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Chikungunya

Queensland Health Guidelines for Public Health Units

Revision History

 Date  Changes
August 2014 Full revision of guideline.

Infectious Agent

The chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus belonging to the family Togaviridae.

Notification Criteria

Clinical evidence
Chikungunya is typically an acute infection with an abrupt onset, characterised by high fever, polyarthralgia (which can be intense), myalgia, headache and rash.

Laboratory definitive evidence:
• Isolation of CHIKV

OR
• detection of CHIKV by nucleic acid testing 

OR
• IgG seroconversion or a significant increase in antibody level (in qualitative assays) or a fourfold or greater rise in titre to CHIKV, in the absence of a corresponding change in antibody levels to Ross River virus (RRV) or Barmah Forest virus (BFV)

OR
• detection of CHIKV-specific IgM, in the absence of IgM to RRV or BFV.

Laboratory suggestive evidence:
Single high IgG titre to CHIKV, in the absence of antibody levels to Ross River virus or Barmah Forest virus.

Outbreak criteria
As autochthonous CHIKV does not routinely occur in Australia, any case of locally acquired chikungunya defines an outbreak of the disease. In the absence of travel history to areas with known endemic or epidemic activity, confirmation of laboratory results by an arbovirus reference laboratory is required to meet national case definition requirements.  However, public health management of the outbreak should not be delayed. 

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Notification Procedure

In the case of north Queensland and other areas where Aedes aegypti or Aedes albopictus are known to be present, treating doctors should notify clinically suspected cases to the relevant local public health unit immediately, before laboratory results become available. Laboratories are to notify a case with laboratory definitive or suggestive evidence, immediately by fax or telephone if the case is in north Queensland or other areas where Aedes aegypti or Aedes albopictus are known to be present.

Laboratory Aspects

Queensland Forensic and Scientific Services has specific tests for CHIKV. It is important that appropriate diagnostic tests are carried out at the appropriate time in relation to the onset of symptoms. There are three categories of laboratory tests used for the diagnosis of CHIKV infections:

  • serological tests to identify IgM and IgG antibodies
  • RT-PCR (reverse transcriptase - polymerase chain reaction)
  • virus isolation.

Days post onset

Test

Day 1-5

RT-PCR
Viral isolation
IgM (baseline)

> Day 5 gM
> Day 8

IgM
IgG

Reporting to NOCS

Only confirmed cases should be reported to NOCS.
Confirmed case: A confirmed case requires laboratory definitive evidence.

Objectives of surveillance

  1. To monitor the epidemiology of chikungunya in Queensland.
  2. Early detection and response to viraemic importations of CHIKV in north Queensland and other receptive areas.
  3. Early detection and response to locally acquired cases of CHIKV in Queensland.

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Public Health Significance and Occurrence

The incidence of CHIKV is emerging around the world facilitated in part by the adaptation of the virus to Aedes albopictus, which has spread to many countries globally.  The disease is endemic to most of Africa and has now become established in the India Ocean region, South East Asia and some parts of the Western Pacific, and Caribbean where explosive and extensive epidemics have occurred.  Delays in response due to difficulty in identifying the first few cases and an underestimate of the impact tend to result in large-scale outbreaks.  Greater than 95% of CHIKV-infected adults are symptomatic, and most adults become disabled for a period of time. On average, infected individuals are absent from work for one week.

Importation of CHIKV into Europe in 2007 caused an outbreak of chikungunya in Italy. This outbreak demonstrates the ability of the virus to move into novel ecological niches where suitable vectors are present, including north Queensland. An outbreak in Queensland would cause significant morbidity (as the Australian population is immunologically naïve to CHIKV), with significant social and financial impacts. Tourism would be adversely affected. 

The risk of local transmission across Queensland is not uniform, and is determined by local conditions and the distribution of competent vectors, as outlined in the Queensland chikungunya management plan 2014-2019. The virus is transmitted by two primary vectors, Aedes aegypti and Aedes albopictus, both of which occur in Queensland, although Aedes albopictus is currently (July 2014) restricted to some islands in the Torres Strait.   It is critical to detect cases of CHIKV in north Queensland, and other areas where Aedes aegypti or Aedes albopictus are present (such as some towns in central and southern Queensland), so that control measures can be deployed immediately where appropriate. Other endemic mosquito species may serve as potential vectors of CHIKV, but they are likely to play a relatively minor role in field transmission, when compared with either Aedes aegypti and/or Aedes albopictus.

Clinical Features

Symptoms of CHIKV could potentially be confused with other causes of fever and arthralgia, such as dengue, Ross River and Barmah Forest viruses.

CHIKV causes an illness characterised by an abrupt onset of high fever, soon followed in virtually all cases by often severe and debilitating polyarthralgia. The arthralgia is usually symmetric and occurs most commonly in the wrists, elbows, fingers, toes, knees and ankles but can also affect more proximal joints. Symptoms typically last for days to weeks.  However, the arthralgia can be very disabling and may persist for months or even years.

Rash can occur, but not as frequently as polyarthralgia. When it occurs, the rash appears after the onset of fever, can be pruritic and is typically maculopapular and erythematous.  It involves the trunk and extremities, but can include the palms, soles of the feet and face.

Other symptoms reported with chikungunya include headache, retro-orbital pain, fatigue, nausea, vomiting, lumbar back pain and myalgia. The acute disease lasts 3 to 10 days, but convalescence may include prolonged joint swelling and pain lasting weeks or months. Older individuals with underlying medical conditions appear to be more likely to develop serious complications (such as myocarditis and encephalitis), and to have a higher risk of death.

