Viral encephalitides, tick-borne

Viral encephalitides, tick-borne refers to a group of viruses that cause encephalitis. The viruses are: Tickborne encephalitis virus (TBEV); Central European tickborne encephalitis; Far Eastern tickborne encephalitis; Siberian tickborne encephalitis; Louping ill; Powassan virus encephalitis;

CASES/YEAR
1 (US); 8,000 (Global)
CATEGORY
AGENT TYPE
Viruses
OTHER NAMES
Tickborne encephalitis virus (TBEV); Central European tickborne encephalitis; Far Eastern tickborne encephalitis (Russian spring-summer); Siberian tickborne encephalitis; Louping ill; Powassan virus encephalitis;
ACUITY
Acute-Severe
INCUBATION
8 days, range of 4-28 days, for TBEV; 3-4 days after milk exposure; [CDC Travel, p. 349]
INITIAL SYMPTOMS
Flu-like illness with fever, headache, nausea/vomiting, and myalgias;
PRECAUTIONS
"Rare cases of human-to-human transmission of certain arboviruses have occurred through blood transfusions, transplanted organs, breast-feeding, and the transplacental route. Percutaneous and aerosol transmission of arboviruses can occur in the laboratory setting." [CCDM, p. 40]
COMMENTS
FINDINGS:
The Far Eastern variety (FEE) causes the most severe disease. All types may cause flaccid paralysis. CEE and Louping ill have a diphasic fever pattern--4-10 days after apparently recovering from the initial febrile illness, the patient develops fever again, this time with symptoms of meningoencephalitis. CEE and Looping ill usually cause a mild illness. [CCDM, 19th Ed., p. 47-9] About one in three people infected with tick-borne encephalitis (TBE) develop symptoms. Initial symptoms include fever, headache, nausea/vomiting, myalgias, and sometimes fasciculations. After a remission of 2-8 days, a minority of patients have the secondary phase of TBE with resumption of high fever, headache, and vomiting. The course for children is usually benign aseptic meningitis. Adults, and especially the elderly, are more likely to suffer complications of meningoencephalitis or meningoencephalomyelitis. Weakness may be temporary or permanent. Of hospitalized patients with Far Eastern encephalitis, up to 20% die, and up to 60% have residual neurological impairment. Hemorrhages have been reported in some cases of TBE. Other findings include tremor, paresthesias, incoordination, dysphagia, dysphasia, leukocytosis (second phase), leukopenia (initial and late phases), thrombocytopenia (initial phase) and elevated transaminases. Patients with TBE (tick-borne encephalitis) and Powassan encephalitis may have weakness and paralysis secondary to myelitis. Tick-borne hemorrhagic fevers (CEE, Powassan, Louping Ill, Russian, FEE, Crimean-Congo, Kyasanur Forest, and Omsk) are typically biphasic illnesses that begin with a flu-like illness and end with hepatomegaly and bleeding diathesis (petechiae, thrombocytopenia, and DIC). [PPID, p. 2016, 2030-1, 3519-21]

EPIDEMIOLOGY:
There is a 10% case fatality rate for Powassan encephalitis, and 50% of patients have neurological sequelae. Ticks and mammals are the main reservoirs. Effective vaccines have been used in Europe and the former USSR. [CCDM, 19th Ed., p. 47-9] TBEV is maintained in deciduous forest areas in Europe and Asia by ticks (vector and reservoir) and small rodents (amplifying hosts). Transmission can occur after ingestion of unpasteurized milk or cheese from infected goats, sheep, or cows, infrequently through laboratory exposure and slaughtering infected animals, and rarely through blood transfusion or breastfeeding. Eight cases of TBE in travelers to Europe and China were reported between 2000 and 2017. [CDC Travel, p. 349]
DIAGNOSTIC
"Serology is typically used for laboratory diagnosis." TBEV (first phase): virus isolation or RT-PCR; TBEV (second phase): virus usually not detectable; IgM-capture ELISA on serum or CSF; [CDC Travel, p. 350]
SCOPE
TBE: endemic in focal areas of Europe & Asia; ~8000 cases/yr reported with most cases in Russia (highest in Siberia, Slovenia, & Baltic States); [CDC Travel] Louping ill: British Isles & W. Europe; Powassan: Canada, US, former USSR; [CCDM, 19th Ed]
SIGNS & SYMPTOMS
  • >fatigue, weakness
  • >fever
  • >fever, biphasic or relapsing
  • >myalgia
  • E dysphagia
  • G hepatomegaly
  • G liver function test, abnormal
  • G nausea, vomiting
  • H leukocytosis
  • H leukopenia
  • H thrombocytopenia
  • N headache
  • N lethargy
  • N muscle weakness
  • N paresthesia
  • N seizure
  • N stiff neck
  • S petechiae and ecchymoses
  • *bleeding tendency
  • *cranial neuropathy
  • *encephalitis
  • *meningitis
  • *myelitis
  • *paralysis
  • *pneumonia
  • *stupor, coma
ANTIMICROBIC

No

VACCINE

Yes

ENTRY
Inhalation, Ingestion, Needle (Includes Drug Abuse), Scalpel or Transfusion
VECTOR
Ticks
SOURCE
Animal Tissue, Eating Contaminated Food, Eating Unpasteurized Milk or Cheese
RESERVOIR
Birds and Poultry, Cattle, Goats and Sheep, Deer, Elk and Antelope, Rodents, Wild Animals
RISK FACTORS
  • Consume unpasteurized milk/cheese
  • Travel to endemic area
  • Work in a medical or research lab
  • Work or play in tick-infested area
TREATMENT
No specific treatment; [CCDM]
DRUG LINK
REFERENCES FOR CASES/YEAR
1. (US) 50 cases of Powassan encephalitis have been recognized; [Harrison ID, p. 961] Guesstimate: 1 case/year;
2. (Global) 4 confirmed cases of travel-related TBE reported in UK, one in 2011 and two in 2012; Worldwide, there are 45 published reports of louping-ill with most cases in laboratory personnel. [Public Health England website] Annual number of cases = thousands (Central European), hundreds (Russian spring-summer, and 1 (Powassan); [Harrison ID, 2nd Ed, p. 1038] See "Scope": 8,000 cases/year;