Poison sumac Toxicodendron vernix [L Kuntzel [Rhus vernix L This poisonous tree a relative of poison ivy and poison oak has seven

to 13 long narrow leaves growing in pairs with a single leaf at the end of the stem. In the spring the leaves are bright orange and look something like velvet; as the season progresses, they become dark green and glossy on the upper surface and light green on the underside. In the fall the leaves turn red or orange. Poison sumac can be differentiated from nonpoisonous sumacs by its drooping clusters of green berries; nonpoisonous sumacs have red, upright clusters of berries. Poison sumac can grow to be 25 feet tall, although it is more often found between five and six feet tall. It is found in swampy areas throughout the eastern United States. (See poison ivy for details on treatment and prevention.)

poliomyelitis (polio) A contagious viral disease that in its severe form can cause permanent paralysis and sometimes death. This extremely dangerous disease causes mild disabilities in about half of all patients; the rest may suffer permanent paralysis. However, due to modern vaccination practices, the Americas were declared polio-free in 1994, and the disease has been almost eliminated in Europe (there was an outbreak in the Netherlands in 1995). The global network of labs that track the disease reported no new cases of Type 2 polio in 2000. The last recorded cases were in India in 1999.

Still, more than 2,800 cases were confirmed in 2000 in southeast Asia, Africa, and the Mediterranean, where war, poverty, and other problems have interfered with efforts to vaccinate children.

Most American doctors have never seen an active case of polio, but in the first half of this century polio (then known as "infantile paralysis"), was called the last of the great childhood plagues.

Polio was known for hundreds of years, but the disease was not much discussed in ancient medical literature and did not occur in large epidemics until modern times. In fact, it was only in the late 18th century that the disease was first identified as polio. In ancient times, sanitation was so appallingly poor that there was plenty of opportunity for people to contract polio, which is carried in feces. The viruses infected each new generation of infants, who were protected in part by antibodies passed from their mothers. These early infections were usually mild and were rarely diagnosed as polio.

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