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GLOSSARY 301

Scabies Scabies is an itchy skin condition caused by a (stomach-foot) mollusk capable of acting as the intermediate
tiny, eight-legged burrowing mite, an arachnid called Sar- host for a number of parasites.
coptes scabiei. The condition is known as the “itch,” and Seroprevalence Refers to the frequency or probability of in-
is the contagious ectoparasite that causes a skin infection dividuals in a population group that have a particular type of
characterized by superficial burrows and intense pruritus antibodies to a certain organism in the blood serum.
(itching). Sexually transmitted diseases (STDs) Any of a variety
Scavengers Term is used for any animal, including both birds of bacterial, viral, fungal, or protozoal organisms that are trans-
and insects, that gains its nourishment from dead or decaying mitted primarily by copulation (sexual intercourse).
matter. Sheather sugar Sheather’s flotation method is a method for
Schistosomiasis A condition of being infected with one of examining fecal samples for the presence of worm eggs or lar-
the blood flukes of the genus of Schistosoma. vae using a saturated solution of sugar or saline.
Schistosomula The cercariae of Schistosoma burrow through Siberian liver fluke A freshwater parasite called the human
the skin of the host and develop into schistosomula that mi- liver fluke is found in areas of Thailand, Japan, and Siberia
grate through the body until they reach their final position in where the species was first identified and studied. This para-
the blood vessels where they mature. site may trigger cancer in humans by creating harmful cell mu-
Schizogony Term used for asexual reproduction by multiple tations, encouraging tumor formation in the liver.
fission, a reproductive process for many sporozoan protozo- Sigmoidoscopic Most frequently a flexible tube connected
ans; fission refers to a division of the cell into two more or less to a fiber-optic camera is used in which a physician examines
equal parts. the large intestine.
Schizont In the infection of malaria, sporozoites migrate Sleeping sickness A parasitic disease found primarily in
to the liver where the parasite matures in the hepatocyte to a sub-Saharan African, trypanosomiasis is a parasitic disease in
schizont containing many merozoites in it. After this hepatic people and other animals that is transmitted by the tsetse fly,
stage, the erythrocytic stage begins following the formation of and is caused by several species of the genus Trypanosoma.
merosomes that contain thousands of merozoites, which bud Slime molds Originally classified as a fungus and no longer
off the hepatocytes. Within the erythrocytes the merozoite considered as such, slime mold is a general term for identifying
grow first to a ring-shaped form and then to a larger tropho- fungi-like organisms that reproduce by spores.
zoite form. Snails Mollusks that have a muscular foot (Gastropoda) and
Scolex The head portion of the cestode; the anterior, first that are capable of being parasitic vectors or intermediate
segment of a tapeworm that possesses organs such as suckers, hosts.
muscular jaws, or hooks for attachment. Soft tick Any tick of the Argasidae family that lacks a dorsal
Scotch tape prep Use of cellophane tape to obtain the eggs shield, or scutum, and has the mouthparts on the underside
laid in the anal region during the night by the female pinworm of the head.
called Enterobius vermicularis. Southern Tick-associated Rash Illness Also called
Scutum Hard shield-shaped chitinous plate covering the STARI; emerging infectious disease related to Lyme disease
upper dorsal surface of hard-bodied ticks, a feature that dis- that occurs in southeastern and south-central United States.
tinguishes them from the wrinkled appearance of soft-bodied The disease is spread by the bites of the tick called the lone
ticks. star tick, Amblyomma americanum. The causative organism
Sebaceous glands Glands of the skin that produce a secre- has not been definitively identified.
tion of fat; an oily solution that resembles fatty materials, the Spirochetes Slender, motile organism with spiral shape; such
sebaceous secretions of some plants, or the sebaceous humor as Treponema pallidum, the pathogen that causes syphilis.
of animals. Splenomegaly Enlargement of the spleen located in the ab-
Secretory IgA Secretory IgA is a dimer of the immunoglobu- dominal region.
lin A and is the primary molecule of the mucosal surfaces and Spontaneous generation An obsolete assertion that life
is one of the first lines of defense against invasion and coloniza- can spontaneously occur from nonliving matter. The appear-
tion by potentially harmful microorganisms. ance of maggots in meat sealed in a lidded container was used
Sedimentation method One of the two major techniques as “proof” that this occurred initially.
available for parasite assays and identification in separating Sporocyst A protective case or cyst where sporozoites de-
eggs and even cysts from fecal material and concentrating the velop and are then transferred to different hosts; also a bladder
organisms or their ova. or saclike larval stage in many trematode worms.
Seed ticks Nymphal form of some ticks that may be capable Sporozoans Class of parasitic protozoa that includes Plasmo-
of transmitting infection. dium, Cryptosporidium.
Segmented neutrophils A phagocytic leukocyte also called Sporozoites Undeveloped sporozoans that are produced by
a seg or poly; when mature has a segmentednucleus (it is called multiple division of a zygote or spore; stage where it may infect
a seg or poly). The immature neutrophil has a horseshoe- a new host cell.
shaped nucleus called a band. Sputum Thick, mucopurulent material from the air pas-
Semisulcospira Species of freshwater snail with an sages of the respiratory system that is coughed up and fre-
operculum (lid-shaped cover) that is an aquatic gastropod quently expelled from mouth; mucus or mucopurulent matter