This month’s article focuses on the emerging Zika virus.

Zika is the name for a virus which causes a flu-like illness that spreads through  bites from a type of mosquito called Aedes. This same mosquito also causes other tropical viral illnesses, such as dengue and chikungunya.

Mosquitoes become infected through biting someone who already has Zika, and once infected mosquitoes can then spread Zika to people by biting them. 

Zika can also be spread from a pregnant woman to her baby during pregnancy or shortly after birth. The virus can also be spread by sexual intercourse. This is less common than it being spread by mosquito bites. 

An outbreak of Zika virus infection began in Brazil in May 2015, where it was noticed that there were more children being born with abnormally small heads (microcephaly). It is possible, but not proven, that Zika virus is linked to the problem of microcephaly. 

It is not known why the possible increased problems of Zika virus infection have emerged in this recent outbreak. One theory is that it is a mutation in the RNA of the virus.  

Symptoms

Most people with Zika virus infection will have no symptoms. Only about one in five people infected will be unwell, and in those, the illness is usually mild. For this reason, many people might not know that they have been infected.

The most common symptoms of Zika virus infection are fever, rash, joint pains and conjunctivitis. The illness associated with the infection usually lasts approximately seven days. Symptoms usually start two to 12 days after being bitten by an infected mosquito.

Not everyone with suspected Zika needs medical attention. If someone is not at high risk of complications from the infection and can manage their symptoms, it may not be necessary to see a doctor. 

If a woman is or may be pregnant, or someone has a poorly functioning immune system or is at high risk of complications and/or their symptoms are severe, they should seek medical advice.  

Differential diagnosis of Zika virus infection:

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Common cold 

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Glandular fever 

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Chest infection in babies and children 

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Chest infection in adults 

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Rubella 

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Measles 

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Whooping cough 

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Sore throat – acute 

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Meningitis (bacterial)/meningococcal septicaemia 

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Malaria (in people with fever who have recently travelled to a malarial area)

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More rarely, dengue fever or chikungunya virus infections, which are common in tropical and subtropical areas of the world. 

Treatment

There is no specific treatment for Zika virus infection and no vaccine for its prevention. The only management is to relieve symptoms, as follows: 

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Taking paracetamol to relieve pain and high temperature

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Drinking adequate fluids to replace losses through perspiration

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Bed rest for symptoms of fatigue

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Staying off work or school – for most people, about one week will be adequate

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Avoiding further mosquito bites 

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Seeking urgent medical attention if person develops shortness of breath, muscle weakness (symptoms of Guillain-Barré syndrome) or is pregnant. 

People with suspected Zika virus infection should not take ibuprofen or other non-steroidal medications until dengue fever has been excluded. This is because dengue fever can cause bleeding, which can be made worse by taking NSAIDs.

Most people with Zika virus recover within one week.

Risks of contracting Zika virus 

Those travelling to or living in areas where Zika virus is active are most at risk of contracting the virus, through a mosquito bite (see Table 1). 

Special considerations in pregnancy

It is thought that microcephaly, a serious birth defect of the brain, may be linked to Zika virus infection. This is a condition in which a baby’s head is abnormally small. Microcephaly can cause problems with brain development but the severity of the condition is variable. 

Other causes of microcephaly include toxoplasmosis, rubella, herpes and HIV, severe malnutrition during foetal growth and maternal exposure to poisons such as heavy metals. 

Zika virus infection has also been linked to other congenital problems such as clubfoot. While it is not yet clear whether Zika virus is the only reason for these birth defects, it is recommended that special precautions are taken during pregnancy until the causes and risks are better understood.  

Pregnant women have been advised to consider postponing travel to any area where Zika virus disease is active. If travel is essential to affected areas, then women should be advised to strictly follow steps to prevent mosquito bites. 

Women who are trying to conceive and are also planning a trip to an affected area should have a pre-conception consultation with a health professional and take specific advice on the risks of developing Zika virus infection.

Travel advice

When travelling to an area with Zika infected mosquitoes, the best way to prevent infection is to avoid mosquito bites. Ways to prevent mosquito bites include:

• Wear long-sleeved clothing and long trousers and dress children in clothing that covers their arms and legs

• Cover children’s bed, stroller or baby carrier with mosquito netting

• Sleep under a mosquito net

• Stay in air conditioned buildings or use window and door screens to keep mosquitoes outside 

• Use insect repellents

• Apply sunscreen, when needed, before applying insect repellent

• Insect repellents are not advised on babies younger than two months of age

• Spray clothing with permethrin – a chemical that kills mosquitoes. 

Role of health professionals

At present there is no vaccine against Zika virus infection. So what can healthcare professionals do for people with suspected Zika virus infection? We can:

• Ask patients questions about symptoms, recent travel and contact with mosquitoes from an infected area

• Examine patients to rule out other causes of their symptoms 

• Arrange tests to exclude Zika or similar viral diseases. Testing includes laboratory confirmation of the presence of viral RNA in blood, urine or saliva. This test involves polymerase chain reaction (PCR) and virus isolation. This diagnosis can be difficult as the virus can cross-react with other viruses, such as dengue, West Nile and yellow fever

• Provide advice to improve symptoms of Zika virus disease

• Advise pregnant women to see an obstetrician who may arrange an ultrasound scan. An ultrasound to measure the size of the foetal head is most useful at the end of the second trimester (around 28 weeks) or in the third trimester. 

Possible complications

For most people, Zika virus infection will mean no symptoms or a mild flu-like illness for up to a week. For a small number of people Zika virus infection can mean more serious health problems. 

There have been reports of a serious birth defect of the brain called microcephaly, which might be linked to Zika virus infection. Zika virus infections also seem to cause other problems in pregnancy such as miscarriage and other congenital abnormalities.

It is not clear if Zika virus infection is the only reason for these problems in pregnancy, further research and analysis is ongoing in the worst affected areas to provide further information. 

There have also been reports of Guillain-Barré syndrome being linked to Zika virus infection. This is a rare condition of the nervous system which can occur as part of a viral illness, such as glandular fever. The symptoms of Guillain-Barré include muscle weakness and breathlessness. Most people will recover from Guillain-Barré syndrome but in a few cases the weakness has progressed over weeks to cause paralysis and then death. 

It is not clear if Zika virus infection has increased the incidence of Guillain-Barré syndrome. 

Practicalities to consider

If someone is at high risk of complications, contact should be avoided with other people with Zika virus infection.

It is known that Zika virus can be present in male semen. There have been two cases of Zika virus being spread by sexual intercourse. It is recommended that men who have lived in or travelled to an area with active Zika virus infection should avoid sex or use condoms for vaginal, anal and oral sex for the duration of the pregnancy. 

References

1. Zika virus, CDC, Centers for Disease Control and Prevention. Available from: http://www.cdc.gov/Zika/
2. Health Protection Surveillance Centre Ireland. Available from: www.hpsc.ie/A-Z/Vectorborne/Zika/
3. UK government Zika virus guidance. Available from: https://www.gov.uk/guidance/zika-virus
4. WHO Zika virus guidance. Available from: http://www.who.int/mediacentre/factsheets/zika/en/