West Nile Virus (WNV) Infection

West Nile virus (WNV) has had a dramatic impact on animal and public health. BioVenic is involved in research related to the diagnosis, prevention, and control of WNV infection. Based on many years of experience in animal disease research, we provide customers with a wealth of diagnostics development services to help eliminate the threat of this disease.

Cause and Effects

WNV belongs to the Flavivirus genus of the Flaviviridae family and is an enveloped positive-sense RNA virus. WNV genotypes are divided into Type I and Type II. North Africa, Europe, Israel, and the United States are the main distribution areas of Type I; West, Central, and East Africa and Madagascar are the main distribution areas of Type II.

This virus is one of the most important mosquito-borne diseases in the continental US. The first case of West Nile virus infection was discovered in the US in 1999. In 2012, the worst outbreak of WNV infection since 2004 broke out. As of 2023, 43 states in the United States have reported cases of infected humans.

Fig.1 Replication and assembly of West Nile virus in the host.^1,2

Transmission

WNV is mainly spread by virus-carrying mosquitoes (mainly Culex mosquitoes). Wild birds are the natural hosts of WNV. When vector mosquitoes bite wild birds carrying WNV, they may become infected and then spread the virus when they bite humans or animals.

Note that this virus is not spread through contact between people or animals. However, some research reports indicate that the virus can be transmitted through blood transfusion or organ transplantation, and WNV may also be passed to offspring through pregnancy or breastfeeding.

Fig.2 Diagram of West Nile virus hosts and their transmission cycle.^3,4

Signs and Symptoms

WNV affects the central nervous system. Symptoms vary depending on immunity, vaccination status, etc. The following symptoms may occur after infection.

• Asymptomatic: The majority of humans and horses infected with WNV do not exhibit any symptoms and are asymptomatic.
• Mild flu-like symptoms: A minority of individuals and horses infected with WNV may experience flu-like symptoms, such as headache, fever, muscle pain, and other associated manifestations.
• West Nile encephalitis: Encephalitis may manifest in less than 1% of individuals and animals infected with WNV. Horses affected by encephalitis may exhibit uncoordinated movements, tripping, muscle twitches, seizures, and paralysis. In humans, severe neurological symptoms can arise, including headache, vomiting, muscle weakness, confusion, altered reflexes, seizures, coma, paralysis, and in severe cases, even death.

Recovery from neurological symptoms may take months and may leave permanent effects.

Public Health Risk

Humans are generally susceptible to the virus. Field workers such as farmers, forest workers, garden workers, or travelers are high-risk groups for this disease. Some infirm people, especially the elderly and children, are prone to West Nile encephalitis after infection.

Diagnosis

WNV may cause symptoms similar to those of the Japanese brain, dengue fever, etc. Therefore, laboratory diagnosis is the top priority in confirming WNV. With extensive experience, BioVenic offers customers a wide range of laboratory diagnostics developments. Our development capabilities cover a variety of technologies in immunodiagnostics and molecular diagnostics, such as,

• PCR
• IgM Capture ELISA
• Plaque Reduction Neutralization Test (PRNT)

Treatment

Currently, there is no targeted treatment available for individuals who have contracted WNV. Mild cases typically resolve on their own without intervention. However, individuals experiencing more severe symptoms require supportive care, including fluid management, respiratory support, and attentive nursing care.

Prevention Measures

The easiest and most effective way to avoid WNV infection is to avoid mosquito bites. BioVenic recommends the following measures.

• Use insect repellent when outdoors.
• Do not graze in the evening or early morning when mosquitoes are active.
• Make sure doors and windows have full screens to keep mosquitoes out.
• Remove mosquito breeding grounds and drain stagnant water from flower pots, barrels, and jars.
• Change the water in pet dishes frequently and in bird baths weekly.
• Drill holes for tire swings, etc.

In addition to the above measures, vaccinating horses against the WNV can effectively prevent horses from getting sick, especially if they live in places where mosquitoes are heavily infested or where there are mosquitoes all year round. Fewer cases of horses also contribute to human safety. BioVenic recommends the following schedule for vaccinating horses.

There are four WNV vaccines approved by the US Department of Agriculture, three of which are inactivated vaccines and one of which is a recombinant vector vaccine. Please note that different vaccination schedules are different, we are just listing the general immunization schedule.

• Adult horses who have never been vaccinated: 2 doses 4 to 6 weeks apart, then annually thereafter.
• Vaccinated adult horses: Get vaccinated annually before mosquito season begins.
• Pregnant horses: Vaccinate 4 to 6 weeks before foaling.
• Foals: 3 doses starting at 4 to 6 months of age. The first and second doses are given 4 to 6 weeks apart, and the third dose is given 10 to 12 months before the next mosquito season begins.

In conclusion, the zoonotic risk of WNV poses a significant threat to animal and human health. BioVenic aims to reduce the infection and risk of WNV by monitoring the outbreak, and developing diagnostics solutions and custom vaccines. If you want to become our partner, please contact us immediately.

References

1. Martin, Marie-France, et al. "West Nile virus restriction in mosquito and human cells: A virus under confinement."Vaccines 8.2 (2020): 256.
2. Image retrieved from Figure 1 "Replication cycle of West Nile Virus in host cells." Martin, Marie-France, et al., 2022, used under [CC BY 4.0], the image title was changed to "Replication and assembly of West Nile virus in the host."
3. Fiacre, Lise, et al. "Molecular determinants of West Nile virus virulence and pathogenesis in vertebrate and invertebrate hosts." International Journal of Molecular Sciences21.23 (2020): 9117.
4. Image retrieved from Figure 1 "West Nile virus (WNV) transmission cycle."Fiacre, Lise, et al., 2020, used under [CC BY 4.0], the image title was changed to "Diagram of West Nile virus hosts and their transmission cycle."