10 Jan 2017
Zika - Risk AssessmentFactors health professionals should consider when advising those travelling to Zika virus affected areas
Zika virus (ZIKV) is a dengue-like virus that is transmitted by Aedes mosquitoes. A small number of cases have also occurred through sexual transmission. The infection often occurs without symptoms but can also cause an illness similar to dengue (and chikungunya, which is also transmitted by Aedes mosquitoes). Illness associated with ZIKV infection is usually mild and short-lived; serious complications and deaths from ZIKV are not common. However, based on a growing body of research, there is now scientific consensus that ZIKV is a cause of microcephaly and other congenital anomalies (also referred to as congenital Zika syndrome) .
There is also scientific consensus that ZIKV is a cause of Guillain-Barré syndrome (GBS). A potential association of ZIKV with GBS was first reported in 2014, during an outbreak in French Polynesia . Since the first locally acquired cases of ZIKV were confirmed in north-east Brazil in May 2015, a number of countries or territories globally have reported increased incidence of GBS and/or laboratory confirmed ZIKV infection in GBS cases. [1, 3-5].
Risk assessment prior to travel
A comprehensive risk assessment should be undertaken for any traveller going to areas with ZIKV transmission.
The following additional factors should be considered for each traveller, and will help health professionals to assess and communicate the potential risks associated with ZIKV infection, and allow the traveller to make as informed a decision as possible regarding their travel plans.
Is the traveller:
- Planning to become pregnant prior to travel, during travel, or during the 8 weeks following return from an area with active ZIKV transmission (6 months if male partner also travelling)
- The male partner of a woman who is pregnant
- The male partner of a woman planning pregnancy or of child bearing age
- Immunosuppressed or do they have any co-morbidities
A. Pregnant travellers and women planning a pregnancy prior to, during or within 6 months after travel
It is recommended that pregnant women should postpone non-essential travel to areas with current active ZIKV transmission designated as ‘high risk’ (see A-Z list) until after pregnancy.
Pregnant women should consider postponing non-essential travel to areas with current active ZIKV transmission designated as ‘moderate risk’ (see A-Z list) until after pregnancy.
In addition it is recommended that women should avoid becoming pregnant while travelling in an area with high or moderate risk of ZIKV transmission, and for a further 8 weeks after leaving an area with high or moderate ZIKV risk, or the date on which unprotected sexual contact with a potentially infectious partner took place (see below for further details if male partner has also travelled to this area).
When advising the traveller who is pregnant or planning a pregnancy, and whose travel to an area with active ZIKV transmission is essential, the traveller should be made aware of the following:
1. Based on a growing body of research, there is now scientific consensus that ZIKV is a cause of microcephaly and other congenital anomalies (also referred to as congenital Zika syndrome) and Guillain-Barré syndrome 
2. It is recommended women should avoid becoming pregnant during travel to an area with high or moderate risk of ZIKV transmission and that on leaving that area, they should avoid becoming pregnant for a further 8 weeks. See advice below if male partner has also travelled to this area.
3. If a woman develops symptoms compatible with ZIKV infection, it is recommended she avoids becoming pregnant for 8 weeks following symptom onset.
4. Pregnant women who have recently travelled in an area reporting active ZIKV transmission in the last 9 months should seek advice from their GP or midwife on their return to the UK, even if they have not been unwell. Further information about when to perform fetal ultrasound scanning, and, if necessary, referral to the local fetal medicine service is available.
ZIKV has been shown to be present in semen  although it is not yet know how long this can persist [7,8]. Cases of sexual transmission are occasionally reported [7, 8]. Therefore effective contraception is advised to prevent pregnancy AND condom (or other barrier method) use during vaginal, anal and oral sex is advised for her partner to reduce the risk of transmission:
- during travel in an area of moderate or high risk of ZIKV transmission and if male partner has travelled, for 6 months following symptom onset orlast possible ZIKV exposure (i.e. date of leaving risk area or unprotected sexual contact with a potentially infectious partner) . This reflects a precautionary approach while further evidence is gathered.
B. Men whose partners are pregnant, planning a pregnancy or of child bearing age
Most cases of ZIKV are acquired via mosquito bites, but sexual transmission of ZIKV is occasionally reported . The virus has been shown to be present in semen, although it is not yet known how long this can persist [7, 8]. In view of this, for male travellers, if your partner is pregnant, condom (or other barrier method) use is advised during vaginal, anal and oral sex during travel and for the duration of the pregnancy. This is a cautious approach until more is known about sexual transmission of ZIKV because of our concern about the link between ZIKV and birth defects.
