West Nile fever
The content of the article:
- Causes and risk factors
- Forms of the disease
- Symptoms
- Diagnostics
- Treatment
- Possible complications and consequences
- Forecast
- Prevention
West Nile fever (WNF) is a zoonotic natural focal transmissible infection caused by arboviruses of the Flaviviridae family, characterized by acute intoxication syndrome with lesions of the central nervous system.
Vector-borne infections are a group of diseases whose pathogens are transmitted by blood-sucking arthropods. In this case, mosquitoes of the genus Culex play the role of carriers of the virus, less often - Aedes and Anopheles, participation in the transmission of the virus of ixodid and argas ticks is not excluded. Wild birds are a natural reservoir for West Nile virus.
West Nile fever is carried by the Culex mosquito
The virus is quite stable in the external environment: it dies at temperatures above 55 ºС with an exposure of at least half an hour, it remains viable for a long time in dried or frozen form.
Initially, West Nile fever was most widely represented in Africa, South America, Asia. Since the end of the last century, the nosoareal of the disease has expanded significantly: cases of infection have been detected in countries not only with hot, but also with temperate climates (in Europe, Russia), which is due to the seasonal migration of infected birds.
In regions with a temperate climate, there is a characteristic seasonality; the peak of incidence (more than 90% of all detected cases) falls on the period from July to October, which correlates with the maximum number of blood-sucking insects in these months.
The risk groups for infection with the West Nile virus are people who work or rest in their backyards, as well as hunters, fishermen - people who spend a lot of time in the favorite places of arthropods (on water bodies, shady areas with massive vegetation, in swampy or wooded areas).
Causes and risk factors
In most cases, the cause of the disease is the bite of an infected mosquito or tick.
The virus enters the blood-sucking organism with blood (where it circulates for several days) after being bitten by an infected bird. In the future, the causative agent of West Nile fever is concentrated in the salivary glands of an insect or tick, from where, when a person or animal is bitten, it moves into its bloodstream, causing a chain of pathological changes.
In addition to being bitten by insects, the virus can be transmitted vertically (from mother to child), as well as through transfusion of infected blood or transplantation of infected organs, but this happens extremely rarely.
Forms of the disease
West Nile fever can occur in 2 forms:
- manifest - a typical clinical picture with violent symptoms develops;
- asymptomatic - in this case, there are no manifestations of the disease (according to the World Health Organization, the frequency of this form is close to 80% of the total incidence).
The manifest form of the disease is represented by two clinical variants:
- WNV without damage to the central nervous system (it proceeds in a flu-like form or in a flu-like form with neurotoxicosis);
- WNN with CNS damage (meningeal and meningoencephalitic forms).
Symptoms
The incubation period of the disease lasts up to 3 weeks, more often - 5-6 days. In the future, if there is a manifest form of the disease, symptoms characteristic of a particular variant of infection appear.
Manifestations of West Nile fever, not accompanied by damage to the central nervous system:
- acute onset of the disease;
- rise in body temperature to 39-40 ºС, in exceptional cases - above 40 ºС (the duration of the febrile period can reach 12 days, although on average it is limited to 2-3 days);
- tremendous chills;
- pouring sweat;
- polymorphic maculopapular rash (noted quite often);
- headache;
- soreness when moving the eyeballs;
- hypersensitivity to light, photophobia;
- muscle and joint pain;
- increase and soreness of the lymph nodes of the head and neck on palpation;
- hyperemia of the mucous membranes of the pharynx;
- a long period of asthenization after relief of intoxication symptoms (general weakness, drowsiness, decreased performance, feeling of weakness).
West Nile fever usually starts with a rise in temperature
In the case of an infection with symptoms of neurotoxicosis, the headache becomes intense, episodes of dizziness are possible, nausea, vomiting at the height of fever, unsteadiness of gait, rigidity of the occipital muscles are characteristic. In this case, no changes were recorded in the analysis of cerebrospinal fluid.
When the central nervous system is involved in the infectious process (with the meningeal form), the symptoms are as follows:
- acute onset with a rapid increase in body temperature to critical numbers, chills, sweating;
- intense headache, on the 3-4th day acquiring a painful character;
- stiff neck;
- photophobia;
- nausea, vomiting with identification of meningeal symptoms.
According to the results of the lumbar puncture, changes in the cerebrospinal fluid are determined, characteristic of serous viral meningitis.
With the meningoencephalitic form of the disease, the patient's condition is severe or extremely severe, there is a gross cerebral symptomatology against the background of meningoencephalitis phenomena (impaired consciousness, headache, dizziness, vomiting, generalized convulsive seizures), further developing a cerebral coma. Mortality in this form of the disease is 5-10%, in extremely severe cases - up to 40%.
Diagnostics
Diagnosis of West Nile fever is difficult, due to the large number of asymptomatic cases of the disease, the absence of specific manifestations in influenza-like forms.
The main diagnostic measures:
- collection of an epidemiological history (connection with a previous stay in high-risk areas, bites of blood-sucking insects, seasonality of the disease);
- conducting enzyme-linked immunosorbent assay (ELISA) to detect specific IgM, IgG (titer confirming the diagnosis - 1: 800 or more);
- polymerase chain reaction (PCR) to detect West Nile virus RNA;
- virological research to identify the pathogen;
- in the presence of meningeal symptoms, lumbar puncture followed by examination of the cerebrospinal fluid.
Treatment
WNN treatment is medication. Appointed:
- interferon inducers;
- diuretics;
- glucocorticosteroid hormones;
- inhalation of humidified oxygen.
Detoxification therapy, correction of electrolyte disturbances and blood osmolarity are carried out. If necessary, anticonvulsants, sedatives, antioxidants, drugs that improve cerebral blood flow, broad-spectrum antibiotics are used.
Possible complications and consequences
Complications of West Nile Fever are very serious:
- acute violation of cerebral circulation;
- swelling of the brain;
- coma, death.
Forecast
With timely diagnosis and complex treatment, the prognosis is favorable. The likelihood of a successful outcome of the disease decreases with an infection of the meningoencephalitic form of a severe or extremely severe course.
Prevention
Preventive measures are as follows:
- Carrying out activities aimed at reducing the population of blood-sucking insects.
- Decrease in the population of wild birds, the way of life of which is associated with direct living next to humans.
- Use of repellents during long-term stay in natural foci with a high risk of arthropod bites.
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Olesya Smolnyakova Therapy, clinical pharmacology and pharmacotherapy About the author
Education: higher, 2004 (GOU VPO "Kursk State Medical University"), specialty "General Medicine", qualification "Doctor". 2008-2012 - Postgraduate student of the Department of Clinical Pharmacology, KSMU, Candidate of Medical Sciences (2013, specialty "Pharmacology, Clinical Pharmacology"). 2014-2015 - professional retraining, specialty "Management in education", FSBEI HPE "KSU".
The information is generalized and provided for informational purposes only. At the first sign of illness, see your doctor. Self-medication is hazardous to health!
