Organising resistance to the Zika virus in Réunion

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The World Health Organization (WHO) stated on 1 February that the Zika virus constitutes “a Public Health Emergency of International Concern.

The organisation is advising pregnant women not to visit the regions affected by Zika. Links have been confirmed between the virus and foetal malformations.

In addition to microcephaly and Guillain-Barré syndrome, there is now a new concern: myelitis, a disease affecting the nervous system.

The virus and its disease burden are spreading across South and Central America — especially in Brazil, where 1.5 million people are affected — but it is also being reported in other areas.

These include French Overseas Departments such as Guadeloupe, Martinique and French Guiana, with one notable exception: the island of Réunion.

Réunion is in the Indian Ocean, on the opposite side of the planet to the current epidemic, but it is also host to the dreaded vector, the tiger mosquito.

“Zika has the same mode of transmission as dengue fever or chikungunya, so we are experienced in prevention and intervention: eliminating breeding sites surrounding an affected person, and using insecticide to control adult mosquitoes,” explains Hélène Thebault, head of vector control at the Agence régionale de santé Océan indien (regional health authority for the Indian Ocean — ARSOI).

One hundred and forty workers are employed to visit homes throughout the island, and 50,000 households receive door-to-door visits each year.

But surveillance is currently being stepped up. “There has been a marked improvement in preventive practices since the chikungunya crisis. The people of Réunion have adopted good practices but there is still some negligence, resulting in breeding sites remaining in one in five houses during the rainy season.”

It is not only the island’s health authorities who are making preparations; researchers are also mobilising.

The director of the Processus infectieux en milieu insulaire tropical (infectious processes in tropical island environments — PIMIT) unit, Dr Patrick Mavingui, calls his working environment an “in natura laboratory”.

With biologists, virologists and chemists, the PIMIT unit is both international and multidisciplinary.

“As part of research into Zika, we need to develop diagnostic tools long before a vaccine comes to market,” says Gilles Gadea, one of the thirty researchers on Dr Mavingui’s team.

“Our mixed research team was established as a result of the chikungunya crisis in 2006,” explains the director. There is a high likelihood that Réunion will experience a Zika epidemic at some point, but it also has a unique resource in the biodiversity of its land. Medical biology is one of the priority routes for prevention.

Sixteen plants native to the island have recently been recorded in France’s pharmacopoeia. Some of them have proven anti-viral qualities.

“We are currently carrying out extractions from these Réunion plants in the laboratory. We prefer not to mention them by name, as it is vital to establish dosage and assess toxicity,” says Chaker El Kalamouni, a Lebanese researcher who joined the PIMIT unit following the chikungunya crisis.

“We are testing their effects on the ancestral strain of the Zika virus, discovered in Uganda in 1947. The aim is to apply our results to the epidemic strain from Brazil,” he adds.

The natural medicine project of this university hospital team could be suitable for pregnant women.


International race to develop a vaccine

On the opposite workbench in the same laboratory, Wildriss Viranaicken’s team is developing a vaccine candidate. Here too, the target community is clearly defined.

“Given the current situation, our aim is to enable women to be vaccinated, even at the beginning of their pregnancy,” says the researcher.

Huge challenges lie ahead in this new pharmaceutical race.

And, despite the urgency, populations in emergence zones will have to wait years for a vaccine to become available on the market.

As in the past, it is the United States laboratories that are issuing the most information on their vaccine candidate project. In 2006, the researchers from Réunion were not yet in a position to join the pharmaceutical race against chikungunya.

“The US launched into developing a vaccine for chikungunya. That was ten years ago and it is still not on the market. The testing and quality control stages mean that there is a very long process before launch,” claims Viranaicken.

This time, the Réunion scientists have been involved from the start. This is in response to the official global demand: WHO called on the researchers to work on Zika.

“For vaccines, the landscape is evolving swiftly, and numbers change daily. About 15 companies and research groups have been identified so far, though most have only just started work,” states Dr Marie-Paule Kieny, WHO Assistant Director-General.

The PIMIT unit is not one of the most advanced vaccine candidate projects.

WHO quotes an Indian project and a US project: “a DNA vaccine from the US and an inactivated product from India.”

Even if they are not among the frontrunners, the Réunion chemist knows that his team are off to a good start.

“The PIMIT unit is working in collaboration with a start-up in Montpellier. We are using patented technology to develop our vaccine candidate, so we know we are the only ones who have it. We have also inherited the knowledge of our team leader.”

The team leader at Wildriss Viranaicken is Dr Philippe Desprès. Before joining the PIMIT unit in Réunion, he worked for the Institut Pasteur and was involved in research into a vaccine candidate for dengue fever. His researchers are able to draw on his experience, but need to adapt it to the characteristics of the Zika virus.

A primary characteristic of Zika is that 80 per cent of infections are asymptomatic, which is a double-edged sword.

“We can now use molecular techniques to detect Zika in a variety of biological fluids and products when it is not infectious, i.e. capable of causing a new infection in itself,” explains Dr Desprès.

So Zika can be detectable but silent. Its speed and methods of transmission make the virus unique.

The scientific community is both fascinated and worried by it. “The first mention of sexual transmission of the virus was in a US publication in 2008; the second was in 2013, during the Zika epidemic in French Polynesia.”

On 27 February 2016, the first case of sexual transmission was identified in Paris.

“The tiger mosquito is a vector, as for dengue fever or chikungunya, but in the case of Zika, humans can be amplifying hosts,” explains the team’s director.

“Zika can also be found in urine or saliva. However, urine is virucidal and the virus cannot survive for long in saliva. It is likely that sperm has preservative properties which enable the virus to survive.”

When a virus is under the spotlight, new real-time information emerges on how it interacts with humans. In his 30-year career working on flaviviruses, Dr Desprès has never encountered a sexually transmissible one.

As the Zika virus progresses, there may be more surprises in store.


This article has been translated from French.

This story has been translated from French.