What is La Crosse Encephalitis?
La Crosse encephalitis is a disease spread by mosquitoes that is most often seen in the mid-Atlantic and midwestern states of the U.S. The illness gets its name from La Crosse County in Wisconsin, where it was first spotted by doctors in the 1960s. Doctors identified the illness as causing inflammation in the brain, primarily in children, usually around the summer season. It is now known as the most commonly reported brain inflammation condition caused by mosquito-borne viruses in children.
This disease is caused by the La Crosse virus, which comes from a broader family of viruses known as the Bunyaviridae, specifically those belonging to the California serogroup. This virus is spread via a specific type of mosquito called the eastern treehole mosquito, also known as Aedes triseriatus, identified as the main carrier and spreader of the La Crosse virus.
Yet, two other types of mosquitoes, the Aedes albopictus and the Aedes japonicus, have been recognized as transmitters of the La Crosse virus and are believed to have an increasing role in keeping the virus present in areas where the disease is commonly found.
What Causes La Crosse Encephalitis?
La Crosse encephalitis is a sickness caused by a virus carried by a type of mosquito known as the Aedes triseriatus, or the treehole mosquito. There are two ways this virus can be passed around. One is horizontal transmission, which is when it passes from adult mosquitoes to small creatures like squirrels. Humans can also get infected this way, but we can’t pass it back to mosquitoes because our bodies don’t produce enough of the virus. Another way is vertical transmission. This happens when a female mosquito passes the virus directly to her baby mosquitoes, which can then potentially infect other animals and people.
Risk Factors and Frequency for La Crosse Encephalitis
La Crosse encephalitis is a not so common disease that mostly affects children and tends to happen during the summer. Most of the cases reported happen in the rural areas of the central and midwestern states, and the disease majorly occurs between July and September. Over the recent years, there have been between 60 to 80 cases reported yearly in the United States.
- Around 75% of all La Crosse encephalitis cases are in children.
- Most cases occur during the summertime.
- The disease is found mostly in the rural areas of the central and midwestern U.S. states.
- Between 2003 and 2012, the number of reported cases was 665.
- Almost 81% of all pediatric cases between 2003 and 2012 were in Ohio, North Carolina, West Virginia, and Tennessee.
- On average, 68 cases of the disease were reported each year between 2009 and 2018 according to the Center for Disease Control and Prevention.
However, it is important to note that there may be some under-reporting of less severe cases.
Signs and Symptoms of La Crosse Encephalitis
Most people with La Crosse encephalitis don’t have any symptoms, so it often goes undiagnosed. Only about 4% of cases show symptoms. For those that do show symptoms, the severity can range. It might just be a mild fever that lasts a few days, but sometimes it can cause very severe brain inflammation (encephalitis). The vast majority of people survive La Crosse encephalitis – the death rate is less than 1%. However, when the disease is severe, it can lead to lasting health problems.
Of the cases that show symptoms, 80% to 90% experience a mild illness. Symptoms typically last for 1 to 3 days and include headaches, fever, and sometimes vomiting. These symptoms improve over a week. Some people experience tiredness, changes in behavior, and brief seizures. Almost half of all children admitted to hospital with La Crosse encephalitis have seizures. Of these seizures, 40% to 60% are focused in one area or effect the whole brain (focal and generalized seizures), and 10% to 15% become status epilepticus, a serious condition with continuous, long-term seizures.
In children, the disease might cause brain inflammation with brain disease and seizures (meningoencephalitis with encephalopathy and seizures). In contrast, adults usually experience fever, headaches, and low sodium levels (hyponatremia). Adults can also have an altered mental state but don’t often have seizures. Severe cases can lead to brain swelling (cerebral edema) with breathing difficulties, which might require up to 25% of patients to be put on a ventilator.
Common symptoms of La Crosse encephalitis include:
- Fever
- Tiredness
- Headaches
- Confusion
- Vomiting
- Seizures (most common in children)
Less common symptoms can include:
- Low sodium levels (most common in adults)
- A stiff neck
- Light sensitivity
- Difficulty breathing
- Deep unconsciousness (coma)
Testing for La Crosse Encephalitis
Diagnosing La Crosse encephalitis mainly involves a test called the enzyme-linked immunosorbent assay (ELISA). This test checks for two types of proteins, IgM and IgG, in the patient’s blood. If these levels quadruple within two weeks, it generally means the patient has La Crosse encephalitis.
The Centers for Disease Control and Prevention suggest that a preliminary diagnosis of La Crosse encephalitis should be based on the symptoms, as well as the patient’s recent travel history, especially if they live in an area where the disease is not commonly found. Additional tests could be done on the fluid surrounding the brain and spinal cord, known as cerebrospinal fluid, to check for the presence of La Crosse virus IgM protein. Although, these results could take one to two weeks. In severe cases where the patient dies, an autopsy, including studying the brain tissue, can confirm the diagnosis.
Often, the cerebrospinal fluid test may reveal high levels of protein, normal glucose, and an increased number of lymphocytes (a type of white blood cell). A viral culture test on the cerebrospinal fluid might not be as useful, as it often comes back negative. Other tests like a basic metabolic panel and complete blood count can also be done to check for increased white blood cells and electrolyte imbalances, such as low sodium, which can be related to La Crosse encephalitis.
Imaging techniques such as CT scan and MRI of the head typically do not show any specific signs of La Crosse encephalitis and can be normal most of the time. In some cases, however, a CT scan may show swelling in the brain or a life-threatening condition called cerebral herniation due to increased pressure in the skull. In very rare cases, it may show bleeding in the basal ganglia, an area in the brain. On MRI, some children with severe La Crosse encephalitis may show unusual enhancement in the brain’s cortex.
