Ross River Fever
Encyclopedia
Ross River Fever is a mosquito
-borne infectious disease
caused by infection with the Ross River virus
. The illness is typically characterised by an influenza-like illness
and polyarthritis
. The virus is endemic
to Australia
, Papua New Guinea
, Fiji
, Samoa
, the Cook Islands
, New Caledonia
and several other islands in the South Pacific
.
and Narrandera
region in New South Wales, Australia. The virus was first isolated in 1959 from a mosquito trapped along the Ross River in Townsville, Queensland
. Since then, outbreaks have occurred in all Australian states, including Tasmania, and metropolitan areas. The largest outbreak occurred in 1979-1980 in the Western Pacific, and affected more than 60,000 people.
Before the identification of this infectious agent, the disease was referred to as "epidemic polyarthritis". This term was also used for a similar Australian disease caused by another mosquito
-borne virus, Barmah Forest Virus
.
. Geographical risk factors include areas of higher rainfall and higher maximal tides. In the tropics, Ross River Fever is more prevalent during the summer/autumn "wet season
", particularly January - March, when mosquito
populations numbers are high. In southern parts of Australia, this time period may shift to earlier in the year during spring/summer. Areas near suitable mosquito breeding grounds — marsh
es, wetland
s, waterways and farms with irrigation systems — are high risk areas for outbreaks. As such, the disease is more characteristic of rural and regional areas. Infection is most common in adult aged 25–44 years old, with males and females equally affected. Ross River Fever is on the Australian Department of Health and Ageing's list of notifiable disease
s.
s are kangaroos
and wallabies
, although horses, possums and possibly birds and flying foxes
play a role. Over 30 species have been implicated as possible vectors, but the major species for Ross River Fever are Culex annulirostris in inland areas, Aedes vigilax in northern coastal regions and Ae. camptorhynchus in southern coastal regions.
, arthritis
, fever
, and rash
. The incubation period is 7–9 days. About a third of infections are asymptomatic, particularly in children.
and headache occur in 50-60%. The rash occurs in 50% and is widespread and maculopapular. Lymphadenopathy occurs commonly; sore throat and coryza less frequently. Diarrhea is rare. About 50% of people report needing time off work with the acute illness. If the rash is unnoticed, these symptoms are quite easily mistaken for more common illnesses like influenza
or the common cold
. Recovery is expected within a month.
Less common manifestations include splenomegaly, hematuria and glomerulonephritis. Headache, neck stiffness, and photophobia may occur. There have been three case reports suggesting meningitis or encephalitis.
and Q fever
. The presence of a pre-morbid diagnosis of depression strongly influences the chance of significant illness at 12 months.
is the only way to confirm a case of Ross River Fever. Several types of blood tests may be used to examine antibody levels in the blood. Tests may either look for simply elevated antibodies (which indicate some sort of infection), or specific antibodies to the virus.
and repeated infection with the virus is very rare.
. Mice infected with RRV develop hind-limb arthritis/arthralgia which is similar to human disease. The disease in mice is characterized by an inflammatory infiltrate including macrophages which are immunopathogenic and exacerbate disease. Furthermore, mice deficient in the C3 protein do not suffer from severe disease following infection. This indicates that an aberrant innate immune response is responsible for severe disease following RRV infection.
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
-borne infectious disease
Infectious disease
Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...
caused by infection with the Ross River virus
Ross River virus
Ross River virus is a small encapsulated single-strand RNA alphavirus endemic to Australia, Papua New Guinea and other islands in the South Pacific. It is responsible for a type of mosquito-borne non-lethal but debilitating tropical disease known as Ross River fever, previously termed "epidemic...
. The illness is typically characterised by an influenza-like illness
Influenza-like illness
Influenza-like illness , also known as acute respiratory infection and flu-like syndrome, is a medical diagnosis of possible influenza or other illness causing a set of common symptoms, with SARI referring to Severe Acute Respiratory Infection.Symptoms commonly include fever, shivering, chills,...
and polyarthritis
Polyarthritis
Polyarthritis is any type of arthritis which involves 5 or more joints simultaneously. It is usually associated with autoimmune conditions.Polyarthritis may be experienced at any age and is not gender specific.-Causes:...
. The virus is endemic
Endemic (epidemiology)
In epidemiology, an infection is said to be endemic in a population when that infection is maintained in the population without the need for external inputs. For example, chickenpox is endemic in the UK, but malaria is not...
to Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, Papua New Guinea
Papua New Guinea
Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...
, Fiji
Fiji
Fiji , officially the Republic of Fiji , is an island nation in Melanesia in the South Pacific Ocean about northeast of New Zealand's North Island...
, Samoa
Samoa
Samoa , officially the Independent State of Samoa, formerly known as Western Samoa is a country encompassing the western part of the Samoan Islands in the South Pacific Ocean. It became independent from New Zealand in 1962. The two main islands of Samoa are Upolu and one of the biggest islands in...
, the Cook Islands
Cook Islands
The Cook Islands is a self-governing parliamentary democracy in the South Pacific Ocean in free association with New Zealand...
, New Caledonia
New Caledonia
New Caledonia is a special collectivity of France located in the southwest Pacific Ocean, east of Australia and about from Metropolitan France. The archipelago, part of the Melanesia subregion, includes the main island of Grande Terre, the Loyalty Islands, the Belep archipelago, the Isle of...
and several other islands in the South Pacific
Oceania
Oceania is a region centered on the islands of the tropical Pacific Ocean. Conceptions of what constitutes Oceania range from the coral atolls and volcanic islands of the South Pacific to the entire insular region between Asia and the Americas, including Australasia and the Malay Archipelago...
.
History
The first outbreak of RRF was in 1928 in the HayHay, New South Wales
Hay is a town in the western Riverina region of south western New South Wales , Australia. It is the administrative centre of Hay Shire Local Government Area and the centre of a prosperous and productive agricultural district on the wide Hay Plains....
and Narrandera
Narrandera, New South Wales
-Transport:Narrandera is well served for transport. The Sturt Highway and the Newell Highways cross, just south of Narrandera. Greyhound buses pass daily - note that the destination can be listed as Jillenbah....
region in New South Wales, Australia. The virus was first isolated in 1959 from a mosquito trapped along the Ross River in Townsville, Queensland
Townsville, Queensland
Townsville is a city on the north-eastern coast of Australia, in the state of Queensland. Adjacent to the central section of the Great Barrier Reef, it is in the dry tropics region of Queensland. Townsville is Australia's largest urban centre north of the Sunshine Coast, with a 2006 census...
. Since then, outbreaks have occurred in all Australian states, including Tasmania, and metropolitan areas. The largest outbreak occurred in 1979-1980 in the Western Pacific, and affected more than 60,000 people.
Before the identification of this infectious agent, the disease was referred to as "epidemic polyarthritis". This term was also used for a similar Australian disease caused by another mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
-borne virus, Barmah Forest Virus
Barmah Forest virus
Barmah Forest virus is a virus currently found only in Australia. According to a Queensland Public Health Services fact sheet, "there is no specific drug treatment" for the virus, but the disease is non-fatal and relatively mild. The virus is transmitted to humans by bites from infected...
.
Incidence and epidemiology
Most notifications are from Queensland, tropical Western Australia and the Northern TerritoryNorthern Territory
The Northern Territory is a federal territory of Australia, occupying much of the centre of the mainland continent, as well as the central northern regions...
. Geographical risk factors include areas of higher rainfall and higher maximal tides. In the tropics, Ross River Fever is more prevalent during the summer/autumn "wet season
Wet season
The the wet season, or rainy season, is the time of year, covering one or more months, when most of the average annual rainfall in a region occurs. The term green season is also sometimes used as a euphemism by tourist authorities. Areas with wet seasons are dispersed across portions of the...
", particularly January - March, when mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
populations numbers are high. In southern parts of Australia, this time period may shift to earlier in the year during spring/summer. Areas near suitable mosquito breeding grounds — marsh
Marsh
In geography, a marsh, or morass, is a type of wetland that is subject to frequent or continuous flood. Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, other herbaceous plants, and moss....
es, wetland
Wetland
A wetland is an area of land whose soil is saturated with water either permanently or seasonally. Wetlands are categorised by their characteristic vegetation, which is adapted to these unique soil conditions....
s, waterways and farms with irrigation systems — are high risk areas for outbreaks. As such, the disease is more characteristic of rural and regional areas. Infection is most common in adult aged 25–44 years old, with males and females equally affected. Ross River Fever is on the Australian Department of Health and Ageing's list of notifiable disease
Notifiable disease
A notifiable disease is any disease that is required by law to be reported to government authorities. The collation of information allows the authorities to monitor the disease, and provides early warning of possible outbreaks. Many governments have enacted regulations for reporting of both human...
s.
Transmission
The virus is not contagious and is spread only by mosquitoes. The main reservoir hostNatural reservoir
Natural reservoir or nidus, refers to the long-term host of the pathogen of an infectious disease. It is often the case that hosts do not get the disease carried by the pathogen or it is carried as a subclinical infection and so asymptomatic and non-lethal...
s are kangaroos
KangaROOS
KangaROOS are an American brand of sneaker originally produced from 1979 through the 1980s, with a later revival that continues in present. They were notable for having a small zippered pocket on the side of the shoe, large enough for a small amount of loose change, keys, or more recently,...
and wallabies
Wallaby
A wallaby is any of about thirty species of macropod . It is an informal designation generally used for any macropod that is smaller than a kangaroo or wallaroo that has not been given some other name.-Overview:...
, although horses, possums and possibly birds and flying foxes
Pteropus
Bats of the genus Pteropus, belonging to the megabat or Megachiroptera sub-order, are the largest bats in the world. They are commonly known as the fruit bats or flying foxes among other colloquial names...
play a role. Over 30 species have been implicated as possible vectors, but the major species for Ross River Fever are Culex annulirostris in inland areas, Aedes vigilax in northern coastal regions and Ae. camptorhynchus in southern coastal regions.
