Only a month into the new year and a virus sweeping across the Americas has been described as “a new global threat for 2016”.
The Zika virus is spread by the same species of mosquito that carries dengue fever. It has been identified in at least 24 countries, affecting hundreds of thousands of people.
Last Thursday, the World Health Organisation (WHO) said it was “deeply concerned” about the situation because the virus was “spreading explosively”.
What is most shocking are those who are the worst affected by the virus: pregnant women and the babies they give birth to.
Otherwise, Zika poses little threat to those who are not pregnant. Only about one in five people who are infected will feel ill. Those who do fall sick will have a rash, fever, joint pain and maybe conjunctivitis. The symptoms usually clear up within a week, making it difficult to know for certain whether someone has been infected or not.
Brazil reported its first case last May, and at the same time saw a 20-fold increase in the incidence of a childhood condition known as microcephaly from the previous year.
Microcephaly is a neurological condition that stops the brain from developing properly in the womb or after birth. As a result, children afflicted by microcephaly have heads that are noticeably smaller than others of the same age.
Although the connection between the Zika virus and microcephaly is still to be confirmed, most public health authorities and experts agree that a direct link is highly probable.
The government of El Salvador has taken the threat so seriously that it is urging women to avoid getting pregnant until 2018.
Columbia is also warning its women not to get pregnant for now, and Britain is advising pregnant women to consider delaying trips to affected areas.
Zika virus was first identified in a rhesus monkey in Uganda in 1947 but only sporadically appeared in human populations.
In 2007, an outbreak was documented in the Pacific islands, in the Federated States of Micronesia. Between 2013 and 2014, four additional islands declared large outbreaks.
A January editorial in The Lancet, a medical journal, described the Zika virus as "a new global threat for 2016".
“With an estimated 440,000 to 1,300,000 cases currently in Brazil alone, the Zika virus could be following in the footsteps of dengue and chikungunya, which is also transmitted by the Aedes aegypti mosquito,” it said. “Given that an outbreak anywhere is potentially a threat everywhere, now is the time to step up all efforts to prevent, detect and respond to the Zika virus.”
No large outbreaks were reported by the WHO before 2007, so there were few opportunities to study how the virus operates.
An outbreak in French Polynesia in 2013, in the South Pacific Ocean, led health officials to investigate a connection with Guillain-Barre syndrome, which occurs when the body’s immune system begins to attack the nervous system.
But last year’s outbreak in Brazil raised questions for the first time about the connection of the Zika virus to microcephaly.
The virus is now spreading fast.
Dr Margaret Chan, director general of the WHO, said last Thursday that “the level of alarm is extremely high”.
Although the link between the Zika virus and birth malformations had not been strongly established, she said, the recent suspicions have changed the risk profile from a mild threat to “one of alarming proportions”.
Also on last Thursday, the WHO set up an International Health Regulations Emergency Committee to investigate the increase in neurological disorders and neonatal malformations. It will comprise the world’s best and most experienced experts in infectious diseases.
The committee will convene today in Geneva to determine whether the Zika virus constitutes a Public Health Emergency of International Concern, which could lead to travel restrictions.
For Brazil, such a move would be potentially disastrous. This summer, Rio de Janeiro is to host the Olympics and Paralympics.
Troublingly, some scientists now think that the virus arrived in Brazil via an infected football fan from Polynesia during the Fifa World Cup in 2014.
For a travel ban to be imposed, a situation must pose a public health risk to other states through international spread of the disease and be “serious, unusual or unexpected”.
The WHO was heavily criticised during the recent Ebola epidemic in West Africa for waiting too long to declare a public health emergency of international concern, with some suggesting that international aid and action came too late to save more lives because of the WHO’s delay.
Dr Chan said the lack of immunity in the population of the newly-affected areas was one of the biggest concerns for the WHO.
The population of the Americas, where the virus is rapidly spreading, lack immunity against the virus because they had not been exposed to it.
But an even more worrisome factor is the ability of the Aedes mosquito to spread.
The Pan American Health Organisation, the local branch of the WHO, warned that the species was already present in all countries of the region, except Canada and continental Chile.
The WHO also warned that the El Nino weather pattern would create more breeding sites for the insect in areas already at risk.
Dr Chan said she would be asking the emergency committee to assess the level of international concern and look at what measures should to be taken to help the affected countries.
The National Institute of Allergy and Infectious Diseases (NIAID) in the United States has informed US researchers that grants are now available for studies of the Zika virus.
Areas of high priority include basic research to understand how the virus operates, studies into how best to use animals to examine trial vaccines, and development of rapid diagnostic tests for the virus.
As with the Ebola outbreak in West Africa in 2014, health officials and governments may wish that the hunt for a vaccine had begun sooner.
But writing in the New England Journal of Medicine last month, NIAID director Dr Anthony Fauci said a vaccine would not necessarily signal an end to the devastation caused by the Zika virus and that the emergence of the virus in the Western Hemisphere was only the most recent of four unexpected arrivals of viral diseases.
It follows dengue, the West Nile virus and chikungunya, which was found for the first time in the Americas on the Caribbean islands in late 2013 after only previously being seen elsewhere.
Dr Fauci wrote: “The [Zika] virus circulated predominantly in wild primates and arboreal mosquitoes such as Aedes Africans and rarely caused ‘spillover’ infections in humans, even in highly enzootic areas. Its current pandemic re-emergence is, therefore, truly remarkable.”
These arboviruses, as they are known scientifically, developed when North African villagers began storing water in mosquitoes’ dwellings. Aedes aegypti mosquitoes laid eggs in water-carrying vessels and as adults, fed on humans, enabling the viruses to adapt to infect humans.
“The possibility that Zika may yet adapt to transmission by Aedes albopictus, a much more widely distributed mosquito found in at least 32 states in the United States, is cause for concern,” Dr Fauci wrote.
He also voiced concern about finding a possible Zika virus, saying epidemics appear sporadically and unpredictably, so “pre-emptively vaccinating large populations in anticipation of outbreaks may be prohibitively expensive and not cost-effective, yet vaccine stockpiling followed by rapid deployment may be too slow to counter sudden explosive epidemics”.
The WHO committee is expected to release its findings on Monday.
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A genetic way to kill mosquitoes
The Aedes aegypti mosquito is more than just a pest. Each year it infects hundreds of millions of people with dengue fever, yellow fever virus, chikungunya virus and Zika virus.
Only the female mosquitoes suck the blood of humans and animals because they need protein to develop their eggs.
As well as spraying the nesting areas of mosquitoes with pesticide, scientists have developed another method to reduce their numbers. It has been hailed as the solution to the Zika virus epidemic.
Oxitec, a British biotech company, has genetically modified the species to suppress their reproduction. Male mosquitoes that were modified with a gene that prevents the offspring from surviving have been released into general populations to mate with female mosquitoes. The resulting offspring die before they are mature enough to bite or mate.
The gene – OX513A – is then “switched off” in the laboratories to allow scientists to produce more adult mosquitoes to use in the project.
Under a year-long study in a suburb of Bahia, Brazil, a series of male mosquitos with the OX513A gene were released, They helped to reduce the local population of the species by 90 per cent.
The scientists noted: “The observed level of suppression would likely be sufficient to prevent dengue epidemic in the locally tested and other areas with similar or lower transmission”.
Oxitec is building a mosquito production facility in Brazil, which it says will have the capacity to protect more than 300,000 people.
