Tick-borne meningoencephalitis
Encyclopedia
Tick-borne encephalitis (TBE) is a viral
infectious disease
involving the central nervous system
. The disease most often manifests as meningitis
, encephalitis
, or meningoencephalitis
. Although TBE is most commonly recognized as a neurological disorder
, mild fever can also occur. Long-lasting or permanent neuropsychiatric sequela
e are observed in 10-20% of infected patients.
The number of reported cases has been increasing in most countries.
The virus is known to infect a range of hosts including ruminants, birds, rodents, carnivores, horses and humans. The disease can also be zoonotic, with ruminants and dogs providing the principal source of infection for humans.
(encephalitis), the meninges
(meningitis) or both (meningoencephalitis).
In general, mortality is 1% to 2%, with deaths occurring 5 to 7 days after the onset of neurologic signs.
In dogs, the disease also manifests as a neurological disorder with signs varying from tremors to seizures and death.
In ruminants, neurological disease is also present, and animals may refuse to eat, appear lethargic, and also develop respiratory signs.
It is transmitted by the bite of several species of infected tick
s, including Ixodes scapularis
, Ixodes ricinus
and Ixodes persulcatus
, or (rarely) through the non-pasteurized
milk
of infected cows.
in the family Flaviviridae
. It was first isolated in 1937. Three virus sub-types are described: European or Western tick-borne encephalitis virus, Siberian tick-borne encephalitis virus, and Far-Eastern tick-borne encephalitis virus (formerly known as Russian spring summer encephalitis virus).
Russia and Europe report about 5,000-7,000 human cases annually.
The former Soviet Union conducted research on tick borne diseases, including the TBE viruses.
strain or subtype. In such cases a marker for TBE infection is elevated IFN-g in CSF.
Viral antigen can usually be found in brain tissue. Serological testing can also be performed with an ELISA
.
s, may be considered under specific circumstances for symptomatic relief. Tracheal intubation
and respiratory
support may be necessary, but infection can be reliably prevented by vaccination
.
Prevention includes non-specific (tick-bite prevention, tick checks) and specific prophylaxis (vaccine, TBE immunoglobulin). TBE vaccine is very effective and available in some disease endemic areas.
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
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...
involving the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
. The disease most often manifests as meningitis
Meningitis
Meningitis is inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. The inflammation may be caused by infection with viruses, bacteria, or other microorganisms, and less commonly by certain drugs...
, encephalitis
Encephalitis
Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue...
, or meningoencephalitis
Meningoencephalitis
Meningoencephalitis is a medical condition that simultaneously resembles both meningitis, which is an infection or inflammation of the meninges, and encephalitis, which is an infection or inflammation of the brain.-Causes:...
. Although TBE is most commonly recognized as a neurological disorder
Neurological disorder
A neurological disorder is a disorder of the body's nervous system. Structural, biochemical or electrical abnormalities in the brain, spinal cord, or in the nerves leading to or from them, can result in symptoms such as paralysis, muscle weakness, poor coordination, loss of sensation, seizures,...
, mild fever can also occur. Long-lasting or permanent neuropsychiatric sequela
Sequela
A sequela) is a pathological condition resulting from a disease, injury, or other trauma.Chronic kidney disease, for example, is sometimes a sequela of diabetes, and neck pain is a common sequela of whiplash or other trauma to the cervical vertebrae. Post-traumatic stress disorder may be a...
e are observed in 10-20% of infected patients.
The number of reported cases has been increasing in most countries.
The virus is known to infect a range of hosts including ruminants, birds, rodents, carnivores, horses and humans. The disease can also be zoonotic, with ruminants and dogs providing the principal source of infection for humans.
Presentation
The virus can infect the brainBrain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
(encephalitis), the meninges
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...
(meningitis) or both (meningoencephalitis).
In general, mortality is 1% to 2%, with deaths occurring 5 to 7 days after the onset of neurologic signs.
In dogs, the disease also manifests as a neurological disorder with signs varying from tremors to seizures and death.
In ruminants, neurological disease is also present, and animals may refuse to eat, appear lethargic, and also develop respiratory signs.
