Lecture 11 - West Nile Virus Flashcards
WEST NILE VIRUS INFECTION is
a mosquito-borne viral disease of birds, mammals and reptiles, caused by Flavivirus, characterized by variable clinical signs and death.
Causative agent of west nile
West Nile virus (WNV)
Genus Flavivirus, family Flaviviridae
RNA virus
Two genetic lineages of WNV.
- Lineage 1: contains 3 clades (1a, 1b ja 1c).
Many of the virulent viruses from recent outbreaks belong to 1a (widespread).
- Lineage 2
WNV is Part of the Japanese encephalitis virus complex or serogroup.
Stability of WNV.
Disinfectants work, e.g. sodium hypochlorite solutions (bleach).
Inactivated be UV light and gamma irradiation.
Does not persist in the environment for long.
Infectivity in avian feces decreases dramatically after 24 hours.
Host range of WNV.
birds, mammals, reptiles
Birds are the main reservoir host.
NB! ZOONOSIS!
Clinical cases seen in birds, horses, humans, alligators.
Distribution of WNV.
worldwide
Morbidity of WNV.
Morbidity:
birds <50%,
horses <90%
Humans: 1% who are infected with West Nile develop severe illness.
Mortality of WNV.
Birds <30%
Horses <60%, other mammals <100%
Humans <15%
Excretion of WNV.
oral and cloacal secretions (in some bird species)
Transmission of WNV.
Mosquitoes (mainly genus Culex; >60 species).
Direct transmission and Horizontal transmission too!
Cannibalism, feather picking, Eating infected animals or mosquitoes also transmit it.
Humans get it from mosquito bites (also blood transfusion, transplants),
In mammals, WNV is usually cleared from the body during the illness.
IP of WNV.
In horses: 3-15 days
In birds: IP 5 days
In humans: 2-14 days (longer in transplant patients)
Clinical signs of WNV in horses.
Mostly asymptomatic
Anorexia, depression, neurologic signs
Recovery after 7 days
Clinical signs of WNV in birds.
Some species are asymptomatic, other develop clinical signs (e.g. geese).
Weight loss, decreased activity, depression, neurological signs.
Affected birds usually found dead.
Clinical signs of WNV in alligators.
Anorexia, lethargy, weakness and neurological signs.
Death in 24-48 hours after the onset of clinical signs.
Clinical signs of WNV in humans.
Depends on the form of disease.
Forms of WNV in humans:
West Nile fever – most common form (20%)
West Nile neuroinvasive disease which consists of 3 syndromes.
- encephalitis
- meningitis
- acute flaccid paralysis
Post mortem WNV lesions of birds.
Wide variety of gross and microscopic lesions – often nonspecific.
Emaciation and dehydration, multiorgan hemorrhages, petechia and congestion.
Histopathologic lesions in CNS, heart, spleen, liver and kidney.