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Reservoir

Humans. Primates are involved in sylvatic transmission cycles in Africa.

Mode of Transmission

Chikungunya is a mosquito-borne disease; the two major vectors are Aedes aegypti and Aedes albopictus.

Aedes aegypti is a domestic urban mosquito found in the tropics and sub-tropics; it usually lays eggs in man-made containers where larvae develop. The preferred resting sites of adults are indoor sheltered dark spaces.  Humans are the preferred source of blood meals for female Aedes aegypti mosquitoes, which are daytime biting mosquitoes.

Aedes albopictus is a highly invasive peri-domestic mosquito found not only in the tropics and subtropics, but also some temperate regions.  It utilises artificial containers and some naturally occurring sites, such as tree holes and coconut shells, as larval habitats.  The preferred resting sites of adults are heavily shaded outdoor and indoor areas.  The female takes blood from a wide range of mammals.  It is also a day-biting mosquito. Aedes albopictus presents a significant public health risk to the Australian mainland, should it become established.

Other endemic mosquito species including Aedes vigilax and Aedes notoscriptus are competent vectors of CHIKV in the laboratory. However, their role in field transmission of CHIKV is likely to be less important than that of Aedes aegypti or Aedes albopictus.

Incubation Period

The incubation period in a susceptible human (the intrinsic incubation period) is typically 3-7 days (range 2-12 days).

Period of Communicability

CHIKV infections cause high levels of viraemia, which typically last 4-6 days, but can persist for up to 12 days after the onset of illness. A human case is infective to mosquitoes during the period of symptomatic viraemia. For public health purposes, the duration of viraemia is assumed to be from the date of onset of symptoms, until 12 days after the onset of symptoms. After feeding on a viraemic human, CHIKV replicates within the female mosquito and can be transmitted to another person. The mosquito becomes infectious on average 10 days after ingesting CHIKV in a blood meal (extrinsic incubation period). However under some conditions, it has been demonstrated that the extrinsic incubation can be as short as 2 days. This exemplifies the need for rapid public health response to identified cases. The sum of the intrinsic and extrinsic incubation periods indicates a minimum serial interval between generations of human cases.

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Susceptibility and Resistance

There is no vaccine against CHIKV.  As most Australians have not been exposed previously to CHIKV, it is expected that most will be susceptible. It appears that infection with CHIKV results in long term immunity to future infection.

Management

Cases:
 
Investigation

  • Confirm date of symptom onset
  • Obtain travel history and determine possible source of infection and where the case resided/visited while viraemic
  • Ensure specimens are taken or referred for confirmation of the case.


Management

  • Treatment is symptomatic; aspirin should not be used.
  • If a case resides in north Queensland, or other areas where Aedes aegypti or Aedes albopictus mosquitoes could be present, they should be advised to prevent being bitten by mosquitoes whilst unwell with fever by:
    • Staying in screened or air conditioned accommodation
    • Using personal insect repellent containing DEET or picaridin and reapplying according to the manufacturer's instructions
    • Using mosquito coils or plug-in mosquito repellent devices indoors
    • Ensure containers in and around the house are emptied of water and wiped clean.
  • Household contacts and others living or working in close geographic proximity to the case should also avoid mosquito bites and present to their doctor for possible CHIKV testing if unwell.
  • If there is any suggestion or evidence of local transmission of CHIKV anywhere in Queensland, the public health unit Director and medical entomologist (or the Director of environmental health services) should be informed immediately, and an outbreak control team established urgently.  The Senior Director, Communicable Diseases Unit should be informed and a Ministerial briefing prepared. Alerts should be provided to local medical practitioners (GPs and Emergency Departments) and the general public.
  • In some locations, public health units conduct risk-based mosquito surveillance around case residences and may require communication to the medical entomologist and /or designated environmental health officer to initiate this action.

Contacts

Contact Tracing: Yes.
Ask cases whether any travel-companions are also sick, and if any family members, work colleagues etc. have a similar illness. Conduct follow-up interviews with contacts if necessary, and arrange prompt sample collection and urgent testing if CHIKV infection is suspected.

Community Outbreaks/Epidemics

In the event of an outbreak in Australia, significant disease surveillance, mosquito control and public awareness measures will be required. Local medical practitioners and local hospitals will need to be informed, and may require extra resources to manage the increased work load.

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Preventive Measures

A combination of mosquito control and personal protective measures (as listed above) would be necessary to control CHIKV infection should local transmission occur in Australia.  Measures to control Aedes aegypti and Aedes albopictus mosquitoes in Queensland to control the threat of dengue will also reduce the risk of CHIKV transmission.

Feedback

Report to notifying agency.

Summary

Prepare a report for the Communicable Diseases Unit, Queensland Health, on request.

References

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

Simon F, Savini H, Parola P. Chikungunya: A paradigm of emergence and globalization of vector-borne diseases.  Med Clin N Am 2008; 92: 323-1343.

Staples JE, Breiman RF, Powers AM. Chikungunya fever: an epidemiological review of a re-emerging infectious disease. Clin Infect Dis 2009; 49: 942-948.

Queensland chikungunya management plan 2014-2019: http://www.health.qld.gov.au/cdcg/documents/chikungunya-management-plan.pdf

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Last updated: 10 September 2014