Eastern equine encephalitis virus
Encyclopedia
Eastern equine encephalitis virus (EEE), commonly called sleeping sickness (not to be confused with Trypanosomiasis
) 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 horse
s died of encephalitic
illness. Epizootics in horses have continued to occur regularly in the United States. EEE is found today in the eastern part of the country and is often associated with coastal plains.
This virus has two distinct antigenic variants, the more pathogenic North American and the less pathogenic South American.
s, bird
s, reptile
s and amphibian
s. The virus is maintained in nature through a bird
- mosquito
cycle. There are two mosquito species primarily involved in this portion of the cycle, they are Culiseta melanura and Cs. morsitans. These mosquitoes feed on the blood of birds. The amount of virus found in nature increases throughout the summer as more birds and more mosquitoes become infected. Transmission of EEEV to mammals occurs via other mosquitoes. These other mosquitoes are called bridge vectors because they bring the virus from avian populations to mammalian populations. They include Coquiletidia perturbans, Aedes vexans, Ochlerotatus sollicitans and Oc. canadensis. All these mosquitoes are primarily mammalian feeders. Generally, people only become sick through the bite of an infected mosquito. Humans, horses and other infected mammals do not circulate enough virus in their blood to infect additional mosquitoes. There have been some cases where EEEV has been contracted through lab exposures or from exposure of the eyes, lungs or skin wounds to brain or spinal cord matter from infected animals.
, muscle pain, altered mental status, headache
, meningeal
irritation, photophobia, and seizures, which occur three to 10 days after the bite of an infected mosquito
.
s. These vaccinations are usually given together with vaccinations for other diseases, most commonly WEE
, VEE
, and tetanus
. Most vaccinations for EEE consist of the killed virus.
, and antipyretics. Some 30-35% of infected humans die, and half of survivors are left with neurologic sequalae.
There is no cure for an EEE infected horse, and 75–90% of horses die. Survivors are left with severe sequalae. Intravenous ribavirin
has been considered as a possible treatment.
Several states in the northeast US have seen increased virus activity since 2004. Between 2004 and 2006, there were at least 10 human cases of EEE reported in Massachusetts. In 2006, approximately 500000 acres (2,023.4 km²) in southeastern Massachusetts were treated with mosquito adulticides to reduce the risk of humans contracting EEE. There have been several human cases reported in New Hampshire as well. http://www.boston.com/news/local/massachusetts/articles/2006/08/18/mosquito_borne_virus_infects_2d_in_mass/http://www.boston.com/news/globe/city_region/breaking_news/2006/08/middleborough_b.html
In October 2007, a citizen of Livingston, West Lothian, Scotland
became the first European victim of this disease. The man had visited New Hampshire during the summer of 2007 on a fishing vacation, and was diagnosed as having EEEV on 13 September 2007. He fell ill with the disease on 31 August 2007, just one day after flying home.http://news.bbc.co.uk/1/hi/scotland/edinburgh_and_east/7033203.stm
EEEV is closely related to Venezuelan equine encephalitis virus
and Western equine encephalitis virus
.
Trypanosomiasis
Trypanosomiasis or trypanosomosis is the name of several diseases in vertebrates caused by parasitic protozoan trypanosomes of the genus Trypanosoma. Approximately 500,000 men, women and children in 36 countries of sub-Saharan Africa suffer from human African trypanosomiasis which is caused by...
) or Triple E, is a zoonotic
Zoonosis
A zoonosis or zoonoseis any infectious disease that can be transmitted from non-human animals to humans or from humans to non-human animals . In a study of 1415 pathogens known to affect humans, 61% were 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...
and arbovirus
Arbovirus
Arbovirus is a term used to refer to a group of viruses that are transmitted by arthropod vectors. The word arbovirus is an acronym . Some arboviruses are able to cause emergent disease.-Transmission:...
present in North, Central and South America and the Caribbean. EEE was first recognized in Massachusetts
Massachusetts
The Commonwealth of Massachusetts is a state in the New England region of the northeastern United States of America. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. As of the 2010...
, USA in 1831 when 75 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...
s died of encephalitic
Encephalitis
Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue...
illness. Epizootics in horses have continued to occur regularly in the United States. EEE is found today in the eastern part of the country and is often associated with coastal plains.
Virus
The causal agent, EEE, was first isolated from infected horse brains in 1933. In 1938, the first confirmed human cases were identified when thirty children died of encephalitis in the northeastern United States. These cases coincided with outbreaks in horses in the same regions. The fatality rate in humans is 35% and there is currently no cure for human infections.This virus has two distinct antigenic variants, the more pathogenic North American and the less pathogenic South American.
Life cycle
EEE is capable of infecting a wide range of animals including mammalMammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, bird
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...
s, reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s and amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s. The virus is maintained in nature through a bird
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...
- 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...
cycle. There are two mosquito species primarily involved in this portion of the cycle, they are Culiseta melanura and Cs. morsitans. These mosquitoes feed on the blood of birds. The amount of virus found in nature increases throughout the summer as more birds and more mosquitoes become infected. Transmission of EEEV to mammals occurs via other mosquitoes. These other mosquitoes are called bridge vectors because they bring the virus from avian populations to mammalian populations. They include Coquiletidia perturbans, Aedes vexans, Ochlerotatus sollicitans and Oc. canadensis. All these mosquitoes are primarily mammalian feeders. Generally, people only become sick through the bite of an infected mosquito. Humans, horses and other infected mammals do not circulate enough virus in their blood to infect additional mosquitoes. There have been some cases where EEEV has been contracted through lab exposures or from exposure of the eyes, lungs or skin wounds to brain or spinal cord matter from infected animals.