If your partner of child bearing age or planning pregnancy, effective contraception is advised to prevent pregnancy AND use of barrier methods is advised during vaginal, anal and oral sex to reduce the risk of transmission during travel and:
- for 6 months after your return from an area with moderate or high risk of ZIKV transmission .
- for 6 months following the start of symptoms if you have had a clinical illness compatible with ZIKV infection or had a laboratory confirmed ZIKV infection.
C. Preventing sexual transmission in other travellers
Most cases of ZIKV are acquired via mosquito bites, but cases of sexual transmission of ZIKV are occasionally reported . The vast majority of cases have involved men who experienced typical ZIKV symptoms at or before the estimated time of sexual transmission to their female partners .
There is only one published report of transmission by a man who had travelled to an area with active ZIKV transmission but never experienced ZIKV symptoms. Transmission of ZIKV from a female to a male sexual partner, and from a male to a male sexual partner has also been reported but these appear to be very rare events .
ZIKV has been shown to be present in semen, although it is not yet known how long this can persist, or whether the duration of virus persistence is longer in men who experience ZIKV symptoms . There have been reports of Zika virus RNA being detected (by PCR) in the female genital tract but it is not yet known how long this can persist .
Transmission of ZIKV infection between sexual partners can be prevented by using barrier methods during vaginal, anal and oral sex. The consistent use of barrier methods during sexual contact should begin while travelling to high or moderate ZIKV risk countries and continue to be used for the period of time specified below, depending on gender.
Male with or without symptoms
- Comdoms or other barrier methods should be used for 6 months following return from an area with high or moderate ZIKV risk or after last possible ZIKV exposure (*see footnote) .
See specific guidance above if the female sexual partner is pregnant, planning a pregnancy or of child-bearing age.
Female with or without symptoms
- Condoms or other barrier methods should be used for 8 weeks following return from an area with high or moderate ZIKV risk or after last possible ZIKV exposure (*see footnote).
See specific guidance above if the patient is pregnant, planning a pregnancy or of child-bearing age.
*Footnote: Last possible ZIKV exposure is defined as the date of leaving an area with high or moderate ZIKV risk, or the date on which unprotected sexual contact with a potentially infectious partner took place.
This is a precaution and may be revised as more information becomes available. Individuals with further concerns regarding potential sexual transmission of Zika virus and options for contraception should contact their GP for advice. Further information is also available from Public Health England.
D. Travellers with co-morbidities, immunosuppression or at extremes of age
In the travel health consultation, these travellers should be offered advice regarding the likely impact of any travel related infection on them. More information on ZIKV infection and immunosuppression is available from Public Health England.
Destination related factors
Countries, territories or areas with active or past ZIKV transmission have been classified into four categories based on the current and potential epidemiological situation. These categories ensure travel advice is appropriate and proportionate to the defined Zika virus transmission risk, see Table 1 below.
Maps showing Public Health England's Zika virus risk categories
In addition, a map of countries or territories that have reported active Zika virus transmission in the past nine months has been provided by ECDC to assist healthcare professionals advising returned travellers who are pregnant.
Countries, territories or areas reporting current or previous locally acquired Zika virus cases are now grouped in to four risk categories shown in Table 1 below:
Table 1: Risk categories
|High risk (a)||All countries/territories/areas that have reported active and increasing or widespread Zika virus transmission in the past 3 months or|
|High risk (b)||Countries/territories/areas, within the main outbreak regions (1), that have reported active but sporadic Zika virus transmission in the past 3 months|
|Moderate risk||Countries/territories/areas outside of the main outbreak regions (1) reporting active but sporadic Zika virus transmission in the past 6 months|
|Low risk||Countries/territories/areas with evidence of recent Zika virus transmission since 2007 but no cases have been recorded in the past 6 months|
|Very low risk||Countries/territories/areas for which there is historical evidence of Zika virus transmission (pre-2007) (2)|
Currently the main outbreak regions refer to South and Central America, tthe Caribbean, Oceania (Melanesia, Micronesia and Polynesia only) and South East Asia.
Prior to 2007, Zika virus was not known to be responsible for widespread outbreaks.
Information about ZIKV transmission in specific countries along with the specific recommendations for travellers can be found on our Country Information pages, listed in the Other Risks and Outbreaks tab.
