In British Columbia, the CSG viruses most often discussed in relation to human illness are Jamestown Canyon virus and Snowshoe Hare virus
California serogroup (CSG) viruses are a group of related viruses spread by mosquitoes. Most people who are infected have no symptoms or only mild illness, such as a headache, fatigue, and low-grade fever. In rare cases, these viruses can cause more serious illness, including inflammation of the brain (encephalitis) or the lining around the brain and spinal cord (meningitis). People who become infected do not pass the virus on to others through mosquito bites.
CSG viruses are spread to people through the bite of an infected mosquito. Mosquitoes become infected when they feed on animals carrying the virus and can then pass it on during later bites.
In rare situations, transmission between people has been reported through blood transfusion, organ transplantation, from a pregnant person to their baby, and possibly through breast milk.
These viruses are maintained in nature by small mammals (such as squirrels, chipmunks, and hares) and larger animals (such as deer and elk). Several types of mosquitoes in Canada, including
Aedes,
Culiseta, and
Anopheles, can carry these viruses and help them persist from year to year. These mosquitoes are most active from May to October, usually biting between dusk and dawn, although some Aedes mosquitoes also bite during the day.
CSG viruses are not spread through casual contact between people or by touching infected animals.
In most cases, people infected with a CSG virus do not develop any symptoms.
However, some individuals may develop symptoms 2 to 14 days after the mosquito bite. The type of symptoms associated with CSG infection varies. The most frequent symptoms are:
- Fever and chills
- Headaches
- Fatigue
- Muscle or joint pain
- Nausea, sometimes accompanied by vomiting, abdominal pain and diarrhea
In rare cases, CSG may cause a severe neurological infection, such as meningitis (infection of the lining of the brain), encephalitis (brain inflammation) or myelitis (spinal cord inflammation), which can cause the following symptoms:
- Numbness or muscle weakness
- Hypersensitivity of the eyes to light
- Visual disorders
- Stiff neck
- Confusion and disorientation
- Agitation
- Seizures
There is no specific treatment or vaccine against CSG viruses. However, most people who are infected recover without treatment. People who are seriously ill may have to be hospitalized.
