 blood samples for the presence of antibodies against the Mers virus. Positive results indicate past infection.

Antibodies were found in 15 people, most of them in rural areas, but the rate among people working with camels or camel meat was five in 140, 23 times as high as the overall rate.

Based on this, the authors, who include Saudi Arabia’s former deputy health minister Dr Ziad Memish, concluded that about 40,000 people had been infected during the past decade.

“The antibodies don’t last for life. We are quite sure they are short lived,” Prof Drosten says. “We estimate they are detectable for about five to 10 years. The projection has been on a small population sample but at least it’s a sample aligned to the general population.”

While Mers lingers, the WHO continues to convene its emergency committee to discuss the epidemiology – the patterns, causes and effects of health and disease conditions in a population – of the coronavirus.

The committee last met during a teleconference in February and noted that “although the pattern of transmission appears relatively unchanged, the overall situation and the possibility of international spread remains of concern”.

The previous meeting, in September last year, warned that transmission could be seasonal and that a surge would be expected “next Spring”. Given the latest surge, it is fair to say the prediction is coming true.

On May 29, Qatar reported a Mers fatality, the first since 2013, according to the country's official news agency.

On the same day, China notified the WHO of its first laboratory-confirmed case. The South Korean national in his mid-40s had close contact with a confirmed case in South Korea before travelling to the Guangdong province of China through Hong Kong on May 26.

The man was the son of South Korea’s third confirmed case and younger brother of its fourth. He developed symptoms of the virus on May 21 but ignored advice and instead took the flight to China through Hong Kong.

He also travelled within China by bus before health authorities traced him and sent him to hospital. Some local news sources claim the man gave false information about his condition to airport medics in Hong Kong and could face prosecution if he returns.

The WHO says he is in a stable condition and is being kept under isolation in a Huizhou hospital, although no further details have been released.

The organisation’s China office said health authorities were tracing all known contacts of the patients and the Guangdong health commission had sent an expert team to Huizhou for epidemiological sampling and investigation.

Hong Kong authorities were also tracing people with whom the patient came into close contact during his transit through the country.

Dr Doug Quarry, an International SOS medical director, says about 700 people have been quarantined after contact with patients in this outbreak, which started after a South Korean man running a farm equipment company in Bahrain returned from the region in early May.

“The good news is both Korea and Hong Kong were the epicentre of Sars, so they are experienced with isolation, quarantining and management of these viral outbreaks,” Dr Quarry says. “If anybody can control it they can.”

In most of the Middle East outbreaks the numbers of transmissions from individual patients has been low compared with the Far East. The Korean is believed to have already infected at least another 25 other people.

In 2013, the WHO raised the possibility of Mers super-spreaders, the term used to describe outbreaks where one individual is responsible for a much higher than average number of secondary cases.

In the Sars outbreak, up to three quarters of cases were thought to be linked to super-spreaders.

“This one man has come from the Middle East and infected 25 people,” says Dr Quarry. “There’s a bit of chatter around the epidemiology world. Is he a bit like the super-spreader that started Sars? To infect 25 people is just amazing.”

It is not known exactly what makes a person a super-spreader and theories range from abnormalities in the patient’s immune system to the setting in which the cases were transmitted.

With the “patient zero” in the latest Korean outbreak, the virus was transmitted to close relatives, patients in the same room and to health care workers and others on the hospital ward. The exposures happened before Mers was suspected or diagnosed, meaning that the opportunity for transmission was high.

“Sars and Mers are really the same type of virus,” Dr Quarry says. “Could this become a Sars-like thing? Absolutely. Will it become a Sars-like thing? Probably not, because public health authorities are so much more aware and ready to jump on things and isolate and quarantine as soon as they get an inkling of what’s going on.

“With Sars it was all new and people were running round and scrambling.”

One area that needs further investigation is the cases from this region that appear to have had no risk exposure at all, where officials have been unable to trace a connection to camels or to another infected person.

The serological study (the assessment of antibodies in the blood) in Saudi Arabia may go some way to explaining these cases. If people are asymptomatic or have mild symptoms, they may infect others without knowing it, Dr Quarry says.

“Understand the epidemiology and you understand the problem. You can’t come up with a solution until you understand the problem.”

The role played by camels in the spread of the disease is still not fully understood either.

The WHO has repeatedly called for better epidemiological study of camels in the region, particularly in areas where there has been direct links between camels and confirmed Mers cases, such as in the UAE.

The most recent research indicates it is camels less than one year old that pose the biggest threat, Prof Drosten says, but these potentially useful facts are not necessarily being acknowledged. “There are some quite useful pieces of information that seem to not have made their way to the region, somehow,” he says.

Despite mounting evidence about the links between camels and Mers, some are still reluctant to take advice.

“It would be good and beneficial if people who are interested in and love camels don’t close their eyes, but inform themselves a bit,” Prof Drosten says.