On the 1st February 2016, The World Health Organization declared that the Zika Virus constitutes a public health emergency of international concern, prompted by growing concern that the virus could cause significant birth defects. It is estimated that as many as 4 million people could be infected globally by the end of this year.
What is the Zika Virus?
Zika virus is a member of the virus family Flaviviridae and the genus Flavivirus, related to the dengue, yellow fever and West Nile Virus. It is spread by daytime-active Aedes mosquitoes, such as A. aegypti and A. albopictus. Although it was discovered in the Zika forest in Uganda in 1947 and is common in Africa and Asia, it did not begin spreading widely in the Western Hemisphere until May 2015, when an outbreak occurred in Brazil. Few people here have immune defenses against the virus, so it is spreading rapidly. Millions of people in tropical regions of the Americas may now have been infected. Yet for most, the infection causes no symptoms and leads to no lasting harm. Scientific concern is focused on women who become infected whilst pregnant and those who develop a temporary form of paralysis after exposure to the virus.
How is the Virus Transmitted?
Only female mosquitoes bite people as they require blood in order to lay their eggs. The mosquito feeds on virus-infected blood, which in turn is digested and then enters the circulatory system of the mosquito. Once inside the circulatory system the virus is transported to the salivary glands of the mosquito. When a mosquito bites they first inject saliva as this contains proteins that prevent blood from clotting and it is as a result of injecting infected saliva that a new transmission occurs.
What Areas Are Affected?
Since the 1950s, the Zika Virus it has been known to occur within a narrow equatorial belt from Africa to Asia. The virus spread eastward across the Pacific Ocean between 2013 and 2014 to French Polynesia, New Caledonia, the Cook Islands, and Easter Island, and in 2015 to Mexico, Central America, the Caribbean, and South America, where the Zika outbreak has reached pandemic levels. In January 2016, the U.S. Centers for Disease Control and Prevention (CDC) issued travel guidance on affected countries, including the use of enhanced precautions, and guidelines for pregnant women including considering postponing travel. Other governments or health agencies also issued similar travel warnings while Colombia, the Dominican Republic, Ecuador, El Salvador, and Jamaica advised women to postpone getting pregnant until more is known about the risks.
Symptoms of Infection
Most people infected with the Zika virus won’t even know they have the disease because they won’t have symptoms. Deaths are rare and only one-in-five people infected is thought to develop symptoms. These include mild fever, conjunctivitis, headache, join pain and a rash. The nervous system disorder Guillian-Barre Syndrome, that can cause temporary paralysis in patients has been linked to the infection.
The incubation period for Zika virus disease is not known, but is likely to be a few days to a week. For patients who do develop symptoms, these have been reported as lasting for several days to a week after being bitten by an infected mosquito. People usually don’t get sick enough to go to the hospital, and they very rarely die of Zika virus and this is one reason why so many people many not realise that they have been infected.
Zika virus usually remains in the blood of an infected person for about a week but it can be found longer in some people. As of March 2016, more than a dozen instances of transmission through sex have been reported in four different countries.
There is no vaccine or drug treatment so patients are advised to rest and drink plenty of fluids. Once a person has been infected, he or she is likely to be protected from future infections.
The biggest concern of disease caused by the Zika Virus is the impact it could have on babies developing in the womb and the surge in microcephaly.
Microcephaly and Zika Virus?
Babies who are born with microcephaly have unusually small heads. In roughly 85 percent of cases the infants brain may not have developed properly during pregnancy or may have stopped growing in the first years of life. It usually results in a head circumference of 31.5-32cm of an infant at birth and it currently affects 25,000 children each year in the US alone. The severity varies, but it can be deadly if the brain is so underdeveloped that it cannot regulate the functions vital to life. There is currently no treatment for Microcephaly but children that do survive may develop a range of problems, like developmental delays, intellectual deficits or hearing loss.
As well as being linked to the Zika Virus, Microcephaly can be caused by infections such as rubella, substance abuse during pregnancy or genetic abnormalities.
The possibility that the Zika virus causes microcephaly emerged in October 2015, when doctors in northern Brazil noticed a surge in babies with the condition. Several reports since have now shown that the virus can cross the placenta and attack foetal nerve cells, including some that develop into the brain. Studies to prove whether the virus was to blame for the surge are expected to be reported in June 2016, but the evidence continues to mount. Normally, Microcephaly occurs in about 1 in 5,000 to 1 in 10,000 of all births. Scientists analysing outbreaks of the Zika virus in French Polynesia and Northeast Brazil have estimated that the incidence rose to nearly 1 in 100 births nine months after those outbreaks peaked.
Key Message to Patients
There is no vaccine against the Zika virus and the efforts to develop one have only just begun. Travellers to the affected countries are advised to avoid or minimise mosquito bites by staying in screened or air conditioned rooms or sleeping under mosquito nets; wearing insect repellent at all times; and wearing long pants, long sleeves, shoes and hats.
The best evidence so far suggests that people can spread the virus via mosquitoes for a week after being infected. It is impossible to completely prevent mosquito bites, therefore pregnant women should be advised to avoid going to regions where the virus is being transmitted, and the CDC has advised women thinking of becoming pregnant to consult doctors before going.
There have been reported cases of the virus being spread by sexual transmission with the virus spreading to people who have not visited an affected area or recently travelled. Some countries are advising men who are returning from an affected country to use condoms if their partner is pregnant or there is a risk that they may become pregnant in the future. The virus may persist in semen for up to two weeks and therefore current guidance is that a condom should be used for 28 days after coming home, in the absence of symptoms. If symptoms develop then this guidance extends to 6 months.
Patients should be cautioned on donating blood when returning from an affected area for at least one month after their return home, again adjusted for longer periods if they developed symptoms.