What is Venezuelan Equine Encephalitis?
The Venezuelan Equine Encephalitis Virus (VEEV) causes Venezuelan Equine Encephalitis (VEE), a disease that often affects both kinds of equines like horses, donkeys, mules, zebras, and also humans. These outbreaks can cover a large area and last for several months or even years. They occur most often in Central and South America.
Interestingly, the VEEV also exists as a natural disease-causing agent as well as a biologic weapon developed in labs. Outbreaks have been reported in many Central and South American countries, including Venezuela, Colombia, Peru, Ecuador, Costa Rica, Nicaragua, Honduras, El Salvador, Guatemala, Panama, and Mexico. Even the United States has had cases of VEE. The impact of these outbreaks can be substantial, with previous ones affecting up to 75,000 people during one epidemic.
What Causes Venezuelan Equine Encephalitis?
VEEV is a kind of virus that belongs to the Togaviridae family. These types of viruses are called alphaviruses, which are usually passed on to humans and other species through mosquito bites. Since they spread in this way, we also classify them as arboviruses. These viruses normally stay in mosquitos and then get passed to animals with a backbone, like people.
There are two types of alphaviruses: “New World” alphaviruses and “Old World” alphaviruses. New World alphaviruses, which include VEEV, Eastern Equine Encephalitis Virus (EEEV), and Western Equine Encephalitis Virus (WEEV), are most commonly found in the Americas. They can cause severe inflammation of the brain and spinal cord. On the other hand, Old World alphaviruses, such as the chikungunya virus, are common in Europe, Asia, and Africa and typically result in a fever and joint pain. The first appearance of VEEV was recorded in 1935 during horse epidemics in Venezuela, Columbia, and Trinidad. It first appeared in humans in 1950 during an outbreak in Colombia.
VEEV has six different versions (named as I-VI) and many variants within each type. The types named IAB and IC are recognized for causing inflammation of the brain in horses and humans. These types are dangerous and can spread rapidly through horse populations. Horses are particularly significant in the spread of these dangerous strains of the virus.
Other versions of VEEV, such as (ID, IE, subtypes II-VI), normally do not make horses sick. However, they can still cause severe illness in humans. These versions are usually found in rodents. When mosquitos transfer the virus from rodents to humans, it can potentially result in widespread human diseases. There seem to be no differences in disease symptoms in humans, whether they are caused by the dangerous or less dangerous strains of VEEV.
Risk Factors and Frequency for Venezuelan Equine Encephalitis
Epizootic subtypes IAB and IC can trigger a serious disease in both humans and horses. This disease, called VEE, can happen to anyone, regardless of their age or gender. But it is worth noting that infected children are more prone to having severe ongoing nerve damage and fatal brain inflammation. Another group particularly at risk are pregnant women. If they catch VEE, there’s a chance they could experience issues such as birth defects, miscarriages, premature births, and stillbirths.
Signs and Symptoms of Venezuelan Equine Encephalitis
VEEV infection is a condition with a number of symptoms and signs. These include low white blood cell count, fast heart rate, and fever. Patients may also develop pneumonia in the space between the lungs. In a physical examination, doctors might find symptoms like red eyes, throat inflammation, and muscle tenderness. Some common complaints from patients could be muscle pains, especially in the thighs or lower back, headaches, fever, and chills. The initial symptoms are similar to flu but can become more serious and develop into brain inflammation in about 14% of patients. Children are more susceptible to this severe disease, which can have a higher rate of complications and fatality than in adults. This severe illness can cause symptoms like shaking, seizures, changes in behavior, weakness on one side of the body, abnormal involuntary movements, issues with facial muscles, loss of coordination, muscle jerks, confusion, excessive sleepiness, and even coma. Lethal cases, which are very rare – less than 1% of all infections, could show symptoms like generalized congestion, fluid buildup, bleeding, and inflammation in the brain, gastrointestinal tract, and lungs. It’s important to note that these symptoms can be similar to other arbovirus infections.
- Low white blood cell count
- Fast heart rate
- Fever
- Pneumonia
- Red eyes
- Throat inflammation
- Muscle tenderness
- Muscle pains
- Headaches
- Chills
- More serious symptoms leading to encephalitis
- Shaking
- Seizures
- Changes in behavior
- Weakness on one side of the body
- Abnormal movements
- Issues with facial muscles
- Loss of coordination
- Muscle jerks
- Confusion
- Excessive sleepiness
- Coma
- Generalized congestion
- Fluid buildup
- Bleeding
- Inflammation in the brain, gastrointestinal tract, and lungs
Testing for Venezuelan Equine Encephalitis
Venezuelan equine encephalitis is often identified based on the symptoms a patient is experiencing, but it can sometimes be mistakenly diagnosed as another type of feverish illness. Yet, there are laboratory tests available that can accurately identify this disease.
VEEV, the virus that causes this disease, can be detected in a patient’s blood or cerebrospinal fluid (the fluid around the brain and spinal cord). Special laboratory tests, like serological analysis or virus isolation, can confirm if the virus is present.
There is also an ELISA test (a kind of lab test that measures the immune response in the blood) specifically designed to identify the strain of the VEEV virus. However, these tests can be quite expensive, which can make them hard to access for people living in countries with fewer resources.
