Generality
West Nile virus infections are sporadic episodes, characterized by fever, headache and, in very rare cases, by encephalitis and meningitis. The reservoir of the pathogen is represented by birds, but the transmission of the virus occurs through the bite of mosquitoes.
Usually, the West Nile virus does not cause any symptoms or particular signs. However, in those rare cases in which it causes fever, encephalitis, etc., the only feasible treatment is the administration of painkillers.
Prevention is essential to prevent the spread of the disease.
What is the West Nile virus?
The West Nile virus is transmitted to humans and animals (horses in particular) through the bite of mosquitoes and can cause an infection with flu-like characters, known by the same name.
This organism belongs to the genus Flavivirus, such as, for example, yellow fever, dengue and some encephalitis viruses.
West Nile virus infection does not present particularly dramatic symptoms, except on rare occasions; such breakers, as will be seen, may be characterized by neurological disorders (encephalitis, meningitis, etc.), sometimes even dangerous and with a permanent outcome, which require due attention.
WHERE IS IT?
The West Nile virus has spread, over the last 20 years, in numerous temperate and tropical geographical areas. In these regions, the climate of the summer season (from June to September) favors the proliferation of mosquitoes, responsible for the infection.
Areas of the world where the virus is considered endemic (ie characteristic of the territory):
- United States
- Sub-eastern Africa
- Eastern Europe
- Mediterranean Europe
- Middle East
- India
- Australia
HISTORY OF THE VIRUS IN THE MAN
The discovery of the existence of the West Nile virus dates back to 1937, in Uganda. Other cases of contagion were discovered in neighboring areas, near the Nile river, still between eastern and sub-eastern Africa. This explains, therefore, the origin of the name.
At the beginning, the virus did not arouse particular interest: the effects on man seemed scarce and not dangerous. However, an epidemic occurred in Algeria in 1994, which caused the first cases of encephalitis. These were followed by similar episodes, a couple of years later, in 1996, in Romania.
In 1999, the virus appeared in New York and, from that moment, it spread widely throughout the Americas, from north to south, and in Europe. In 2012, 286 deaths in the United States for West Nile virus.
The first cases, in Italy, were recorded in 2008 and in 2012 in the areas of the Po Valley, where an epidemic was feared.
Causes
The main cause of spreading the West Nile virus is the mosquito bite. The latter becomes a carrier of the pathogen only after having struck an infected bird. In fact, the true reservoir of the West Nile virus is the passerine birds.
The mosquito species involved in the transmission are:
- Culex tarsalis
- Culex pipiens
- Culex quinquefasciatus
OTHER TRANSMISSION CAUSES
The West Nile virus can also be transmitted in different ways than mosquito bites.
You can get the infection later:
- Exposure to infected blood
- Blood transfusion, from infected donors
- Organ transplantation, from infected donors
- Feeding time
Following the widespread use of the West Nile virus in the United States, starting in 2003, precise checks on its identification began to be performed on donors.
In the United Kingdom, precautionary measures are even closer: a blood test is performed on the blood of donors who have been in the US in the last month.
THE RISK FACTORS
There are a number of circumstances, or factors, that increase the likelihood of contracting the West Nile virus. They are:
- The season of the year . In the United States and in all those countries where the virus is endemic, it has been observed that most patients get sick during the summer months (from June to September), as this is the period of greatest spread of mosquitoes.
- The geographical region . The climate of certain areas of the world has meant that the basis was there for the virus and infection to become endemic.
- Time spent outdoors . If an individual does an outdoor job, for example, and lives in an area where the West Nile virus is present, he can get sick more easily.
Symptoms
To learn more: West Nile Virus Symptoms
Usually, people who contract the West Nile virus do not show any symptoms. In other words, the infection goes unnoticed and completely unknown to the patient.
However, this is not always the case.
In fact, in some cases (about 20%), the West Nile virus can cause a series of mild symptoms, very similar to the flu ones; however, episodes in which the infection causes serious disorders of the central nervous system are even rarer (only 1%).
But what are these symptoms and why do some people manifest them and others do not?
WEST NILE VIRUS: THE SYMPTOMS OF A LIEVE INFECTION
When symptoms of West Nile virus appear in mild form, it is called West Nile fever . This lasts a few days and is characterized by the following manifestations:
- Temperature
- Headache
- Musculoskeletal pains
- fatigue
- Lumbar pain
- Rash
- Swollen lymph nodes
- Eye pain
As can be seen, there is a vague resemblance between these symptoms and those of a normal flu. However, the two pathologies are caused by two different viruses, belonging to two different genera.
WEST NILE VIRUS: THE SYMPTOMS OF A SERIOUS INFECTION
A very small percentage (1%) of West Nile virus infections can manifest with very serious symptoms. On these occasions, the entire central nervous system ( brain and spinal cord ) and the membranes that cover it ( meninges ) are affected. All this results in the onset of: encephalitis, meningitis, and acute forms of flaccid paralysis (also called West Nile poliomyelitis ).
To complete the symptomatology, we must include, in addition to the aforementioned disorders, the following symptoms:
- High fever
- Severe headache
- Stiff neck
- Disorientation or confusion
- Torpor or coma
- Tremors and muscles that move in spurts
- Loss of coordination
- Convulsions
- Musculoskeletal pains
Unlike West Nile fever, infections that cause encephalitis and meningitis last for several weeks. Indeed, in the most unfortunate cases, it can happen that some disorders, such as flaccid paralysis, cause permanent effects.
What is flaccid paralysis?
