Symptoms, Progression, and Warning Signs of La Crosse Encephalitis

La Crosse encephalitis (LACV) often begins like many other childhood illnesses, which can make it difficult to identify initially. However, the transition from a common fever to a neurological emergency can happen rapidly ^[1][2]. Recognizing the pattern of how this disease progresses is vital for getting your child the specialized care they need.

The Stages of Progression

The illness typically moves through two distinct phases. Understanding this timeline can help you explain the history of the illness to your medical team.

1. The Prodromal Phase (Early Warning)

The first signs of LACV are prodromal, meaning they are early symptoms that signal the onset of a disease but aren’t specific to it. In this stage, your child may appear to have a “stomach flu” or a typical virus. Common early signs include:

• Fever ^[3]
• Nausea and vomiting ^[2]
• Headache ^[1]

This phase can be very short, sometimes lasting only one day before more serious symptoms appear ^[1].

2. The Neuroinvasive Phase (Neurological Symptoms)

If the virus crosses the blood-brain barrier ^[4], it enters the neuroinvasive stage, where it begins to affect the brain and spinal cord. Most children will develop encephalitis (inflammation of the brain itself), while a smaller number develop meningitis (inflammation of the protective lining around the brain) ^[5][3]. To learn more about how doctors identify these changes on scans, see Diagnosis, Testing, and Recognizing Look-Alikes.

Emergency Warning Signs

There are two “red flag” symptoms that indicate a medical emergency and often serve as signs that the illness is severe:

• Altered Mental Status: This is more than just being “tired” from a fever. It includes significant confusion, being unusually difficult to wake up, or behaving in a way that is completely out of character for your child ^[2][6].
• Seizures: About 54% of children with LACV will experience seizures during the acute phase ^[2]. These can range from “staring spells” to full-body convulsions. Seizures at the start of the illness are a primary indicator that the infection is serious ^[7][6].

Predictors of Severity

Doctors look for specific clinical signs to determine how aggressively they need to manage the infection. Factors that often point toward a more severe course of illness include:

• Seizure Activity: Experiencing seizures early in the illness is a known predictor of a more severe hospital stay ^[7].
• Imaging Findings: MRI or CT scans may show cerebral edema (brain swelling) or inflammation in specific areas like the temporal lobe or basal ganglia ^[1][8].
• Altered Mental Status: Children who arrive at the hospital with significant confusion or disorientation are often monitored more closely for potential complications ^[7].

Children vs. Adults

While adults can contract La Crosse virus, the disease behaves very differently in them. Adults often experience a much milder illness, sometimes without any neurological symptoms at all ^[9]. In contrast, children are uniquely predisposed to severe encephalitis and are much more likely to experience seizures than adults ^[2][6]. This is why the disease is primarily considered a pediatric health concern.