The coming of fall does not lessen the threat of the mosquito-borne West Nile virus or hundreds of other diseases that affect both humans and animals, scientists caution. These are called zoonotic diseases. The good news is most of the ailments are avoidable and treatable, said the investigators from Purdue University. So, when the leaves turn color, people should continue to be on their guard. In fact, October can be among the worst months for mosquitoes, entomologists said. Last October, Indiana recorded its first West Nile fatality in a horse. This year, by the end of September, the illness had infected more than 3,500 horses nationwide and about 2,200 people, causing 95 human deaths. Many other zoonotic diseases aren't spread by mosquitoes, and most aren't passed directly from animals to humans, said Larry Glickman, professor of epidemiology and environmental health. The general public is familiar with many of these ailments, such as rabies and Lyme disease, but others, such as Ehrlichiosis and larva migrans, are relatively unknown. "Zoonotic diseases run the whole gamut of types of organisms," Glickman said. "Some of these organisms don't appear to cause disease in the animal that harbors them, while others are as toxic to the animal host as they are to the human or animal to which the illness is passed." The best way to avoid mosquito- and tick-borne diseases is to limit exposure to the insects, said Ralph Williams, an expert on disease-spreading insects. For protection, wear light-colored clothing with long sleeves and long pants and use insect repellent containing diethyl-meta-toluamide (DEET), Williams advised.