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Zika virus

Queensland Health Guidelines for Public Health Units

Revision History

Date Changes
August 2014 Full revision of guideline.

Infectious Agent

Zika virus (ZIKV) is a mosquito-borne flavivirus originally identified in Uganda during 1947 which has subsequently spread to the Asia and Pacific regions where large outbreaks have occurred.

Infection with the virus causes an acute febrile illness similar to dengue fever characterised by macular-papular rash and arthralgia.

Notification Criteria

Clinical evidence

A clinically compatible illness characterised by; fever, arthralgia, macular-papular rash, and/ or headache, myalgia, non-purulent conjunctivitis, retro-orbital pain.

Epidemiological evidence

An epidemiological link is established when there is;

  1. recent travel to a country with known ZIKV activity
    OR
  2. exposure in Australia where local transmission has been documented within the previous month.

Laboratory suggestive evidence

Detection of Flavivirus IgM in serum by screening ELISA which is subsequently shown to be specific to ZIKV. False positives may occur. Cross-reactivity with other flavivirus (such as dengue) may be expected. IgM may not be detectable early in the illness. Confirmation by reference laboratory is required.

Laboratory definitve evidence

Detection of ZIKV by nucleic acid testing or virus isolation.

Commmunity outbreak criteria

One or more confirmed cases of locally acquired ZIKV.


 

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Notification Procedure

Pathology Laboratories

Notify on laboratory definitive evidence, immediately by telephone or facsimile if the case is in north Queensland or where Aedes aegypti or Aedes albopictus are known to be present, or by usual means in other areas.

Attending Medical Practitioners/Medical Superintendents (or delegates)

Notify clinically suspected cases to the relevant local public health unit immediately by telephone or facsimile, before laboratory results become available, if the case is in north Queensland, or where Aedes aegypti or Aedes albopictus are known to be present.

Reporting to NOCS

Report confirmed cases only.

Confirmed case

A confirmed case requires laboratory definitive evidence AND clinical evidence.

Probable case

A probable case requires laboratory suggestive evidence AND clinical evidence AND epidemiological evidence.

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Objectives of Surveillance

  1. Early detection and response to locally acquired cases of ZIKV in Queensland.
  2. Early detection and response to viraemic importations of ZIKV into north Queensland and other receptive areas.
  3. To monitor the epidemiology of ZIKV and its vector mosquitoes in Queensland.

Public Health Significance and Occurrence

Zika virus was originally identified in Uganda, Africa and has subsequently spread to Asia and Pacific regions where several large outbreaks have occurred. Infection with ZIKV causes a self-limiting acute febrile illness.

Zika virus is not endemic in Australia however imported cases of the virus have been reported. The mosquito Aedes aegypti, which is established in north Queensland coastal towns and some areas in central Queensland, is the primary vector of concern for ZIKV. These areas are particularly receptive to local transmission following viraemic importations of the virus.

Aedes aegypti has also been detected in towns as far south as Goomeri near the coast and Charleville inland. Historically it was also present in other parts of Queensland and in other Australian states and territories. Changes in vector range and numbers could increase the area receptive to outbreaks of ZIKV.

Another mosquito, Aedes albopictus, has been shown to be a possible vector of ZIKV. Ae. albopictus has colonised the majority of islands in the Torres Strait since 2005. A small incursion on the northernmost tip of Cape York during January 2010 highlights the risk of this vector expanding its range within Queensland and interstate.

Clinical Features

Clinical features of ZIKV infection include acute onset of fever, macular-papular rash, arthralgia, myalgia, headache, non-purulent conjunctivitis and less frequently retro-orbital pain, anorexia, vomiting, diarrhoea and abdominal pain.

Zika virus infection has been described as a self-limiting febrile illness lasting 4 to 7 days without severe complications. Fatalities have not been reported.

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Reservoir

Human and Aedes mosquitoes.

Mode of Transmission

Bites from infected females of certain Aedes  mosquito species. Ae. aegypti is the major vector of concern in Queensland while Aedes albopictus has also been implicated in transmission of the virus.

Ae. aegypti is a domesticated, urban mosquito found in the tropics and subtropics, and in Australia is currently confined to Queensland; it usually breeds in man-made containers and prefers indoor, sheltered, dark resting sites. Humans are the preferred source of blood meals for female Ae. aegypti; they are day-biting mosquitoes.

