What is St Louis Encephalitis?
Saint Louis encephalitis virus is a disease that’s passed onto humans when they are bitten by a type of mosquito called the Culex, if the mosquito was already infected with the virus. The virus, scientifically known as a flavivirus and resembling viruses like the Japanese encephalitis, Powassan, and West Nile virus, usually infects people in the eastern and central parts of the United States during summer and early fall.
Most of the time, people who catch this virus might not even know it because they won’t have any symptoms, or they might feel like they have the flu because of symptoms like tiredness, headaches, feeling sick, and throwing up, as well as experiencing body aches. Luckily, most people will get better on their own without the disease becoming worse and leading to encephalitis, which is a serious health issue involving inflammation of the brain and its surrounding tissues, the meninges.
The condition only gets severe, turning into encephalitis, in unusual cases. It’s more common for the condition to become this severe in older adults, and its symptoms include feeling dizzy, acting strangely, getting confused, shaking uncontrollably, and even falling into a coma after the flu-like symptoms. If the disease does become this severe, between 5% and 15% of these serious cases are fatal.
Unfortunately, there isn’t a specific treatment available for Saint Louis encephalitis other than supportive measures, and anti-viral drugs haven’t been found to change the symptoms. A vaccine for this disease isn’t available either, so the main focus is on preventing mosquito bites to avoid getting infected in the first place.
What Causes St Louis Encephalitis?
Saint Louis encephalitis virus is a type of virus known as a Flavivirus, which uses RNA (a molecule similar to DNA) as its genetic material. This virus is spread by mosquitoes, especially those from the Culex species. The main mosquito types that transmit the virus are Culex pipiens, Culex quinquefasciatus, Culex tarsalis, and Culex nigripalpus.
Interestingly, this virus uses wild birds as carriers, meaning that these birds can become infected with the virus and help to spread it to more mosquitoes, but they don’t actually get sick themselves. This can happen in both city and country settings, with birds like pigeons, blue jays, robins, and house sparrows.
On the other hand, when humans and pets like dogs and cats get the virus, they may become sick, but they don’t spread the virus further to other mosquitoes. Basically, the virus hits a dead-end with us. It’s important to note that you can’t get Saint Louis encephalitis virus from another person.
While it’s possible but very rare to get the virus from inhaling it in a laboratory setting, getting it from a blood transfusion might also be possible.
Risk Factors and Frequency for St Louis Encephalitis
The virus that causes St. Louis encephalitis can be found across a broad area, from Canada to Argentina. However, most instances of the disease occur in the United States. There have been outbreaks and epidemics in the Mississippi River valley, the Gulf Coast, and other areas, including the Caribbean, Canada, Mexico, and Central America.
In places with a moderate climate, the virus tends to spread mainly in late summer and early fall. But in warmer places, it can spread throughout the year. The largest recorded epidemic of St. Louis encephalitis happened in 1975, with nearly 2000 cases primarily in the central states along the Ohio-Mississippi River basin.
The yearly count of reported cases can vary greatly due to occasional epidemics. It’s important to note that most people with the disease don’t have symptoms, and testing is not widely available, so the data we have is not fully comprehensive.
Signs and Symptoms of St Louis Encephalitis
If a person has been bitten by a mosquito in an area known for carrying diseases, they may have been infected. The period from the bite to the appearance of symptoms usually ranges from 5 to 15 days. Early symptoms might include fever, headache, feeling sick, vomiting, diarrhea, and muscle pain, which can last for several days.
- Fever
- Headache
- Nausea
- Vomiting
- Diarrhea
- Muscle pain
In rare cases, the symptoms may get worse, leading to conditions like meningitis and even more seldomly, encephalitis. These conditions may be accompanied by symptoms such as changes in behavior, agitation, confusion, and even coma.
- Altered behavior
- Agitation
- Confusion
- Coma
About 40% of children and young adults may only experience fever, headache, or aseptic meningitis. However, almost 90% of elderly patients may develop more severe symptoms including encephalitis. People who have had transplants and those with weakened immune systems are also at a greater risk of severe illness. This infection doesn’t usually come with a rash.
Testing for St Louis Encephalitis
If you have symptoms like those of encephalitis, a condition where the brain gets inflamed, doctors usually start by taking pictures of your brain (known as neuroimaging) and taking a sample of fluid from around your spine (known as a lumbar puncture). They might use a magnetic resonance imaging (MRI) or a computed tomography (CT) scan for the imaging. These scans often come out normal in cases of encephalitis.
During the lumbar puncture, the pressure might be higher than normal, and the fluid might have a normal or slightly low sugar level. An important marker doctors look for is what’s called lymphocytic pleocytosis in the cerebrospinal fluid (CSF) – basically, there’s an increased number of a certain type of white blood cells called lymphocytes in the fluid. Usually, the cell counts in the CSF don’t exceed 500 cells per cubic millimeter. In half to two-thirds of the cases, the protein level in the CSF is higher than usual.
They might also conduct blood tests to count white blood cells. But these tests often don’t show anything unusual. It’s noteworthy that these findings are not unique to encephalitis – they can be found in many types of encephalitis or viral meningitis too. Out of the patients who show these neurological symptoms, about 30% also have low sodium levels in their blood (known as hyponatremia) and fluid overload due to an inappropriate release of a hormone called antidiuretic hormone (SIADH).
Another test done is called an electroencephalography (EEG). This is done to measure the electrical activity in your brain. It may show a general slowing of activity with certain types of waves and occasional spikes. However, these EEG abnormalities don’t always match with actual symptoms a patient might be experiencing.