An electroencephalography (EEG), a type of brain wave test, may show abnormal findings, such as slowed brain activity, unusual periodic electrical discharges, or seizures in up to 90% of patients.
Treatment Options for La Crosse Encephalitis
La Crosse encephalitis is a disease for which there is no well-known treatment. Therefore, doctors often aim to manage the symptoms that come with the disease.
Sometimes, a medication called intravenous ribavirin is used in the treatment process, although its effectiveness is not certain. This medication works by inhibiting RNA virus replication, a crucial process in the spread of viruses. However, studies regarding its effectiveness are inconsistent. Earlier studies revealed promising results in children, citing that the medicine could penetrate vital parts of the brain effectively. However, more recent research disputes these findings. Oral ribavirin is not recommended due to its reduced effectiveness when compared to the intravenous form.
If you catch La Crosse encephalitis and experience milder symptoms such as fevers and headaches, often the treatment will be simple: rest, hydration, and painkillers. In more severe cases, like when a patient comes in with symptoms suggesting brain inflammation (encephalopathy), doctors often start treatment with intravenous acyclovir until they can rule out certain causes, such as Herpes Simplex Virus (HSV).
If the disease triggers seizures, antiseizure medications can be administered to help manage these symptoms. In some cases, these medications might also be used in the long-term if the patient develops epilepsy.
In extreme cases, where patients fall into comas with breathing problems, doctors may have to take over their breathing with a ventilator. This procedure is often accompanied by inserting a tube into the patient’s airway to ensure they are getting enough oxygen.
In some scenarios with La Crosse encephalitis, doctors may need to monitor a patient’s central venous pressure. This can help them balance the patient’s internal fluid levels during the treatment of a condition known as hyponatremia, a common occurrence in patients with this disease.
What else can La Crosse Encephalitis be?
When diagnosing La Crosse encephalitis, a variety of other conditions need to be explored carefully first. These conditions fall into different categories such as:
- Vascular conditions like stroke or subarachnoid hemorrhage (bleeding in the area surrounding the brain)
- Toxic/metabolic conditions that include extremes of blood sugar levels, abnormal sodium levels, buildup of waste products in the blood (uremia), Wernicke’s encephalopathy (brain damage due to thiamine deficiency), or drug intoxication
- Epileptic conditions such as focal seizures or generalized seizures followed by a state of confusion
- Traumatic conditions such as epidural or subdural hematoma (blood accumulation outside the brain), or fat embolus (blockage of blood vessels by fat droplets)
- Autoimmune, cancer-related, limbic (brain region-related), or vasculitic (blood vessel inflammation-related) encephalitis (brain inflammation)
- Infectious conditions like Cryptococcal meningitis, Enteroviral meningitis, Histoplasmosis (fungal infection), Varicella-zoster virus encephalitis, Herpes simplex virus encephalitis, and other insect-borne viral brain infections such as dengue, Japanese encephalitis, St. Louis encephalitis, West Nile virus, Western equine encephalitis, and chikungunya.
What to expect with La Crosse Encephalitis
The outlook for patients with La Crosse encephalitis is generally positive as the risk of death is low. Most people with this disease do not even show symptoms, and less than 1% of all cases result in death. Sometimes, though—about 1% of the time—hospitalized patients might pass away because of complications from La Crosse encephalitis.
The difficulties or problems that arise from having La Crosse encephalitis vary. Some people who have recovered from it, about 5% to 15%, may experience recurring seizures.
Possible Complications When Diagnosed with La Crosse Encephalitis
La Crosse encephalitis could lead to various complications. Some might be mild and self-recoverable or lead to severe illness, which could be life-threatening. Moreover, this illness could also cause long-term effects.
Here are the short-term complications:
- Fevers
- Headaches
- Throwing up
- Low sodium levels in the body
- Sensitivity to light
- Seizures
- Swelling in the brain
- Pressure buildup causing parts of the brain to shift position
- Bleeding in the brain’s basal ganglia area
- Coma
- Potential death
And here are potential long-term effects:
- Repeated seizures
- Difficulties in thinking and understanding
- Poor school performance
- Changes in behavior
- Attention Deficit Hyperactivity Disorder (ADHD)
- Cognitive delays in children
- Alteration of one’s character
- Delayed motor skill development
Preventing La Crosse Encephalitis
Teaching patients how to prevent diseases and how to recognize early signs and symptoms of certain diseases is important for their health.
Right now, there’s no vaccine to protect against the disease called La Crosse encephalitis. But there are steps you can take to lower your chances of getting it. This disease is more common in the Midwestern states, and people are at a higher risk in the summer when they are outdoors more often. To avoid getting bitten by mosquitoes (which can carry the disease), you can use bug spray, wear long-sleeve shirts and pants, and get rid of standing water where mosquitoes might live. At home, use screens on your windows and make sure there’s good air circulation to keep mosquitoes out.[2]
It’s crucial for people – and particularly parents of young kids – to know about the signs of La Crosse encephalitis. If you or your child start to have confusion, headaches, or a fever after being bitten by a mosquito, it could be a sign of this disease. Even if you don’t remember being bitten by a mosquito, but you’ve recently traveled to or spent time outdoors in the Midwestern states, and you have these symptoms, you should see a doctor. They can check to see if it’s La Crosse encephalitis.
