Six years on from when Middle East Respiratory Syndrome was first reported, new infections are still being recorded and, sadly, people are still dying.
Usually referred to as Mers, this viral illness has affected more than 1,750 individuals, according to recent figures from the International Society for Infectious Diseases, and more than 700 of them have lost their lives – a death rate of about 40 per cent.
In a typical week several more cases are announced and, while most have been in Saudi Arabia, the UAE is among the handful of other nations most severely affected.
It is appropriate, then, that a scientific institute in the Emirates, Dubai’s Central Veterinary Research Laboratory (CVRL), is playing an important role in efforts to combat the threat.
Some of the people who have fallen ill with Mers contracted the virus, MERS-CoV (it is a coronavirus, as it belongs to the coronaviridae family), from camels they worked with. Dromedaries, or one-humped camels of the kind familiar in the Gulf, are a “reservoir” for MERS-CoV: they carry the virus but do not fall ill.
“You wouldn’t call it a disease in camels; they don’t get sick – they’re infected, they are carriers of the virus,” said Dr Ulrich Wernery, the CVRL’s scientific director.
Very young camels are protected from the virus by antibodies in the milk from their mothers, but by the time a calf is four to six months old, it will have lost this immunity. After that, there is a “window” of three to five months during which the animal may become infected – and pass the virus to people.
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“Maybe 95 per cent of all camel calves [that get infected] are infected during this time of three to five months. At this time, we can isolate the virus from the [calf’s] nose; not from the lung,” said Dr Wernery.
“Then after that they become immune again because they produce antibodies against the virus. The dangerous time for camel keepers is during this window.”
Fortunately, young camels tend to be lively and so direct contact with people, even those who work with camels, is rare. But it does happen, and there have been cases in Saudi Arabia of people being infected this way.
“There’s no need to vaccinate adult camels, but you vaccinate camels when they’re four, five, six months old, then they cannot transmit to humans,” said Dr Wernery.
Researchers in Germany, the Netherlands and Spain have genetically engineered a vaccine called the modified vaccinia virus Ankara (MVA). This vaccine is used to stimulate immunity against pox, a type of disease caused by members of the poxviridae virus family, but can be used in combination with MERS-CoV virus. Part of the MERS-CoV virus is inserted in the pox vaccine.
In a study published in early 2016 in the journal Science, one of the world's top scientific publications, the researchers said that this recombinant vaccine appeared to confer immunity to Mers in camels on which it had been tested. Vaccinated animals produced antibodies against MERS-CoV and had much lower levels of the virus in their system.
However, only a small number of animals was involved in that study and the CVRL is set to undertake a much larger field trial. This will be carried out by Dr Wernery at a secure location – to prevent the spread of the virus – away from the CVRL’s Dubai headquarters.
“We are interested to include more animals [in a trial],” said one of the scientists involved in the project, Professor Christian Drosten, a researcher at Charité, a large university hospital in Berlin.
“We would like to do the first studies in the beginning of next year after preparatory work in the second half of this year.”
The researcher leading the initiative, which is funded by the German government, is Professor Gerd Sutter of the Ludwig Maximilian University of Munich. Trials in Dubai would, he said, indicate whether the laboratory results could be replicated “in the field”.
“That’s more difficult to evaluate … It’s not an easy experiment to do in the dromedary population in the field,” he said.
The scientists hope that the field trials will indicate the optimum dose to use and will help them to determine the most effective way of vaccinating camels to prevent the spread of Mers to people.
“Are we able to identify the dromedary camels that you would want to vaccinate in order to have an impact on human public health?” said Prof Sutter.
“There’s a huge camel population: camels needed for meat, for milk, hobby, sports animals. There we still lack data. It’s highly unlikely you would vaccinate all of them.
“The camel population is highly infected with Mers and we certainly need to learn more about what’s their normal infection cycle, what are the drivers of the infection in the camel population. Probably when we understand that a bit better, that might help to answer that question.”
One consequence of using, as a starting point, a vaccine against pox disease is that it means that the camels vaccinated against Mers will also develop immunity to camelpox, a condition that can kill as many as one in four young camels that contract it.
“That’s a very nice bystander effect of the vaccine. Because this MVA is a pox virus and is derived from smallpox, it will elicit automatically preventive immunity against orthopox [a group of pox diseases] including camelpox,” said Prof Sutter.
This, suggested Dr Wernery, could encourage camel owners to get their animals vaccinated. Because camels do not develop Mers, but are only carriers, owners might hesitate before paying for a vaccine against that disease alone. Camelpox, by contrast, can stop camels from racing, so owners are more likely to be willing to pay for vaccination.
Parallel to the work with camels, phase one of clinical trials of a human form of the vaccine are currently taking place.
And a separate research project, in Canada, is using a camelpox vaccine developed and supplied by CVRL called Ducapox (Dubai camelpox) instead of the MVA vaccine as the starting point for a parallel effort to develop a vaccine against Mers. This project is less well advanced, but could yet yield positive results.