The diagnosis for St. Louis encephalitis, a specific type of encephalitis, is usually confirmed by finding certain antibodies (IgM) against the virus in the blood. To do this, they use a test called enzyme-linked immunosorbent assay (ELISA). The ELISA test can be done on the CSF too. The polymerase chain reaction (PCR) test is often performed on CSF to make sure the symptoms are not being caused by enterovirus or herpes virus, as these can look quite similar. However, trying to grow the virus from infected patients in a lab (known as a culture) is usually not successful.
Treatment Options for St Louis Encephalitis
As of now, we don’t have an effective antivirus medication or vaccine for St. Louis encephalitis, a disease caused by a virus. Because of this, doctors mainly focus on relieving the patient’s symptoms and keeping them comfortable. This is known as supportive care and it typically includes giving fluids through a vein (this is called intravenous or IV fluids) and medication to reduce fever (these are called antipyretics).
One possible complication of St. Louis encephalitis is a condition called SIADH which affects your body’s water balance. However, this is usually mild and can often be managed by limiting the amount of fluids the patient drinks.
Without a way to treat or prevent St. Louis encephalitis directly, the emphasis is on avoiding getting the disease in the first place. The virus that causes the disease is usually passed on to humans by mosquito bites. This means the best way to prevent St. Louis encephalitis is to avoid mosquito bites. This is particularly important when spending even short periods of time outside. Wearing long sleeved shirts, long pants, socks, and shoes that cover the whole foot can help reduce the chance of being bitten. There’s an added benefit if pants are tucked into socks to protect ankles. Remember, mosquitoes can bite through very thin clothing, but you can ward them off by treating your clothes with mosquito repellents like permethrin, DEET or oil of lemon eucalyptus. Permethrin should not be applied directly to skin, but it stays effective on clothes even after washing them.
Mosquitoes feed mostly at dawn and dusk so, if possible, it’s best to stay indoors at these times. If you’re traveling, try to sleep in an air-conditioned room or use a bed net or screens to keep mosquitoes away while you’re asleep. It’s also a good idea to remove standing water from places like flower pots and buckets because mosquitoes lay their eggs in water. If you have children’s wading pools and tire swings, make sure you drain them and keep them stored away or make sure they have holes for trapped water to drain out.
What else can St Louis Encephalitis be?
When trying to diagnose St. Louis encephalitis, doctors consider a wide range of other conditions that share similar symptoms. A detailed travel history can often provide crucial clues. Some of these other conditions include:
- Murray Valley encephalitis
- Powassan Virus encephalitis
- West Nile virus encephalitis
- Japanese encephalitis
- Herpes simplex encephalitis
- Western and Eastern equine encephalitis
- Venezuelan Equine encephalitis
- Zika virus
- Ehrlichiosis
- Enterovirus meningitis
- Mycoplasma meningitis
- Cytomegalovirus infection in people with weak immune systems
- 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
Therefore, to diagnose St. Louis encephalitis correctly, doctors must carefully investigate each patient’s symptoms and history, ruling out these other potential conditions in the process.
What to expect with St Louis Encephalitis
Most people who get infected with the Saint Louis Encephalitis Virus (SLEV), which causes inflammation of the brain, either have no symptoms or experience mild, flu-like symptoms from which they will fully recover. The overall death rate for Saint Louis encephalitis is between 5% and 15%. However, the risk of fatal disease increases with age. It stands at about 20% in patients over 60, compared to 3% to 6% in children and young adults.
In the first two weeks of infection, death can occur due to the brain inflammation. Deaths that occur after two weeks are often due to hospital-related complications such as pneumonia, which is a type of lung infection. Becoming infected with the virus is believed to give you immunity to future infections for life.
Possible Complications When Diagnosed with St Louis Encephalitis
Most people recover from this illness, but complications can occur, including bleeding in the digestive system, blood clots in the lungs, and pneumonia. In certain cases, lung inflammation and severe respiratory issues can occur if the patient inhales fluids or particles while their brain is affected during severe phases of the viral brain infection. Roughly a third of patients with brain infections from this disease also develop an electrolyte disorder known as hyponatremia from a condition named SIADH, which can lead to further complications such as brain swelling and a neurological disorder known as central pontine myelinolysis if hyponatremia is corrected too quickly.
Some adults who survive the St. Louis encephalitis may need a long recovery period, typically experiencing symptoms such as:
- Fatigue
- Anxiety
- Mood swings
- Depression
- Tremors
- Dizziness
- Problems with paying attention
- Memory problems
- Unsteady walking
These symptoms can last for months.
In children, younger ones are more likely to have brain issues, especially those who are younger than ten years old. These problems can include seizures, signs related to damage in different parts of the brain, and intellectual disability.
Moreover, there have been isolated instances of post-infectious encephalomyelitis and underactive thyroid associated with an infection from the St. Louis encephalitis virus.
Preventing St Louis Encephalitis
Since there’s no specific cure for a disease called St. Louis Encephalitis, which could lead to severe health issues, it’s extremely important to work on avoiding getting this disease in the first place. The best way to prevent St. Louis Encephalitis is by avoiding mosquito bites. Even a short time spent outdoors could lead to mosquito bites, so wearing appropriate protective clothing is crucial. This means wearing things like long-sleeve shirts, long pants, socks, and closed-toe shoes. To help further avoid bites, you can tuck your pants into your socks so your ankles aren’t exposed.
During warmer months, you’re more likely to get bitten by mosquitoes, and they can even bite through very thin clothing. To minimize this risk, you can treat your clothes with bug sprays that contain substances like permethrin, DEET, oil of lemon eucalyptus, or other similar products that are approved by the Environmental Protection Agency (EPA).
Also, remember to prevent places where water can collect and stagnant as they attract mosquitoes. Things like kiddie pools should be emptied and put away when they’re not being used, and if you have tire swings, you should drill holes into the bottom of them, so any water that gets trapped inside can drain out.
