West Nile Virus: Risks And Prevention Strategies

West Nile Virus (WNV) is a severe mosquito-borne disease commonly found in Africa, Europe, North America, West Asia, and the Middle East. Human transmission occurs through mosquito bites causing neurological disease and sometimes death.¹ 

Importance of understanding WNV risks and prevention

According to the World Health Organisation (WHO), 80% of people infected with WNV do not show any symptoms.¹ This raises significant alarms as disease prevention and treatment rely on the early identification of infected individuals. Effective prevention and risk strategies are crucial to prevent WNV transmission and hospitalisation. 

What is a virus? 

Viruses are infectious agents that can only survive by replicating in a host organism (e.g. plants and animals).² A microscope is required to visualise them due to their small size. An effective way that viruses spread to a body's surface is via a mosquito bite. Other mosquito-borne diseases include yellow fever and Eastern equine encephalitis (EEE).³ 

This article will provide insight into the following: 

• What is WNV?
• Origin and history of WNV
• How is WNV transmitted?
• What are the symptoms of WNV?
• What are the risk factors?
• What are the prevention strategies?
• How to treat and manage WNV

Understanding WNV

Origin and history of WNV

WNV originates from the West Nile district in Uganda.¹ First isolated in 1937, WNV belongs to the Flaviviridae family.¹ Almost 20 years later, in 1953 it was identified in birds in the Nile delta region. WNV can infect a variety of mammals including birds, horses, humans and mosquitoes. WNV was introduced into the Western hemisphere in 1999 when infected individuals were diagnosed in New York State.⁴ Between 1999 and 2010, more than 2.5 million people were infected.⁴ Data shows that there were 1,3000 deaths and 12,000 cases of meningitis (inflammation of the membranes surrounding the spinal cord and brain) or encephalitis (inflammation of the brain) demonstrating the serious nature of the disease.⁴  

How WNV is transmitted to humans

Mosquito bites

Mosquitoes become infected with WNV by biting infected birds.¹ Infected mosquitoes can transmit WNV through their saliva.³ A bite can inject the virus into your cells, hijacking certain biological processes and allowing them to replicate and spread. During replication where the viruses multiply, the new viruses can kill host cells through cell lysis (damage to the cell leads to the release of its internal contents).² The virus can then spread to organs, and the central nervous system (CNS), whereby it can cross the blood-brain barrier leading to inflammation and neuron loss.⁵ New viruses produced are then able to infect a new host allowing WNV to continue in its natural transmission cycle.² 

Other possible routes of transmission

Viruses require attachment to a body surface to enable infection. These surfaces can include the skin or the mucosa (inner lining) of the digestive or respiratory systems.⁶ WNV is primarily transmitted through mosquito saliva, however, there are other routes of transmission including infected donor blood for transfusions, organ transplants, and mother’s breast milk.⁵ Transmission from mother to child can also occur during pregnancy and delivery.⁷ 

Symptoms and health impacts

Mild symptoms (west nile fever)

Although the majority of infected individuals do not show any symptoms, 1 in 5 people develop a mild illness which can cause a fever, headache, rash, diarrhoea, body aches, joint pains, and vomiting.⁷ Most individuals with mild WNV symptoms recover quickly (~10 days) but some have fatigue or weakness which can continue for months.^5,7 

Severe symptoms (neurological effects)

1 in 150 patients diagnosed with WNV develops severe neurological symptoms that impact the CNS including meningitis or encephalitis.⁷ Those patients who have a weakened immune system (immunocompromised) due to a health condition or are over the age of 50 are considered at a higher risk of contracting WNV and developing severe illness.¹ Severe disease with neurological effects can be fatal. Other extreme symptoms are listed below:

• Tremors
• Vision loss
• Neck stiffness
• Muscle weakness
• Numbness
• Paralysis
• Coma
• Convulsions

Long-term health consequences

Patients who recover from severe illness may have long-term neurological damage that can lower their quality of life. The most commonly reported neurological complications from WNV are memory loss, depression and loss of muscle control.⁸ WNV-diagnosed patients can find these debilitating symptoms interfere with their daily routine. The consequences of severe WNV symptoms are similar to other neurodegenerative diseases such as Alzheimer’s or Parkinson’s.⁸

Risk factors for WNV

Defining risk factors for contracting WNV is vital for effective prevention strategies.⁹ Differences between individuals (host diversity) can increase your risk of contracting WNV.¹⁰ These include;

