About Kunjin Fever

About West Nile virus or Kunjin Fever

Kunjin Fever

Kunjin is caused by infection with the Kunjin virus, which is now considered to be a variant of West Nile virus (another potentially serious illness spread by the bite of an infected mosquito).

Kunjin virus (KUNV) is a zoonotic virus of the family Flaviviridae and the genus Flavivirus. It is a subtype of West Nile virus endemic to Oceania.Kunjin virus has been shown to be closely related to West Nile virus and is usually referred to as West Nile virus Kunjin subtype.

Kunjin virus is spread by the bite of an infected mosquito. Although only a small number of cases of Kunjin are reported annually, the virus is known to occur in many parts of Australia.

About West Nile virus/Kunjin

West Nile virus is a viral infection carried by mosquitoes. It belongs to a group of viruses called flaviviruses. A person infected with the virus may have no symptoms. About 20% of people infected develop mild flu-like symptoms such as fever, fatigue and aching muscles. In rare cases, the West Nile virus can lead to serious complications such as meningitis (infection or inflammation of membranes surrounding the brain) or encephalitis (inflammation of the brain). West Nile virus can be found in Africa, Europe, and the Middle East and in the USA.

West Nile virus/Kunjin is a strain of West Nile virus and is found in parts of Australia, particularly the Northern Territory and northern Western Australia. No other subtypes of West Nile virus are found in Australia. West Nile virus/Kunjin is less virulent (severe) than other strains of West Nile virus. Symptoms can appear from 7 to 28 days after becoming infected. However, many people infected with West Nile virus/Kunjin will never develop symptoms. People with antibodies to West Nile virus/Kunjin may be immune to infection with West Nile virus. 

When in mosquito-prone areas, wear long, loose-fitting, light coloured clothing and use insect repellent containing DEET or Picaridin to help reduce the chance of being bitten by mosquitoes.

Abstract

Kunjin (KUN) is a flavivirus in the Japanese encephalitis antigenic complex that was first isolated from Culex annulirostris mosquitoes captured in northern Australia in 1960. It is the etiological agent of a human disease characterized by febrile illness with rash or mild encephalitis and, occasionally, of a neurological disease in horses. KUN virus shares a similar epidemiology and ecology with the closely related Murray Valley encephalitis (MVE) virus, the major causative agent of arboviral encephalitis in Australia. Based on traditional antigenic methods, KUN was initially found to be similar to, but distinct from, reference strains of West Nile (WN) virus and designated as a new species.

However, more recent phylogenic analyses have revealed that some strains of WN virus, including the isolates from New York, are more similar to KUN virus and form a separate lineage to other WN viruses. An unusual KUN isolate from Malaysia and the African virus Koutango appear to form additional lineages within the WN group of viruses. While these findings are in agreement with the Seventh Report of the International Committee for the Taxonomy of Viruses that designates KUN as a subtype of West Nile, they also suggest that the species should be further subdivided into additional subtypes.

History Of Kunjin virus

The virus was first isolated from Culex annulirostris mosquitoes in Australia in 1960.The name of Kunjin virus derives from an Aboriginal clan living on the Mitchell River close to where the virus was first isolated in Kowanyama, northern Queensland.

Virology

Kunjin virus is a zoonotic virus of the family Flaviviridae and the genus Flavivirus. It is an arbovirus which is transmitted by mosquitoes and is part of the Japanese encephalitis serological complex.It is antigenically and genetically very similar to West Nile virus and in 1999 was reclassified as a subtype of WNV. Its genome is positive-sense single stranded RNA made up of 10,644 nucleotides.

What is Kunjin virus disease?

Kunjin virus disease is a viral infection caused by a flavivirus (Kunjin virus) found in mainland Australia and Papua New Guinea. It is closely related to West Nile virus which is found in Africa, Europe and the USA. The virus is spread by the bite of certain mosquitoes.

How Kunjin virus is spread?

Kunjin virus is endemic (always present) in tropical parts of Australia, in birds. Illness in humans is rare and most reported cases occur in northern Australia.

