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Zika virus – WHO warns of potential 4 million cases across the Americas in next 12 months
The World Health Organization (WHO) has warned that an outbreak of the Zika virus, currently circulating in Central and South America, may spread across North America, infecting an estimated 3-4 million people in total over the next 12 months.
WHO Director-General, Dr Margaret Chan, is to convene an International Health Regulations Committee on the Zika virus and the possibility of a link between microcephaly and other reported neurological effects on Monday, February 1.
While a causal link between the Zika virus and the increase in microcephaly and nervous system disorders has not yet been established, it has been described as “strongly suspected”. Dr Chan describes the virus as having moved from posing a “mild threat” to one of “alarming proportions”.
The WHO says since the first case in Brazil in May 2015, the virus has spread within the country and to 22 other countries and territories where it has been associated with what the WHO describes as a “steep increase” in babies born with microcephaly, where babies heads do not develop normally in the womb and are abnormally small, and Guillain-Barré syndrome, where the immune system attacks the nervous system.
As a precautionary measure, Public Health England has also issued advice to pregnant women to avoid travelling to areas experiencing an outbreak.
The Zika virus is transmitted by infected mosquitoes, with the first cases in humans identified in 1952 in Uganda and Tanzania and outbreaks have since been recorded in Africa, the America’s, Asia and the Pacific. Because the symptoms exhibited are usually mild and very short-lived, until relatively recently the virus has posed no significant threat to human health.
However, following widespread outbreaks in French Polynesia in 2013 and Brazil in 2015, health authorities first began to observe an increase in babies born with microcephaly –– often characterised by cognitive delay, difficulties with speech and movement and other problems.
Carried by two specific types of mosquito – Aedes aegypti and Aedes Albopictus, with their distinctive white and black markings, are the same genus responsible for the transmission of dengue, West Nile and Yellow Fever. While the former type, said to be the primary carrier, thrives in tropical and subtropical regions, the latter type has been known to survive in much cooler regions, with the ability to hibernate through cold snaps. While neither type is capable of flying long distances, there is a possibility that the insects may be inadvertently transported by humans, via vehicle or other means, to other destinations where - if able to survive – it may begin reproducing.
The WHO says it is supporting countries to control the virus by helping to eliminate mosquito populations, strengthening surveillance, increasing laboratory testing capacity and supporting research into the possible complications.
The Aedes mosquito is said to prefer an urban habitat, where, unlike other mosquitoes, they actively feed during the day. Prevention and control methods in situ include the removal of breeding sites – usually bodies of still, stagnant water - the use of insecticides and the application of physical barriers, such as mosquito nets, screens on doors and windows and by keeping skin covered with appropriate clothing.
Professor Jonathan Ball, Professor of Molecular Virology, at the University of Nottingham, says: “The numbers likely to be infected by Zika in the current Americas outbreak are immense, but not so surprising. The virus has been unleashed in an area where its insect vector is widespread and the human population has never been exposed in the past – they don’t have any immunity and so the mosquito can pass the virus from person to person unhindered.
“Eventually the outbreak is likely to burn itself out as people become exposed then immune. But it is unlikely to disappear completely. In future it will probably survive by causing sporadic outbreaks and by infecting people who haven’t been exposed to the virus, for example children. An infection of children wouldn’t be a bad thing as it would probably mean that they are immune to later infection, particularly when they are at a child-bearing age. So by a natural process we would hope that the really serious effects that Zika might be having on unborn children will dwindle in those areas where the virus does become endemic.
“But these are possible scenarios but until we know how the virus behaves, in this and in previous outbreaks, and where it is endemic, we won’t be able to make predictions with any degree of certainty.”
What are the symptoms of the Zika virus?
It’s important to remember that, although several cases have been diagnosed in the UK, the virus is not able to pass from person to person and those that have been diagnosed here are said to have recently returned from regions where there is currently an outbreak.
There is no direct treatment, however, the virus is usually relatively mild and some people do not notice any symptoms at all. For those that do, the following are commonly reported symptoms:
- Low-grade fever
- Joint pain, possibly accompanied by swelling of the joints in the hands and feet
- Conjunctivitis, pain in the eyes
- Muscle pain
- Malaise, or lethargy
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