is the study of protozoan and helminthic parasites of animals and humans

in which adult or sexual stages reproduce

in which immature stages live

is the process of cyst formation

refers to the process by which cysts become trophozoites.

- unicellular eukaryotes found in a wide range of habitats - majority of it are free living and do not adversely affect humans or animals - some can cause debilitating and deadly diseases.

- called a trophozoite - lives within the host,

- can survive in the environment and is infective to new hosts. - Once ingested by a host, cysts undergo excystment and develop into new trophozoites which resume feeding and reproducing - Trophozoites undergo encystment before leaving the host in the feces, becoming available to infect other hosts.

- the only ciliate to cause disease in humans. - a relatively large (50 μm × 100 μm) - commonly found in animal intestinal tracts - PIGS are its most common host • also found in RODENTS and NONHUMAN PRIMATES - Humans become infected by consuming food or water contaminated with FECES containing cysts - is responsible for BALANTIDIASIS, usually a mild gastrointestinal illness. - Persistent diarrhea, abdominal pain, and weight loss characterize the disease - Severe infections produce: • dysentery - frequent and painful diarrhea, often containing blood and mucus • ulceration and bleeding from the intestinal mucosa. - Balantidium infection is rarely fatal

- does not kill B. coli directly but modifies the normal microbiota of the digestive tract such that the small intestine is unsuitable for infection by the ciliate. - Prevention of balantidiasis relies on good personal hygiene, especially for those who live around or work with pigs - efficient water sanitation is necessary - to kill cysts or remove them from drinking water.

are protozoa that move and feed using pseudopods.

- a relatively common protozoan parasite - causes amebiasis - can be mild luminal amebiasis, more severe amebic dysentery, or very severe invasive extraintestinal amebiasis - the parasite causes lesions in the liver, lungs, brain, and other organs

- are protozoa that possess at least one long flagellum, which is used for movement. • number and arrangement of the flagella are important features for determining the species of flagellate present within a hostare protozoa that possess at least one long flagellum, which is used for movement. • number and arrangement of the flagella are important features for determining the species of flagellate present within a host

• transmitted by the kissing bug (Triatoma) • causes Chagas' disease • cause of heart disease • Transmission occurs through the bite of true bugs • Bloodsucking bugs feed preferentially from blood vessels in the lips • gives the bugs their common name-kissing bugs

• transmitted by the tsetse fly • causes African sleeping sickness • Epimastigotes in the insect gut develop into infective trypomastigotes introduced to the human host by the insect vector • trypomastigotes remain in the blood • Antigenically variable, can spread to the CNS, and can be fatal.

- trypomastigotes develop intracellularly in macrophages and heart muscle as amastigotes

frequent cause of gastrointestinal disease • Cysts are immediately infective upon release • leading to a significant incidence of person-to-person and self-to-self transmission. • Cysts survive and remain infective for several months • watery diarrhea, abdominal pain, bloating, nausea, vomiting, ineffective absorption of nutrients, and low-grade fever • Stools are foul smelling • "rotten-egg" smell • Incubation lasts roughly one to two weeks, and symptoms resolve after one to four weeks in normal. health adults

- is rarely fatal environment because of the protective outer shell of its cyst. - Infection usually results from the ingestion of cysts in contaminated drinking water or accidental ingestion during swimming. - Hikers, campers, and their pets are at particular risk because infected wild animals shed Giardia into mountain stream • Cysts are immediately infective upon release • leading to a significant incidence of person-to-person and self-to-self transmission. • Cysts survive and remain infective for several months • watery diarrhea, abdominal pain, bloating, nausea, vomiting, ineffective absorption of nutrients, and low-grade fever • Stools are foul smelling • "rotten-egg" smell • Incubation lasts roughly one to two weeks, and symptoms resolve after one to four weeks in normal. health adults

• the most common protozoan disease of humans. • sexually transmitted protozoan • causes vaginosis • Prevention: • Abstinence • Monogamy • condom usage purulent (pus-filled) odorous discharge • vaginal and cervical lesions • abdominal pain • painful urination • painful intercourse

Five species • falciparum • vivax • ovale • malariae • knowlesi • cause malaria • female Anopheles mosquitoes • 3 stages of the life cycle of Plasmodium • Sporozoites travel to the liver to initiate the exoerythrocytic phase • Rupture of liver cells releases merozoites from intracellular schizonts • Merozoites infect erythrocytes to initiate the erythrocytic cycle • sporogonic phase in the mosquito has an oocyst that divides to form sporozoites, which are injected into humans when the mosquito feeds

PLASMODIUM generally causes mild disease

PLASMODIUM usually results in chronic malaria, with periodic recurrence of symptoms

PLASMODIUM cause more serious malaria

PLASMODIUM • fatal • causes a form of malaria called blackwater fever

are produced by P. ovale and P. vivax

produces the deadliest form of malaria

- ingesting undercooked meat containing the parasite - People at greatest risk - butchers, hunters, and anyone who tastes food while preparing it. - Ingestion or inhalation with contaminated soil - Generally mild in humans, but it can cross the placenta to cause serious harm to fetuses - Wild and domestic mammals and birds - are major reservoirs for it, and cats are the definitive host - in which the protozoan reproduces sexually

are multicellular eukaryotic worms, some of which are parasitic

• scolex • attaches it to the intestine of its definitive host • From this extends a neck region from which proglottids grow • When fertilized eggs (sometimes within gravid proglottids) are eaten by an intermediate host, they hatch to release Larval stages that invade tissues of the intermediate host and form cysticerci • When the cysticerci are eaten by a definitive host, they undergo development into adult.