Other lab tests may show low levels of white blood cells and lymphocytes (types of cells of the immune system); elevated transaminases (enzymes released by the liver); and a cerebrospinal fluid (CSF) that appears abnormal in laboratory tests. Sometimes it is necessary to perform a procedure called a lumbar puncture to get a sample of the CSF. Abnormal CSF results may show increased levels of protein and lymphocytes, which can suggest inflammation in the nervous system.
Treatment Options for Venezuelan Equine Encephalitis
Currently, there is no specific cure for encephalitic arboviruses, including a type called Venezuelan equine encephalitis (VEE). These are a group of viruses that can cause inflammation of the brain. Treatment focuses on relieving symptoms, sometimes referred to as supportive or palliative care. Most people do get better on their own, although some can experience persisting neurological symptoms.
There is ongoing research to develop a vaccine for VEE, but none have been fully approved for use in humans yet. A type of vaccine called TC-83, which is a weakened form of the virus, has been used in both people and horses. However, its availability is limited, and it is mainly used for lab and military workers who are at high risk of coming into contact with the virus.
Some people, about 40%, may experience flu-like symptoms after getting the vaccine. The vaccine can teach the body to fight off the virus in roughly 80% of the people who receive it. However, there is a chance that the weakened virus used in the vaccine could turn back into its harmful form and potentially cause outbreaks.
There’s another version of the vaccine, called TC-83, where the virus has been inactivated, and it has also been used in people and horses who didn’t respond to the live-attenuated vaccine. But this type requires repeated doses to maintain the protection.
Once a person has recovered from a particular type of VEE, it seems that they are immune to that specific type for the rest of their life. However, this immunity may not extend to different types of the virus.
What else can Venezuelan Equine Encephalitis be?
Several viruses carried by insects can be found in many areas in Central and South America. Venezuelan equine encephalitis (VEE) can be difficult to tell apart from other tropical diseases carried by insects, and without costly tests, it can be nearly impossible to tell the difference. When a person shows up with a fever in a place where VEE is common, it’s essential for the doctor to know if they’ve been traveling and if they’ve been around any sick horses, since this can help identify VEE. However, lab tests are the most precise way to diagnose it.
The doctor may need to rule out a number of other conditions similar to VEE. These conditions include:
- Bacterial meningitis
- Chikungunya
- Dengue fever
- Eastern equine encephalitis
- Herpes simplex virus encephalitis
- Lyme disease
- Malaria
- Rocky Mountain spotted fever
- Western equine encephalitis
- Yellow fever
- Zika virus
What to expect with Venezuelan Equine Encephalitis
Death rates in horses due to disease outbreaks range between 19% to 83%, which signifies a serious impact on the equine population. However, in humans, the fatality rate is much lower, with less than 1% of disease cases being deadly.
Adults who get infected are more likely to experience symptoms similar to the common flu. Children, on the other hand, are at a higher risk of developing brain disease, also known as encephalitis. Symptoms of such brain diseases can include lack of coordination (ataxia), feeling down (depression), confusion, unconsciousness (coma), and fits (seizures).
Furthermore, children are more likely to face lasting neurological consequences even after they’ve recovered from the disease. These might involve ongoing issues related to brain function.
Possible Complications When Diagnosed with Venezuelan Equine Encephalitis
After recovering from an initial VEEV infection, some people may still experience ongoing neurological symptoms. Although no specific treatment for VEEV exists, advances in medical technology have greatly improved general supportive treatments, which means many patients will survive even encephalitic disease. Patients may, however, still experience ongoing symptoms like seizures, confusion, intellectual disabilities, and behavioral changes. The symptoms can vary greatly, ranging from mild and manageable to life-changing. These ongoing symptoms can occur no matter how severe their initial fever was.
Pregnant women in particular are at risk of complications from arbovirus infections, such as VEEV. It is known to cause birth defects and is the first identified arbovirus that can affect developing babies. Risks to pregnant women include birth defects, miscarriage, premature birth, and stillbirth. The virus can also be passed from mother to baby during pregnancy. Research has found VEEV in the brains of aborted fetuses. Babies born to mothers with Venezuelan Equine Encephalitis can have neurological symptoms or fatal brain damage. Across the globe, infectious diseases are a leading cause of death during pregnancy. It is estimated that up to 90% of pregnancies in areas where diseases like VEEV are prevalent or commonly occurring.
Common Side Effects:
- Ongoing neurological symptoms
- Seizures
- Confusion
- Intellectual disabilities
- Behavioral changes
- Complications in pregnant women
- Birth defects
- Miscarriage
- Premature birth
- Stillbirth
- Transmission from mother to baby during pregnancy
- Babies born with neurological symptoms
- Fatal brain damage in babies
Preventing Venezuelan Equine Encephalitis
Since there’s no specific cure for Venezuelan horse encephalitis, the best defense is to avoid getting infected in the first place. This can be achieved by lessening the number of mosquitos, since they are the main carriers of this infection. To protect themselves, humans—particularly those who often interact with horses—should keep mosquitos away by wearing clothes that cover their entire body and regularly applying bug spray. Spraying insecticide from aerosol cans in areas where the disease is common can also help reduce the number of mosquitoes.
Large-scale vaccinations of horses using a vaccine called TC-83 can also prevent the disease from spreading. This vaccine is approved and available for use in horses in areas where the disease is prevalent. Continued vaccinations between outbreaks could help horses develop herd immunity, which is a way of preventing the disease from spreading to humans.
