fhey are able to invade the host using different portals of entry, but the most common is still through the mouth. A few are able to actively penetrate the skin or are passively introduced into the host by some insects. lnfected individual s may or may not show signs and symptoms of infection. Those who do not show the signs and symptoms may however serve as carriers and extra source of infection. Most parasites live in humal) and animal intestines, and are usually passed out with the feces. Howeve r, parasites ha. ve also been recovered from other organs like the liver, lungs, brain, meninges, lymph nodes, lymph vessels, subcutaneous tissues, muscles, reproductive organs, blood vessels, blood cells and even the eyes. Parasites may be single celled culled tbe protozoa or may be multicellular call "worms~ or "helminthes. " The collective term applied to wonns found in the human intestines is hintestinal heliminths " and infection is "intestinal helminthiases" which is one of the top causes of morbidity worldwide. The most vulnerable sector of the population. are the children. There are few parasitic infections which can cause death like malaria and capillariasis. A few may cause permanent disability like elephantiasis due to filariasis. There are increasing evidences today that associate parasitic infections with malnutrition, poor . learning ability and growth retardation. Infected individuals oftenmanifost abdominal discomfort, lack of appetite, hunger pangs and loss of weight. As a whole, parasitic infections can affect the economic productivity and quality of life of an infected individual in particular. If the parasitic infection is present among a big segment of the population, then the effect of this parasitic infection is magnified. The following sections will discuss the parasites according to the different modes of transmissio n. The life cycle of each parasite show the points where spread of infection can be prevented or controlled. Illustrations of the life cycles were adapted from l1andouts given to students of the course on parasitology at the Uniformed Services University of Health Sciences in Maryland, USA. DIRECTLY-TR ANSMITTED PARAS'ITE Enterobius (Oxyuris) vermicularis This parasite is also known as the human pinworm or seatwonn.. It causes an intestinal infection with worldwid edisl-ributi on. Jnfected individuals usuallysufferfrom intense perianal itching whlch maybe complicated w1th secondary bacterial infection. Because of itching, most patients have disturbed sleep resulting to nervousness and irritability. Enterobiasis or o:-. ')'U. riasis is observed in places where there is overcrowding and water supply is inadequate for personal hygiene. Eggs of the parasite have been found in fingernail clippings, door knobs, faucet tops. and even from the keys of the piano and keys of typewrite rs. Eggs are deposited in the perianal region causing contamination of underwear and bed linens. Outside the host, eggs become infective in four to sh: hours. Transmission takes place either through ingestion or inhalation of the eggs (See Illus. 15. 1). Infection is easily transmitted to the othe. r members of a family or a group. Adult worms may be found crawling out of the anus but the choice of diagnosis is recovery of eggs using the Scotch tape method in S\Vabbing the perianal region (See 11lus. 15. 2). Specimen 357 