Zika virus infection

Notification requirement for Zika virus infection

As an arbovirus infection, Zika virus infection is a ‘routine’ notifiable condition and must be notified by medical practitioners and pathology services in writing within 5 days of diagnosis.

This is a Victorian statutory requirement.

Primary school and children’s services centre exclusion for Zika virus infection

Exclusion is not applicable.

Infectious agent of Zika virus infection

Zika virus is a flavivirus and is related to dengue and yellow fever viruses.

Identification of Zika virus infection

Clinical features

Zika virus infection typically causes a mild illness characterized by fever, rash, conjunctivitis, muscle and joint pain, and malaise or headache. Most cases of Zika virus infection are asymptomatic. When symptoms occur, they are usually mild and last for 2-7 days. However, infection during pregnancy can cause congenital Zika syndrome, including congenital malformations such as microcephaly. A small proportion of people recently infected with Zika virus can develop Gullain-Barré Syndrome, a rare neurological condition.

Diagnosis

Diagnosis may be determined with the following tests:

• isolation of Zika virus
• detection of Zika virus through nucleic acid testing of blood or urine samples
• seroconversion or a significant rise in antibody level or a fourfold or greater rise in titre to Zika virus
• detection of Zika virus-specific IgM.

Early diagnosis (within 7 days of illness onset) may be achieved through polymerase chain reaction (PCR) testing, and later (7 days or more after illness onset) through serological testing.

Importantly, Zika virus serology may cross react non-specifically, or with other viruses and may require expert interpretation in the context of other testing.

Incubation period of Zika virus

The incubation period (the time from exposure to symptoms) for Zika virus infection is estimated to be 3–12 days.

Public health significance and occurrence of Zika virus infection

Zika virus was first identified in Uganda in 1947. Prior to 2007, Zika virus infection outbreaks were reported in tropical Africa, Southeast Asia, and the Pacific Islands. However, major outbreaks have occurred in the Americas starting in 2015.

No locally acquired cases have been reported in Australia.

Reservoir of Zika virus

Humans and non-human primates are the main hosts of Zika virus, but the range of vertebrate hosts is not well understood. The possibility of Australian animal species acting as hosts has not been determined.

Mode of transmission of Zika virus

The virus is primarily transmitted through the bite of an infected female mosquito, primarily Aedes aegypti, a mosquito that also transmits dengue and chikungunya viruses. It can also be transmitted through sexual contact, and from a pregnant woman to the foetus.

Period of communicability of Zika virus

The precise period of communicability for Zika virus is not fully understood. A person with Zika virus in their blood can pass the virus to a mosquito through mosquito bites. The infected mosquito can then spread the virus to other people.

Sexual transmission of Zika virus has been documented. The duration of communicability is uncertain, however transmission from males to their sexual partners may occur for up to 3 months from infection. Transmission from females to their sexual partners may occur for up to 2 months.

Susceptibility and resistance to Zika virus infection

Once a person has recovered from Zika virus infection, they are generally considered to be immune to future infections.

Control measures for Zika virus infection

Preventive measures

The best way to avoid Zika virus infection is to prevent mosquito bites. Travellers to Zika-affected areas should take the following precautions to reduce their risk of Zika infection:

• avoid mosquito-prone areas
• ensure accommodation is mosquito-proof. Use mosquito nets, flying insect spray, mosquito coils or plug-in insecticide mats in rooms
• use personal repellents containing diethyltoluamide (DEET) or picaridin
• wear long, loose-fitting, light-coloured protective clothing.

Due to the concerns about the risk of severe outcomes for unborn babies, women who are pregnant or planning to become pregnant should consider delaying their travel to areas with active outbreaks of Zika.

There is currently no vaccine or preventive drug for Zika virus infection.

Control of case

Treatment for Zika is symptomatic; rest, fluids, and use of analgesics and antipyretics are recommended. Aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) should be avoided until dengue is ruled out to reduce the risk of haemorrhage.

Prevention of sexual transmission

In Victoria, guidance on the prevention of sexual transmission of Zika virus is adapted from the World Health Organization (WHO) ‘Guidelines for the prevention of sexual transmission of Zika virus (2018)’.

For males returning from a Zika-affected country:

• Abstain from sexual activity (vaginal, anal, or oral) or consistently use condoms for at least 3 months upon return.
• Wait for at least 3 months before donating sperm.

For females returning from a Zika-affected country:

• Abstain from sexual activity or consistently use condoms for at least 2 months upon return.

For males with a Zika diagnosis:

• Abstain from sexual activity or consistently use condoms for at least 3 months from the onset of symptoms or date of Zika diagnosis (for asymptomatic cases).
• Wait for at least 3 months before donating sperm.

For females with a Zika diagnosis:

• Abstain from sexual activity or consistently use condoms for at least 2 months from the onset of symptoms or date of Zika diagnosis (for asymptomatic cases).

For males with a pregnant partner, it is particularly important to follow the above recommendations. Males with a pregnant partner should abstain from sexual activity or consistently use condoms for the duration of the pregnancy or for at least 3 months after they were last in the at-risk country or diagnosed, whichever is longer.

Control of contacts

Routine contact management seeks to identify pregnant females at increased risk of Zika virus infection, either from:

• co-travel with a confirmed or probable case (so potentially exposed to infected mosquitoes);
• as a sexual partner of a confirmed or probable case while the case was potentially infectious.

Pregnant individuals at increased risk should be referred for specialist obstetric assessment and counselling about Zika virus testing.

Infants born to mothers infected with Zika virus during their pregnancy should be referred for specialist paediatric assessment and Zika virus testing.

If a case is suspected of acquiring the infection in Australia, more intensive contact tracing may be undertaken.

Control of environment

Since Zika virus infection has not yet been acquired in Australia (people have only acquired their illness overseas), environmental evaluation is not routinely necessary.

Outbreak measures for Zika virus infection

In the event of a locally acquired outbreak, the following measures may be considered:

• Where an infection appears to have occurred through exposure to a mosquito vector in the local area, enhanced surveillance through active case finding may occur
• Identify vector breeding places and promote their control.
• Promote the use of mosquito repellents and other mosquito avoidance measures for people exposed to bites.