West Nile fever - Symptoms.

The incubation period of West Nile fever lasts from 2 days to 3 weeks, most often 3-8 days. Symptoms of West Nile fever begin acutely with an increase in body temperature to 38-40 ° C, and sometimes higher for several hours. The increase in temperature is accompanied by severe chills, intense headache, pain in the eyeballs, sometimes vomiting, muscle pain, lower back, joints, and severe general weakness. Intoxication syndrome is expressed even in cases with short-term fever, and after normalization of temperature, asthenia persists for a long time. The most characteristic symptoms of West Nile fever caused by "old" strains of the virus, in addition to those listed, are scleritis, conjunctivitis, pharyngitis, polyadenopathy, rash, hepatosplenic syndrome. Dyspeptic disorders (enteritis without pain syndrome) are not uncommon. CNS lesions in the form of meningitis and encephalitis are rare. In general, the course of the disease is benign.

The symptoms of West Nile fever caused by the "new" strains of the virus differ significantly from those described above. Yu. Ya. Vengerov and A. E. Platonov (2000) proposed a clinical classification of West Nile fever based on observations and serological studies. Subclinical infection is diagnosed during population screening studies based on the presence of IgM antibodies or an increase in the IgG antibody titer by four or more times. The flu-like form has no clinical specificity. It is the least studied, since often, due to the short duration of the health disorder, patients do not seek medical attention or their illness is assessed at the clinic level as influenza or acute respiratory viral infection.

Clinical classification of West Nile fever

Form	Severity	Diagnostics	Exodus
Subclinical	-	Screening for the presence of IgM antibodies or an increase in the titer of IgG antibodies	-
Flu-like	Light	Epidemiological, serological	Recovery
Influenza-like with neurotoxicosis	Medium-heavy	Epidemiological, clinical. PCR. serological	Recovery
Meningeal	Medium-heavy heavy	Epidemiological, clinical, liquorological. PCR, serological	Recovery
Meningoencephalitis	Heavy, very heavy	Epidemiological, clinical, liquorological, PCR, serological	Mortality up to 50%

In the flu-like form with neurotoxicosis, a sharp deterioration in the condition occurs on the 3rd-5th day of the disease, which is expressed by increased headache, nausea, vomiting, muscle tremor, ataxia, dizziness and other symptoms of CNS damage. The fever in these cases is high, lasting 5-10 days. Specific clinical symptoms of West Nile fever - scleritis, conjunctivitis, diarrhea, rash - are observed in isolated cases. Symptoms of CNS damage dominate: intense headache of a diffuse nature, nausea, in half of the patients - vomiting. Frequent symptoms are dizziness, adynamia, lethargy, radicular pain, hyperesthesia of the skin. More than half of the patients have meningeal syndrome, in some cases - increased blood pressure. When examining the cerebrospinal fluid, in addition to an increase in LD, there is no other pathology.

In patients with the meningeal form of the disease, meningeal symptoms of West Nile fever increase over 2-3 days; the most pronounced is the rigidity of the muscles of the back of the head. In comparison with the flu-like form with neurotoxicosis, general cerebral symptoms are also expressed, transient focal symptoms are noted. The most characteristic are: stupor, muscle tremor, anisoreflexia, nystagmus, pyramidal signs.

During a spinal puncture, transparent or opalescent cerebrospinal fluid flows out under increased pressure. Cytosis varies widely - from 15 to 1000 cells in 1 μl (in most cases 200-300 cells in 1 μl) and is often mixed. When examining in the first 3-5 days of the disease, some patients have neutrophilic cytosis (up to 90% neutrophils). Mixed cytosis often persists for up to 2-3 weeks, which is apparently due to the presence of necrosis of a significant portion of neurocytes. This also explains the slower sanitation of the cerebrospinal fluid, often delayed until the 3rd-4th week of the disease. The amount of protein is within 0.45-1.0 g / l, the glucose content is at the upper limits of the norm or increased, sedimentary tests are weakly positive. The course of the disease is benign. The duration of fever is 12 days. Meningeal symptoms regress within 3-10 days. After the temperature returns to normal, weakness and increased fatigue persist.

The meningoencephalic form of West Nile fever is the most severe. The onset of the disease is rapid, hyperthermia and intoxication from the first days of the disease. Meningeal symptoms of West Nile fever are mild or moderate. From the 3rd-4th day, general cerebral symptoms increase: confusion, agitation, delirium, stupor, in some cases developing into a coma. Convulsions, paresis of the cranial nerves, nystagmus are often noted, less often - paresis of the limbs, in the most severe cases, respiratory disorders and central hemodynamic disorders predominate. Mortality is up to 50%. In recovered patients, paresis, muscle tremors, and prolonged asthenia often persist. Cerebrospinal fluid pleocytosis is from 10 to 300 cells in 1 μl, the protein content reaches 0.6-2.0 g / l.

The blood picture in West Nile fever is characterized by features typical of severe viral infections: a tendency towards leukocytosis, neutrophilia prevails, lymphopenia and an increase in ESR are noted. Despite the absence of clinical symptoms, proteinuria, cylindruria and leukocyturia are found in the urine.

The mortality rate among hospitalized patients is about 4-5%, which allows West Nile fever to be classified as a severe (dangerous) viral neuroinfection.