What Is La Crosse Encephalitis – Causes, Symptoms, Diagnosis, Treatments

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La Crosse Encephalitis 

The NCBI article ‘La Crosse Encephalitis’ defines La Crosse encephalitis as an arboviral illness spread by mosquitoes. The condition was initially noticed by doctors in the 1960s in the Wisconsin county of La Crosse, hence the disease’s name. It was noticed that children experience this encephalitis mostly in the summer. 

The highest documented incidence is paediatric arboviral encephalitis.

The Eastern treehole mosquito, also known as Aedes triseriatus, which carries the La Crosse virus, is a member of the Bunyaviridae family, belongs to the California serogroup, and is responsible for the disease transmission. The primary host and vector for the La Crosse virus are known to be Aedes mosquito. 

Aedes albopictus and Aedes japonicus, two additional mosquito species, have also been identified as vectors in the transmission of the La Crosse virus and are probably beginning to play a prominent role in the spread of the virus in endemic areas.


The Aedes triseriatus mosquito, also known as the treehole mosquito, transmits the La Crosse virus, which causes the viral disease known as La Crosse encephalitis. 

Both vertical (from mother to child) and horizontal (from person to person) transmission are part of the cycle of transmission of the virus. 

According to NCBI, infected humans act as dead-end hosts as they do not reach the level to infect feeding mosquitoes.

Vertical transmission happens from the female adult mosquito to her young, who can then spread the infection to humans and other mammals.

Common symptoms of La Crosse Encephalitis 

Most people with La Crosse (LAC) virus do not exhibit any symptoms. The incubation period (time between an infected mosquito bite and first showing symptoms) for persons with symptoms is between 5 and 15 days.

Common symptoms are

  • Fever (often lasting 1-2 days)
  • Headache
  • Nausea
  • Vomiting
  • Exhaustion (tiredness) and 
  • Lethargy.

Children under the age of 16 are more likely than adults to experience severe illness.

This can manifest as 

  • High temperature
  • Stupor
  • Confusion
  • Tremors
  • Seizures
  • Muscle weakness
  • Vision loss
  • Numbness and 
  • Paralysis, among other symptoms. 

Brain infections can also arise due to the LAC virus (encephalitis).

Less common signs include,

After a severe illness, recovery takes time, and effects on the central nervous system may last for some time. Recurrent seizures and cognitive or behavioural problems are common. Most patients tend to recover, and mortality is rare.

Who gets La Crosse Encephalitis? 

The LAC virus can be transmitted to people by the bite of an infected mosquito. However, humans rarely acquire blood levels of LACV that infect actively feeding mosquitoes. Therefore, people are regarded as dead-end or accidental hosts for LACV. Any individual who contracts LACV can become unwell, although those between the ages of 5 and 15 are more likely than older adults to have a severe neurological illness from LACV infection.

How is La Crosse Encephalitis diagnosed? 

Consulting a healthcare professional is essential for noticing any LAC virus disease symptoms.

Medical professionals determine whether a patient has the LAC virus by

  • Looking for symptoms and signs
  • History of residing in or visiting a region where the LAC virus is known to be present
  • History of potential exposure to the LAC virus-carrying mosquitoes
  • Testing of spinal fluid or blood in a lab
  • A doctor may request testing to check for the LAC virus or other illnesses that manifest similar symptoms.

Physical examination 

The following are typical physical examination results for La Crosse encephalitis.

  • Fever 
  • Ataxia 
  • Myalgia
  • Seizures
  • Hemiparesis
  • Somnolence 
  • Obtundation
  • Acute Myelitis flaccida. 

Symptoms and history 

The patient is requested for a complete and detailed history if possible. Fever, headache, nausea, vomiting, seizures, altered state of mind and fatigue are typical signs of La Crosse encephalitis that patients must note.

Blood test 

For La Crosse encephalitis, laboratory testing is the preferred technique of diagnosis. The following laboratory findings support a diagnosis of La Crosse encephalitis.

  • Presence of IgM antibody 
  • Serologic cross-reactivity
  • Normal glucose level
  • Mild increase in white blood cell count
  • Persistence of neutralising antibodies and IgG
  • Enzyme-Linked Immunosorbent Assay (ELISA) confirmation of neutralising antibodies specific for arboviral infections.

Treatment for La Crosse Encephalitis 

The LACV disease has no specific treatment. Currently, no effective antiviral medications are available, and antibiotics are ineffective against viruses. Supportive care, which may include hospitalisation, respiratory assistance, intravenous (IV) fluids and the avoidance of secondary infections, helps treat severe illnesses.

According to an NCBI article titled ‘La Crosse Encephalitis’, Ribavirin has an off-label application in La Crosse encephalitis. It has been linked to in vitro reduction of RNA virus replication. Although its efficacy is frequently questioned, intravenous ribavirin likely targets the RNA-dependent RNA polymerase. 

Prior research on paediatric patients revealed that ribavirin adequately penetrated the Cerebrospinal Fluid (CSF) and reached levels close to 70% of plasma. More recent clinical studies do not support these results. 

Due to significantly lower CSF levels than intravenous dosing, oral Ribavirin for La Crosse encephalitis is not regarded as a viable alternative. In vitro, La Crosse virus replication was inhibited by relatively low amounts of ribavirin (0.3 umol/L).

