Four new human cases of West Nile virus have been confirmed by the Louisiana Department of Health and Hospitals, bringing the total in the state so far this year up to 23. Health authorities have reported no human deaths linked to WNV (West Nile virus) in 2010. Louisiana health authorities characterize WNV in three ways: Neuroinvasive, West Nile fever, and asymptomatic.

When characterized as a neuroinvasive illness, signs and symptoms are severe, usually with swelling of the brain (encephalitis) and spinal cord (myelitis). Patients have a higher risk of brain damage, and even death.

West Nile fever has flu-like symptoms, and less much less severe.

Asymptomatic people are infected but have no symptoms; they only know about their infection after a blood test is carried out for some unrelated reason, such as when they donate blood.

Doctors say that all four new cases had the neuroinvasive form – three of them from East Baton Rouge Parish, and one from Livingston Parish.

  • East Baton Rouge has had 12 reported human WNV cases, of which 7 were Neuroinvasive disease, one was West Nile fever, and four were asymptomatic.
  • Ascension Parish has had 9 confirmed cases – one neuroinvasive, 5 West Nile Fever and 3 asymptomatic.
  • Red River and Livingston Parishes have had one neuroinvasive case each.

Health officials inform that approximately 90% of all cases tend to be asymptomatic, while about 10% develop West Nile fever. A very small proportion of infected people develop neuroinvasive disease symptoms.

Individuals aged 65 or over, patients with chronic diseases, as well as those with weakened immune systems have a higher risk of developing WNV complications. However, everyone has some risk, albeit very small.

People in areas where infected mosquitoes exist have a significantly higher risk of becoming infected. Precautionary measures, such as applying mosquito repellent, wearing adequate clothing that exposes as little skin as possible, making sure window netting is in good repair, as well as some other measures can help reduce the risk of being bitten.

According to the CDC (Centers for Disease Control and Prevention), USA, over 15,000 people in the United States have tested positive for WNV since 1999 – including over 500 deaths. Authorities say the real number of infected people is much higher, because those with either no symptoms or very mild ones would not have sought medical help.

A bird-mosquito life cycle maintains West Nile virus in the environment. According to the U.S. Geological Survey’s National Wildlife Health Center, American crows (Corvus brachyrhynchos) and other corvids (e.g., blue jays) seem more susceptible to fatal infection – nobody knows why. The death of these birds has allowed many local health departments to utilize dead birds as an indicator of the virus emergence or re-emergence in their areas.

Since 1999, thousands of horses have been infected in the USA, with some regions reporting that more than one third of infected horses either die from WNV infection or are euthanized due to poor prognosis.

West Nile virus is most commonly spread to humans from infected mosquitoes. However, it may also spread through blood transfusions and organ transplants (rare). Also, evidence indicates that a baby might become infected during pregnancy, at birth or through breast milk.

Click here to read about West Nile virus in more detail.

Source: Louisiana Department of Health and Hospitals

Written by Christian Nordqvist