chapter 23

ascaris

Ascaris lumbricoides; endemic in the rural southeastern United States; causative agent of ascariasis; most common nematode infection of humans worldwide; eggs are ingested in water or on vegetables; adult worms grow and reproduce in the small intestine; most infections are asymptomatic; proper sanitation and hygiene are important for prevention

fasciola

Fasciola hepatica and F. gigantica; infect sheep and cattle worldwide; humans are accidental definitive hosts; ingest metacercariae from aquatic vegetation; parasite migrates from the intestine to the liver; chronic infections occur when flukes reside in the bile ducts; symptoms coincide with episodes of bile duct obstruction and inflammation

symptoms of malaria

P. falciparum can cause blackwater fever; high fever, erythrocyte lysis, renal failure, and dark urine; cerebral malaria results in tissue death in the brain; immunity develops if victim survives acute stage; periodic episodes become less severe over time; prevent malaria by limiting contact with mosquitoes

toxoplasma

T. gondii is causative agent; one of the world's most widely distributed parasites; wild and domestic mammals and birds are major reservoir; cats are the definitive host; infection due to consumption of undercooked meat containing the parasite; ingestion or inhalation of contaminated soil can also occur; the protozoan can cross the placenta and infect the fetus

apicomplexans

alveolate protozoa; infective form characterized by ornate complex of organelles at their apical end; parasites of animals; life cycles involve at least two types of hosts; schizogony is major feature of apicomplexan life cycles; multinucleate schizonts form before the cells divide; four important apicomplexan parasites are plasmodium, toxoplasma, cryptosporidium, and cyclospora

arthropod vectors

animals that carry microbial pathogens; arthropods are common vectors; some arthropods are biological vectors; serve as hosts for the pathogens they transmit; disease vectors belong to two classes of arthropods, Arachnida and Insecta

entamoeba

carried asymptomatically in the digestive tracts of humans; no animal reservoir exists; infection occurs by drinking water contaminated with feces containing cysts

cryptosporidium parvum

causative agent of cryptosporidiosis; once thought to only infect livestock and poultry; humans can carry the parasite asymptomatically; infection usually results from drinking contaminated water; fecal-oral transmission can occur; causes severe diarrhea that can last up to two weeks; chronic Cryptosporidum enteritis indicator a person has AIDS; infection of AIDS patients can be life threatening

plasmodium

causative agent of malaria; four species cause malaria P. falciparum, P. vivax, P. ovale, and P. malariae; malaria is endemic throughout the tropics and subtropics; mosquitoes are vector; life cycle has three prominent stages

acanthamoeba and naegleria

cause rare and usually fatal brain infections; common inhabitants of natural and artificial water systems; individuals who wash their contact lenses with tap water can become infected

trypanosoma brucei

causes african sleeping sickness; the insect vector is the tsetse fly; humans usually infected when bitten by infected tsetse flies

trypanosoma cruzi

causes chagas' disease; endemic in central and south america; opossums and armadillos are the primary reservoir; transmission occurs through bite of insects in genus triatoma; "Kissing bugs" feed preferentially from blood vessels in the lips

leishmania

causes leishmaniasis; endemic in parts of the tropics and subtropics; wild and domestic dogs and small rodents are common hosts; leishmania have two developmental stages; amastigotes multiply in host's macrophages and monocytes; promastigotes develop extracellularly within a vector's gut

life cycle of schistosoma

cercariae burrow through skin of humans who contact contaminated water; larvae mature and mate in the circulatory system; eggs move to the intestines or the urinary bladder and ureters; dermatitis may occur at the site where cercariae entered; infections can become chronic and can be fatal; prevention relies on improved sanitation and avoiding contaminated water

enterobius vermicularis

commonly known as the pinworm; most common parasitic worm found in the United States; humans are the only host for Enterobius; female pinworms deposit their eggs in the anus; infections are often asymptomatic; intense perianal itching occurs if symptomatic; rreventing fecal-oral spread from infected individuals limits disease

clinical forms of leishmania

cutaneous leishmaniasis. mucocutaneous leishmaniasis, visceral leishmaniasis; most cases of leishmaniasis heal without treatment; prevention limited to reducing exposure to reservoir and vector

schistosoma

dioecious blood flukes; causative agent of schistosomiasis; humans are the principal definitive host; three geographically limited species infect humans are S. mansoni, S. haemotobium, and S. japonicum

echinococcus

echinococcus granulosus is the canine tapeworm; canines infected by eating cysticerci in various herbivore hosts; humans are accidental intermediate hosts; consume food or water contaminated from dog feces; causes hydatid disease; larvae travel throughout body and form hydatid cysts; symptoms follow enlargement of cysts in infected tissue; prevent with good hygiene practices

trophozoite

feeding and reproducing stage that lives within the host

wuchereria bancrofti

filarial nematode; infects the lymphatic system; causative agent of filariasis; transmitted by various genera of female mosquitoes; mosquitoes ingest microfilariae when feeding on human; mosquitoes then transmit the parasite to new individual; remains asymptomatic for years; lymphatic damage can result in elephantiasis; prevention relies on avoiding infected mosquitoes

cestodes

flat, segmented intestinal parasites; all tapeworms lack digestive systems; all possess the same general body plan

trematodes

flukes are flat, leaf-shaped worms; lack complete digestive tract; attach to host tissues via a ventral sucker to obtain nutrients; geographical distribution limited because the intermediate host is limited; grouped according to the site in the body they parasitize

