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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 particularly from outbreaks of Zika virus in Brazil and French Polynesia 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 for clinicians and public health practitioners
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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 areas 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.
- Pregnant women are advised to consider postponing travel to any area with current or recent local Zika virus transmission
- Pregnant women who do decide to travel to one of these areas 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 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, refer to Interim recommendations for assessment of pregnant women returning from Zika virus-affected areas.
- Men who have returned from a country with current or recent local Zika virus transmission and have a partner who is pregnant or planning pregnancy are advised to consult a doctor to discuss recommendations for preventing sexual transmission, refer to Interim recommendations for reducing the risk of sexual transmission of Zika virus.
- 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 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.
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 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 and feed both indoors and outdoors near dwellings.
Outbreaks of Zika virus have previously been reported in tropical Africa, Southeast Asia, and the Pacific Islands 1.
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:
- Low-grade fever
- Arthralgia, notably of small joints of hands and feet, with possible swollen joints
- Headache, retro-ocular headaches
- Cutaneous maculopapular rash
- Post-infection asthenia which seems to be frequent.
More rarely observed symptoms include digestive problems (abdominal pain, diarrhoea, constipation), mucous membrane ulcerations (aphthae), and pruritus.
Zika virus infection generally causes a non-severe disease. Exceptions are the possible effects to the fetus in pregnant women, and the possibility of the development of Guillain-Barré Syndrome (GBS), which are discussed below. As Zika 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. Diagnosis of Zika virus infection will firstly be by exclusion, based on symptoms, travel history and exclusion of other diseases including measles and dengue.
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 is a cause of Guillain-Barré Syndrome.
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 different diseases, including infections with campylobacter, influenza, Epstein-Barr Virus, HIV and Mycoplasma pneumonia. 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.
Transmission of Zika virus is through the bite of an infected mosquito, most commonly Aedes aegypti.
There are no reports at this time of infants becoming infected through breastfeeding.
Multiple instances of probable or confirmed sexual transmission have now been reported, and to date, almost all have involved a symptomatic man transmitting the virus to a woman, with the exception of one known instance of male-to-male sexual transmission7,8,9,10,11,12. Zika virus has also been found in the semen of cases.
Please refer to the CDC website for further details (www.cdc.gov/zika/transmission/index.html).
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Zika virus and pregnancy
Pregnant women who become infected with Zika virus may transmit the disease to their unborn babies, with potentially serious consequences. Where Zika virus outbreaks are occurring, most notably Brazil, and published studies indicate that there has been a concurrent increase in severe congenital abnormalities such as microcephaly and that these congenital abnormalities can be caused by Zika virus infection in-utero. Additional research is necessary to quantify the risk of adverse outcomes occurring, and the factors affecting this risk.
Women who are pregnant (in any trimester) or who plan to become pregnant are advised to consider postponing travel to any area 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.
Pregnant women who have travel history in areas that had current or recent local Zika virus transmission at the time of travel, are advised to speak with their health care provider. Testing for Zika virus is recommended. Follow up with an obstetric specialist is recommended if a positive test is returned. It is not possible at the current time to quantify the risk to the unborn baby of a person infected with Zika virus and a positive test in the mother gives no information on whether the fetus is infected or harmed.
For guidance on assessing pregnant women returning from countries with current or recent local Zika virus transmission 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 who have travelled to a country with current or recent local Zika virus transmission should defer pregnancy for 28 days following the last potential exposure. If her partner has also been exposed, 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 is only one consideration.
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.
- Wear long-sleeved shirts and long pants.
- Use insect repellents containing DEET or picaridin. Always use as directed.
- 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 you use both sunscreen and insect repellent, apply the sunscreen first and then the repellent.
- Use permethrin-treated clothing and gear (such as boots, pants, socks, and tents).
- Use bed nets as necessary.
- Stay and sleep in screened-in or air-conditioned rooms.
Given the potentially serious implications of sexual transmission of the virus to a pregnant woman, recommendations have been developed to reduce the risk of transmission.
Further details can be found at Interim recommendations for reducing the risk of sexual transmission of Zika virus.
- Men who have travelled to a country with current or recent local Zika virus transmission, whose partner is pregnant, should abstain from sexual activity (vaginal, anal, or oral) or consistently use condoms for the duration of the pregnancy, whether symptomatic or asymptomatic.
- Men who have had a confirmed Zika virus infection, whose partner is not pregnant should abstain from sexual activity (vaginal, anal, or oral) or consistently use condoms for 3 months following the resolution of symptoms.
This cautious advice is directed toward the population of most concern: pregnant women and those planning pregnancy; however partners of men with a confirmed Zika virus infection would also be protected from potential sexual transmission by this advice. This is of most relevance to people in North Queensland where the vector is present and the potential for further spread of the virus is present.
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A person diagnosed with Zika virus infection should be advised that they cannot donate blood for a minimum of 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 donation is not possible for four weeks after sexual contact 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 is suspected, clinicians are advised to discuss testing with their local pathology provider. Testing for Zika virus infection may include IgM, IgG and PCR (positive only in early infection) of blood and urine.
- 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.
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 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 North Queensland and parts of Central 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.