Using analgesics, taking adequate rest and proper hydration help treat milder types of conditions that manifest with fevers and headaches. When a patient has acute encephalopathy, it is okay to start intravenous acyclovir treatment until HSV encephalitis has been ruled out. 

Anti-seizure drugs may be necessary to control people who tend to have seizures. Patients with epilepsy may want to consult a doctor about taking anti-seizure medications for a long time.

It may be necessary to do mechanical intubation and airway treatment for patients who have a coma with respiratory compromise. Occasionally, La Crosse encephalitis patients with hyponatremia may benefit from central venous pressure monitoring to keep their intravascular volume normal.

Complications of La Crosse Encephalitis 

There are numerous issues connected to La Crosse encephalitis. Acute complications could be mild and self-limiting, or they could cause a critical illness that could be fatal. La Crosse encephalitis can also cause long-term effects in addition to acute symptoms.

Acute complications

  • Fever
  • Vomiting
  • Seizures
  • Headache
  • Herniation
  • Hyponatremia
  • Photophobia
  • Cerebral oedema
  • Basal ganglia haemorrhage
  • Coma
  • Death.

Chronic complications

  • Seizures
  • Poor performance in school
  • Cognitive impairment 
  • Changes in behaviour
  • Cognitive disabilities in children
  • Personality disorder
  • Attention deficit hyperactivity disorder
  • Neuromotor retardation.

La Crosse Encephalitis prevention 

Protecting from mosquito bites is the best preventive method against LACV.

  • Apply insect repellent containing DEET, IR3535, picaridin or lemon eucalyptus oil on exposure to clothing or skin. 
  • Permethrin, an insecticide and repellent, can be applied to garments to provide protection. 
  • Put-on long sleeves and pants.
  • To keep mosquitoes out, have sturdy, unbroken screens on the windows and doors.
  • One can prevent mosquito breeding grounds around the house by eliminating standing water from flower pots, buckets, barrels and other containers. 
  • Drill drainage holes in tyre swings to let water out. After usage, empty children’s wading pools and keep them on their sides.
  • When mosquito eggs develop into infected mosquitoes in the spring, LACV can survive the winter there. The number of infected eggs hatching into infected mosquitoes can be decreased by cleaning potential nesting locations like old tyres or buckets. 
  • Filling tree holes in and around the yard with sand will reduce mosquitoes because the various Aedes mosquito species that transmit LACV will also lay their eggs there.


La Crosse encephalitis is a mild infection occurring in the central nervous system. Typically, mosquitoes spread the La Crosse encephalitis virus to the human host. One contracts the La Crosse encephalitis virus by being bitten by an infected mosquito, primarily an Aedes triseriatus mosquito. 

The age range of newborns and children who contract the La Crosse encephalitis virus is between six months and fifteen years. The La Crosse encephalitis virus seldom returns and often clears up in 1 to 2 weeks. 

Fewer than 1% of cases are fatal. Laboratory testing is the preferred way for diagnosing the La Crosse encephalitis virus. The cornerstone of therapy for the La Crosse encephalitis virus is supportive care.


What is La Crosse encephalitis? 

La Crosse encephalitis is a viral disease spread by infected mosquitoes. La Crosse encephalitis virus (LACV) is one of several mosquito-transmitted viruses that can cause brain inflammation.

Is there a vaccine or cure for the La Crosse virus? 

There is no human La Crosse virus vaccine (LACV) available. Infections can be avoided by avoiding mosquitoes by using protective clothes and repellent sprays. These viruses do not have any particular antiviral medication.

How can people lower the chance of getting infected with LACV? 

1. Preventing mosquito bites is considered the best way to lower the risk of infection.
2. When outdoors, prefer long sleeve shirts and pants and bug repellant that has been approved by the Environmental Protection Agency (EPA).
3. To prevent mosquitoes from entering, fix or install screens on windows and doors.
4. Aedes triseriatus, the mosquito that transmits the LAC virus, favours laying its eggs in tree cavities. Eliminating stagnant water near the home can limit the number of mosquitoes there.
5. When mosquito eggs hatch into infected mosquitoes in the spring, the LAC virus can survive the winter in those eggs. 
6. Prevent mosquitoes from depositing their eggs near or in water. Items holding water should be emptied, scrubbed, turned over, covered or thrown away once weekly.

How soon do symptoms of La Crosse Encephalitis appear? 

LAC encephalitis symptoms appear 5 to 15 days after being bitten by an infected mosquito.

How do people get infected with the LAC virus? 

The LAC virus is transmitted through mosquito bites. Most infections are spread by the treehole mosquito (Aedes triseriatus). Coughing, sneezing, touching or other types of contact with an infected person do not spread the LAC virus. It is unknown if blood or tissue donation might spread the LAC virus.


The Information including but not limited to text, graphics, images and other material contained on this blog are intended for education and awareness only. No material on this blog is intended to be a substitute for professional medical help including diagnosis or treatment. It is always advisable to consult medical professional before relying on the content. Neither the Author nor Star Health and Allied Insurance Co. Ltd accepts any responsibility for any potential risk to any visitor/reader.

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