Overview

California encephalitis is a mosquito-borne viral disease caused by viruses from the California serogroup of viruses. The prototype California encephalitis virus was first reported in 1943 in California.¹ The disease affects mainly children, with the majority of human infections occurring in the western United States and Canada.² The clinical manifestations of California encephalitis can range from asymptomatic or moderate febrile sickness to serious neurological consequences including meningitis or encephalitis.³

West Nile virus belongs to the Flavivirus genus and is part of the Japanese encephalitis antigenic complex. While it's commonly found in regions like Africa, Europe, the Middle East, North America, and West Asia, it's particularly prevalent in warmer areas.⁴ About 80% of human infections are asymptomatic.⁵ However, in some cases, symptoms can range from mild fever to severe neurological issues, which can even lead to death.⁵ Long-term effects like weakness, fatigue, and cognitive problems are reported in those who recover from the neuroinvasive West Nile virus infection.⁶

California encephalitis

California encephalitis viruses include infections with the following viruses: La Crosse, Jamestown Canyon, snowshoe hare, trivittatus, Keystone, and California encephalitis viruses.⁸ Infections are most commonly caused by the La Crosse virus and Jamestown Canyon virus.⁹

The La Crosse virus stands out as the primary cause of paediatric arboviral encephalitis in the USA.⁸ The La Crosse Encephalitis virus is spread to humans through bites from the Aedes triseriatus mosquito. This mosquito species typically feeds on chipmunks and squirrels.¹⁰

Despite being one of the most prevalent and widespread arboviruses in North America, the Jamestown Canyon virus remains largely unfamiliar to both the general public and the medical community.¹¹ This virus is transmitted by mosquitoes (Aedes, Coquillettidia, Culex, and Culiseta spp.),¹² being common in high temperate regions of the United States and Canada, often infecting humans. White-tailed deer are probably the main amplifying hosts, although moose, elk, bison, and pronghorns might also contribute to the transmission cycle.¹³ 

Symptoms

California encephalitis virus infections are often asymptomatic in humans. However, after an incubation period of 3 to 7 days, some individuals may develop mild fever, encephalitis, or meningoencephalitis.¹⁴

Many individuals infected with La Crosse Encephalitis virus are asymptomatic. The incubation period typically ranges from 5 to 15 days. Symptoms commonly include fever (lasting around 2–3 days), headache, nausea, vomiting, fatigue, and lethargy. In severe cases, the disease can progress to encephalitis, leading to seizures, coma, and paralysis. Children under the age of 16 are most susceptible to severe forms of the disease. While rare, long-term disability or death can occur as a result of La Crosse encephalitis.¹⁵

Common symptoms of Jamestown Canyon virus disease include fever, headache, and fatigue. In severe instances, the Jamestown Canyon virus can lead to serious conditions such as encephalitis, characterised by inflammation of the brain.¹⁶

While the La Crosse encephalitis virus predominantly affects children, the Jamestown Canyon virus primarily impacts elderly individuals in northern regions of the United States.²

Transmission

California encephalitis viruses are transmitted by the bite of infected mosquitoes and are more prevalent during the summer and early autumn months.⁷

Figure 1: Transmission cycles of Jamestown Canyon and La Crosse encephalitis viruses. Created with BioRender.

West nile virus

West Nile virus is an arbovirus that was originally isolated in Uganda in 1937.¹⁷ It is the world's most widely distributed arbovirus and the primary cause of arboviral encephalitis, being maintained in an enzootic cycle involving predominantly Culex spp. mosquitos and birds, with human infection and illness emerging from enzootic spillover.¹⁸ The enzootic/epizootic cycle is inextricably linked to the arthropod vectors' active phase, which in Europe produces a season of WNV activity that varies in length from mid-June to mid-November.^19,20

Symptoms

Approximately 20% of West Nile Virus (WNV) infections in humans result in a condition known as West Nile Fever (WNF). Commonly reported symptoms are fever, headache, tiredness, body aches, nausea, vomiting, occasionally a skin rash (on the trunk of the body) and swollen lymph glands.⁴

Less than one per cent of WNV infections can lead to a more severe condition called West Nile Neuroinvasive Disease (WNND), which affects the nervous system.⁵  Symptoms include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis.⁴

Transmission

In nature, the West Nile virus transmission cycle is kept between mosquitoes (mainly Culex spp.) and birds. Mosquitoes can become infected when they feed on infected birds presenting with high levels of the virus in their bloodstream. One week after getting infected, mosquitoes can transmit the virus to other birds during other blood meals.

