What is Western Equine Encephalitis?
Western Equine encephalitis is a disease transmitted by mosquitoes that can lead to serious inflammation of the brain and its surrounding tissues. This illness is caused by a virus, known as an Alphavirus, which is mainly spread through the bite of specific mosquito species, including the Culex and Aedes. It can also potentially be spread by small, wild mammals. Birds can harbor the virus, but they aren’t the main carriers responsible for spreading it to humans. Infections usually happen during the summer, particularly in the western United States.
Most of the time, people infected with the virus won’t show any symptoms, but they can sometimes experience flu-like symptoms such as fever, chills, fatigue, and muscle aches. While generally people recover on their own, in some cases, the infection can lead to encephalitis, an inflammation of the brain. Encephalitis can cause confusion, sleepiness, coma, and in rare cases, even death. Infants are more likely to get infected than adults, and those who are older, or very young children, are more at risk for developing severe disease affecting the nervous system.
Fortunately, most patients with minor neurological symptoms will recover. Adults generally have better outcomes than children, who are more likely to develop ongoing issues such as persistent seizures, cognitive and behavioral problems, and muscle stiffness.
What Causes Western Equine Encephalitis?
Western Equine encephalitis is a disease caused by the Alphavirus, a member of the Togaviridae family. This range of viruses is also responsible for several other types of encephalitis in horses. The Alphavirus is quite similar to the virus that causes Eastern Equine encephalitis, which is probably one of its genetic ancestors.
The disease is passed to humans by certain types of mosquitoes – namely the Culex tarsalis, Culiseta, and Aedes species. During outbreaks, it’s common to also see infections in mules, horses, pheasants, and various other kinds of birds. The birds play a crucial role by ‘amplifying’ the virus (increasing the amount of virus), but they’re not known to pass the disease directly to humans, hence they serve as a reservoir, not a carrier.
There’s no evidence to suggest that Western Equine encephalitis is transmitted through the air, but it might be possible for the virus to cross over from a pregnant mother to her fetus. While transmission through a blood transfusion from an infected person is considered unlikely because of the low amount of virus typically present, it can’t be ruled out entirely.
Risk Factors and Frequency for Western Equine Encephalitis
Western Equine encephalitis is a disease that has been found in many parts of the world, including the western United States, Canada, and a specific type found in Argentina. It’s most common in rural areas, usually west of the Mississippi River, west of the Rocky Mountains, and in California.
The number of infections reported each year can change a lot, as there are periods with no cases followed by outbreaks. Warm weather and heavy rainfall can increase the mosquito population, which carries the disease, leading to these outbreaks. The biggest outbreak was in 1941, with more than 3000 confirmed cases. Since 1964, fewer than 700 cases have been confirmed in the United States.
- Reports of the disease are more common in males, likely because they tend to work and play outdoors more often.
- It’s often transmitted between April and September, with most cases in July and August.
- Age can affect how likely a person is to get the disease: infants are most likely to get infected after a mosquito bite, but adults can be bitten more often.
- If adults get infected, older ones are more likely to have serious neurological complications or die.
- Infants and young children can also experience neurological symptoms and seizures, and they’re more likely than adults to have permanent disabilities after infection.
- The reported rates of infection are 1:1000 for adults, 1:58 for children aged 1-4, and 1:1 in infants.
Signs and Symptoms of Western Equine Encephalitis
Most people who contract this virus are exposed to it during bird or horse epidemics or through mosquitos. Many people don’t show any symptoms, and there’s no skin rash associated with it. Those who do have symptoms often experience common signs of infection such as fever, chills, discomfort, weakness, and muscle aches, which are common for many viral and mosquito-borne illnesses. These symptoms typically go away on their own within a few days with no lingering issues.
In some cases, people may also deal with headaches, neck stiffness, nausea, and vomiting. The disease can affect the nervous system, particularly in very young or old people, leading to dizziness, sensitivity to light, confusion, restlessness, sleepiness, and even coma, muscle tightness, and seizures. These neurological symptoms may appear more rapidly in children. Young children face the highest risk of long-term nerve damage, while older adults have a higher risk of dying from complications. Even after recovering from the severe nerve-related symptoms, some people may battle with fatigue, headaches, and irritability for years.
- Fever
- Chills
- Discomfort
- Weakness
- Muscle aches
- Headaches
- Neck stiffness
- Nausea
- Vomiting
- Neurological issues (in severe cases)
Testing for Western Equine Encephalitis
Diagnosing conditions that have symptoms similar to many other infections can often be complex or delayed. When patients show signs related to the nervous system, doctors usually perform brain scans using techniques like computed tomography (CT) or magnetic resonance imaging (MRI). Changes due to inflammation can sometimes be seen in certain parts of the brain, but these signs are not unique, as they could also appear with inflammation from various other causes.