Transmission
Tick
Ticks are small arachnids in the order Ixodida, along with mites, constitute the subclass Acarina. Ticks are ectoparasites , living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians...
s, including Ixodes scapularis
Ixodes scapularis
Ixodes scapularis is commonly known as the deer tick or blacklegged tick , and in some parts of the USA as the bear tick. It is a hard-bodied tick of the eastern and northern Midwestern United States...
, Ixodes ricinus
Ixodes ricinus
Ixodes ricinus, the castor bean tick, is a chiefly European species of hard-bodied tick. It may reach a length of when engorged with a blood meal, and can transmit both bacterial and viral pathogens such as the causative agents of Lyme disease and tick-borne encephalitis.-Description:In common...
and Ixodes persulcatus
Ixodes persulcatus
Ixodes persulcatus, the taiga tick, is a species of hard-bodied tick distributed throughout eastern Europe and Asia to the People’s Republic of China and Japan. The sexual dimorphism of the species is marked, the male being much smaller than the female...
, or (rarely) through the non-pasteurized
Pasteurization
Pasteurization is a process of heating a food, usually liquid, to a specific temperature for a definite length of time, and then cooling it immediately. This process slows microbial growth in food...
milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...
of infected cows.
Etiology
TBE is caused by tick-borne encephalitis virus, a member of the genus FlavivirusFlavivirus
Flavivirus is a genus of the family Flaviviridae. This genus includes the West Nile virus, dengue virus, tick-borne encephalitis virus, yellow fever virus, and several other viruses which may cause encephalitis....
in the family Flaviviridae
Flaviviridae
The Flaviviridae are a family of viruses that are primarily spread through arthropod vectors . The family gets its name from Yellow Fever virus, a type virus of Flaviviridae; flavus means yellow in Latin...
. It was first isolated in 1937. Three virus sub-types are described: European or Western tick-borne encephalitis virus, Siberian tick-borne encephalitis virus, and Far-Eastern tick-borne encephalitis virus (formerly known as Russian spring summer encephalitis virus).
Russia and Europe report about 5,000-7,000 human cases annually.
The former Soviet Union conducted research on tick borne diseases, including the TBE viruses.
Diagnosis
The TBE virus may be present in a seronegativeSerostatus
Serostatus is a term used to refer to the presence or absence of specific substances in the blood serum. Most commonly, this medical test is looking for specific antibodies in an effort to diagnose a particular disease....
strain or subtype. In such cases a marker for TBE infection is elevated IFN-g in CSF.
Viral antigen can usually be found in brain tissue. Serological testing can also be performed with an ELISA
ELISA
Enzyme-linked immunosorbent assay , is a popular format of a "wet-lab" type analytic biochemistry assay that uses one sub-type of heterogeneous, solid-phase enzyme immunoassay to detect the presence of a substance in a liquid sample."Wet lab" analytic biochemistry assays involves detection of an...
.
Treatment and Prevention
The disease is incurable once manifested, so there is no specific drug therapy for TBE. Symptomatic brain damage requires hospitalization and supportive care based on syndrome severity. Anti-inflammatory drugs, such as corticosteroidCorticosteroid
Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex. Corticosteroids are involved in a wide range of physiologic systems such as stress response, immune response and regulation of inflammation, carbohydrate metabolism, protein catabolism, blood electrolyte...
s, may be considered under specific circumstances for symptomatic relief. Tracheal intubation
Tracheal 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 respiratory
Respiratory physiology
Respiratory physiology is the branch of human physiology focusing upon respiration.Topics include:-Volumes:* lung volumes* vital capacity* functional residual capacity* dead space* spirometry* body plethysmography* peak flow meter-Mechanics:...
support may be necessary, but infection can be reliably prevented by vaccination
Vaccination
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...
.
Prevention includes non-specific (tick-bite prevention, tick checks) and specific prophylaxis (vaccine, TBE immunoglobulin). TBE vaccine is very effective and available in some disease endemic areas.
External links
- Tickborne encephalitis at Centers for Disease Control and PreventionCenters for Disease Control and PreventionThe Centers for Disease Control and Prevention are a United States federal agency under the Department of Health and Human Services headquartered in Druid Hills, unincorporated DeKalb County, Georgia, in Greater Atlanta...