Mosquitoes carrying West Nile virus can also bite and infect humans, horses and other mammals, which are considered to be “dead-end hosts” because infection in these animals does not yield high levels of virus in their bloodstream, therefore they cannot transmit the virus to other mosquitos through bites.

Figure 2: West Nile virus transmission cycle. Created with BioRender.

Additionally, contact with the blood or other tissues of infected animals could transmit the virus. Rarely have transfusions of blood, breast milk, and organs resulted in infections in humans. There is only one case of WNV transmission from mother to child that has been documented to this day.⁴

Key differences

FAQs

How is the west nile virus transmitted?

West Nile virus is primarily transmitted to humans through the bite of infected mosquitoes, mainly from the Culex spp.

What are the symptoms of west nile virus infection?

Symptoms can vary but commonly include fever, headache, body aches, fatigue, and sometimes a skin rash. In severe cases, individuals may experience neurological symptoms such as stiff neck, confusion, and paralysis.

How can I protect myself from west nile virus infection?

To reduce the risk of West Nile virus infection, it's important to avoid mosquito bites by using insect repellents containing DEET (N, N-diethyl-meta-toluamide), wearing long-sleeved shirts and pants when outdoors, and eliminating standing water reservoirs around your home where mosquitoes can breed.

Is there a treatment for west nile virus infection?

There isn't a specific antiviral treatment for West Nile virus infection currently available. The main goal of supportive treatment is to manage symptoms and provide ease. In severe cases, you might need to stay in the hospital for close tracking and supportive care.

What are la crosse and jamestown canyon encephalitis viruses?

La Crosse and Jamestown Canyon viruses are both members of the California serogroup of viruses, primarily transmitted by mosquitoes. 

How are la crosse and jamestown canyon viruses transmitted?

Both La Crosse and Jamestown Canyon viruses are primarily transmitted to humans through the bite of infected mosquitoes, such as Aedes triseriatus.

What are the symptoms of la crosse and jamestown canyon virus infections?

Symptoms of La Crosse and Jamestown Canyon virus infections can vary but commonly include fever, headache, nausea, vomiting, fatigue, and lethargy. In severe cases, individuals may develop encephalitis, leading to seizures, coma, and paralysis.

How can I protect myself from la crosse and jamestown canyon virus infections?

Taking steps to avoid mosquito bites is important to lower your chance of getting La Crosse and Jamestown Canyon viruses. This means using bug spray, wearing long-sleeved clothes, and getting rid of places around your home where mosquitoes can grow, like standing water. Staying inside during the times of day when mosquitoes are most active, like dawn and dusk, can also lower your risk of being bitten.

How are la crosse and jamestown canyon encephalitis diagnosed?

Tests using either blood or spinal fluid are used for diagnosis. These tests often check for antibodies that the body produces in response to the viral infection.

Summary

To summarise, California encephalitis viruses and West Nile virus represent significant mosquito-borne viral diseases with distinct characteristics and impacts on human health. California encephalitis viruses, primarily transmitted by mosquitoes of the Aedes genus, predominantly affect children, causing a spectrum of clinical manifestations ranging from asymptomatic to severe neurological complications. In contrast, West Nile virus, mainly transmitted by Culex mosquitoes, has a wider geographic distribution and can infect various vertebrate hosts, including humans. While the majority of West Nile virus infections are asymptomatic, a small percentage can lead to severe neurological diseases such as meningitis and encephalitis. Understanding the key differences between these viruses, including their transmission cycles, peak seasons, and clinical presentations, is crucial for effective diagnosis, treatment, and prevention strategies.