West Nile Fever: Diagnosis

Clinical diagnosis of Western Nile fever sporadic cases of Western Nile fever is problematic. In the endemic region of the Western Nile region, any case of influenza-like illness or neuro-infection in June-October is suspected of West Nile fever, but can only be diagnosed using laboratory tests. During outbreaks, the diagnosis can be made with a significant degree of reliability on the basis of clinical and epidemiological data: the connection of the disease with mosquito bites, travel outside the city, living near open water bodies; absence of repeated cases of diseases in the outbreak and the connection of the disease with the use of food products, water from open reservoirs; Increase in the incidence of neuroinfections in the region in the warm season.

The virus of the West Nile fever can be isolated from blood samples and, more rarely, cerebrospinal fluid taken from patients in the acute period of the disease, usually up to the fifth day from the onset of the disease. Laboratory models for virus isolation can be newborn and young mice and various types of cell cultures.

At the same time, it is possible to detect RNA of the West Nile fever virus by PCR. The material for the PCR test (plasma and / or blood serum, cerebrospinal fluid) should be collected using only disposable test tubes and medical equipment in accordance with aseptic rules and stored at -70 ° C or in liquid nitrogen until the time of the study.

Serological diagnosis of fever of the western Nile is possible with the use of the methods of RTGA, RSK, RN. Currently, in practice, the greatest use of ELISA, which allows to detect antibodies to the virus class IgM and IgG. Early antibodies of the IgM class are determined in the early days of the disease, and their titers reach a very high level 1-2 weeks after the onset of the disease.

For serological diagnosis it is necessary to take two blood samples: the first sample - in the acute period of the disease until the 7th day from the onset of the disease; the second test - 2-3 weeks after the first.

Diagnosis of the western Nile fever can be made based on the detection of antibodies to the IgM class virus in a single blood sample taken during the acute period of the disease, and also by determining the decrease or increase in IgM content in paired blood serums.

Indications for hospitalization

Fever of the western Nile - an occasion for hospitalization, with the condition of hyperthermia 40 ° C and higher, the presence of meningeal, cerebral and focal neurological symptoms.

Differential diagnosis of West Nile fever

Differential diagnosis of Western Nile fever is carried out depending on the clinical form of the disease. Unlike influenza with West Nile fever, there are no signs of laryngotracheitis, the duration of the fever often exceeds 4-5 days. From the acute respiratory viral infection, the fever of the western Nile is distinguished by the absence of catarrhal phenomena from the upper respiratory tract, high fever and severe intoxication.

From meningitis of another etiology, first of all enterovirus. The meningeal form of the western Nile fever is distinguished by a high and prolonged fever, severe intoxication, mixed pleocytosis, and slow sanitation of the cerebrospinal fluid. With enteroviral meningitis, neutrophilic and mixed pleocytosis is possible at the first examination of the cerebrospinal fluid in the early periods, and after 1-2 days becomes lymphocytic (more than 90%).

The most difficult is the differential diagnosis of West Nile fever with herpetic encephalitis. In its presence, more often against the background of fever, a sudden attack of generalized seizures followed by coma, but differential diagnosis is possible only on the basis of studies of blood and cerebrospinal fluid using a full range of immunological methods and PCR, as well as CT or MRI of the brain.

Unlike bacterial meningitis in meningeal and meningoencephalic variants of the West Nile fever, the spinal cord fluid is transparent or opalescent, there is a clear discrepancy between the severe disease pattern and the mild inflammatory response of the cerebrospinal fluid, with an elevated or normal glucose level in it. Even in the presence of leukocytosis, there is no neutrophil shift left.

From tuberculous meningitis, the symptoms of CNS involvement in patients with Western Nile fever are different in that they appear earlier and grow in the first 3-5 days of the disease (in case of tuberculous meningitis, the second week). Fever and intoxication in the first days of the disease are more pronounced, for the 2nd-3rd week, the condition improves, fever is reduced, neurological symptoms are registered, and the glucose level remains unchanged against the background of decreasing cytosis of the cerebrospinal fluid.

In contrast to rickettsiosis, western Nile fever does not have a primary affect, a characteristic rash, hepatolienal syndrome, inflammatory changes in the cerebrospinal fluid are observed with great consistency, RCC and other serological tests with rickettsial antigens are negative. Distribution area, seasonality of the western Nile fever may coincide with the area of the Crimean hemorrhagic fever, but with the Crimean hemorrhagic fever, a hemorrhagic syndrome is revealed, inflammatory changes of the cerebrospinal fluid are absent. In the study of blood from the 3-5th day of the disease, leukemia and neutropenia, thrombocytopenia are detected.

In contrast to malaria, fever in patients with Western Nile fever remittent, there is no apyrexia between seizures, repeated chills and hyperhidrosis, no jaundice, hepatolienna syndrome, anemia.

Differential diagnosis of West Nile fever with other diseases without affecting the central nervous system

Index	LZN	ARVI	Flu	Entero-viral infection
Seasonality	July-September	Autumn-winter-spring	Autumn-Winter	Summer-autumn
Fever	Up to 5-7 days 37.5-38.5 ° С	2-3 days 37.1-38.0 ° С	Up to 5 days 38.0-40.0 ° С	2-3 days to 38.5 ° С
Headache	Expressed	Weak, moderate	Sharply expressed	Expressed
Vomiting	Possible	Not typical	Possible	Possible
Chills	Available	Not visible	Available	Not typical
Myalgia	Characteristic	Not typical	Characteristic	Possible
Cough	Not typical	Characteristic	Characteristic	Not typical
Runny nose	Not typical	Characteristic	Characteristic	Not typical
Hyperemia of the pharynx	Not typical	Typical	Typical	Possible
Hyperemia of the face	Possible	Not typical	Typical	Typical
Injection of sclera and conjunctiva	Possible	Possible	Typical	Typical
Cervical lympho-adenitis	Not typical	Available	Not visible	Available
Rash	Possible	Not visible	Not visible	Possible
Increase spleen	Not visible	Not typical	Not visible	Maybe
Diarrhea	Not typical	Not typical	Not visible	Possible
Number of leukocytes in the blood	Possible leukocytosis	More often leukopenia	More often leukopenia	More often leukocytosis

[1], [2], [3], [4], [5],