West Nile Fever: Causes and Pathogenesis
Last reviewed: 23.04.2024
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Causes of West Nile fever
The cause of the western Nile fever is the West Nile virus of the Flavivirus family of Flaviviridae. The genome is represented by single-stranded RNA.
Virus replication occurs in the cytoplasm of affected cells. The virus of the West Nile fever has a significant ability for variability, which is due to the imperfection of the mechanism of copying genetic information. The greatest variability is characteristic for genes encoding the envelope proteins responsible for the antigenic properties of the virus and its interaction with the membranes of tissue cells. Strains of the West Nile fever virus, isolated in different countries and in different years, do not have a genetic similarity and have different virulence. A group of "old" strains of the western Nile fever, which were mainly allocated before 1990, is not associated with severe CNS lesions. A group of "new" strains (Israel-1998 / New York-1999, strains Senegal-1993 / Romania-1996 / Kenya-1998 / Volgograd-1999, Israel-2000) is associated with massive and severe human diseases.
[Pathogenesis of West Nile fever
The pathogenesis of the western Nile fever has been studied little. It is assumed that the virus spreads hematogenously, causing damage to the vascular endothelium and microcirculatory disorders, in some cases - the development of thrombohemorrhagic syndrome. It was established that the virusemia is short-term and non-intensive. Leading in the pathogenesis of the disease - the damage to the membranes and brain material, leading to the development of meningeal and cerebral syndromes, focal symptomatology. Death occurs, as a rule, on the 7-28th day of the disease due to disruption of vital functions due to swelling-swelling of the brain substance with the dislocation of stem structures, necrosis of neurocytes, and hemorrhages into the brain stem.
At autopsy, there is edema and fullness of the brain membranes, fine-focal perivascular hemorrhages, large hemorrhages (up to 3-4 cm in diameter). Expansion of the ventricles of the brain, plethora of the vascular plexus, multiple foci of softening in the cerebral hemispheres, small-point hemorrhages in the bottom of the IV ventricle, and 30% of deaths - dislocation of the brainstem. At a microscopic examination, vasculitis and perivasculitis of the brain envelopes, focal encephalitis with the formation of mononuclear infiltrates are determined. In the vessels of the brain - a picture of fullness and stasis, fibrinoid swelling and necrosis of the vascular wall. In ganglionic cells - pronounced dystrophic changes up to necrosis, pronounced perivascular and pericellular edema.
Significant changes are detected from the heart: muscle flabbiness, stromal edema, myocyte dystrophy, fragments of muscle fibers and myolysis. In the kidneys - dystrophic changes. In some patients, signs of generalized thrombohemorrhagic syndrome are determined.
The virus of the West Nile fever is detected by PCR in the spinal cord, brain tissue, kidneys, heart, to a lesser extent - in the spleen, lymph nodes, liver.