Nile fever is a disease caused by the West Nile Virus (Wnv), a virus from the family of Flaviviridae isolated for the first time in 1937 in Uganda, precisely in the West Nile district (from which it takes its name). The virus has spread to Africa, West Asia, Europe, Australia and America.
The reservoirs of the virus are wild birds and mosquitoes, whose bites are the main means of transmission to humans. Other documented means of infection, although much rarer, are organ transplants, blood transfusions, and mother-to-fetus transmission in pregnancy. West Nile fever is not spread from person to person through contact with infected people. The virus also infects other mammals, especially horses, but in some cases also dogs, cats, rabbits and others.
Incubation and symptoms
The incubation period from the moment of the infected mosquito bite varies between 2 and 14 days, but it can be as long as 21 days in subjects with deficiency in the immune system.
Most infected people show no symptoms. Among the symptomatic cases, about 20% have mild symptoms: fever, headache, nausea, vomiting, swollen lymph nodes, skin rashes. These symptoms can last a few days, in rare cases a few weeks, and can vary greatly depending on the age of the person. In children a mild fever is more frequent, in young people the symptoms are characterized by medium-high fever, redness of the eyes, headache and muscle aches. In the elderly and in debilitated people, however, the symptoms can be more severe.
The most severe symptoms occur on average in less than 1% of infected people (1 in 150 people), and include high fever, severe headaches, muscle weakness, disorientation, tremors, visual disturbances, numbness, seizures, up to to paralysis and coma. Some neurological effects can be permanent. In severe cases (about 1 in a thousand) the virus can cause lethal encephalitis.
Diagnosis
Diagnosis is mainly carried out through laboratory tests carried out on serum and, where indicated, on cerebrospinal fluid, for the search for IgM antibodies. These antibodies can persist for very long periods in sick subjects (up to a year), therefore the positivity to these tests may also indicate a previous infection. Samples collected within 8 days of the onset of symptoms may be negative, therefore it is advisable to repeat the laboratory test after some time before ruling out the disease. Alternatively, the diagnosis can also be made through PCR or viral culture on serum and cerebrospinal fluid samples.
PREVENTION
There is no vaccine for West Nile fever. Currently vaccines are being studied, but for the moment prevention consists mainly in reducing exposure to mosquito bites.
Therefore it is advisable to protect yourself from bites and prevent mosquitoes from reproducing easily:
- using repellents and wearing long pants and long-sleeved shirts when outdoors, especially at sunrise and sunset
- using mosquito nets on the windows
- frequently emptying flower pots or other containers (e.g. buckets) with standing water
- often changing the water in the bowls for the animals
- holding the paddling pools for children upright when not in use.
Therapy and treatment
There is no specific therapy for West Nile fever. In most cases, the symptoms go away on their own after a few days or can last for a few weeks. In severe cases, hospitalization is instead required, where the treatments administered include intravenous fluids and assisted breathing.