What is tick-borne encephalitis?

Tick-borne encephalitis is inflammation of the brain caused by a virus carried by ticks, which are small, blood-sucking parasites. The virus can be transmitted from an infected tick to humans through a tick bite.

Tick-borne encephalitis occurs across a vast area ranging from western Europe to the east coast of Japan. This includes regions between eastern France to northern Japan and also from northern Russia to Albania. It most commonly occurs from April through to November, with about 8,500 cases being reported each year worldwide. [1]

1. Fischer M. Yendell S.J. and Rollin P.E. “Tickborne Encephalitis - Chapter 3 - 2014 Yellow Book | Travelers’ Health | CDC.” Accessed June 25, 2015.

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Causes

The tick-borne encephalitis virus enters the body from the saliva of a tick during a bite. Once inside the body, the virus replicates within cells and particularly affects the central nervous system, leading to inflammation of the brain. Tick-borne encephalitis can also be caused by drinking unpasteurised milk from infected animals. There have also been reports of the condition being passed on through:

  • Slaughtering of infected goats;
  • Blood transfusions, and;
  • Breastfeeding.

A tick can cause tick-borne encephalitis.The tick carries the virus that causes tick-borne encephalitis. 

Central nervous system

The part of the body's nervous system that includes the brain and the spinal cord.

Unpasteurised milk

Milk that has not undergone pasteurisation, a partial sterilisation process that kills bacteria by heating it to 65°C for 30 minutes, or 72°C for 15 minutes, followed by rapid cooling.

1. Fischer M. Yendell S.J. and Rollin P.E. “Tickborne Encephalitis - Chapter 3 - 2014 Yellow Book | Travelers’ Health | CDC.” Accessed June 25, 2015.

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Risk factors

Risk factors associated with tick-borne encephalitis can include:

  • Age - older people are more at risk;
  • Travelling to, or living in, an infected area, and;
  • Having a weakened immune system.

Immune system

The organs and cells involved in protecting the body against infection.

1. Fischer M. Yendell S.J. and Rollin P.E. “Tickborne Encephalitis - Chapter 3 - 2014 Yellow Book | Travelers’ Health | CDC.” Accessed June 25, 2015.

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Types

There are three virus types that cause tick-borne encephalitis, including:

  • European or Western tick-borne encephalitis virus;
  • Far Eastern tick-borne encephalitis virus, and;
  • Siberian tick-borne encephalitis virus.

The different types can vary in severity, with the Far Eastern type tending to be more severe and having a higher fatality rate.

Countries at risk of tick-borne encephalitis.Countries where tick-borne encephalitis occurs. 

1. Fischer M. Yendell S.J. and Rollin P.E. “Tickborne Encephalitis - Chapter 3 - 2014 Yellow Book | Travelers’ Health | CDC.” Accessed June 25, 2015.

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Signs and symptoms

Following an initial tick bite, there may be an incubation period of 4-28 days, though it typically lasts about eight days. Often there are no symptoms at this stage. Signs and symptoms occur at different stages of the condition and these can vary from none to severe symptoms.

During the first stage, which occurs which usually follows a week without symptoms, it is possible to experience:

  • Flu-like symptoms;
  • Fever;
  • Fatigue;
  • Malaise, or a feeling of general discomfort;
  • Headache, and;
  • Body pain.

During the second stage, which usually follows a week without symptoms, it is possible to experience:

  • A stiff neck and difficulty looking at bright lights;
  • Confusion and agitation;
  • Muscle weakness;
  • Difficulty with speech or hearing;
  • Seizures, and;
  • Paralysis.

Paralysis

An inability to move or feel; a loss of muscle function or sensation.

Seizures

A sudden, involuntary contraction of muscle groups caused by abnormal electrical activity in the brain.

1. Fischer M. Yendell S.J. and Rollin P.E. “Tickborne Encephalitis - Chapter 3 - 2014 Yellow Book | Travelers’ Health | CDC.” Accessed June 25, 2015.

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Methods for diagnosis

If a tick-borne encephalitis infection is suspected, the doctor will carry out specific blood tests to detect the presence of the virus. To assist with diagnosis, a lumbar puncture may also be performed to get a sample of fluid from around the brain and spinal cord. This involves inserting a small needle through the back of your spine, under local anaesthetic, to collect the fluid.

Local anaesthetic

A type of medication that, when administered to an area, creates a localised loss of sensation by blocking nerve activity.

1. Fischer M. Yendell S.J. and Rollin P.E. “Tickborne Encephalitis - Chapter 3 - 2014 Yellow Book | Travelers’ Health | CDC.” Accessed June 25, 2015.

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Types of treatment

There is no specific treatment for tick-borne encephalitis. If you are suffering from the condition, treatment will focus on managing your symptoms and supporting your body's immune system as it handles the infection. Some supportive treatments to help your body recover include rest, drinking plenty of fluids, and medications to help with fever and pain, such as paracetamol, or non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen.

Immune system

The organs and cells involved in protecting the body against infection.

NSAIDs

Non-steroidal anti-inflammatory drugs are commonly used to manage arthritis-related pain and inflammation and other musculoskeletal disorders. NSAIDs include aspirin and ibuprofen.

1. Fischer M. Yendell S.J. and Rollin P.E. “Tickborne Encephalitis - Chapter 3 - 2014 Yellow Book | Travelers’ Health | CDC.” Accessed June 25, 2015.

External link

Prognosis

Tick-borne encephalitis can be a serious, life-threatening condition. Although most people will make a full recovery, there is small chance for death, especially in elderly people. The Far Eastern type can have a death rate of greater than one in five. [2]   Depending on the severity of the initial condition, there is a risk of ongoing symptoms including headaches, concentration difficulties and memory impairment.

2. Lindquist L. and Vapalahti O. (2008) Tick-borne encephalitis. Lancet 371:1861–1

Prevention

Effective vaccines exist against tick-borne encephalitis. They can be administered to people living in, or travelling to, areas where the virus is commonly found. Currently there is no tick-borne encephalitis vaccine registered in Australia. However, in Europe, there are two vaccines based on the European subtype. There are also two other vaccines available in Russia that are based on the Far Eastern subtypes. Other prevention methods include:

  • Covering exposed skin with long-sleeved shirts and pants to avoid tick bites;
  • Consuming only pasteurised dairy products;
  • Checking your clothing and body for ticks, and;
  • Using insect repellent.

Vaccination.Vaccines are effective in preventing tick-borne encephalitis. 

Vaccine

A preparation containing a microorganism (that causes a specific disease) in a dead or weakened state, or parts of it, for the purpose of inducing immunity in a person to that microorganism.

Pasteurised

Having undergone pasteurisation, a partial sterilisation process that kills bacteria by heating the milk to 65°C for 30 minutes, or 72°C for 15 minutes, followed by rapid cooling. Pasteurisation kills bacteria responsible for conditions such as typhoid and tuberculosis.

2. Lindquist L. and Vapalahti O. (2008) Tick-borne encephalitis. Lancet 371:1861–1