Zika virus

Background

Zika virus was first detected in Uganda almost 70 years ago and until last year was considered of little concern. The infection spread to South East Asia, the Pacific Ocean islands and in 2015, to Latin America and the Caribbean.
Zika virus is spread from person to person primarily by Aedes mosquitoes that bite during the day, inside or close to homes and other inhabited buildings.
Direct person to person transmission has also been reported in several countries via sexual transmission and blood transfusions.
There is no vaccine or medication to prevent Zika infection and experience from related diseases suggests development of a vaccine could take several years.
Zika infections are preventable by avoiding mosquito bites (see below) and using condoms to prevent sexual transmission.
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Zika virus disease

Most infected individuals will not know they had an infection or will experience only a mild illness. The most common symptoms: fever, headache, skin rash, joint pains, and conjunctivitis (red eyes) usually only last from 3 days to a week. Severe disease requiring hospitalization is very rare.
In adults, Guillain-Barré syndrome, an autoimmune condition that affects the nerves, can be another complication of Zika virus infection.
There is no specific treatment or vaccination to treat Zika virus infection. Management consists of maintaining fluid intake and taking paracetamol for fever or pain.
Patients with Zika infections should be protected from mosquito bites to avoid transmitting the infection to others and should abstain from unprotected sex (or attempting to conceive a baby) for eight weeks (WHO, May 30, 2016).
The most concerning feature of Zika virus infection is its effect in pregnancy (see below).

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Zika and pregnancy

Zika virus infection has now been linked to the development of adverse pregnancy and poor foetal outcomes, including foetal death, placental insufficiency, foetal growth restriction, and injury to the nervous system in the unborn baby.
The number of cases of microcephaly appears to have increased in countries particularly Brazil, at the same time as Zika infection has become more common.
Microcephaly means ‘small head’ and is associated with brain growth restriction, reduced life expectancy for the child and neurodevelopmental delay. Babies who are born with microcephaly will require extra and specialised care.
Pregnant women (during all trimesters) therefore should try to avoid travel to areas where Zika is present. If travel is absolutely critical, every effort possible should be taken to avoid mosquito bites (see below).
Women wishing to become pregnant should try to defer this until after travel is completed and should certainly discuss this with their healthcare provider.
Women who may have been exposed to Zika virus during pregnancy are advised to consult their healthcare provider and may need closer monitoring during the remainder of their pregnancy.
There is some evidence that the virus is present in breast milk of mothers with recent infection. There is no evidence to date the breast milk is infectious to the baby.

How Zika virus is transmitted

Aedes mosquitoes that spread Zika virus bite mostly during the daytime, typically soon after sunrise or in late afternoon, both indoors and outdoors. Aedes aegypti is a common mosquito in warm climates worldwide and appears to be the most important vector
Mosquitoes species that carry Zika can also transmit yellow fever, dengue and chikungunya viruses.
Protecting yourself from all of these viruses involves the same measures.
It is now clear that Zika virus can reach high levels in semen and can lead to sexual transmission. Although this route is still a relatively minor route of transmision compared to insect bites, sexual transmission does pose considerable public health problems. .

Preventing Zika (and other arbovirus) infections

There are no currently available vaccines or preventative medicines for the mosquito-born virus called chikungunya. Also, a dengue vaccine has been recently licensed in Mexico and Brazil, but it is only available from private practitioners in those countries (not available in the UK). The same vaccine will be routinely used in the Philippines. Both dengue and chikungunya infections can have serious symptoms in children and adults. There is no vaccine for Zika although many companies and research labs across the world have made this a priority.

Insect repellents containing DEET (50%) should be applied to skin or clothing of children (aged 2 months or more) and adults to minimise mosquito bites safely. Insect repellents should be used exactly as directed by the manufacturer. Note that stated re-application times are often the maximum effective duration, and repellent should be reapplied after heavy exertion, swimming or washing.
Stocks of effective repellents are low in some areas of Brazil and prices have increased. Carry with you sufficient supplies to last for your entire journey.
If sleeping during the day (infants or adults), use an insecticide-treated bed net.
Cover your skin as much as possible by wearing long-sleeved shirts trousers and socks, whether indoors and outdoors.
When indoors, use window/door screens, air conditioning or fans to prevent or inhibit mosquitoes from entering.
You can reduce numbers of mosquitoes breeding at your home or room by eliminating all standing water from flowerpots, buckets, rubbish etc. If you cannot drain the container (e.g. drinking water), it should be covered tightly to prevent mosquitoes entering.

What are the important areas for research?

Epidemiological assessment of the links between Zika infection during pregnancy and foetal abnormalities and understanding the mechanisms causing these neurological complications.
Improved surveillance of outcomes for women who contract Zika virus infection during or just before pregnancy, to establish if there are any other adverse outcomes either for the mother or for her baby.
Development of more sensitive and specific diagnostic tests for Zika. Fever symptoms only occur in 20% of cases and are easily confused with other diseases especially mild dengue. Rapid accurate diagnosis is key to investigating the epidemiology and clinical patterns of the disease.
Proving if mothers previously infected with Zika virus be protected for future pregnancies?
Better knowledge of key factors determining transmission dynamics including:
- What mosquito species can transmit Zika and how serious a threat is each one (i.e. what is their potential vectorial capacity)?
- Are there multiple strains of Zika, how infective are they, what is impact of coinfection?
- What is impact of coinfection with chikungunya and/or dengue, particularly on the development of neurological complications in adults like Guillian-Barré syndrome?
What are the most effective methods for controlling populations of the Aedes mosquito vectors?

A special symposium on the ongoing Zika virus outbreak in South America took place at LSTM on 12 February 2016 with over 130 in attendance comprising of LSTM staff, postgraduate students and students undertaking the Diploma and Tropical Medicine and Hygiene (DTM&H) course.