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Zika virus infection is generally a non-severe febrile viral illness transmitted by mosquitoes. Zika virus infection should be considered in people who have recently travelled overseas.
Scientific evidence from outbreaks of Zika virus show that a Zika virus infection in a pregnant woman can be transmitted to the fetus, and can cause certain congenital abnormalities (including microcephaly). Further studies are required to understand the degree of risk of an adverse outcome occurring and the factors that influence this risk.
Specific travel precautions are recommended for pregnant women or women planning pregnancy.
Summary of recommendations
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- Zika virus infection should be considered in patients with acute fever, rash, arthralgia or conjunctivitis, who have travelled in the two weeks prior to onset of illness to countries with current or recent local transmission of Zika virus; refer to the Department of Health webpage for the current country list.
- All travellers should take steps to avoid mosquito bites in order to prevent Zika virus infection and other mosquito-borne diseases such as dengue, malaria and chikungunya.
- All travellers are advised to avoid unprotected sex (vaginal, oral, or anal) while travelling in a country affected by Zika virus.
- Pregnant women are advised to defer travel to any country with current or recent local Zika virus transmission.
- Pregnant women who do decide to travel to one of these countries are advised to consult with a doctor first and strictly follow mosquito bite prevention measures during their trip.
- Women trying to become pregnant are advised to defer travel to a Zika affected country, or to defer pregnancy for at least eight (8) weeks after return. If their partner has also travelled, a longer delay may apply. They are advised to consult with a doctor before travelling and strictly follow mosquito bite prevention measures.
- Women who have returned from a country with current or recent local Zika virus transmission and who are pregnant are advised to consult a doctor and be evaluated. Please refer to Interim recommendations for assessment of pregnant women returning from Zika virus-affected areas for advice
- Men who have returned from a country with current or recent local Zika virus transmission are advised to avoid unprotected sex (vaginal, oral, or anal) for at least 8 weeks after their return. If they have a partner who is pregnant or planning pregnancy they are advised to consult a doctor to discuss recommendations for preventing sexual transmission as longer time periods may apply, please refer to Interim recommendations for reducing the risk of sexual transmission of Zika virus Information for GP’s on Zika virus Sexual Transmission.
- Zika virus infection is notifiable in Australia as a flavivirus (unspecified) infection and should be notified to state and territory health departments.
- In North Queensland and parts of Central or Southwest Queensland where suitable mosquito vectors are present, clinicians should immediately report clinically suspected cases of Zika virus infection to local public health units, as they do for suspected cases of dengue. Public health Authorities will take action to mitigate the risk of local transmission.
- Testing should be offered to all symptomatic travellers, all pregnant women who have travelled to a Zika-affected country during or just prior to the pregnancy, and to asymptomatic men who have partners who are pregnant or are planning a pregnancy and are unable to avoid unprotected sex for the recommended time periods. Please talk with a pathologist to ensure correct testing is ordered and interpreted.
About Zika virus
Zika virus is a flavivirus, closely related to dengue. It is transmitted to humans primarily through the bite of certain infected Aedes species mosquitoes. Aedes aegypti mosquitoes are commonly found in tropical and sub-tropical regions around the world including North Queensland and some areas in Central and Southwest Queensland. Another similar mosquito, Aedes albopictus, also has the potential to transmit Zika virus, but in Australia is only found in the Torres Strait. These mosquito vectors typically breed in domestic water-holding containers; they are daytime biters (including dawn and dusk) and feed both indoors and outdoors near dwellings.
Outbreaks of Zika virus have previously been reported in tropical Africa, Southeast Asia, and the Pacific Islands1. In 2015, Zika virus emerged in South America with widespread outbreaks reported initially in Brazil and Columbia2,3, with spread to many countries in South and Central America and the Caribbean.
Symptoms of Zika virus infection
Approximately one person in five who becomes infected with Zika is likely to have symptoms. For cases with a clinical illness, symptoms may include one or more of:
- Low-grade fever
- Cutaneous maculopapular rash
- Arthralgia, notably of small joints of hands and feet, with possible swollen joints
- Headache, retro-ocular headaches
- Post-infection fatigue.