Ae. albopictus is a peri-domestic mosquito found not only in the tropics and subtropics but also in some temperate regions. It is an aggressive coloniser, but in Australia is currently confined to the Torres Strait. It breeds not only in artificial containers but also in some naturally occurring sites such as tree holes and coconut shells. Adults prefer heavily-shaded outdoor resting sites; the female takes blood from a wide range of mammals. It is an aggressive day-biting mosquito.

Incubation Period

Following a bite by an infected mosquito, the incubation period in a susceptible human (i.e. the intrinsic incubation period) has been reported to be up to 10 days however, current clinical evidence is limited.

From available evidence the extrinsic incubation period (length of time for a mosquito to become infectious after ingesting ZIKV) appears to be approximately 10 days.

Period of Communicability

Information on the period that a case is infectious to mosquitoes is limited however, ZIKV has been detected in human blood from the onset of illness. The length of the viraemic period has not been established but is believed to be short.

It is possible transfusion related cases could occur.

Susceptibility and Resistance

Susceptibility to primary infection appears universal.

Testing Guidelines

Nucleic acid testing detects ZIKV during the viraemic phase, which usually lasts approximately 5 days from onset of illness. RT-PCR testing is vital in early cases of suspected ZIKV infection as early diagnosis is important for rapid control measures. Virus may also be isolated from patient samples during this phase.

Detection of Flavivirus IgM in serum from day 5 post onset of illness by screening ELISA which is subsequently shown to be specific to ZIKV. False positives may occur. Cross-reactivity with other flaviviruses (such as dengue) may be expected. IgM may not be detected early in the illness. Confirmation by a reference laboratory is required.

A second sample may be required, 10-14 days after the first, to detect seroconversion or exclude cross-reaction with another flavivirus.

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Management

Cases

Investigation
Determine the likely location(s) of exposure to ZIKV (i.e. where the infection was presumably acquired), and addresses where the case lived/worked/visited while viraemic (for public health purposes this is assumed to be during the period of illness). Ensure specimens are taken and referred for confirmation of the case.

Management
If a viraemic case stays in, or travels to, an area where Aedes aegypti are present, particularly in north Queensland:

  • Share appropriate case information between local communicable disease, environmental health and/or medical entomology senior staff.
  • Advise the case and household contacts to prevent bites and kill mosquitoes for at least as long as the case is febrile and unwell. Persons geographically close to the case who develop symptoms should see their doctor for testing.
  • Consider urgent house to house mosquito control and surveys to detect further cases, in conjunction with local government.
  • Consider alerts to general practitioners, laboratories, emergency departments and the public.

Contacts

Contact Tracing
Yes

Ask patients if relevant co-travelers, family members, work colleagues, etc. are sick. Do follow up interviews with these and arrange testing if ZIKV infection is suspected.

Community outbreaks/epidemics

One locally acquired case would constitute an outbreak.

In an outbreak disease surveillance, mosquito control and community awareness measures will be required.

Blood donation services in outbreak locations may be restricted. Liaison with the Australian Red Cross Blood Service is essential (refer protocol).

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Preventive Measures

Travelers to tropical countries should take precautions to prevent ZIKV infection:

  • ensuring accommodation is free of mosquitoes, by closing window screens, using insecticide sprays indoors, etc.
  • wearing long sleeved clothing in urban or residential areas to minimise skin exposure to day-biting mosquitoes
  • using an appropriate mosquito repellent containing DEET (diethyl toluamide) or picaridin on exposed skin.

Someone who becomes unwell with a high fever during, or soon after, travel to tropical destinations should seek medical advice as soon as is practicable. If the person is told that they may have ZIKV, the person should use an appropriate mosquito repellent and stay in well screened premises for at least as long as the fever persists.

If the person is in coastal north Queensland, or other areas where Aedes aegypti or Aedes albopictus are present, mosquito control and other preventive measures may be required.

Summary

Prepare a report of the investigation for the Communicable Diseases Unit, Department of Health on request.

References

Heymann D (Ed). 2008. Control of Communicable Diseases Manual, 19th edition. American Public Health Association: Washington.

European Centre for Disease Prevention and Control. 2014. Rapid risk assessment: Zika virus infection outbreak, French Polynesia, February 2014. Stockholm: ECDC.

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Last updated: 12 September 2014