Introduction:
Arbovirus is an arthropod-borne virus belonging to a broad spectrum of viruses transmitted through sandflies, ticks, or mosquitoes. Arbovirus belongs to the family flaviviridae, togaviridae, reoviridae, and bunyaviridae. These have identical RNA genomes that allow mutations that help them cope with changing environments or host conditions.
These viruses have a unique trait as they require vectors for human transmission. This can cause a threat, given the increasing frequency of infections and emerging diseases. Arbovirus can lead to neurological diseases involving neuritis, myelitis, myositis, meningitis, and encephalitis. Mortality rates are directly related to the diagnosis of encephalitis. Thus arbovirus becomes a vital differential diagnosis while treating febrile individuals with neurological symptoms.
What Is the Cause of Arboviral Encephalitides?
Togaviridae Family:
- Chikungunya virus is transmitted to humans by carrier Aedes mosquitoes, blood products, and maternal-fetal transmission; the virus causes chikungunya fever and, in severe cases, causes meningoencephalitis. These infections have been noted as a reemergence in the Caribbean and La reunion island.
- Eastern equine encephalitis virus is transmitted through culiseta melanura, Aedes, culex, and coquillettidia mosquitoes. Infection is common in August and September. Two percent of individuals develop neuroinvasive diseases, which lead to rapid neurological deterioration. No vaccinations for eastern equine encephalitis, which has a high mortality rate.
- The culex mosquito spreads the western equine encephalitis virus. The virus is found in North and South America. Only one percent of affected individuals develop encephalitis. No vaccination is available for western equine encephalitis.
- Venezuelan equine encephalitis has epizootic subtype and enzootic subtypes. Mosquitoes cause the epizootic subtype, and Culex mosquitoes cause the enzootic subtype. The incubation lasts from one to six days, followed by a febrile illness. Only 0.5 percent of individuals infected develop a neuroinvasive illness.
Flaviviridae Family:
- Dengue is transmitted by Aedes albopictus or Aedes aegypti mosquitoes.
Clinically it is classified into three types:
- Dengue without warning signs.
- Dengue with warning signs.
- Severe dengue.
Studies have reported that these viruses are neurotrophic and can cause encephalitis.
- Japanese encephalitis virus is a major cause of arthropod-borne virus encephalitis in Asia. The virus is transmitted by the culex species, mainly the Culex tritaeniorhynchus, which is endemic in Asia. This virus causes infection in 68000 individuals yearly; less than one percent of infections lead to neurologic disease. There is a vaccine available for individuals traveling to endemic areas.
- Culex annulirostris mosquitoes transmit the Murray Valley encephalitis virus. The incubation lasts one to four weeks, and the individual may present with flu-like symptoms. The mortality rate is around 15 to 30 percent. This virus is only seen in Australia, Indonesia, and New Guinea.
- St.Louis encephalitis is a flavivirus transmitted by culex mosquitoes. Transmission occurs in the summertime because they are most active during summer. Individuals present with flu-like illnesses. Mortality rates are high for individuals above the age of sixty.
- West Nile virus is a mosquito-borne flavivirus suspected in people who have undergone organ transplantation, mosquito exposure, or blood transfusion. Additional risk factors include individuals with multiple comorbidities, immunosuppression, and the elderly. The culex mosquitoes transmit it, replicating it in the macrophages and dendritic cells, leading to dissemination within the human body. Usually, the cases are asymptomatic, and less than one percent have neurological findings. Currently, there is no vaccine for the West Nile virus.
Bunyaviridae Family:
- La crosse encephalitis family is transmitted by Aedes triseriatus and is very pathogenic in the encephalitis serogroup.
- Aedes mosquitoes transmit the California encephalitis virus. The mortality rate is found to be less than one percent.
Reoviridae Family:
- Dermacentor andersoni transmits the Colorado tick fever virus. They are commonly seen in the western USA and Canada. 10 percent of affected children may have a neuroinvasive disease, but the mortality rate is low.
What Is the Epidemiology of Arboviral Encephalitides?
Epidemiology depends on exposure history and recent travel, including place of residence, insect contact, occupation, animal contact, diet, and recreational activities that may help with diagnostic testing. Other factors such as vaccination history, age, seasonal variation, and immune status may help the differential diagnosis.
What Is the Pathophysiology of Arboviral Encephalitides?
The range in which the arbovirus can cause neurological effects depends on the virus and host factors. The exact pathway and mechanism of action of the virus are unknown. The infection then leads to neuronal injury and apoptosis.
What Are the Signs and Symptoms of Arboviral Encephalitides?
Arboviral encephalitides may present with varying degrees of clinical symptoms. Individuals may develop nonspecific symptoms. Typical findings include headaches, fever, altered mental status, focal neurological deficits, and seizures. Occasionally individuals may experience flu-like symptoms before having neurological diseases. The triad of headache, fever, and altered mental status can signify acute encephalitis syndrome.
Physical examination may help in detecting other causes of encephalitis. For example, skin rashes are seen in both the zika virus and the West Nile virus. West Nile virus has ocular findings such as retinal hemorrhages, chorioretinitis, and vitritis. Neurologic findings help detect specific etiologies, such as West Nile virus and St.louis encephalitis causes signs and symptoms of parkinsonism. These viruses also lead to cerebellitis, seizures, and brain stem involvement.
How Are Arboviral Encephalitides Evaluated?
Individuals may be advised to undergo a lumbar puncture if they do not have any contraindications for it. Cerebrospinal fluid is collected and analyzed for glucose concentration, cell, and differential, protein concentration, gram stain, and culture. Cerebrospinal fluid, virus-specific IgM, and polymerase chain reaction (PCR) may help in obtaining a diagnosis. Neuroimaging studies such as magnetic resonance imaging (MRI) help evaluate individuals with encephalitis. Distinct MRI findings aid in an accurate diagnosis. Electroencephalograms show abnormal findings such as diffuse irregular slow waves with viral encephalitis. Brain biopsy is done in individuals with neurological deterioration.
What Is the Treatment for Arboviral Encephalitides?
Management mainly focuses on supportive treatments as there are no antiviral treatment modalities. Supportive care is given to individuals with neurological disease progression secondary to arbovirus. Preventive measures are mandatory in endemic areas, which include personal protective measures, vector control, and vaccination if available. Travelers should avoid visiting endemic areas and avoid exposure by donning long clothing, using insect repellants, or considering getting vaccinated.
Conclusion
Arboviruses are transmitted through ticks, mosquitoes, or sandflies that cause diseases. Individuals should be aware of the complications of arbovirus that mosquitoes or ticks can transmit. Prevention measures should be followed while traveling to endemic areas. Asymptomatic individuals show complete recovery, and the prognosis depends on the virus type.
