The Highlands J virus is a zoonotic alphavirus

Alphavirus

In biology and immunology, an alphavirus belongs to the group IV Togaviridae family of viruses, according to the system of classification based on viral genome composition introduced by David Baltimore in 1971. Alphaviruses, like all other group IV viruses have a positive sense single stranded RNA...

 native to North and South America. It maintains a natural reservoir

Natural 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...

 in the songbird

Songbird

A songbird is a bird belonging to the suborder Passeri of the perching birds . Another name that is sometimes seen as scientific or vernacular name is Oscines, from Latin oscen, "a songbird"...

 population of freshwater swamps (generally scrub jays and blue jay

Blue Jay

The Blue Jay is a passerine bird in the family Corvidae, native to North America. It is resident through most of eastern and central United States and southern Canada, although western populations may be migratory. It breeds in both deciduous and coniferous forests, and is common near and in...

s) and is transmitted by the bite of the female Culiseta melanura

Culiseta

Culiseta is a genus of mosquitoes. Most Culiseta are cold-adapted species which only occur in warmer climates during the colder parts of the year or at higher elevations where temperatures are low...

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...

.

Though nearly identical in structure and natural cycle to the Eastern equine encephalitis virus

Eastern equine encephalitis virus

Eastern equine encephalitis virus , commonly called sleeping sickness or Triple E, is a zoonotic alphavirus and arbovirus present in North, Central and South America and the Caribbean. EEE was first recognized in Massachusetts, USA in 1831 when 75 horses died of encephalitic illness...

, it is considerably less virulent than its cousin, causing relatively mild symptoms in its primary avian

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

 reservoir and only nominally capable of transmission to mammals. A 1995 study conducted in Florida

Florida

Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...

 swampland found that 15% of swamp-dwelling jays tested positive for HJ antibodies, all of which were asymptomatic

Asymptomatic

In medicine, a disease is considered asymptomatic if a patient is a carrier for a disease or infection but experiences no symptoms. A condition might be asymptomatic if it fails to show the noticeable symptoms with which it is usually associated. Asymptomatic infections are also called subclinical...

 and in apparent good health. Recorded bird deaths from HJ infection are uncommon but not rare, and include several domestic turkey

Turkey

Turkey , known officially as the Republic of Turkey , is a Eurasian country located in Western Asia and in East Thrace in Southeastern Europe...

s at a commercial facility and young broiler chicken

Chicken

The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...

s in an experimental setting.

Transmission to equines or humans via mosquito is also possible, though even more rare. During the 1990-1991 St. Louis encephalitis

St. Louis Encephalitis

St. Louis Encephalitis is a disease caused by the Culex mosquito borne St. Louis Encephalitis virus. St. Louis encephalitis virus is related to Japanese encephalitis virus and is a member of the Flaviviridae subgroup. This disease mainly affects the United States...

 outbreak in Missouri

Missouri

Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...

, 4 patients were found to be comorbidly infected with SLE and HJ, though no harmful effects were attributed to the HJ alone. A limited survey of swamp-dwelling rodent

Rodent

Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....

s in Florida found one cotton mouse

Cotton Mouse

The Cotton Mouse is a species of rodent in the family Cricetidae.It is found in the woodlands of the south-eastern states of the United States. Adults are about 7-8 inches, and have an appearance very similar to the white footed mouse. The cotton mouse is larger in size and has a longer...

 and one cotton rat

Cotton rat

A cotton rat is any member of the rodent genus Sigmodon. They are called cotton rats because they build their nests out of cotton, and can damage cotton crops. Cotton rats have small ears and dark coats, and are found in North and South America....

 with antibodies to HJ, both asymptomatic. The sole mammalian fatality attributed to HJ was a Florida horse

Horse

The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...

 originally diagnosed with Western equine encephalitis in 1964, which was later redetermined in 1989 to have been caused by HJ.

Despite its negligible virulence in humans, it is often tested for in US domestic mosquito control

Mosquito control

Mosquito control manages the population of mosquitoes to reduce their damage to human health, economies, and enjoyment. Mosquito control is a vital public-health practice throughout the world and especially in the tropics because mosquitoes spread many diseases, such as malaria.Mosquito-control...

programs as an indicator of fruitful conditions for other mosquito-borne zoonoses to multiply.