Flaccid paralysis is the progressive loss of motor skills of body muscles. This condition manifests itself with weakness and a decrease in muscle tone : those who suffer from it no longer manage to contract their muscles. The patient may die after involving swallowing and respiratory muscles, which, by failing to function properly, cause death by suffocation. Other causes of flaccid paralysis include botulism, poliomyelitis, Lyme disease, severe neuronal trauma, etc.
WHO HITS?
The second question asked why certain individuals, points to an infected mosquito, do not show any symptoms, while others, points from the same mosquito, become seriously ill.
The answer is the following.
It has been observed that the West Nile virus is more likely to develop a dramatic infection in elderly and immunosuppressed subjects (ie with poor immune defenses). The classic examples of immunosuppressed patients are organ transplants, since they must take immunosuppressive drugs to prevent the new organ from being considered foreign to the body.
Age and state of health, therefore, are two fundamental factors in ensuring that the virus has harmful effects on humans.
INCUBATION TIMES
The incubation period, which is the period of time between the sting of an infected mosquito and the appearance of the first symptoms, ranges from 3 to 15 days.
WHEN REFER TO A DOCTOR?
Mild symptoms do not require special attention. In these circumstances, the patient gets back in a few days.
Conversely, if an individual experiences severe headaches, stiff neck, disorientation and confusion, it is good to take precautions and contact your doctor for a thorough checkup.
Serious infections with West Nile viruses require hospitalization.
Diagnosis
For a correct diagnosis of a West Nile virus infection, the doctor first assesses the patient's symptoms and recent history . In fact, knowing if the latter has stayed in areas where the disease is endemic is fundamental information.
However, for full confirmation, further investigation is needed. Here, then, that the next step involves several laboratory and instrumental exams, such as:
- Blood tests
- Lumbar puncture
- Electroencephalogram (EEG) or nuclear magnetic resonance (RMN)
BLOOD TESTS
The blood of an infected patient has high levels of specialized antibodies to fight the West Nile virus (in medicine, virus-specific antibodies are defined). These are type G immunoglobulins ( IgG ) and neutralizing antibodies .
Furthermore, by means of a specific test, it is possible to trace small fragments of RNA, or the genetic material of the virus.
LUMBAR PUNCTURE
When inflammation of the brain, meninges and spinal cord is suspected, one of the most indicated diagnostic tests is lumbar puncture. It consists in the removal of liquor (or cerebrospinal fluid ), by introducing a needle between the L3-L4 or L4-L5 vertebrae, and in its analysis in the laboratory. It is a mildly invasive procedure. Therefore, it requires the due attention at the time of execution.
The liquor of a patient infected with West Nile is characterized by lymphocytosis and neutrophilia .
What are lymphocytosis and neutrophilia?
The two terms, lymphocytosis and neutrophilia, identify, respectively, an increase in the number of lymphocytes and neutrophils . Lymphocytes represent 20-40% of circulating white blood cells; neutrophils, on the other hand, are 70% of circulating white blood cells.
When lymphocytosis and neutrophilia occur in CSF, lymphocytic pleocytosis and neutrophilic pleocytosis are more commonly referred to. These conditions are very significant, as they mean that an inflammation or viral infection is occurring in the central nervous system.
EEG and NMR
Through an electroencephalogram ( EEG ) it is possible to analyze the brain activity and the anomalies that characterize a West Nile virus infection. It is a fairly useful and non-invasive exam.
By means of a nuclear magnetic resonance ( RMN ) to the brain, instead, it is possible to detect a cerebral inflammation. It is not an invasive diagnostic test, but despite this, it is not widely practiced in such circumstances.
Treatment
Since most patients do not show any striking symptoms, it is not necessary to resort to particular therapeutic treatments. The infection, if it does not pass by itself in a few days, can be treated with the help of painkillers, such as aspirin or paracetamol . The latter reduce headaches and the general feeling of fatigue.
The cases characterized by encephalitis and meningitis deserve a different discourse. Unfortunately, for these patients, there is no effective therapy that can reduce the most serious effects of the West Nile virus. The path pursued, therefore, is the hospitalization and the administration of antibiotic drugs to prevent other infections (of bacterial type), which could aggravate the situation.
RESEARCH
Investigations are currently underway to see if West Nile encephalitis can be treated with interferon- based therapy. In some cases, the outcomes were comforting, as treated patients showed noticeable improvements compared to untreated patients. However, further confirmations are needed.
Prognosis
The prognosis of a West Nile virus infection depends on what effects it has had on the affected individual. Asymptomatic cases have a positive prognosis; the same can be said for cases characterized by mild symptoms. In fact, West Nile fever takes a few days to resolve and has no consequences.
The circumstances change when one encounters the forms of serious infection. In fact, the damage caused by inflammation of the central nervous system could be permanent.
Prevention
The best solution, to avoid the spread of the West Nile virus (thus also reducing the risks of an epidemic) is the application of simple anti-mosquito measures. To reduce the proliferation of this insect and the likelihood of coming into contact with it, it is good:
- Eliminate the stagnant waters in your garden or in the green areas of the city, as they are among the mosquitoes' favorite sites
- Clearing the gutters, thus avoiding water stagnation and the proliferation of mosquitoes.
- If you own domestic birds, change the cage troughs regularly.
- Empty unused pools.
- Do not go to the areas most populated by mosquitoes during the critical hours (sunrise or sunset).
- Wear long-sleeved shirts and trousers when planning to go to a mosquito-infested area.
- Apply anti-mosquito repellents on the skin.
ANTI-WEST NILE VIRUS VACCINE
Currently, there is still no human-friendly West Nile virus vaccine.
