West Nile Virus Epidemiology
The incidence and distribution in Montana and elsewhere, along with the information regarding the spread of the disease.
Prevalence
Since it's discovery in New York City in 1999 -- West Nile Virus has established itself in the Western Hemisphere. In temperate climates (latitudes 23.5° and 66.5°). Find the latitude of your city
West Nile Virus transmission occurs primarily during the summer and early fall when mosquito activity is the highest. In southern climates, WNV can be transmitted year round. The virus has been documented to survive cold winters in northern regions to appear again the following year. How the virus survives the cold is not completely understood.
| Horses:
|
Humans:
|
| Montana’s first case of West Nile virus in a horse was reported in Shepherd in August 2002.
|
The first case of West Nile virus contracted by a person in Montana was confirmed in Yellowstone County, Fall 2002. The Billings resident’s onset of illness was in mid-September. The resident required brief hospitalization for meningitis, but made a full recovery.
|
| States with Equine Cases
|
CDC Daily Report
|
Transmission
Humans and animals that become infected are considered to be "dead-end hosts" in the transmission cycle. Neither is thought to become viremic enough to pass along sufficient virus to a bloodsucking mosquito.
Horses
Horses are affected by WNV much more often than any other domestic animals. It is important to remember that humans cannot contract the disease from horses and WNV is not a contagious disease from horse to horse, so no quarantine is necessary for infected premises or animals.
Humans
Humans acquire the disease the same way horses do - through a mosquito bite of an infected mosquito. There is no evidence that a person can get the virus from handling live or dead infected animals. However, avoid bare-handed contact when handling any dead animals and birds. Use gloves or double plastic bags to place the carcass in a garbage can.
There is no evidence of transmission of the disease through eating meat of an animal infected with the virus.
The CDC has a web site that addresses issues of contracting WNV through blood transfusions, organ transplants, and breast milk. For more information on this topic, please visit the CDC web site at: http://www.cdc.gov/ncidod/dvbid/westnile/qa/transmission.htm
What about other Livestock?
| The vast majority of infections have been identified in birds. The CDC reports that WNV has also been shown to infect:
|
- horses
- cattle
- sheep
- goats
- camelids (alpacas, llamas, camels)
- cats
|
- bats
- chipmunks
- skunks
- squirrels
- domestic rabbits.
|
The USDA reports that other livestock and poultry do not commonly show any illness if infected with WNV. Again, animals CANNOT transmit WNV to people.