More rarely observed symptoms include digestive problems (abdominal pain, diarrhoea, and constipation), mucous membrane ulcerations (aphthae), and pruritus.
Zika virus infection generally causes a non-severe disease. Exceptions are the potential to cause congenital abnormalities of the fetus in pregnant women, and the chance of Guillain-Barré Syndrome (GBS), which are discussed below. As Zika virus infection may cause a rash that could be confused with other diseases such as measles or dengue, these more serious diseases need to be ruled out.
The incubation period is typically 3–12 days. There is no specific therapy for Zika virus infection and acute symptoms typically resolve within 4-7 days.
Association with Guillain-Barré Syndrome (GBS)
Based on a growing body of research, there is a strong scientific consensus that Zika virus infection is a cause of Guillain-Barré Syndrome (GBS)5-8.
In French Polynesia, after a local Zika virus outbreak in 2013 and 2014, an increase in autoimmune and neurological diseases (including GBS) was observed1. Further reports and studies have also noted this temporal association. The simultaneous circulation of dengue serotype 1 and 3 viruses may also play a role2,3. Increased numbers of cases of GBS are also being reported from Colombia, Venezuela, Brazil, El Salvador and Suriname4. Some of these cases have a history of symptoms consistent with Zika virus infection (with or without laboratory confirmation), while others do not.
In French Polynesia, all 42 GBS cases identified during the 2013 – 2014 Zika virus outbreak tested positive for Zika virus infection5, and 56% of controls were infected with Zika virus6.
The cause of the increase in GBS incidence observed in Brazil, Colombia, El Salvador, Venezuela and Suriname is not fully explained, and dengue, chikungunya and Zika virus have all been circulating simultaneously in the Americas. In some countries, there have been confirmed Zika virus infections in some of the GBS cases, but not in others.
It is to be noted that GBS is a known complication of a number of infectious diseases, including Campylobacter spp., influenza virus, Epstein-Barr Virus, HIV and Mycoplasma pneumoniae. In addition, GBS can occur following surgery or in those with Hodgkin’s lymphoma. In rare cases it can be life-threatening in the absence of appropriate care.
In French Polynesia, after a local Zika virus outbreak in 2013 and 2014, an increase in autoimmune and neurological diseases (including GBS) was observed4,5
Zika virus infection is transmitted to humans primarily though the bite of infective Aedes mosquitoes, most commonly Aedes aegypti. This is the most important mode of transmission.
To date, there are no reports of infants becoming infected through breastfeeding. The World Health Organization recommends breastfeeding continues, with benefits for the infant and mother outweighing any potential risk of Zika virus transmission through breast milk9.
Multiple instances of probable or confirmed sexual transmission have now been reported, and to date, almost all have involved a symptomatic man transmitting the8,9,10,11Zika virus to a woman. From these cases, it is known that the sexual transmission can occur before, during or after symptoms. It is not known if men with Zika virus infection who never develop symptoms can transmit it through sexual activity although there has been one case of likely sexual transmission from an asymptomatic male10. It is also not known if a woman can transmit Zika virus sexually. Current recommendations are cautious, as evidence is still emerging.
There is one (1) known instance of male-to-male sexual transmission11,12,13,14,15,16. Zika virus RNA has also been found in the semen of one (1) case up to 62 days following infection17.
Please refer to the CDC website for further details.
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Zika virus and pregnancy
There is strong scientific consensus that Pregnant women who become infected with Zika virus can transmit the infection to their unborn babies, with potentially serious consequences18,19. Reports from several countries, most notably Brazil, where Zika virus outbreaks have occurred indicate that there has been a coincident increase in cases of congenital abnormalities, some of which were severe, and include microcephaly20,21. Based on current evidence, the risk of congenital abnormalities appears to relate to all trimesters of pregnancy20,22. Additional research is necessary and ongoing, to determine the likelihood and spectrum of adverse fetal outcomes associated with Zika virus infection.
Women who are pregnant (in any trimester) or who plan to become pregnant are advised to defer travel to any country with current or recent local Zika virus transmission (refer to the Department of Health webpage). If women do decide to travel, they are advised to talk to their doctor first and strictly follow mosquito bite prevention measures.