• Medical history; cardiovascular disease or infection with other viruses like hepatitis C
• Advanced age (over 50 yrs)
• Immunocompromised 
• Mosquito exposure
• Genetics (family history)

Geographic regions at higher risk

The transmission of WNV is complex as it is influenced by bird migration, mosquito population, and host diversity.¹¹ A wide distribution of WNV cases has been reported in popular tourist destinations such as Egypt, Morocco, Tunisia, and Africa, where you are more likely to be exposed to this mosquito-borne disease.¹² Outbreaks have occurred in Germany, Belgium, and the United Kingdom due to tourists returning home from these destinations.¹² Some high-risk areas have been identified where WNV cases have yet to be reported such as Gambia, Equatorial Guinea, and Malawi.¹² 

Seasonal patterns of WNV

Travelers may be unaware of WNV in comparison to other mosquito-borne diseases such as malaria. In Egypt, Morocco, and Tunisia, WNV outbreaks occur mainly during the warmer months in the spring and summer.¹² Western Africa often attracts nature tourists in the dry season when mosquito seasonal activity is low and the risk of malaria is reduced. However, the transmission of WNV is high at this time of year due to migrating birds.¹² Climate conditions also impact the transmission of WNV. For example, rainfall and temperature can increase the population of mosquitoes leading to a higher transmission rate.¹⁰ 

Activities increasing exposure to mosquito bites

The species of mosquito (Culex) that spread WNV can be found both outdoors and indoors.¹² Research has shown that increased time outdoors is linked to mosquito infection.¹⁰ Exposure to mosquito-breeding sites such as stagnant water also increases the risk of WNV infection.¹⁰ In geographical areas that have a high rate of WNV transmission, outdoor activities should be avoided or reduced with protective measures.  

Prevention strategies

Personal protective measures

Certain protective measures can help to reduce your risk of WNV infection. In high-risk areas, it is crucial to use insect repellent, wear protective clothing (e.g. long sleeves and trousers) and avoid outdoor activities during peak mosquito-biting times.¹ Insect repellents should contain chemicals such as DEET or picaradin.⁵ These efforts can reduce the risk of mosquito transmission.¹ Wearing protective clothing (e.g. gloves) whilst handling unwell animals can also limit animal-human transmission.¹ 

Environmental control measures

Environmental factors can influence the spread of WNV by influencing host and carrier (mosquito) populations. Standing water sources near homes and higher temperatures can increase mosquito breeding.¹³ Eliminating these water sources by drainage or surface spraying with insect repellents is essential to reduce WNV infection rates.¹⁴ WNV prevention also relies on mosquito netting indoors for mosquito-proofing living spaces. Netting can also be sprayed with repellents to stop mosquito bites.¹⁴  WHO encourage community-based prevention strategies to destroy mosquito breeding sites in residential areas.¹

Public health and awareness

Importance of public health campaigns

The public awareness of WNV is relatively low compared to other mosquito-borne diseases such as malaria. Individuals may lower their protective measures in malaria-free areas where WNV infection can still occur.¹² WNV can be unfamiliar in some countries leading to a perception of a low risk of infection.¹² Public health guidelines highlighting risks and prevention strategies for WNV are imperative to control transmission. In outbreak areas in the Western Hemisphere, communities may lack the knowledge to prevent mosquito bites. Public health education through media can aid in the promotion of personal protection and the reduction of mosquito breeding sites.¹⁶ 

Community participation in prevention efforts

Community-wide programmes are essential for WNV surveillance. For instance, monitoring local mosquito populations and ensuring that blood and organ donors are screened can lower the spread of WNV.⁷ Education on WNV is essential for communities to participate in prevention programmes.  

Role of government and non-governmental organisations in WNV prevention

Local governments and professionals use integrated mosquito management (IMM) to control the number of mosquitoes.¹⁵ IMM includes several methods, such as mosquito surveillance, to help prevent virus spread. Mosquito control relies on checking how many mosquitoes are in the area, what species they are, and the location of standing water sources containing the eggs and larvae.¹⁵ Professionals at mosquito control agencies may clean up local areas such as public parks and dispose of illegally dumped tyres.¹⁵

Treatment and management of west nile virus

Overview of treatment options

No specific antiviral treatment for WNV

Currently, there are no FDA-approved vaccines or treatments for WNV.⁴ Management through protective measures is vital to prevent the spread of this mosquito-borne disease. 