giardia intestinalis

found in intestinal tracts of animals and in the environment; causative agent of giardiasis; common gastrointestinal disease in the United States; ingest cysts in contaminated water or when swimming; range from asymptomatic infection to gastrointestinal disease; has a life cycle similar to that of Entamoeba; trophozoites multiply in the small intestines; prevent infections in endemic areas by use of filtered water

naegleria disease

infection occurs when swimmers inhale contaminated water; amoebic meningoencephalitis can result; prevention difficult since organisms are environmentally hardy

cyst

infective form that survives in the environment; undergo excystment when ingested developing into trophozoites; trophozoites undergo encystment before leaving the host in feces

helminths

macroscopic, multicellular, eukaryotic worms; life cycles are complex; intermediate hosts are often needed to support larval stages; adult worms are either dioecious or monoecious; three groups are Cestodes (tapeworm), Trematodes (fluke) and Nematodes (roundworm)

trichomonas vaginalis

most common protozoan causing human disease in industrialized nations; lives in the genitourinary system of men and women; transmitted almost exclusively via sex; occurs in people with preexisting STD or multiple sex partners; infection of women results in vaginitis; infection of men is typically asymptomatic; prevention involves abstinence and safe sex

toxoplasmosis

most infections are asymptomatic but toxoplasmosis develops in a small number of people; fever-producing illness combined with other symptoms; usually is a self-limited infection; toxoplasmosis is more severe in two populations; AIDS patients; fetuses; prevent by cooking meats and avoiding contaminated soil

life cycle of roundworms

number of reproduction strategies; intestinal nematodes shed eggs into lumen of the intestine; eggs are consumed in contaminated food or water; larvae of some intestinal nematodes hatch in the soil; larvae actively penetrate the skin of a host; some nematodes encyst in muscle tissue; consumed in raw or undercooked meat; mosquitoes transmit a few species of filarial nematodes; adult sexually mature stages are found only in definitive hosts

acanthamoeba disease

occurs through cuts, scrapes, the conjunctiva, or inhalation; acanthamoeba keratitis due to conjunctival inoculation; amebic encephalitis is the more common disease

balantidium coli

only ciliate known to cause disease in humans; commonly found in animal intestinal tracts; humans infected by food or water contaminated with feces containing cysts; trophozoites attach to mucosal epithelium lining the intestine; infections generally asymptomatic in healthy adults; balantidiasis occurs in those with poor health, persistent diarrhea, abdominal pain, and weight loss

parasites of humans

parasites presented based primarily on their mode of locomotion; ciliates, amoebae, flagellates, and apicomplexans; protozoa that enter the body via ingestion have two morphological forms

chagas' disease

progresses through four stages; acute stage characterized by chagomas; generalized stage; an asymptomatic chronic stage; symptomatic stage characterized by congestive heart failure following formation of pseudocysts; parasite-induced heart disease is a leading cause of death in latin america

african sleeping sickness

progresses through three stages if left untreated; site of the fly bite becomes a lesion with dead tissue; fever, lymph node swelling, and headaches; meningoencephalitis; infections characterized by cyclical waves of parasitemia; clearing tsetse fly habitats reduce the cases of disease

flagellates

protozoa that possess at least one flagellum; number and arrangement of flagella important to determining the species; the flagellates include members of the genera Trypanosoma, Leishmania, Giardi, and Trichomonas

ciliates

protozoa that use cilia in their trophozoite stage

amoebae

protozoa with no truly defined shape; move and acquire food through the use of pseudopodia; found in water sources throughout the world; few cause disease

parasitic diseases

protozoan and helminthic parasites exist worldwide; occur among people in rural, undeveloped, or overcrowded places; emerging as serious threats in developed nations; parasitic infections often involve several hosts, such as definitive host and intermediate hosts; parasites can infect humans in three ways

nematodes

roundworms are long, cylindrical worms that taper at each end; possess complete digestive tracts; have a protective outer cuticle; parasites of almost all vertebrates

genetic traits increasing plasmodium resistance

sickle-cell trait; sickle-shaped cells resist penetration by plasmodium; hemoglobin C; two genes for hemoglobin C protect against malaria; glucose-6-phosphate-dehydrogenase deficiency; needed by the trophozoites to synthesize DNA; lack of duffy antigens on erythrocytes; P. vivax requires Duffy antigen to infect erythrocytes

taenia

taenia saginata is the beef tapeworm; taenia solium is the pork tapeworm; cattle and swine serve as the intermediate hosts; humans living close to livestock have highest incidence of infection; adults attach to the intestinal epithelium; most individuals shed strobila without having symptoms; intestinal blockage can occur if the tapeworm is large

amebiasis

three types can result from infection, luminal amebiasis, invasive amebic dysentery, invasive extraintestinal amebiasis; maintaining clean water is important in prevention

ancylostoma and necator

two hookworms infect humans, ancylostoma duodenale and necator americanus; larvae burrow through skin; travel to the heart, lungs, and eventually the small intestine; adult worms suck the blood of their hosts; causes chronic anemia, iron and protein deficiencies; ground itch occurs at the site of larvae penetration; wearing shoes in endemic areas helps prevent exposure

cyclospora cayetanensis

water borne apicomplexan; linked to raspberries imported from Central and South America; infection occurs from ingestion of oocysts in contaminated food or drink; environmental reservoir is unknown; symptoms include cramps, watery diarrhea, myalgia, and fever; AIDS patients can experience more severe disease; thoroughly washing fruits and vegetables can prevent infection