a. Intestinal Nematodes. This group of nematodes is wide spread in the
tropics and subtropics. In the Western Hemisphere, tropical Africa, the Far East, and
the Mediterranean, infection from these nematodes is prevalent where there are
overcrowding and poor sanitary conditions. Hookworm and pinworm are examples of
intestinal nematodes commonly found in the United States. For both, the normal vector
for transmission is contact with fecal material of infected organisms. Threadworms and
whipworms are two more types of intestinal nematodes that attack man. Threadworm
disease is endemic (a constant presence) in the tropics, generally in the same
unsanitary conditions favorable to the spread of hookworm. Whipworm disease, found
worldwide and especially in warm, moist regions, flourishes in areas of inadequate
sanitation and poor personal hygiene habits.
Figure 3-2. Intestinal nematode.
b. Tissue Nematodes. Tissue nematodes are found in all areas of the world.
Trichinella spiralis, which causes trichinosis, is a tissue nematode found in temperate
climates. Humans become infected by eating inadequately cooked pork and pork
products that are contaminated. Figure 3-2 shows this parasite encapsulated in a
muscle. Contact with the feces of infected dogs or cats is the source of infection for
toxacariasis. Other tissue nematodes are transmitted by bites of infected mosquitoes
and flies, usually in the tropics.
Figure 3-3. Tissue nematode.