11.   Mosquitoes feeding on birds infected with West Nile virus become carriers of the virus, and may then infect animals the insects bite subsequently, including humans.

12.   Occasionally, viruses from birds infect animals like pigs, and then jump to people.

13.   Others have more carefully reasoned concerns about safety precautions at the lab, and its occasional requests to transport viruses or infected animals on and off the island.

14.   Some horses that test positive for the disease show no symptoms and are able to compete, but there is a risk of infecting other animals.

15.   Some, like scrapie and bovine spongiform encephalopathy, also known as mad cow disease, infect animals.

16.   That is to give the officials time to determine whether other animals have been infected and where the virus may have come from.

17.   The animal was infected after being fed meat and bone meal purchased in Belgium.

18.   The organism that causes anthrax, Bacillus anthracis, is a spore-forming bacteria that infects warm-blooded animals and that can persist in the soil for many years.

19.   The same strain extensively infected animals in many urban centers, including Washington, Baltimore, Philadelphia and Newark.

20.   The vaccinated animals became infected, but their killer T-cells managed to keep the virus in check, and they never got sick.