Mosquito Control | Frequently Asked Questions
About West Nile Virus (continued)
How many human cases have there been in the United States? How many deaths?
In 1999, 62 cases of severe disease, including seven deaths, occurred in the New York area. In 2000, 21 cases were reported, including two deaths in the New York City area. In 2001, there were 66 human cases of severe disease and nine deaths. No reliable estimates are available for the number of cases worldwide of West Nile encephalitis, the disease caused by the West Nile Virus.
For 2002 in the United States, there were 4, 156 cases of human disease due to West Nile Virus infection reported to the Center for Disease Control and Prevention (CDC). For 2003, there were 9862 cases of human disease due to West Nile Virus infection and in 2004 there were 2535 cases. The latest count of human cases in the United States can be found on CDC's Web site.
For the latest up-to-date information, go to the United States Geological Survey Web site and read the summaries.
How many cases have there been in Texas? How many deaths?
The first human death in Texas occurred on August 16, 2002. For the latest up-to-date information on human cases in Texas, go to the Texas Department of State Health Services Web site.
Where in Texas has the virus been found?
For the most up-to-date information, go to the Texas Department of State Health Services Web site.
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How many cases of West Nile Virus were there in Dallas County in 2002?
In 2002, cases of the West Nile Virus in Dallas County confirmed by the Texas Department of State Health Services were: 25 humans; 28 birds and 26 horses.
Do birds or mosquitoes get it first? Where does the virus live?
This is a chicken and egg question. It is usually found first in birds. Generally, surveillance by the Texas Department of State Health Services finds the virus in birds a week or two before finding positive mosquitoes. The virus is in their bloodstream. Mosquitoes become infected when they feed on infected birds. The infected mosquitoes can then transmit West Nile Virus to humans and animals while biting to take blood. The virus is located in their salivary glands and, during blood feeding, the virus can be injected into the animal or human, where it can multiply, possibly causing illness in the animal or human.
In addition to being infected by the West Nile Virus, what else can cause bird ‘die-offs'?
Chemical spills, pesticides, drought, severe weather, food and other diseases.
What's an arbovirus?
Any of various viruses that are the causative agents of encephalitis, yellow fever and dengue and that are transmitted chiefly by arthropods, such as insects.
What kinds of laboratory tests are done to identify the West Nile Virus?
Various tests can be done. The type of test will vary among mosquitoes, humans and horses. The type of test also depends on the kind of samples available (blood serum, cerebrospinal fluid, brain tissue). Samples may be tested to find antibodies to the West Nile Virus, or there may be an attempt to isolate particles from the sample. More details are available at the Texas Department of State Health Services web site.