When trying to ascertain the risk of ZIKV infection at any given destination, the following should also be considered:
1. The current outbreak situation in the Americas and the Caribbean is evolving and it is anticipated that ZIKV is likely to spread through the Americas in the coming weeks and months.
2. Areas of active transmission of ZIKV will vary within a specific country. Where specific information exists this will be provided.
3. In most cases, it will not be possible to identify which specific areas are experiencing active transmission in a particular country. In these situations it is prudent to assume that the whole country is affected. However, the following factors should be considered and should inform your risk assessment:
- Areas may have sporadic transmission; that is no more than 10 locally acquired cases have been reported in a single area within this time period
- Areas may have increasing or widespread transmission; this is the case if-
– more than 10 locally acquired cases of ZIKV are reported in a single area, or
– at least two separate areas report locally acquired cases of ZIKV, or
– ZIKV transmission is ongoing in an area for more than three months
- Countries and territories are reviewed on a regular basis and will move to a new category (high, moderate, low) as appropriate.
1. The mosquito vector (tropical Aedes species) that transmits ZIKV bites predominantly during daylight hours.
2. These mosquito species will bite both outdoors and indoors and throughout the day (and night) and is most active during mid-morning and late afternoon to dusk.
3. Aedes spp mosquitoes are adapted to human habitation and commonly live in urban environments, laying their eggs in collections of water in the domestic environment (e.g. buckets, vases, tyres, flower pots) .
4. Tropical Aedes mosquitoes:
- Favour high humidity and warmth.
- Are unlikely to be found at altitudes ≥ 2,000m (this will be relevant for some areas in Latin America where some cities/travel destinations may be at high altitude).
- Are likely to be more abundant during seasonal rainfall. There may be regional variations in seasonal rainfall. Season alone however should not be relied upon as an indicator of risk.
5. Risk of exposure may be reduced in areas with good vector control programmes for Aedes infestation.
Traveller activity and behaviour factors
A traveller’s risk will also be affected by their behaviour and activities:
1. A traveller who is aware of, and is scrupulous regarding bite avoidance measures, may reduce the risk of mosquito bites and infection.
2. In general, the risk of exposure to the ZIKV will increase with the length of stay.
Travellers visiting areas with active ZIKV transmission or surrounding areas should avoid mosquito bites, monitor news updates and obtain comprehensive travel health insurance. A number of useful quick links can be found below:
- Latest news on the current outbreak (including advice for pregnant women and those planning to become pregnant)
- Country information
- General information on ZIKV
- Algorithm – Zika advice for pregnant women, those planning pregnancy and their partners
- Advice on insect bite avoidance measures
- Advice on travelling when pregnant
- Algorithm for assessing pregnant women with a history of travel to areas with active ZIKV
- ZIKV infection, guidance for primary care
- Mosquito bite avoidance leaflet
- Foreign and Commonwealth Office guidance on foreign travel insurance
First Published : 10 Jan 2017
Last Updated :  10 Jan 2017
- World Health Organization, Zika situation report. 14 April 2016. [Accessed 15 April 2016]
- European Centre for Disease Prevention and Control. Zika virus outbreak French Polynesia. 14 February 2014. [Accessed 15 April 2016]
- European Centres for Disease Prevention and Control. Rapid Risk Assessment – Zika virus disease epidemic: potential association with microcephaly and Guillain- Barré. Fifth update 11 April 2016 [Accessed 15 April 2016]
- World Health Organization. Zika virus microcephaly and Guillan Barré syndrome: Situation Report. 7 April 2016. [Accessed 15 April 2016]
- Public Health England. Zika virus and Guillain-Barré syndrome. 9 March 2016 [Accessed 15 April 2016]
- Atkinson B, Hearn P, Afrough B, Lumley S, Carter D, Aarons EJ, et al. Detection of Zika virus in semen [letter]. Emerg Infect Dis. 2016 May [Accessed 15 April 2016]
- Foy BD, Kobylinski KC, Chilson Foy JL, Blitvich BJ, Travassos da Rosa A, Haddow AD, et al. Probable non-vector-borne transmission of Zika virus, Colorado, USA. Emerg Infect Dis. 2011 May; 17(5):880-2 [Accessed 15 April 2016]
- Public Health England. Zika virus: prevention infection by sexual transmission 23 November 2016 [Accessed 23 November 2016]
- Service M. Medical Entomology for students. Fifth edn. Cambridge [Accessed 15 April 2016]
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