Women who were pregnant during travel to countries with current or recent local Zika virus transmission current or recent local Zika virus transmission are advised to seek advice from their health care provider. Testing for Zika virus is recommended in these women. Follow up with an obstetric specialist is recommended if Zika virus infection is confirmed. It is not possible to quantify the risk of harm that maternal Zika virus infection may pose to the fetus.
For guidance on assessing pregnant women returning from countries with current or recent local Zika virus transmission Zika virus affected countries please refer to the Interim recommendations for assessment of pregnant women returning from Zika virus-affected areas.
Further information on management of a pregnant woman who has had a positive Zika test is available in the RANZCOG guideline Care of women with confirmed Zika virus infection during pregnancy in Australia.
Non-pregnant women traveling to a country with current or recent local Zika virus transmission should avoid pregnancy for at least eight (8) weeks following the last day in the Zika virus-affected country.
All non-pregnant women (whether at risk of or planning pregnancy or using a reliable form of contraception) should avoid unprotected sex with an asymptomatic partner, who has travelled to a country affected with Zika virus for at least eight (8) weeks following the last day in an affected country.
All non-pregnant women should avoid unprotected sex for six (6) months with a partner, who has travelled to a country affected with Zika virus and has a confirmed Zika virus infection.
If the partner of a woman who is pregnant or planning pregnancy travels to a Zika affected country, please see the recommendations on sexual transmission.
It should be noted that a range of communicable diseases pose particular risks for pregnant women (such as malaria) and Zika virus is only one consideration.
Info for GP’s on sexual transmission and Table on travel/preg/sexual transmission
No vaccine is available for Zika.
All travellers are advised to take the following mosquito bite prevention measures when travelling to countries with current or recent local transmission of Zika virus or wherever mosquito borne diseases are present. These precautions are necessary in the daytime as well as night time.
- Cover as much exposed skin as possible, including wearing light coloured long-sleeved shirts and long pants.
- Use insect repellents, per manufacturer’s instructions.
- The most effective mosquito repellents contain Diethyl Toluamide (DEET) or picaridin. Repellents containing oil of lemon eucalyptus (OLE) (also known as Extract of Lemon Eucalyptus) or para menthane diol (PMD) also provide adequate protection.
- Note that Insect repellents containing DEET or picaridin, are safe for pregnant and breastfeeding women and children older than 2 months when used according to the product label.
- If using both sunscreen and insect repellent, apply the sunscreen first and then the repellent.
- Use insecticide-treated (such as permethrin) clothing and gear (such as boots, pants, socks, and tents).
- Stay and sleep in screened-in or air-conditioned rooms
- Use bed nets as necessary
Medical advice should be sought, as soon as practicable, if unwell with a high fever during or soon after travel.
On return from a country with current or recent local transmission of Zika virus, people who live in or travel to areas of Australia where dengue outbreaks can occur should avoid mosquito-bites for 4 weeks following their return by strictly following mosquito bite prevention measures (refer to section “Mosquito bites” above). This is to help prevent spread from a traveller to the local mosquito population.
Interim recommendations for reducing the risk of sexual transmission of Zika virus To avoid transmitting Zika virus to sexual partners (male or female), all males who have travelled to a country with current or recent local Zika virus transmission and remain asymptomatic should for at least eight (8) weeks abstain from sexual activity (vaginal, anal, or oral), or consistently use condoms. Do not donate sperm during this time. All males with a confirmed Zika virus infection should avoid unprotected sex and sperm donation for at least six (6) months from the time of diagnosis.
If their partner is pregnant, unprotected sex should be avoided for the duration of the pregnancy, regardless of symptoms, due to the potentially serious implications for the fetus.
Further details can be found at Information for GP’s on Zika Virus sexual transmission.
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A person who has been to a country with current or recent local Zika virus transmission should defer donation of blood for four (4) weeks after they have returned.
A person diagnosed with Zika virus infection should be advised that they cannot donate blood for a minimum of four (4) weeks after recovery of all symptoms.