People can be infected with West Nile virus/Kunjin when they are bitten by a mosquito that is carrying the virus. Throughout Australia, Culex annulirostris is the most important mosquito species that can carry this virus. This mosquito breeds in fresh water and is most active at dusk and dawn. Mosquitoes can pick up the virus when feeding on water birds such as herons. 

The virus is spread by the bite of the common banded mosquito, Culex annulirostris. This mosquito breeds in fresh water and tends to be found in spring, summer and autumn around natural wetlands and irrigation waters. The mosquito is especially common around the Murray Darling River basin areas in NSW during summer and into autumn. This mosquito tends to be most active after sunset and around dawn.

Kunjin virus is a virus of birds. Various water bird species are thought to be infected with the virus, although other animals such as horses can also become infected. Mosquitoes become infected by feeding on infected birds and possibly other animals. An infected mosquito can then bite a human and transmit the infection.

The infection is spread from infected animals, including water birds and other birds, and mammals, to humans by mosquito bites.

There is no evidence that West Nile virus/Kunjin can be spread directly from one person to another.

Who is at risk?

As some mosquitoes may carry the Kunjin virus, people who are bitten by mosquitoes are most at risk. People working, living or visiting areas of rural NSW where there are rivers, wetlands, flooded areas or heavily irrigated areas may be at greater risk of Kunjin virus infection because the mosquitoes are more likely to be infected from water birds that naturally carry high levels of virus.

Kunjin virus is more common in some parts of northern Australia.

NSW Health has established a several flocks of sentinel chickens around the state. During the mosquito season, the chickens are tested weekly for the mosquito-borne diseases (Kunjin and Murray Valley encephalitis viruses). New infections in chickens serve as an early warning that local mosquitoes in the area may be carrying the virus. Kunjin virus has been found on several occasions in the chicken sentinel flocks and in mosquitoes in NSW. Mosquitoes are also trapped, counted and tested for Kunjin virus.

To reduce the risk of infection: 

  • Wear long, loose-fitting, light coloured clothing and use effective insect repellents that contain DEET or Picaridin applied regularly, according to the manufacturer’s instructions.
  • Avoid mosquito-prone areas, especially at dusk and dawn when mosquitoes are more active and likely to bite.
  • Ensure that your accommodation has fly screens properly fitted to windows and external doors.
  • Reduce the number of potential mosquito breeding habitats around your home by ensuring no stagnant water is present. Containers holding water should be emptied and washed regularly.

Transmission and control

Kunjin virus is transmitted by mosquito vectors, especially the Culex annulirostris.They pass the virus to water bird reservoir hosts; a major example is the nankeen night heron.It is also passed to horses and humans.The virus has been isolated in mosquitoes in South East Asia but in humans, only in Australia. It has been found all over Australia and is particularly prevalent in areas near wetlands and rivers.

The control of Kunjin virus is achieved in the same ways as other mosquito-borne diseases. These include individuals using insect repellent, wearing long-sleeved clothes and avoiding areas where mosquitoes are particularly prevalent.Habitat control by government agencies can take the form of reducing the amount of water available for mosquitoes to breed in, and the use of insecticides. There is no available vaccine against Kunjin virus.

Use in medicine

In 2005, scientists at the Queensland Institute of Medical Research and the University of Queensland found that modified Kunjin virus particles injected into mice were able to deliver a gene into the immune system targeting cancer cells. This research may lead to vaccines for cancer and HIV.

Signs and symptoms of Kunjin virus infection

The vast majority of infections do not show symptoms. A small number of people develop mild illness with fever, enlarged lymph nodes, rash, swollen and aching joints, headache, muscle weakness and fatigue. Some people with Kunjin virus disease may develop encephalitis, a severe brain infection which may require hospitalization.

Infection with the virus often causes no symptoms, but it can lead to either an encephalitic disease or a non-encephalitic disease.Non-encephalitic Kunjin virus disease can cause symptoms including acute febrile illness, headache, arthralgia, myalgia, fatigue and rash. Kunjin virus encephalitis features acute febrile meningoencephalitis.