Symptoms
Symptoms of the disease may vary widely in severity, but major indicators are arthralgiaArthralgia
Arthralgia literally means joint pain; it is a symptom of injury, infection, illnesses or an allergic reaction to medication....
, arthritis
Arthritis
Arthritis is a form of joint disorder that involves inflammation of one or more joints....
, fever
Fever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
, and rash
Rash
A rash is a change of the skin which affects its color, appearance or texture. A rash may be localized in one part of the body, or affect all the skin. Rashes may cause the skin to change color, itch, become warm, bumpy, chapped, dry, cracked or blistered, swell and may be painful. The causes, and...
. The incubation period is 7–9 days. About a third of infections are asymptomatic, particularly in children.
Acute illness
About 95% of symptomatic cases report joint pain. This is typically symmetrical and with acute onset, affecting the fingers, toes, ankles, wrists, back, knees and elbows. Fatigue occurs in 90% and fever, myalgiaMyalgia
Myalgia means "muscle pain" and is a symptom of many diseases and disorders. The most common causes are the overuse or over-stretching of a muscle or group of muscles. Myalgia without a traumatic history is often due to viral infections...
and headache occur in 50-60%. The rash occurs in 50% and is widespread and maculopapular. Lymphadenopathy occurs commonly; sore throat and coryza less frequently. Diarrhea is rare. About 50% of people report needing time off work with the acute illness. If the rash is unnoticed, these symptoms are quite easily mistaken for more common illnesses like influenza
Influenza
Influenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals...
or the common cold
Common cold
The common cold is a viral infectious disease of the upper respiratory system, caused primarily by rhinoviruses and coronaviruses. Common symptoms include a cough, sore throat, runny nose, and fever...
. Recovery is expected within a month.
Less common manifestations include splenomegaly, hematuria and glomerulonephritis. Headache, neck stiffness, and photophobia may occur. There have been three case reports suggesting meningitis or encephalitis.
Chronic illness
Reports from the 1980s and 1990s suggested RRV infection was associated with athralgia, fatigue and depression lasting for years. More recent prospective studies have reported a steady improvement in symptoms over the first few months, with 15-66% of patients having ongoing arthralgia at 3 months. Arthralgias have resolved in the majority by 5–7 months. The incidence of chronic fatigue is 12% at 6 months and 9% at 12 months, similar to Epstein-Barr virusEpstein-Barr virus
The Epstein–Barr virus , also called human herpesvirus 4 , is a virus of the herpes family and is one of the most common viruses in humans. It is best known as the cause of infectious mononucleosis...
and Q fever
Q fever
Q fever is a disease caused by infection with Coxiella burnetii, a bacterium that affects humans and other animals. This organism is uncommon but may be found in cattle, sheep, goats and other domestic mammals, including cats and dogs...
. The presence of a pre-morbid diagnosis of depression strongly influences the chance of significant illness at 12 months.
Diagnosis
A blood testBlood test
A blood test is a laboratory analysis performed on a blood sample that is usually extracted from a vein in the arm using a needle, or via fingerprick....
is the only way to confirm a case of Ross River Fever. Several types of blood tests may be used to examine antibody levels in the blood. Tests may either look for simply elevated antibodies (which indicate some sort of infection), or specific antibodies to the virus.
Treatment and prevention
There are no specific treatments, for example, antiviral drugs, that target infections with RRV. Patients are usually managed with simple analgesics, anti-inflammatories, anti-pyretics and rest while the illness runs its course. Infection usually affords lifelong immunityImmunity (medical)
Immunity is a biological term that describes a state of having sufficient biological defenses to avoid infection, disease, or other unwanted biological invasion. Immunity involves both specific and non-specific components. The non-specific components act either as barriers or as eliminators of wide...
and repeated infection with the virus is very rare.
Prevention
There is currently no vaccine available. The primary method of disease prevention is minimizing mosquito bites, as the disease is only transmitted by mosquitoes. Typical advice includes use of mosquito repellent and mosquito screens, wearing light coloured clothing, and minimising standing water around homes (e.g. removing Bromeliads, plant pots, garden ponds). Staying indoors during dusk/dawn hours when mosquitos are most active may also be effective. Bush camping is a common precipitant of infection so particular care is required.Research
The study of RRF has been recently facilitated by the development of a mouse modelAnimal testing on rodents
Rodents are commonly used in animal testing, particularly guinea pigs, hamsters, gerbils, rats, and mice.-The statistics:In the UK in 2004, 1,910,110 mice, 464,727 rats and 37,475 other rodents were used...
. Mice infected with RRV develop hind-limb arthritis/arthralgia which is similar to human disease. The disease in mice is characterized by an inflammatory infiltrate including macrophages which are immunopathogenic and exacerbate disease. Furthermore, mice deficient in the C3 protein do not suffer from severe disease following infection. This indicates that an aberrant innate immune response is responsible for severe disease following RRV infection.