A test called the lumbar puncture can provide more clues. It might show increased pressure or protein levels and might have more lymphocytes (a type of white blood cell) which can indicate inflammation. However, these results also can be seen with many other types of viral or inflammation-related conditions that affect the brain or the spinal cord.
It can be challenging to directly detect the virus from body fluids like blood or cerebrospinal fluid (which bathes the brain and spinal cord). After infection, a type of antibody, known as IgG, generally shows up in the blood within 1 to 3 weeks and peaks around 1 to 2 months. IgG presence suggests exposure to the virus and, depending on the levels, it can hint at a recent infection. If the IgM antibody, which correlates with an ongoing infection, is present, it can be detected within 1 to 3 weeks from the start of symptoms.
However, testing for certain viral infections can cross-react with others, making it difficult to distinguish between them. For example, tests for a virus called Western equine encephalitis can show similar reactions with St. Louis encephalitis virus, making it harder to identify the exact infection.
Treatment Options for Western Equine Encephalitis
As of now, there is no approved vaccine to prevent Western Equine encephalitis, a disease spread by mosquitoes. However, relevant research and experiments are currently taking place under the supervision of the U.S. Army Medical Research and Material Command. Likewise, there’s no specific antiviral treatment for this disease, meaning that doctors typically focus on managing the symptoms and complications.
For patients who develop encephalitis, a condition that causes inflammation of the brain, they may need to be on a breathing machine and have their brain pressure controlled. Seizures are also common in patients with encephalitis, and they might require seizure medications. Patients who experience seizures due to this disease are more likely to have a long-term seizure disorder.
With a lack of effective treatment or preventive vaccine, the best strategy to combat Western Equine encephalitis is to avoid mosquito bites entirely. It’s important to note that even brief periods spent outdoors could result in mosquito bites. Protection can be enhanced by wearing clothing that covers most of the body- long sleeves, long pants, socks and closed shoes. Tucking pant legs into socks can further prevent mosquito bites on the ankles.
Since mosquitoes are more active during warmer months, it’s crucial to use insect repellants on clothing, particularly those containing substances like permethrin, DEET, or oil of lemon eucalyptus. Permethrin should not be applied directly on the skin, but it provides protection when used on clothing even after washing.
It’s advisable to avoid outdoor activities during mosquito feeding hours, which typically occur between dawn and dusk. For prevention during sleep, using air-conditioned rooms, mosquito nets, or screens can be beneficial.
Another effective preventive strategy involves draining standing water, a breeding site for mosquitoes, from flower pots and other containers. Children’s wading pools and tire swings should be properly drained and stored to prevent mosquito breeding.
What else can Western Equine Encephalitis be?
When diagnosing Western Equine Encephalitis, a type of disease that affects the brain, doctors consider other conditions that may show similar symptoms. These conditions could be related to your recent travel history. The possible conditions include:
- Murray Valley encephalitis
- Powassan Virus encephalitis
- West Nile virus encephalitis
- Japanese encephalitis
- Herpes simplex encephalitis
- Eastern equine encephalitis
- Venezuelan Equine encephalitis
- Creutzfeldt-Jacob disease
- Ehrlichiosis
- Enterovirus meningitis
- Mycoplasma meningitis
- Cytomegalovirus infection in the immunocompromised host
- Typhoid fever
- Dengue fever
- Malaria
- Brain abscess
- Tuberculous meningitis
- Nipah virus infection
- Rocky Mountain spotted fever
- Fungal meningitis
- Leptospirosis
- Neurocysticercosis
- Amebic meningoencephalitis
- Lupus with central nervous system involvement
- CNS tumor
- Cerebrovascular accident
- Overdose
This long list of potential conditions is why it’s crucial for doctors to carefully check medical and travel history and conduct comprehensive tests to establish the right diagnosis.
What to expect with Western Equine Encephalitis
When individuals catch the virus and don’t show any neurological symptoms, they will recover completely. This also applies to most adults who have minor neurological illnesses. Kids who show symptoms of neurological diseases have a chance of 30% to develop long-term conditions such as seizures, stiffness or tension in muscles (spasticity), and learning or behaviour-related issues.
Compared to Eastern equine encephalitis, which has a death rate close to 70%, the mortality rate for this virus is relatively low, at around 4%. Most of the deaths occur mainly in older patients.