Both forms of Kunjin virus disease are milder than the diseases caused by West Nile virus and Murray Valley encephalitis virus.

Most people with Kunjin virus infection have mild or no symptoms.

Symptoms of Kunjin virus infection may include:

  • fever
  • malaise (feeling of being unwell)
  • headache
  • muscle aches
  • swollen lymph nodes
  • fatigue
  • rash
  • swollen and aching joints.

Rarely infection may progress to encephalitis (infection or inflammation of the brain). 

Encephalitis

Symptoms of encephalitis may include:

  • fever
  • rigors
  • headache
  • neck stiffness
  • irritability
  • confusion
  • drowsiness (excessive sleepiness)
  • Seizures (fits).

Kunjin virus encephalitis is similar to Murray Valley encephalitis but is usually milder.

Diagnosis of Kunjin virus infection

Diagnosis is made by blood tests or by detecting Kunjin virus in CSF (cerebrospinal fluid: the fluid surrounding the brain and spinal cord).

Blood tests can show whether there are antibodies to Kunjin virus. Blood samples are taken while the person is unwell and then again two weeks later to see if there has been a change in the antibody levels. This can indicate that there has been a recent Kunjin virus infection.

Incubation period

(Time between becoming infected and developing symptoms)

Unknown. Likely to be 2 to 6 days and may extend to 14 days.

Infectious period

(Time during which an infected person can infect others)

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

Infection with Kunjin virus is thought to confer lifelong immunity.

Treatment for Kunjin virus infection

Kunjin virus infection is diagnosed by antibody tests performed on blood samples. Two blood samples will usually be required, the first taken when the person is sick and the second two weeks later, to look for a change in antibody levels.

There is no specific treatment available for Kunjin virus disease. People with encephalitis require treatment in hospital, sometimes in intensive care.

There is no specific treatment for Kunjin virus infection and

How is it prevented?

Prevention of Kunjin virus infection

There is no vaccine for Kunjin virus disease. The only way to prevent the disease is to prevent being bitten by infected mosquitoes.

To prevent being bitten by mosquitoes that may transmit Kunjin:

Stay indoors when mosquitoes are most active, from just before sunset after dawn.

Wear loose, light-colored clothing with long sleeves, long trousers and socks (mosquitoes can bite through tight-fitting clothes).

Apply a protective repellent contain­ing up to 20 percent diethyl toluamide (DEET) or picaridin to exposed areas of skin and reapply as directed by the manufacturer. Lotions and gels are more effective and long lasting than sprays.

Use other mosquito protection devices such as mosquito lanterns.

Apply residual pyrethroids around the home or campsite, and/or to nearby shrubbery that provide a harbourage for mosquitoes.

Ensure flyscreens in houses or caravans are in good condition.

If camping out, sleep in a mosquito-proof tent or under a mosquito net. Repellents only protect against mosquito bites for up to four hours, not all night.

There is currently no vaccine against Kunjin virus disease.

To protect against mosquitoes and reduce the risk of diseases they transmit:

  • Cover-up with a loose-fitting long sleeved shirt and long pants when outside
  • Apply mosquito repellent to exposed skin
  • Take special care during peak mosquito biting hours, especially around dawn and dusk
  • Remove potential mosquito breeding sites from around the home and screen windows and doors
  • Take extra precautions when travelling or camping in areas with a higher risk of mosquito-borne diseases.

For more detailed information on reducing the risk of mosquito bites at home and while travelling see the Mosquitoes are a Health Hazard factsheet. This also includes more information on mosquito repellents.

  • Exclusion from childcare, preschool, school or work is not necessary but cases should avoid being bitten by mosquitoes while they are unwell.
  • There is no vaccine to prevent human infection by Kunjin virus.
  • Personal protection and the environmental management of mosquitoes are the keys to prevention. For tips on how to protect yourself, see Fight the Bite.

 

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