Eastern equine encephalitis (EEE) is a mosquito-borne viral disease. It is associated with a high rate of morbidity and mortality.
Important points to consider in patient history are outdoor exposures, recent travels, social history, insect bite history, work/home in high-risk areas, exposure to areas with high prevalence of mosquitoes and work related to marshes or horses.
The presentation is similar to typical viral diseases starting from headaches, vague fevers and tremendous body aches. A short prodrome of 5 to 10 days might be present with symptoms like abdominal pain, fever, diarrhea and headache.
There is rapid progress to CNS involvement, severe fatigue and weakness and high grade fever along with myalgia. Frequent headaches are felt by the patient due to meningeal irritation. Photophobia and neck stiffness are another important feature. Nausea and vomiting are present during the prodromal stage and may persist in the later stages as well. Somnolence, confusion, cranial nerve palsy, abdominal pain and diarrhea, and autonomic disturbances like sialorrhoea are common.
Lastly, patients have seizures and fall into unconsciousness. Seizures are noted in almost 50% patients; mostly generalized tonic clonic. All this eventually leads to death. Hence, this disease though rare, is very fatal.
Tachycardia and tachypnoea might be appreciable with cyanosis, generalized edema and possibly depressed/exaggerated reflexes. Complications are mostly those pertaining to CNS impairment like paralysis, permanent focal deficits and mental retardation.
VecTest antigen test and Vero cell plaque test assay have been shown to be effective in diagnosing humans as well as in arthropod surveillance projects .
The CSF examination will show an increased protein concentration. There will also be increased red blood cells and white blood cells in the CSF. The virus can be isolated from the CSF and it is an excellent technique for confirming the diagnosis. Enzyme linked immunosorbent assay or ELISA technique is useful in detecting immunoglobulin M (IgM) antibodies during the convalescent stage and antiarboviral IgG antibodies .
CT scan of the brain reveals areas of injury in the cerebral matter but the MRI test is more precise in diagnosing the Eastern Equine Encephalitis. MRI differentiates the disease from herpes simplex encephalitis. MRI is more sensitive to the early changes produced by the virus especially when using a T2- weighted imaging for optimal image outcomes. The basal ganglion is most commonly affected in Eastern Equine Encephalitis.
EEG i.e. electro encephalography reveals that there is generalized disorganization of the impulses travelling across the cerebrum. The results of the tests should be correlated very carefully as the Eastern Equine Encephalitis closely mimics encephalitis, meningitis and herpes simplex virus meningitis.
A reverse transcriptase duplex real time polymerase chain reaction or PCR assay has been developed by scientists to detect the virus with a 10 fold greater sensitivity that the current gold standard of viral isolation for diagnosis .
There is no specific treatment for this disease neither do we have any vaccinations for prevention, just like all other diseases caused by the alphaviruses . The only form of treatment includes medications like steroids to control inflammation and anti pyretics to control fever.
A case managed by Wendell et al used high doses of methyprednisolone and immunoglobulins given intravenously with use of anti-epileptic drugs for seizure control.The patient recovered dramatically and ultimately survived .
To control the seizures anti-epileptic drugs like Phenobarbital, phenytoin and benzodiazepines are useful. Only supportive treatment is available for this extremely fatal disease. Analgesics are used to control muscle pain and body aches.
Prognosis of the patient is poor as the patient will invariably have seizures and fever. The morbidity rate of patients is more than 90%. Around 70% of the patients die due to the massive involvement of the central nervous system.
The patients who survive the disease need critical and long term rehabilitation. Depending upon the areas of involvement and the deficits caused one must undergo physiotherapy, occupational therapy or speech therapy as per need.
The mosquitoes which act as carriers of this virus are Culiseta melanura and Culiseta morsitans. Once the blood meal is taken, the infected mosquitoes infect mammals like horses, humans and other animals by biting them. The mosquitoes which infect humans are Aedes vensxa and Coquilleditia pertubans.
The virus is carried in the vector’s proboscis and is injected into the mammal while having a blood meal. The infected mammals cannot transmit the viru; it’s a zoonotic cycle which involves the mosquitoes, birds and mammals.
The disease is seen to affect 12 to 17 people annually in the United States of America. The infection is commonest east to the Mississippi River .
The episodes are seen when the presence of mosquitoes increases in the months of July to September. All the cases are fatal. It can be seen in people of all the age groups.
Eastern Equine Encephalitis has chief involvement of the central nervous system. Groups of immunologically active cells are seen proliferating in the brain tissue along with neuronal destruction and vascular inflammation. On gross inspection, there is oedema, vascular congestion, hemorrhage and cerebral atrophy.
The mosquito injects the Eastern Equine Encephalitis virus into the subcutaneous or cutaneous tissue of skin. The virus may cross the placenta and affect the fetus also; otherwise it cannot be transferred from one human to another human. The virus binds to particular tissue receptors only, undergoes a process of endocytosis and commences a synthesis of protein and RNA which is RNA-dependent .
The viral symptoms of headache and fever along with myalgia are seen due to viral replication in the non neuronal tissue. The meningitis and the seizures are seen due to infection of the central nervous tissue. On coming in contact with the central nervous tissue, the virus undergoes endocytosis and its toxicity increases.
Prevention and control are one of the most important aspects of Eastern equine encephalitis. Individuals planning to undertake trips to endemic or high-risk regions must be warned to take all the necessary prescribed precautions .
Preventing bites from mosquitoes is the mainstay of prevention. It is advisable to always apply a coat of mosquito repellant permethrin 5% cream while going outdoors especially when in forest areas. The permethrin wont help repel the mosquitoes but reduces biting and kills the insect after a bite preventing further spread of disease .
Full sleeved clothes and full pants should be opted for whenever the weather permits. Stagnant water bodies should be emptied as flower pots and marshy places are potential breeding sites for mosquitoes. Window mosquito screens should be used to cover windows and doors.
Eastern Equine Encephalitis is a viral disease also called as EEE disease. It is caused by the Eastern equine encephalitis virus. This virus survives in the birds and the mosquitoes but causes infection in horses, mammals and humans.
Human to human transfer of virus is not possible except when the mother is infected and the virus crosses the placenta to affect the fetus. The mosquitoes participating in the bird-mosquito cycle are Culiseta melanura and Culiseta morsitans while the ones infecting humans are Aedes vensxa, Coquilleditia pertubans etc.
The mosquito while feeding on a blood meal infects the human and transmits the virus subcutaneously into the skin. The virus significantly affects both the non-neuronal tissue and the neuronal tissue.
The disease is very rare but extremely fatal and around 70% of the patients die. The ones which remain have to undergo extensive rehabilitation by following up with physiotherapist, occupational therapist and speech therapist if the speech is also affected.
The diagnostic tests consist of blood tests, Cerebrospinal fluid tests, CT scan, MRI scan and an EEG scan. Isolating the virus is extremely important as prognosis of this disease is very poor while the spread is easy.
Once the diagnosis is confirmed, palliation of the patient’s symptoms with antipyretics for fever, anticonvulsants for seizures and analgesics for joint pains and muscle pains is essential.
Despite significant medical advances in recent years, there is no vaccine available for this fatal disease. Prevention becomes the main stay of the treatment as there is no cure and no vaccinations either.
One must avoid travelling to places where there is a high density of mosquitoes or where mosquito borne diseases are endemic. One must apply insect-repellant creams while going outside. Full length clothes should be worn and potential breeding sites of the mosquitoes should be destroyed. All this will help prevent the Eastern Equine Encephalitis disease from fatally infecting people.