Zika Virus Infection

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Causative agent

Zika virus infection is a mosquito-borne disease caused by Zika virus.

Clinical features

Most Zika virus infection is asymptomatic. For patients with symptoms, they commonly present with skin rash, fever, conjunctivitis, muscle or joint pain and general malaise. These symptoms are usually mild and last for a few days.

The current major concern is the association with adverse pregnancy outcome (microcephaly) and neurological and autoimmune complications such as Guillain-Barré syndrome (GBS). The World Health Organization has concluded that Zika virus infection during pregnancy is a cause of congenital brain abnormalities, including microcephaly, and that Zika virus is a trigger of GBS.

Apart from GBS, acute disseminated encephalomyelitis (a disease of the central nervous system) was found to be one of the neurologic manifestations possibly resulted from Zika virus infection.

Mode of transmission

Zika virus is mainly transmitted to humans through the bite of an infected Aedes mosquito. Aedes aegypti, which is currently not found in Hong Kong, is considered the most important vector for Zika virus transmission to humans. Other Aedes mosquito species such as Aedes albopictus which is commonly found in Hong Kong are also considered as potential vectors.

Zika virus has also been found in human semen and transmission by sexual contact has been confirmed. Sexual transmission of Zika virus between men who have sex with men has been documented in the literature. Other modes of transmission such as blood transfusion and perinatal transmission are possible.

Incubation period

The incubation period of Zika virus infection ranges from 3 – 14 days.

Management

There is no specific medication for Zika virus infection and the mainstay of treatment is symptomatic relief and prevention of dehydration. If symptoms worsen, patients should seek medical care and advice.

Prevention

At present, there is no effective vaccine against Zika virus infection. To prevent Zika virus infection, members of the public are reminded to protect themselves from mosquito bites and help prevent mosquito proliferation. The public is also advised to take precautions to prevent sexual transmission of Zika virus.

General measures on preventing mosquito-borne diseases

1. Wear loose, light-coloured, long-sleeved tops and trousers, and use DEET-containing insect repellent on exposed parts of the body and clothing.
2. Take additional preventive measures when engaging in outdoor activities:

• Avoid using fragrant cosmetics or skin care products
• Re-apply insect repellents according to instructions

3. Special notes when travelling abroad:

• If going to areas with Zika virus transmission (affected areas) , travellers, especially persons with immune disorders or severe chronic illnesses, should arrange a consultation with doctor at least 6 weeks before the trip, and have extra preventive measures to avoid mosquito bites.
• During the trip, if travelling in rural affected areas, carry a portable bed net and apply permethrin (an insecticide) on it. Permethrin should NOT be applied to skin. Seek medical attention promptly if feeling unwell.
• Travellers who return from affected areas should apply insect repellent for at least 21 days after arrival in Hong Kong. If feeling unwell e.g. having fever, should seek medical advice promptly, and provide travel details to doctor.

Pregnant women and children of 6 months or older can use DEET-containing insect repellent. For children who travel to countries or areas where mosquito-borne diseases are endemic or epidemic and where exposure is likely, children aged 2 months or above can use DEET-containing insect repellents with a concentration of DEET up to 30%. For details about the use of insect repellents and the key points to be observed, please refer to 'Tips for using insect repellents'.

Prevention of sexual transmission*

1. Travellers should consider not having sex during travel to affected areas, or else condom should be used.
2. Male and female travellers returning from affected areas should abstain from sex for at least 3 months and at least 2 months respectively upon return, or else condom should be used.
3. Pregnant woman should not have sex with her partner who had travelled to affected areas, or else condom should be used throughout the pregnancy.

*This precautionary measure may be revised as more information becomes available. Individuals with further concerns regarding potential sexual transmission of Zika virus should contact their doctor for advice.

Pregnant women should not travel to areas with Zika virus transmission. Women preparing for pregnancy should note Points A and B above. If they or their male sex partners plan to travel to affected areas, they should consult their doctors for advice on the risk. Use of mosquito repellent containing DEET during travel and returning from these areas for a period of at least 21 days are advised for all travellers including pregnant women. Pregnant women are advised to: attend antenatal follow up regularly and tell the attending doctor history of recent travel; observe for symptoms of Zika virus infection and seek medical advice as soon as possible if feeling unwell; abstain from sex with her partner who had travelled to affected areas, or else condom should be used throughout the pregnancy.

Help prevent mosquito proliferation

1.      Prevent accumulation of stagnant water

• Change the water in vases once a week
• Avoid using saucers underneath flower pots
• Cover water containers tightly
• Ensure air-conditioner drip trays are free of stagnant water
• Put all used cans and bottles into covered dustbins

2.      Control vectors and reservoir of the diseases

• Store food and dispose of garbage properly

For more information about control and prevention of mosquito breeding, please visit the website of Food and Environmental Hygiene Department (FEHD) http://www.fehd.gov.hk/english/pestcontrol/handbook_prev_mos_breeding.html

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