Case 89: West Nile Virus

Question 1

what family is the west nile virus part of?

Answer 1

flaviviridae

Question 2

what are the characteristics of the WNV genome?

Answer 2

flaviridae = enveloped, icosahedral (+) sense ssRNA virus

Question 3

what are the presenting symptoms of WNV?

Answer 3

• fever
• headache
• vomiting
• weakness
• confusion
• course tremor in the chin and upper/lower extremities

fever and altered mental status suggest encephalitis

spending lots of time outdoors and otherwise healthy

Question 4

what would a brain MRI of a WNV patient show?

Answer 4

increased signal in the basal ganglia

Question 5

what type of antibodies does the body make against WNV?

Answer 5

IgM

diagnosis of WNV requires the measurement of
IgM antibodies in blood or CSF

the test is positive in most infected people within 8 days of onset of symptoms

Question 6

where is WNV most geographically common?

Answer 6

• africa
• west asia
• middle east

recently it’s been on North America too which has been a threat to public health and we don’t know how it got here

Question 7

how is WNV transmitted?

Answer 7

it’s transmitted

among wild birds by mosquitoes

Question 8

what is the pathogenesis of the WNV?

Answer 8

WNV gains access to humans via the bite of an infective mosquito

the virus localizes in
the vascular endothelium and the lymphatic cell of the reticuloendothelial system, where
replication occurs, causing primary viremia

in immunocompetent healthy individuals,
primary viremia presents with a febrile illness without involvement of the CNS

Question 9

what is the pathogenesis of WNV in old/immunocompromised patients?

Answer 9

in immunocompetent healthy individuals,
primary viremia presents with a febrile illness without involvement of the CNS

but in the
elderly and immunocompromised individuals, another event of viral replication in the
blood stream (secondary viremia) leads to hematogenous dissemination of the virus, which localizes primarily in the CNS

there, the virus causes inflammation of the brain
(cerebellum) and vascular tissues; characteristic brain pathology reveals scattered
microglial nodules and perivascular inflammatory infiltrates of lymphocytes

head
CT and brain MRI may show chronic microvascular ischemic changes

Question 10

how do you treat WNV?

Answer 10

no treatment available….

only supportive care

usually the virus will clear on it’s own eventually but people can go comatose while trying to recover

Question 11

how do you prevent WNV?

Answer 11

1. surveillance to detect the presence of WNV in
   areas where humans are at risk;
2. sustained and integrated mosquito control;
3. public education on the use of personal protective behaviors and peri-domestic mosquito
   control to reduce the risk for mosquito bites
4. standing water should be eliminated wherever possible
5. use DEET