Parma, Genoa, Rovigo, Calabria. There are a series of reports of cases of infection from West Nile Virusresponsible for West Nile fever. And unfortunately, there have also been some deaths. It must be said that this is not a new development this summer. In 2022, 1,133 human cases and 92 deaths from West Nile virus infection were reported in the EU. In Italy, again in 2022, 723 cases of infection and 51 deaths were recorded.
But what is worrying is the trend. The numbers tell us that cases of West Nile Virus infection (the name of the virus comes from the area where it was first isolated, that is, the West Nile district in Uganda) are growing in our country.
Characteristics of the virus
The disease has a variable average incubation period from five days to two weeks and is linked to a virus of the flavivirus family. Among the characteristics of these strains there is one that is particularly worrying. They are particularly prone to attack the central nervous systemand in particular the brain. In particular, this particular type of virus is a single-stranded RNA virus: it is protected by a sort of “membrane” (capsid) surrounded by a pericapsid.
The flavivirus family includes several disease-causing agents, starting with yellow fever to get to the dengue and to different types of encephalitissuch as Japanese encephalitis.
The role of mosquitoes
The transmission of the virus sees mosquitoes as vectors, since the pathogen passes to humans and other animals such as horses. through the mosquito bite. The “enemy” can spread mainly through migratory birds, which are bitten by the insects and carry the virus inside them. Once bitten by the mosquito, these animals can then release the virus that is transmitted to a new host. Mosquitoes become infected when they come into contact with infected birds that can circulate the virus in their blood for a few days. Infected mosquitoes can then transmit the West Nile virus to humans and animals, which are therefore terminal hosts while they bite to collect blood. The virus It is found in the salivary glands of the mosquito. While they suck blood, the virus can be injected into the animal or human, where it can multiply, and then cause disease. Animal-to-animal contagion does not occur. Human-to-human transmission, in theory, could occur only in very few cases, such as after an organ transplant.
How West Nile Virus Infection Manifests and Is Treated
The disease in humans has an average incubation period ranging from five days to two weeks and can have very different manifestations from case to case. In most cases it occurs as a very common parainfluenza syndromewith fever, headache and muscle pain that tend to go away on their own within a few days. The involvement of the lymph glandsas well as localized redness of the skin. Only in some people, and these are mainly the elderly, the infection can determine encephalitiswhich can be fatal or even leave neurological problems as a “legacy” of contact with the virus. In these cases the clinical picture is very different: in fact, a very strong headache, stiff neck similar to that of meningitis, muscle weakness and loss of consciousness.
There fever It is almost always very high and remains so for several days. However, this is a globally uncommon situation, if one considers that according to some statistics less than one person in a hundred of those infected develops encephalitis.
On the treatment front, There is no specific antiviral treatment. Hospitalization is essential in the forms with encephalitis, because it is necessary to support breathing, ensure adequate nutrition and prevent secondary infections, perhaps caused by bacteria, potentially fatal. In a preventive key, unfortunately There is no specific vaccine yet.
The ever-growing danger of zoonoses
West Nile virus infection is a classic example of zoonosis, as is the case with dengue, yellow fever or Mpox. These are diseases caused by agents transmitted directly or indirectly from animals to humans, including bacteria, viruses, parasites. Zoonoses are a danger to human and animal healthwith significant consequences also at a social and economic level. 75% of human diseases known to date derive from animals and 60% of emerging diseases have been transmitted by wild animals. Statistics say that zoonoses cause approximately one billion cases of disease every year and millions of deaths.
There are many ways of transmitting zoonotic agents to humans, and among these are:
- direct contact of a susceptible host with an infected animal;
- indirect transmission through contact with soil or objects contaminated by zoonotic agents,
- vector-borne transmission by mosquitoes, ticks, fleas and lice which act as vectors for some zoonotic agents;
- transmission through contaminated water or food.
