Arbovirus is a non-taxonomic term coined to refer to viral pathogens transmitted by arthropods. In detail, humans may contract an infection with an arthropod-borne virus after getting bitten by mosquitoes, flies or ticks. Furthermore, infected organ transplants and blood products constitute possible sources of infection  . Patients suffering from an arbovirus infection may present with systemic febrile illness, hemorrhagic fever or encephalitis. Pathogens that may provoke arbovirus encephalitis (AE) and corresponding entities are detailed below.
Pathogens pertaining to distinct families of viruses may trigger the following diseases:
Other arboviruses are primarily known to cause systemic febrile disease or hemorrhagic fever, but affected individuals may occasionally develop AE. For instance, this applies to the causative agents of Colorado tick fever, Kyasanur forest disease, and Rift Valley fever .
While arboviruses are distributed throughout the world, specific viruses may only be encountered in determined geographic areas. For instance, the distribution of vectors, as well as wild animals that constitute the natural reservoir of these pathogens, may demarcate affected geographic regions. The latter, in turn, are strongly influenced by climatic conditions, and the climate change may entail the expansion of arboviruses . To date, distribution patterns of AE are as follows :
Pathogens are inoculated peripherally, replicate and disseminate through the bloodstream. In immunocompetent patients, this process is generally associated with seroconversion and results in virus clearance. Thus, most patients who contract an arbovirus infection remain asymptomatic or merely develop flu-like symptoms. Neuroinvasion and AE are more likely in those individuals suffering from an immune system disorder, receiving immunosuppressive medication, and the elderly, and occurs in less than 1% of cases .
After an incubation period of a few days, AE patients start to suffer from flu-like symptoms such as fever, headaches, and myalgia. A short period of apparent resolution may pass until additional symptoms manifest, namely nausea, vomiting and meningism with neck stiffness . The onset of neurological symptoms clearly indicates central nervous system involvement, and patients may present with an altered mental status, tremor, myoclonic jerks, seizures, limb weakness, paralysis, and photophobia. Reduced consciousness ranging from somnolence to coma may be observed.
AE-associated symptoms generally persist for few weeks, but may occasionally last several months.
Symptoms presented in the case of AE are unspecific. The consideration of anamnestic data is of utmost importance at the time of establishing a list of differential diagnoses. Patients should be queried about recent journeys and stays in endemic areas as described above.
The following diagnostic measures may be undertaken to confirm a tentative diagnosis of AE: