Tick borne encephalitis

 

TBE is transmitted by tick bite (Ixodes)

Western Subtypes- common in central and North Europe. Travellers to forests between spring and autumn seasons are at risk of infections.

Eastern Subtypes which are common in East Europe (Russia) and Asia. Transmissions occur when unpasteurised milk from goat is consumed.

The reservoirs are wild vertebrates but the natural hosts are small rodents.

Other hosts include goats, cows, sheep, deer, swine and humans. It causes mild illness in animals.

The incubation period after tick bite is between 7 and 14 days. However it is shorter if the transmission occur after ingestion of milk (3-4 days).

In general the case fatality rate is around 1 %.

More severe disease is caused by the Eastern TBEV and the case fatality could be as high as 20 %.

 

Clinical Presentation

Asymptomatic infection is common (70 %).

The illness starts with sudden onset of flu like symptoms.

The western subtype causes biphasic febrile illness having afebrile period of 2 to 10 days in between: on the other hand the eastern subtype has monophasic course.

 

1. Febrile form

Fever, pain in the neck, and back.

Mild headache characterised by high grade fever, nausea, vomiting, and headache. Neurological problems are absent in this form..

The majority will recover within a few days.

 

2. Meningeal form

Symptoms are severe. Nausea, vomiting, headache, stiff neck and photophobia are common.

 

 3. Meningoencephalitis form

Fever, headache, meningeal signs, ataxia and tremor.

Cognitive dysfunction-impaired concentration and memory.

Dysphasia.

Altered consciousness and confusion.

Spinal and cranial nerve paralysis.

 

4. Poliomyelitis form (flaccid paralysis)

Patients with this form of illness may not develop any prodromal signs.

Periodic muscle contraction, sense of weakness and numbness are the main manifestations.

 

5. Polyradiculoneuritic form

Damage to peripheral nerve is common.

Focal neurological symptoms may be present.

 

6. Chronic form

Commonly caused by Eastern TBE.

Signs and symptoms may persist for several months or years.

Epilepsy, Parkinson like disease, progressive muscular atrophy, severe demyelination and death are common.

 

Complications

Acute paralysis- hemiplegia

Hearing defect

 

Risk factors for permanent neurological problems

  • Increasing age

  • Impaired consciousness

  • Paralysis

  • Abnormal finding on MRI

 

Investigation

 

CBC- leukopenia and thrombocytopenia

CSF- low leukocytes number. Occasionally pleocytosis with lymphocytosis predominance. Increase in protein level. Normal Glucose level.

CT and MRI have limited role.

 

Tests

EIA- Normally serum is positive for IgM at the time of presentation however the CSF IgM is detectable only after 10 from the onset of illness.

PCR may be used to detect infection with this virus.

EM- brain biopsy is useful but is not recommended unless in post-mortem.

 

Management

 

Supportive

  • Bed rest

  • Paracetamol

TBEV specific immunoglobulin has been used in Russia and it is considered to be effective.

 

 

Prevention

 

Inactivated vaccine is available.

The virus can be inactivated by organic solvents and detergents.

Insect repellents should be advised.

Covering arms and ankles reduce the chance of tick bites.

 

 

 

 

 

Text Box: TBEV vaccine It is inactivated vaccine. It has been shown to be effective to control outbreaks. Routine vaccination in Austria has reduced the incidence of TBEV infection. Three doses are given. More than 95 % individuals respond to the vaccine after the third doses.   Indications for vaccination are Travel to endemic areas Being resident in endemic areas   Contraindication Allergy to eggs.   Adverse effects Local- pain. Systemic- pruritic rash.