LaCrosse Encephalitis (LAC)

Mosquito Borne Illness


No symptoms are really noted however; should one become ill they will have symptoms of:

Fever - Headache - Nausea - Vomiting - Tiredness.

Severe cases: Encephalitis can interfere with brain & spinal cord function. In children under 16 years of age: seizures, coma, paralysis (hemiparesis), and neurological after effects.


There is no vaccine to prevent LAC infection. If LAC encephalitis is suspected patients should be hospitalized, and the appropriate tests completed with supportive treatment (including seizure control) provided. Less than 1% under age 16 die from LAC.

Host Organism

The treehole mosquito (Ochlerotatus triseriatus) and the chipmumk and squirrel are host organisms

Repellent Methods:

  1. Use a repellent containing DEET on skin and clothing. You can buy special clothing that has repellent 'built-in' or add it to clothing.
  2. Wear protective clothing - long sleeves, long pants, and socks to protect skin.
  3. Use screens on your home and avoid going outdoors during peak 'biting' times.
  4. Keep water from settling / standing in areas around home and buildings where mosquitoes can lay eggs and breed.

Behaviors of the Mosquito:

Females: Eat blood meals during dawn & dusk. They tend to bite (probe) more and eat (engorge) less which results in more of the LaCrosse virus transmission. Prefer blood but will eat nectar for food.

Males: Active during dawn & dusk, busy looking for food and mates during this time. Food of choice is nectar.

What do they look like?

Males & females are similar in color however, females are larger. They tend to be multi-colored with black/silver/brown/dark brown/blue-black/white in various body parts. They breathe from their posterior end!

Larvae are long, thin with segmented bodies and they are typically cream-colored or brown.