- The mosquito-borne virus is circulating in 47 of the 51 states. Only Alaska, Vermont and Hawaii have had none.
- Around 75% of cases have been reported from 5 states – Texas, Mississippi, Louisiana, South Dakota and Oklahoma. Half of all cases have been in Texas.
- The epidemic has not yet peaked. Cases are likely to continue through to the end of September and new areas may be affected.
- There is no vaccine, nor any specific treatment for WNV.
- Travellers are generally not at high risk. Most cases not reported The reported cases represent only a small percentage of actual number. Most cases are not reported because people don’t find their illness was serious enough to see their doctor – in fact, many don’t know they were infected.
However, of the 1118 cases reported to the Centers for Disease Control and Prevention (CDC), just over half (56%) have been classified as ‘neuroinvasive’, causing conditions such as meningitis or encephalitis. That proportion of serious infection appears to be higher than in the past. However, as dramatic as it may sound, we can also tell travellers that WNV is not a serious risk for Australians visiting the USA or Europe, the other main region where the virus is found.
MOST COMMON OUTCOME: 80% of people who get West Nile virus have no symptoms.
LESS COMMON OUTCOME: The other 20% have mild, flu-like symptoms of headache and fever. These can last from just a few days to several weeks.
RARE OUTCOME: Only 1-in-150 people infected will experience more serious symptoms that may see them admitted to hospital. These can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. Severe symptoms may last several weeks; neurological effects may be permanent.
About West Nile virus
Here are some facts about WNV:
- The disease is spread by Culex mosquitoes, which bite by day. (Their main feeding times are around dusk and dawn.)
- The mosquitoes pass on the virus to humans after biting migratory birds who ‘host’ the disease.
- The disease occurs as seasonal epidemics in North America – flaring in the northern summer and continuing into autumn.
- If they occur, symptoms typically appear 3-6 days after infection, but can take as long as 12 days.
- There is no specific antiviral medication to treat the infection. Doctors treat each infected person’s individual symptoms. Avoid mozzie bites Dawn and dusk are the main feeding times for the Culex mosquitoes that transmit WNV. Dawn and dusk are the main feeding times for the Culex mosquitoes that transmit WNV.
- Those travellers who will be the USA in coming weeks – especially those visiting Texas, Mississippi, Louisiana, South Dakota or Oklahoma – are advised to use a personal insect repellent when outdoors.
West Nile is a relatively ‘new’ disease, first identified in the USA in 1999. More recently it has appeared in the Mediterranean region where health authorities believe it is establishing a permanent presence through migrating birds. Both Greece and Italy had human cases in July – a month earlier than usual. A new strain was detected in north-eastern Italy (read more). Cases have also been reported in Sardinia, Israel, and the occupied Palestinian territory. In recent years it has become clear that older people are more susceptible to infection, more likely to have severe symptoms, and more likely to die that younger people.
Over 50s more likely to get sick
Why are older people at greater risk? Experts are not sure. Case data also indicates that medical conditions such as cancer, diabetes, high blood pressure, kidney disease, or having had an organ transplant increase an individual’s risk of becoming infected. Of those people who develop WNV-related neuroinvasive disease, around 10% die. Those who survive often struggle with neurological or cognitive problems for years. Those who survive can have long-lasting neurological effects, such as a very rare condition called acute flaccid paralysis, where the person is unable to move their arms or legs. More recently, doctors have found that some people who have previously had WNV have experienced a gradual decline in kidney function.