Humans are the definitive hosts ________ • Beef tapeworm _________ • pork tapeworm • Humans become infected by eating cysticerci in undercooked beef or pork

• forms hydatid cysts • cause hydatic disease in humans • accidental intermediate hosts when they ingest the helminth's eggs • definitive host • canine • it body consist of only three proglottids—- one immature, one sexually mature, and one Gravid • gravid proglottid is released each time the neck forms a new immature proglottid • Humans become accidental intermediate hosts by consuming foods or water contaminated with Echinococcus eggs shed in dogs feces • The eggs release larvae into the intestine • the larvae invade the circulatory system and are carried throughout the body, where they form hydatid cysts and cause hydatid disease • Hydatid cysts form in any organ but occur primarily in the liver.

- or flukes - are often divided into four groups: - blood, intestinal, liver, and lung flukes - Eggs deposited in water hatch to release miracidia, which burrow into freshwater snails - Following asexual reproduction cercariae are released into the water - In intestinal, liver, and lung flukes, cercariae encyst on plants or in a second intermediate host as metacercariae, which are ingested by human hosts. - Cercariae of blood flukes directly penetrate the skin of humans. After maturation occurs in the human, flukes release eggs back into the environment via the feces or urine

• a liver fluke • Humans acquire Fasciola hepatica by ingesting metacercariae on watercress or other vegetables. • Diagnosis involves the correlation of symptoms and patient history with microscopic identification of eggs in fecal matter

• blood flukes • causing schistosomiasis. • common name for the disease is "snail fever," • Three species infect humans: • S. mansoni -is common to the Caribbean Venezuela, Brazil, Arabia, and large areas of Africa. • S. haematobium - found only in Africa and India. • S. japonicum - occurs in China, Taiwan, the A Figure 23.21 sample. Distinctiv Philippines, and Japan, although infections in Japan are relatively rare • Extensive infections significantly damage the liver. - Humans are the principal definitive host - Cercariae burrow through the skin of humans who contact contaminated water while washing clothes and utensils, bathing, or swimming - The larvae enter the circulatory system, where they mature and mate

- Are round, unsegmented worms with pointed ends - Most intestinal nematodes shed their eggs into the lumen of the intestine, where they are eliminated with the feces - eggs are then consumed by the definitive host either in contaminated food (particularly raw fruits and vegetables that grow close to the soil) or in contaminated drinking water

• the largest nematode to infect humans • Ascariasis • the most common nematode disease of humans in the world. • Eggs containing infective larvae are consumed with contaminated vegetables • The eggs hatch in the intestine, and larvae enter the lymphatic system. • Worm migration through the body may be associated with various symptoms, but infections are usually not fatal. • Growing as large as 30 cm in length • After eggs are ingested in water or on vegetables, the larvae invade the intestinal wall to enter the circulatory or lymphatic systems • From there the larvae reach the lungs, where they develop through two more larval stages in approximately two weeks • Worms are then coughed up into the pharynx and swallowed • The parasites subsequently develop into adults in the intestine.

• both hookworms, • the second most common nematodes to infect humans Worldwide • Eggs deposited in soil mature to form infective larvae that leave the egg and actively burrow through human skin to initiate infection. • The circulatory system carries the worms through the lungs and heart. • Eventually worms migrate up the respiratory tract to the pharynx, where they are swallowed. • They become adults in the intestine, where they attach to the intestinal mucosa and feed on blood. • Hookworm infection can lead to anemia and other A Figure 23.23 Mouth of a hook parasite to attach to the intestinal wall blood-related dysfunction.

- Pinworm - the most common parasitic worm infestation of humans in the United States and the third most common in the world - Eggs deposited in the perianal area are introduced into the mouth following scratching to reinfect the human host. - Transmission among family members is also common. - Humans are the only host for Enterobius - After mating in the colon, female pinworms migrate at night to the anus, where they deposit eggs perianally. Scratching dislodges eggs onto clothes or bedding, where they dry out, become aerosolized, and settle in water or on food that is then ingested. scratching deposits eggs on the skin and under the fingernails such that infected individuals can continually reinfect themselves by ingesting the eggs on their hands or in food. - Adult worms mature in several weeks and live in the intestinal tract for approximately two months. - intense perianal itching is the chief complaint - Scratching can lead to secondary bacterial infections

• is a filarial (threadlike) nematode of humans, causing filariasis • lives in the lymphatic system, where adult worms block lymph flow, causing elephantiasis • Lymph accumulates, especially in the lower extremities • Bacterial infections may ensue, and subcutaneous tissues harden, producing permanent disfigurement • The parasite is transmitted when microfilariae, which circulate in the blood, are picked up by feeding mosquitoes.

- are organisms with segmented bodies, jointed legs, and a hard exoskeleton - They are found worldwide in nearly all habitats - Some may serve as biological vectors for many organisms.

VECTORS include mites and ticks.

VECTORS fleas, lice, flies, and kissing bugs.