Supportive care for severe cases

Patients diagnosed with WNV who experience severe symptoms may require hospitalisation. In these cases, treatment involves intravenous fluids, prevention of other infections, and respiratory support.¹ The main treatment for patients with encephalitis is supportive care.¹⁷ This involves pain medication for headaches and antibiotics to treat infections.¹⁷ Long-term neurological problems may persist for months or years after hospitalisation.¹⁷ More severe symptoms such as convulsions may require intensive care.¹⁷ 

Importance of early detection and healthcare consultation

The quicker neurological symptoms from WNV infection are identified, the faster that patient hospitalisation can occur.¹⁷ Rapid diagnosis is essential to improve WNV patient outcomes and reduce the risk of more severe health complications. Individuals suspecting WNV infection should immediately seek health care consultation for advice. 

Future directions in west nile virus management

Research on vaccines and antiviral treatments

Research in animals has shown potential ways to treat WNV. Immunisation in mice against WNV protects from a fatal infection.¹⁰  WNV vaccine development represents an effective method to prevent infection in humans, with some early clinical trials of WNV vaccines having been successful.¹⁸ Studies looking into antiviral defence molecules such as lipocalin 2 (lcn2) or viperin could pave the way for new antiviral treatments.¹⁸ Identifying which agents play a role in the immune response to WNV infection will aid our understanding of this debilitating disease. 

Advances in mosquito control technologies

Mosquito surveillance allows early detection of WNV-reducing outbreaks.¹⁹ Technologies improving mosquito control include sugar-based traps to enable capture, and virus detection using laboratory testing.¹⁹ Sharing data between public health agencies on mosquito surveillance is an important control measure.¹⁹  

Climate change and its impact on WNV transmission patterns

Future WNV transmission patterns will be impacted by climate change. Higher temperatures will increase the likelihood of WNV-infected local birds in European countries including Northern Germany and Italy.¹³ A warmer climate may cause a rise in WNV transmission throughout the year as environmental factors such as temperature, humidity, and rainfall impact bird and mosquito populations.^5,10 Drought conditions can also drive the spread of WNV, as birds and mosquitoes are forced to share the same habitat due to water source competition.¹⁰ 

Summary

• WNV is an uncommon mosquito-borne disease that can lead to long-term neurological complications and in some cases fatality
• No treatments currently exist for WNV-infected individuals
• Early detection is essential to prevent WNV progression, as well as preventative measures to control transmission such as personal protection, mosquito surveillance public health education, and government initiatives
• More research is needed to improve understanding of WNV so that new treatments can be developed

FAQs

When is WNV season?

Typically, the WNV season is from summer to autumn but this can vary depending on the climate and the geographical location. 

How can I reduce my risk of getting infected with WNV?

There are 2 main avenues of protection to prevent WNV infection. Wearing personal protective clothing such as long sleeves and trousers can stop mosquitoes getting in contact with your skin. Additionally, mosquito control methods such as using insect repellents and removing breeding sites can also reduce the spread of WNV. 

Are there any vaccines available for WNV?

Currently, there are no vaccines available for WNV. Research into WNV may lead to effective treatments in the future. 

What should I do if I think I have WNV?

If you develop symptoms associated with WNV such as headaches, fever, body aches, stiffness or weakness please immediately seek advice from a healthcare professional.

How effective are mosquito repellents in preventing WNV?

Using Environmental Protection Agency (EPA) registered insect repellents such as DEET and oil of lemon eucalyptus are extremely effective in preventing mosquito bites. 

Can WNV be transmitted from person to person?

There is no evidence supporting human-human transmission of WNV. It is primarily spread by mosquitoes that have bitten infected birds. 

How is WNV diagnosed?

Individuals experiencing symptoms can have their blood or cerebrospinal fluid submitted for laboratory testing. 

What treatments are available for WNV?

The only treatments available for WNV include supportive care and in severe cases pain medication, intravenous fluids, and hospitalisation.

Can pets or other animals get WNV?

Yes, WNV can infect humans and other mammals otherwise known as dead-end hosts such as horses. Birds are the natural hosts. 

How does climate change affect the spread of WNV?

A changing climate can expand the geographical range of WNV and increase the length of mosquito seasons by making conditions more favourable for breeding.