Kunjin virus (KUNV) was first isolated from Cx. annulirostris mosquitoes collected in north Queensland in 1960 and given the name of a nearby Aboriginal clan living on the Mitchell River. It is closely related to the West Nile virus, which was probably exported from the Middle East to New York in 1999 and where it has caused thousands of deaths in birds and horses and has caused many cases of human disease including fatal encephalitis. West Nile virus has spread to most mainland States of the USA, down to Mexico, up into Canada and also to the Cayman islands in the Caribbean.

Identification

Clinical features

Subclinical disease is high as indicated by serological surveys. Two main clinical forms of disease have been reported, a mild disease and encephalitis. Mild disease, consisting of lymphadenopathy, fever, lethargy and a rash, was first noted when two laboratory workers acquired the infection in Queensland in 1963. A few other similar cases have been described from around Australia, some with muscle weakness and fatigue. There has been a comparatively small number of reported cases of encephalitis due to KUNV and fatalities are rare or absent. Nevertheless, very few epidemiological studies have been carried out to determine the life cycle, nature and frequency of KUNV infection in Australia.

Method of diagnosis

Infection is confirmed by a significant rise in antibody titre to the virus in two blood specimens taken seven to ten days apart.
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Laboratory evidence

Isolation of KUNV from clinical material;
OR
Detection of KUNV RNA in clinical material;
OR
IgG seroconversion or a significant increase in antibody level or a fourfold rise in titre of KUNV specific IgG proven by neutralisation or another specific test;
OR
KUNV specific IgM detected in the CSF;
OR
KUNV specific IgM detected in serum in the absence of IgM to Murray Valley encephalitis, Japanese encephalitis or Dengue viruses. This is only accepted as laboratory evidence for encephalitic illnesses.

Confirmation of laboratory result by a second arbovirus reference laboratory is required to differentiate from WNV and MVEV if the case occurs in areas of Australia not known to have established enzootic/endemic activity or regular epidemic activity.

Clinical evidence

Non-encephalitic illness
Acute febrile illness with headache, myalgia and/or rash
OR
Encephalitic disease
Acute febrile meningoencephalitis characterised by one or more of the following:

focal neurological disease or clearly impaired level of consciousness
an abnormal CT or MRI scan or EEG
presence of pleocytosis in the CSF

Asymptomatic disease

Incubation period

Probably similar to Murray Valley encephalitis virus (MVEV) disease.

Public Health Significance and Occurrence

KUNV is similar to MVEV but the disease caused by these two viruses can be distinguished by virological tests. This distinction is important in periods when weather patterns and other indicators suggest that an outbreak of MVEV disease, which has a higher mortality rate and can be more prevalent, may be imminent in south-eastern Australia.

Serological surveys have shown that KUNV infection has occurred over wide areas of Australia, infecting humans, wild and domestic animals (cattle, sheep and horses). Similar to MVEV, KUNV occasionally spreads southward from the tropical north to central and south-eastern Australia after heavy rains. Unlike MVEV, KUNV has been detected in south-eastern Australia on several occasions since 1974, the last being in 2001.

Reservoir

The virus is endemic in the tropical north of Australia and Sarawak where it has cycles of infection between birds and mosquitoes in enzootic foci. Top of page

Mode of Transmission

By mosquitoes, particularly Cx. annulirostris.

Period of Communicability

There is no evidence of person-to-person transmission.

Susceptibility and Resistance

Infection confers life-long immunity.

Control Measures

Preventive measures

There is no preventative vaccine available.
KUNV infection can be prevented by:

Mosquito control measures.
Personal protection measures (long sleeves and mosquito repellents).
Avoidance of mosquito-prone areas. Vectors usually bite at dusk and dawn.

Control of case

Investigate the source of infection. Search for unreported or undiagnosed cases of encephalitis.

The patient with suspected infection (or friend or relative) should be asked to recall if, in the month prior to onset of symptoms, he or she had:

Been bitten by mosquitoes; or
Visited regions where arboviruses are endemic; or
Participated in recreational or other activities involving exposure to bushland or other mosquito habitat (as in, for example gardening, bushwalking, camping and picnicking)

Control of environment

To reduce/prevent virus transmission, interruption of human/mosquito contact is required by:

reduction of the vector mosquito population
avoidance of vector contact (vectors usually bite at dusk and dawn}.
apply mosquito control measures
use personal protection measures (long sleeves, long trousers, mosquito repellents).
avoid mosquito-prone areas;
Outbreak Measures
Search for unreported or undiagnosed cases of encephalitis.

Outbreak Measures

Search for unreported or undiagnosed cases of encephalitis.
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