Infectious diseases transmitted by other mosquitoes

West Nile fever

West Nile virus infection or West Nile fever is caused by the West Nile virus (WNV). There are 8 types or "lineages" of West Nile virus, but only 2 of them cause disease in humans. WNV lineage 1 is found in many parts of the world - the Americas, Africa (including the Nile basin), West Asia, the Middle East and Europe, while WNV lineage 2 is more restricted to Africa and Europe.                                                                                                                                The virus is mainly found in (migratory) birds and can be transmitted to humans by certain species of mosquitoes of the Culex genus, to which the domestic mosquito also belongs. In addition to humans, mammals such as horses can also be infected, but these are accidental hosts, as the transmission cycle is solely between birds and mosquitoes. Humans and horses are so-called "epidemiological dead-ends" for the virus, as they no longer contribute to the transmission of the disease. This is because the virus does not develop in these hosts, leaving insufficient virus in the blood to infect a mosquito when bitten.

Most human cases have been reported in North America and Canada. In Europe, the virus was initially introduced by migratory birds from Africa. The virus is currently Endemic Persistent circulation of a disease or Pathogen Micro-organism capable of causing disease. in a population or geographical area. in several regions of southern and central Europe. Since records began, 2018 has seen the highest number of cases. In recent years, Autochthonous Native to the place where it is present. An autochthonous case is one acquired locally. human cases have been reported for the first time in Germany (2019 and 2020) and the Netherlands (2020). 

In exceptional cases, human-to-human transmission is possible through blood transfusion, organ transplantation or during pregnancy, childbirth or breastfeeding.

What are the symptoms and complications?

After an Incubation period Time between infection and appearance of symptoms. of around 2 to 14 days, one in five infected people will develop symptoms such as headaches, muscle pain, fever, a skin rash and swollen lymph nodes. Most people recover completely, but sometimes fatigue can last for weeks or months. 

In rare cases (1% of infections), infected people develop a serious illness such as encephalitis (inflammation of the brain) or meningitis (inflammation of the meninges, i.e. the covering of the spinal cord and brain). The severe form is more common in the elderly and can be fatal (in one in ten sufferers).

How is West Nile virus infection diagnosed?

If the doctor suspects West Nile virus infection, the diagnosis can be made using a blood test or a lumbar puncture. Depending on the stage of the disease, different tests may be used, such as PCR Acronym for polymerase chain reaction, is a technique used in laboratories to amplify DNA fragments. This technique is used for rapid diagnosis of the presence of pathogens, for example. or Serology This involves measuring antibodies (produced by the body in response to the presence of a pathogen) in a blood sample. .

How is the disease treated and prevented?

There is no specific treatment for West Nile fever. Symptoms are treated with analgesics and rehydration in cases of fever. Severe cases require hospitalisation. There is no vaccine available for humans, but there is one for horses. Prevention involves avoiding mosquito bites.