Venezuelan Equine Encephalitis: An Overview

Introduction:

Encephalitis is the infection and inflammation of the brain. Venezuelan equine encephalitis is a rapidly spreading epidemic (a widespread occurrence of a disease in a community at a certain period) in South and Central American countries such as Venezuela, Peru, Colombia, Costa Rica, Ecuador, Nicaragua, Honduras, El Salvador, Guatemala, Panama, Mexico and some parts of the United States of America. It is caused by the Venezuelan equine encephalitis virus (VEEV). This virus affects both males and females of all age groups. In addition, this virus is highly contagious in aerosol form and is used as a bioweapon in warfare.

How Is the Venezuelan Equine Encephalitis Virus Transmitted?

Mosquitoes transmit the virus from equines (horses and members of the horse family such as donkeys and mules) to humans who work closely with equines. Many species of mosquitoes are involved in the transmission of this virus, but two main species are responsible for the transmission of both epizootic and enzootic strains of this virus.

• Epizootic strains of the virus cause an outbreak of a disease that affects many animals of one kind at the same time. And enzootic strains are responsible for the disease affecting animals of the same region or in a particular season. The Ochlerotatus taeniorhynchus is the primary mosquito vector that spreads epizootic disease. Culex species transmit enzootic strains of the virus.

• The mosquito bites and feeds on infected rodents or equines (horses). The virus then enters the mosquito and affects its intestine (initial infection). Next, the virus matures and spreads to other mosquito organs. Finally, the virus accumulates in the salivary glands of the mosquito which are glands present in the oral cavity that produce saliva.

• When the mosquito bites another individual to feed on their blood, the virions (infectious virus particles) are released from the salivary glands and are transmitted into a new host. The virus enters a new host and replicates itself in the cells. The incubation period of this virus is two to five days, after which symptoms start presenting.

What Are the Symptoms of Venezuelan Equine Encephalitis?

The disease may present as regular flu or severe encephalitis that can be fatal if not treated in time. The following are the common symptoms of Venezuelan equine encephalitis -

• Fever.

• Polyarthritis (pain and inflammation occurring in multiple joints at once).

• Leukopenia (reduced white blood cells).

• Tachycardia (Increased heartbeats).

• Interstitial pneumonia (lung disease).

• Muscle aches and pain in the lower back and thighs.

• Headache at the back of the eyes and back of the head behind the ears.

When the disease progresses into its severe form, the following neurological signs and symptoms are present -

• Tremors (shaking hands, legs, and other body parts).

• Seizures (uncontrolled, involuntary movements of the body).

• Behavioral changes like mental confusion, forgetfulness, somnolence (drowsiness), and anxiety.

• Hemiparesis (weakness on one side of the body with difficulty moving).

• Hemichorea (involuntary movements of variable patterns on one side of the body).

• Paralysis of the cranial nerves.

• Ataxia (impaired balance or coordination due to damage to the brain, nerves, or muscles).

• Myoclonus (sudden involuntary jerking or twitching of a muscle).

• Coma (a state of unconsciousness for a prolonged period).

Signs of brain damage include -

• Generalized congestion.

• Edema (brain swelling).

• Hemorrhage (bleeding).

• Vasculitis (inflammation of the blood vessels).

How Is Venezuelan Equine Encephalitis Diagnosed?

Clinical signs and symptoms play an essential role in diagnosing this disease, but they can be commonly mistaken for other febrile illnesses such as malaria, dengue, and chikungunya.

Laboratory tests are reliable and helpful in confirming the diagnosis-

1. ELISA (Enzyme-Linked Immunosorbent Assay) - ELISA is a standard test used to detect antibodies in the blood. VEEV-specific blocking type of ELISA is used to identify the serotype of the virus (variations in the species of the virus).

2. Cerebrospinal Fluid Examination (CSF studies) - The Venezuelan equine encephalitis virus can be isolated in the serum and cerebrospinal fluid. Cerebrospinal fluid studies require lumbar puncture, an invasive and costly procedure. In addition, lymphocytic pleocytosis (abnormal increase in white blood cells) and increased protein levels are recorded in patients affected by the virus.

3. Serological Analysis - This is done to detect the presence of antibodies in the blood.

4. Transaminases - Enzymes that catalyze (speed up) a particular transaminase reaction.

5. Complete Blood Count - A blood test is done to check the levels of the following cells, which usually appear in high levels in the case of Venezuela equine encephalitis, such as -

• • White Blood Cells - These cells increase with any infection or inflammation in the body. They are a part of the immune system of the body.
  • Lymphocytes - They are a type of white blood cell.

What Are the Treatment Options for Venezuelan Equine Encephalitis?

The treatment mainly comprises the management of signs and symptoms, as no FDA-approved (Food and Drug Administration) antiviral drugs are available to treat this condition. Support and self-care are the main aspects of managing this disease. Prevention is the best medicine, and the following practices can be adopted to prevent this disease such as -

• Places favorable for the mosquitoes to breed, such as stagnated water or dirty dustbins, should be kept clean.

• Regular use of mosquito repellants is necessary.

• Individuals coming in contact with horses should often wear protective clothing.

• Patients with high fever and joint pain will require plenty of IV fluids, antipyretics (for fever), and analgesics (for pain).

• Patients with severe neurological symptoms like seizures will need special care from healthcare providers.

What Are the Complications of Venezuelan Equine Encephalitis?

Children are predominantly affected by neurological complications like encephalitis. Patients with severe neurological symptoms may experience seizures and tremors more often. This disease can be transmitted from the mother to the fetus. Pregnant women infected with this virus may experience complications in pregnancy, such as low birth weight of infants, premature delivery, congenital disability, miscarriage, and stillbirth.

What Are the Vaccines Available for Venezuelan Equine Encephalitis?

TC-83 is a live attenuated vaccine (a weakened form of the virus that causes the disease is used in preparing such types of vaccines) used in equines and humans. But, this vaccine may cause illness in individuals, so it is only recommended for people working in the laboratory and military persons at a high risk of exposure. Another vaccine, formalin-inactivated TC-83, is also helpful as this does not cause the disease in the patient who takes it. Booster doses are necessary along with this vaccine to maintain immunity.

Conclusion:

Children are more susceptible to developing complications post-infection from this virus. It is a highly infectious disease with no medicine or vaccination available to cure it. Support from healthcare providers is necessary for managing this disease. Laboratory tests are expensive, and patients living in developing countries cannot afford them and cannot access these newly designed tests. Early detection of symptoms, controlling the breeding of mosquitoes, and vaccination of equines will help prevent disease outbreaks.