The European Centre for Disease Prevention and Control (ECDC), the HSE and HPSC are advising women who are pregnant or who might become pregnant to make every effort to protect themselves against biting mosquitoes while travelling in areas affected by Zika virus disease. Zika virus infection is a febrile illness caused by Zika virus (ZIKAV). ZIKAV is spread by infected biting Aedes mosquitoes and can be found in a number of countries in the tropics (see here for a map of affected areas).

Zika virus (ZIKAV - genus Flavivirus) is a febrile vectorborne disease. ZIKAV is related to other flaviviral viruses responsible for diseases such as Dengue, Yellow Fever (YF), West Nile virus (WNV) disease, St Louis encephalitis (SLE), Tick-borne encephalitis (TBE) and Japanese encephalitis (JE). Flaviviruses produce disease syndromes with a wide spectrum of severity; WNV, ZIKAV and Dengue tending to produce milder syndromes (often febrile exanthemata occasionally with influenza-like symptoms), to more severe encephalitides (JE, SLE, TE) or systemic infections (Dengue haemorrhagic fever, TF). ZIKAV disease is one of the milder flaviviral diseases, typically presenting with fever, headache and maculopapular rash, followed by conjunctivitis and arthralgia (with as many as 80% of infections being asymptomatic).

ZIKAV’s natural transmission cycle involves principally biting mosquitoes (almost exclusively Aedes spp) and monkeys, with humans as an occasional host.(1) There is some evidence that ZIKAV can be transmitted through direct, human-to-human contact, possibly sexual contact, and can, extremely rarely, exhibit haemorrhagic manifestations.

First identified in 1947 in a Rhesus macaque in the Zika Forest of Uganda, ZIKAV has been progressively identified in humans since the 1960s.  Human ZIKAV infection was restricted initially to central Africa, but by the 1980s had emerged in Southern and Southeast Asia. By the early 2000s, ZIKAV had reached Micronesia, in the eastern Pacific. In the last half dozen years, ZIKAV has moved south, from Micronesia, into Melanesia, and in 2014, emerged in South America - appearing first in Chile. Chikungunya (CHIKV) - an alphavirus borne by Aedes mosquitoes - emerged across the Caribbean and South America in the 24 months prior to ZIKAV.(2)

Currently ZIKAV is to be found in a band between the Tropics, stretching across the centre of Africa and through Southeast Asia and Indonesia (in approximately the same regions as malaria is to be found). Of particular concern is the fact that CHIKV (and its associated Aedes mosquitoes) has been found as far north as Ravenna in north-eastern Italy, and Southern France.(3)

Following introduction into Easter Island in Chile in early 2014, ZIKAV cases began to appear in Brazil in May 2015, and have spread rapidly since then.(4) Colombia reported its first cases in October, and in the last week, cases have been reported in Mexico (in Yucatan), in Paraguay and on certain Caribbean Islands.

Associated Congenital Skull and Cerebral Abnormalities

Authorities in Brazil and French Polynesia who have been monitoring extensive outbreaks of ZIKAV disease in these countries (each consisting of many thousands of ZIKAV cases) have begun - in the last two months - to see the emergence of large numbers of brain and skull abnormalities in new born babies. Currently there are 17 cases of brain abnormality under investigation in French Polynesia and more than 700 cases of microcephaly in north-eastern Brazil. Microcephaly is a congenital condition in which a baby is born with an abnormally small head and it is frequently associated with markedly impaired intellectual development.

Until more information becomes available, HSE and HPSC are advising women who are pregnant or who might become pregnant to be aware of this risk and to make every effort to protect themselves against biting mosquitoes while travelling in areas affected by ZIKAV illness (which corresponds very closely with malarious areas in the world).

Pregnant women (or those who are at risk of pregnancy) should discuss this with their Travel Physician and their Obstetrician (if they are already pregnant and booked in). Pregnant women should bear in mind that different mosquitoes (carrying different diseases) can bite at different times of day. When visiting potentially affected areas, travellers (and especially pregnant women) should enquire which type of mosquitoes are most prevalent locally; Aedes mosquitoes that carry ZIKAV tend to bite in the morning and late afternoon; Anopheles mosquitoes that carry malaria tend to bite at night. If pregnant or at risk of pregnancy they should remember to:

1. Ensure they know when local mosquitos are likely to be biting
2. Avoid areas where mosquitoes are likely to congregate (i.e. stagnant water)
3. Wear appropriate clothing: long-sleeved shirts, long pants, boots and socks
4. Protect their rooms: mosquito bites can be reduced by air conditioning, insect-proof screens
5. Protect their beds: Bed nets and cot nets should be used if rooms are not adequately screened or air conditioned
6. Use insect repellents: CDC and the UK’s Bumps (run by the UK Teratology Information Service) advise that pregnant women can use DEET  as a mosquito repellent, if they ensure to a) use it sparingly and b) wash it off when away from risk of biting mosquitoes, as it is a chemical applied to the skin. The risk to a pregnant woman's unborn baby, certainly from malaria, would outweigh any potential risk from DEET.

Full information on ZIKAV disease is available on the HPSC website. Details of General Practitioners listed with the Travel Medicine Society of Ireland are available on their website. 

Paul McKeown, HPSC