Neurological Disorders from West Nile Virus

According to WHO vector-borne diseases are responsible for 17% of all infectious diseases across the globe. The global burden due to vector-borne diseases is 700,000 deaths annually. Mosquitoes are tiny but they are the top public health threat. One of the deadliest diseases caused by mosquito ticks is West Nile virus. WNV is a positive strand RNA flavivirus and belongs to a family of Flaviviridae. The virus is maintained through some birds-mosquito cycle in the environment. The outbreaks of WNV in temperate regions occur during summer months due to an increased population of Culex mosquitoes while in tropical regions during rainy seasons.WNV is known as the most widespread virus among flaviviruses. The West Nile virus is commonly observed in the Americas, Europe, Africa, the Middle East, and West Asia.

 

The virus had been detected nearly 300 species of birds. For example, hawks, owls, crows, ravens, and jays become infected by WNV when they already dead or sick birds infected from the virus. It has been also reported in wild animals like caribou, squirrels, and wolves. The virus is not transmitted by human to human contact. Several birds across different geographical areas work as reservoirs of the WNV. For example passerine birds in North America, hooded crow in Africa, house sparrow in Europe, turtle dove in the Middle East and herons in Oceania. There is no vaccine available for the West Nile Virus for people, although vaccines are available for horses. 

 

West Nile Virus is the main disease caused by mosquito bites in the US. The West Nile virus which is emerged in the US in the summer of 1999(62 cases) rapidly established itself throughout the US. It is estimated that around 3 million people in the US have been infected by WNV until 2010. Since the virus has been introduced in the US, it caused around 130 deaths yearly. In 2018 only, 2544 cases of WNV were reported to CDC in the US.1594 patients had neuroinvasive symptoms while 950 people had mild symptoms. The maximum cases of neuroinvasive disorders were reported in the US in 2002 and 2003(around 10,000 cases).

   

Europe is witnessing an increasing number of WNV cases. In 2018 more cases of WNV have been reported in comparison to previous years. The highest numbers of cases were reported in Italy (576), Greece (311) and Romania (277). Europe is also facing the problem of climate change. The rising temperature is favorable for both mosquito breeding and faster development and spread of the West Nile virus. The movement of the international workforce and travelers is also responsible for the increase in WNV cases. There is a rise of extreme weather conditions due to climate change. The downpours and associated flooding contribute to the growth of the mosquito population. The hot and humid conditions provide more breeding grounds for the mosquitoes. The high temperature is suitable for rapid replication of the virus and its spread in the localities and communities.

                    Read more on global warming and its impact on the mosquito population

  

WNV is also found in India. This virus was found first time in 1956. The seroprevalence of WNV antibodies indicated the presence of WNV virus in India. Over 300 cases with four deaths recorded in the Kerala state of India. The cases were reported from three districts (Alappuzha, Kollam, Thiruvananthapuram) in Kerala.

When West Nile virus was found in human first time?

The West Nile case was reported in people in 1937 in the West Nile district of Uganda. The areas of migratory routes in the world are more affected by WNV. The migratory birds transmitted the virus across the Americas. It was found in New York first time in 1999 since then very quickly it has engulfed entire Americas, Canada, and Mexico.

How West Nile Virus is transmitted?

The mosquitoes are infected by the virus when they feed on infected birds. After circulation for a few days in their blood, the virus ultimately reaches to salivary glands. The virus is multiplied in the human or animal body and causes sickness. The virus can also be transmitted through contact of infected animals. In the rare case, it can also be transmitted through organ transplants, breast milk, and blood transfusions. The humans, horses and mammal animals are infected by WNV. It can cause serious diseases and deaths in horses. The virus is found in the birds and which are the natural hosts of the WNV. The Culex type of mosquito which is found in both tropical and temperate regions works as the carrier of the virus. They are active from dusk to dawn.

What are serious implications of West Nile Virus?

 Fortunately, 80% of people who are infected by mosquito bites do not show any symptoms. Most of the infected people don’t get sick but 1% of people suffer from serious complications. The neurological disorders are scary and sometimes can cause death and permanent impairment to the body. The neurological disorders like inflammation of the brain (encephalitis), membranes or layers of tissue covering the brain and spinal cord (meningitis) and acute flaccid paralysis are caused by WNV.

What are the signs and warnings of the West Nile Virus?

Majority of people do not witness any symptoms. The time taken to show up the symptoms after an infected mosquito bite is generally between 3 to 14 days. Patients who develop symptoms include fever, headache, body pain, nausea and vomiting, and swollen lymph nodes. The severe infection can cause West Nile encephalitis, meningitis, and West Nile poliomyelitis. The patient with a severe case can show symptoms like high fever, headache, neck stiffness, coma, tremors, paralysis, and convulsions. People with above 50 years and low immunity power are at more risk of severe infection. Travelers and military personnel to endemic areas are also more prone to WNV. The patients who are already suffering from diseases like cancer, diabetes, hypertension, and kidney problems are at more risk of developing a severe condition.

About 1 in 5 persons develop a fever with other symptoms. It is observed that 1 out of 150 infected persons will develop a severe form of disease.1 out of 10 people whose central nervous system is infected by WNV is died. The severe cases have around 10% mortality rate. It may take months to recover fully from the virus. The patients with severe cases may have permanent neurological disorders even after the recovery.

In horses, the neurological disorders can include Ataxia (lack of control in movements), confusion (distortion) and paralysis. Birds can show neurological symptoms like lack of coordination, tremors, and weakness.

There is no specific treatment and vaccine available for WNV. The patients with severe cases need to be hospitalized to get supportive care like intravenous fluids, prevention of secondary infection, ventilator and pain medication. The blood test is done to check the antibodies of West Nile virus in the body.

What precautionary measures can be taken to avoid infection?

Since there is no vaccine and specific treatment available to cure the infection of West Nile Virus so keeping ourselves safe from mosquito bites is the best way out.

  • Don’t try to touch dead or sick birds by bare hands. Always use gloves when handling dead or sick birds.  

  • Keep surveillance on dead crows and birds during the summertime and report to health authorities.

  • Use insect repellent having 20-30% DEET, Picaridin, oil of lemon eucalyptus.

  • While sleeping use mosquito nets around the bed.

  • Try to cover the full body with clothes when you go outside the home.

  • During mosquito season try to wear long sleeve shirts and pants.

  • Tightly cover the water storage containers like buckets, tanks etc and throw out the old containers from the house.

  • The mosquitoes lay eggs in the still water so keep vigilance and get rid of still water in ponds, vacant lands gardens etc.

  • Repair the broken doors and windows to stop the mosquitoes from entering the house.

  • Reporting of dead birds in the community to concerned authorities will help in spreading the virus.

  • Keep pet birds inside the house during the summer season.

  • Get vaccinated your horses annually before the onset of mosquito season.

The West Nile Virus is life-threatening and can cause permanent brain disabilities. This fatal disease is also responsible for significant economic and productivity loss. The Culex mosquito population is also increasing with global warming rapidly, therefore, it becomes imperative for the nations that they must implement effective vector control programs. The alert warning should be issued at the right time to the general public when an outbreak occurs. Surveillance and monitoring efforts should be increased. The campaigns for community awareness and sharing information about WNS and safe handling of infected birds should be launched. Sharing is Caring!