Sexual Contact Deferral
A sexual contact of a person diagnosed with Zika virus infection should be advised that they cannot donate blood for a minimum of 4 weeks after sexual contact (vaginal, oral, or anal) with someone who:
- Has current Zika virus infection; or
- Has recovered from Zika virus infection in the preceding three months.
Based on the typical clinical features, the differential diagnosis for Zika virus infection is broad. In addition to dengue, other considerations include leptospirosis, malaria, rickettsia, group A streptococcus, rubella, measles, and parvovirus, enterovirus, adenovirus, and alphavirus infections (e.g., Chikungunya, Mayaro, Ross River, Barmah Forest, O’nyong-nyong, and Sindbis viruses).
Preliminary diagnosis is based on the patient’s clinical features, places and dates of travel, and activities. Laboratory diagnosis is generally accomplished by testing serum or plasma to detect virus, viral nucleic acid, or virus-specific immunoglobulin M and neutralizing antibodies.
Zika virus testing is performed at state public health laboratories in Australia. If Zika virus infection is suspected, clinicians are advised to discuss testing with their local pathology provider.
Testing for Zika virus infection may include IgM, IgG serology and PCR performed on blood, urine, amniotic fluid, cerebrospinal fluid or fetal tissues as appropriate.
- Acute serum (taken soon after exposure or symptom appearance) and convalescent serum (2 weeks later) should be taken wherever possible. The two samples are important to rule out false positive tests due to cross reactivity with similar viruses such as dengue.
- Please provide overseas travel details and clinical history including the onset day of any symptoms. Onset date is extremely important to ensure that the most appropriate test is performed. Details of any previous flavivirus vaccine (e.g. Japanese encephalitis, yellow fever) or previous flavivirus illness (e.g. West Nile virus, Dengue) can be useful for the pathologist in test interpretation.
- Testing asymptomatic males for Zika infection following travel can be considered if a pregnancy is planned and cannot be delayed for the recommended time periods. Serology 4 weeks after the last potential exposure is usually recommended in this situation.
For further information, please refer to Information for travellers about Zika virus testing.
No specific antiviral treatment is available for Zika virus infection. Treatment is generally supportive and can include rest, fluids, and use of analgesics and antipyretics. Because of similar geographic distribution and symptoms, patients with suspected Zika virus infections also should be evaluated and managed for possible dengue or chikungunya virus infection. Aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) should be avoided until dengue can be ruled out to reduce the risk of haemorrhage.
There is a risk of transmission of Zika virus from infected returning travellers in areas of North Queensland where a suitable vector, Aedes aegypti, occurs and which are currently considered dengue receptive. In these areas, public health authorities follow up on notified cases to mitigate the risk of local transmission. Cases in areas where transmission could occur will be advised to take additional measures to avoid being bitten by mosquitoes. until fever subsides.
Zika virus infection is notifiable in Australia as a flavivirus (unspecified) infection and should be notified to state and territory health departments. To guide reporting, the surveillance case definition is located on the Department of Health website.
In North Queensland and parts of Central and Southwest Queensland where mosquito vectors are present, clinicians should immediately report clinically suspected cases of Zika virus infection to local public health units, as they do for suspected cases of dengue.
Public health management of a laboratory confirmed case
People infected with Zika virus should be protected from further mosquito exposure during the first few days of illness to prevent other mosquitoes from becoming infected and reduce the risk of local transmission.
In Australia, this is relevant to confirmed cases in Queensland. Confirmed cases who are not resident in Queensland should be advised to avoid travel to these areas until their symptoms have resolved.
In parts Queensland, where the Aedes vector is known to be present, public health vector control teams may respond to reduce the risk of local transmission. Outside these areas in Queensland, notification is the required public health action.
Further information is available:
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- For a list of countries with current and recent outbreaks of Zika virus, a fact sheet for the general public, guidelines for prevention of sexual transmission and interim guidelines for assessment of pregnant women, refer to the Department of Health webpage.
- European Centre for Disease Prevention and Control – Zika virus infection.
- For the latest travel advice refer to the Smartraveller website.
- To notify clinically suspected Zika virus infection in Queensland, contact the local public health unit.