Presentation
After inoculation by the vector, the virus travels via lymphatics to lymph nodes, and replicates in macrophages and neutrophils, resulting in lymphopenia, leukopenia and fever. Subsequent replication occurs in other organs leading to viremia. Symptoms in horses occur one to three weeks after infection, and begins with a fever that may reach as high as 106 °F (41 °C). The fever usually lasts for 24–48 hours. Nervous signs appear during the fever that include sensitivity to sound, periods of excitement, and restlessness. Brain lesions appear, causing drowsiness, drooping ears, circling, aimless wandering, head pressing, inability to swallow, and abnormal gait. Paralysis follows, causing the horse to have difficulty raising its head. The horse usually suffers complete paralysis and death two to four days after symptoms appear. Mortality rates among horses with the eastern strain range from 70 to 90%. In humans, symptoms include high feverFever
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...
, muscle pain, altered mental status, headache
Headache
A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...
, meningeal
Meninges
The meninges is the system of membranes which envelopes the central nervous system. The meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system.-Dura...
irritation, photophobia, and seizures, which occur three to 10 days after the bite of an infected 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...
.
Prevention
The disease can be prevented in horses with the use of vaccinationVaccination
Vaccination is the administration of antigenic material to stimulate the immune system of an individual to develop adaptive immunity to a disease. Vaccines can prevent or ameliorate the effects of infection by many pathogens...
s. These vaccinations are usually given together with vaccinations for other diseases, most commonly WEE
Western equine encephalitis virus
The Western equine encephalomyelitis virus is the causative agent of relatively uncommon viral disease Western equine encephalomyelitis . An Alphavirus of the family Togaviridae, the WEE virus is an arbovirus transmitted by mosquitoes of the genera Culex and Culiseta...
, VEE
Venezuelan equine encephalitis virus
Venezuelan equine encephalitis virus is a mosquito-borne viral pathogen that causes Venezuelan equine encephalitis or encephalomyelitis . VEE can affect all equine species, such as horses, donkeys, and zebras. After infection, equines may suddenly die or show progressive central nervous system...
, and tetanus
Tetanus
Tetanus is a medical condition characterized by a prolonged contraction of skeletal muscle fibers. The primary symptoms are caused by tetanospasmin, a neurotoxin produced by the Gram-positive, rod-shaped, obligate anaerobic bacterium Clostridium tetani...
. Most vaccinations for EEE consist of the killed virus.
Treatment and prognosis
There is no cure for EEE. Treatment consists of corticosteroids, anticonvulsants, and supportive measures (treating symptoms) such as intravenous fluids, tracheal intubationTracheal intubation
Tracheal intubation, usually simply referred to as intubation, is the placement of a flexible plastic or rubber tube into the trachea to maintain an open airway or to serve as a conduit through which to administer certain drugs...
, and antipyretics. Some 30-35% of infected humans die, and half of survivors are left with neurologic sequalae.
There is no cure for an EEE infected horse, and 75–90% of horses die. Survivors are left with severe sequalae. Intravenous ribavirin
Ribavirin
Ribavirin is an anti-viral drug indicated for severe RSV infection , hepatitis C infection and other viral infections. Ribavirin is a prodrug, which when metabolised resembles purine RNA nucleotides...
has been considered as a possible treatment.
Epidemiology
In October 2007, a citizen of Livingston, West Lothian, Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
became the first European victim of this disease. The man had visited New Hampshire during the summer of 2007 on a fishing vacation, and was diagnosed as having EEEV on 13 September 2007. He fell ill with the disease on 31 August 2007, just one day after flying home.http://news.bbc.co.uk/1/hi/scotland/edinburgh_and_east/7033203.stm
EEEV is closely related to Venezuelan equine encephalitis virus
Venezuelan equine encephalitis virus
Venezuelan equine encephalitis virus is a mosquito-borne viral pathogen that causes Venezuelan equine encephalitis or encephalomyelitis . VEE can affect all equine species, such as horses, donkeys, and zebras. After infection, equines may suddenly die or show progressive central nervous system...
and Western equine encephalitis virus
Western equine encephalitis virus
The Western equine encephalomyelitis virus is the causative agent of relatively uncommon viral disease Western equine encephalomyelitis . An Alphavirus of the family Togaviridae, the WEE virus is an arbovirus transmitted by mosquitoes of the genera Culex and Culiseta...
.
Use as a biological weapon
EEEV was one of more than a dozen agents that the United States researched as potential biological weapons before the nation suspended its biological weapons program.Sources
- Recent case of Triple E, causing (possibly permanent) coma http://news.bbc.co.uk/2/hi/uk_news/scotland/edinburgh_and_east/7033203.stm
- The CDC web page with more complete information:http://www.cdc.gov/ncidod/dvbid/arbor/eeefact.htm
- Source for a portion of this information: Evans, Borton, Hintz, Van Vleck. The Horse. 1977. W.H. Freeman and Company. New York.
External links
- http://www.seacoastonline.com/articles/20081010-NEWS-81010036
- Erich TraubErich TraubErich Traub was a German veterinarian and scientist/virologist who specialized in foot-and-mouth disease, Rinderpest and Newcastle disease. Traub was a member of the National Socialist Motor Corps , a Nazi motorist corps, from 1938–1942...
- Plum Island Animal Disease CenterPlum Island Animal Disease CenterPlum Island Animal Disease Center is a United States federal research facility dedicated to the study of animal diseases. It is part of the DHS Directorate for Science and Technology....
- Virus Pathogen Database and Analysis Resource (ViPR): Togaviridae