Microbio Ch 23 – Flashcards
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| Parasitology |
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| The study of eukaryotic parasites, protozoa, and helminthes; Focusing on “macro-parasites”; Cause 20% of all infectious diseases; Less prevalent in industrialized countries; increasingly common in AIDS patients |
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| Typical Protozoan Pathogens |
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| Single-celled, animal-like microbes, most having some form of motility; Estimated 100,000 species, approximately 25 are important pathogens; Life cycles vary : a) Most propagate by simple asexual cell division of the active feeding cell (trophozoite)…b) Many undergo formation of a cyst– infective stage c) Others have a complex life cycle that includes asexual and sexual phases |
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| Entamoeba histolytica and Amebiasis |
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| Trophozoite: growing stage of life cycle; Alternates between a large trophozoite, motile by means of pseudopods and a smaller nonmotile cyst; Trophozoite has a large nucleus and lacks most other organelles; Humans are the primary hosts; Cysts are swallowed and arrive at the small intestine; alkaline pH and digestive juices stimulate cysts to release 4 trophozoites; Trophozoites attach, multiply, actively move about and feed; Asymptomatic in 90% of patients ; Ameba may secrete enzymes that dissolve tissues and penetrate deeper layers of the mucosa; Causing dysentery, abdominal pain, fever, diarrhea, and weight loss; Carried by 10% of world population; Asymptomatic in 90% of patients ; Ameba may secrete enzymes that dissolve tissues and penetrate deeper layers of the mucosa; Causing dysentery, abdominal pain, fever, diarrhea, and weight loss; Carried by 10% of world population; Life-threatening symptoms: hemorrhage, perforation, appendicitis, and tumorlike growths – amoeboma; May invade liver and lung; Severe forms of disease result in 10% fatality rate --confirmed infections; Effective drugs are iodoquinol, metronidazole, and chloroquine |
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| Amebic Infections of the Brain |
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| Caused by Naegleria fowleri and Acanthamoeba; Ordinarily inhabit standing water; Primary acute meningoencephalitis is acquired through nasal contact with water or traumatic eye damage; Infiltration of brain is usually fatal |
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| An Intestinal Ciliate: Balantidium coli |
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| Normal flora of intestines of domestic animals: pigs, cattle; Acquired by ingesting cyst-containing food or water; Trophozoite erodes intestine and elicits intestinal symptoms but rarely penetrates the intestine; Healthy humans are resistant; Treatment – tetracycline, iodoquinol, nitrimidazine or metronidazole |
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| Trichomonads: Trichomonas |
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| Small, pear-shaped; 4 anterior flagella and an undulating membrane; Exist only in trophozoite form; 3 infect humans: a)T. vaginalis b)T. tenax c)T. hominis |
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| Trichomonas vaginalis |
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| Causes an STD: trichomoniasis; 3 million cases yearly; Reservoir: human urogenital tract; 50% of infected are asymptomatic; Strict parasite, cannot survive long outside of host; Female symptoms – foul-smelling, green-to-yellow discharge; vulvitis; cervicitis; urinary frequency, pain;; Male symptoms – urethritis, thin, milky discharge, occasionally prostate infection; Metronidazole treatment |
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| Giardia lamblia and Giardiasis |
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| Unique symmetrical heart shape with concave ventral surface that acts like a suction cup; Cysts are small, compact, and multinucleate; Reservoirs include beavers, cattle, coyotes, cats, and humans; Cysts can survive for 2 months in environment; Transmission: contaminated water/food; Infections dose (ID) 10 to 100 cysts; Cysts enter duodenum, germinate, travel to jejunum to feed and multiply---Results in giardiasis – diarrhea, abdominal pain; Difficult diagnosis - organism is shed in feces intermittently; Treatment: quinacrine or metronidazole; Agent is killed by boiling, ozone, and iodine |
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| Hemoflagellates: |
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| Vector-Borne Blood Parasites --Obligate parasites that live in blood and tissues of human host; Cause life-threatening and debilitating zoonoses; Spread in specific tropical regions by blood-sucking insects that serve as intermediate hosts; Have complicated life cycles and undergo morphological changes; Categorized according to cellular and infective stages |
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| Hemoflagellates |
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| Amastigote: the form lacking a free flagellum ; Promastigote: the stage bearing a single, anterior flagellum ; Epimastigote: the flagellate stage ; Trypomastigote: large, fully formed stage |
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| Trypanosoma Species and Tropanosomiasis |
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| Distinguished by their infective stage - trypomastigote is an elongate, spindle-shaped cell with tapered ends, eel-like motility; 2 types of trypanosomiasis: a)T. brucei – African sleeping sickness b)T. cruzi – Chagas disease – endemic to Central and South America |
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| T. brucei – African Sleeping Sickness |
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| Spread by tsetse flies; Two variants of disease caused by 2 subspecies: a) T.b. gambiense – Gambian strain; West Africa b)T.b. rhodesiense – Rhodesian strain; East Africa ; fly bite a inoculates skin with trypomastigotes a damages spleen, lymph nodes, and brain; Harbored by mammals ; Chronic disease symptoms are sleep disturbances, tremors, paralysis, and coma ; Trypanosomes are readily demonstrated in blood, spinal fluid, or lymph nodes ; Treatment before neurological involvement melarsoprol, eflornithine ; Control involves eliminating tsetse fly |
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| Trypanosoma cruzi (Chagas disease) |
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| Reduviid bug (kissing bug) is the vector; Infection occurs when bug feces is inoculated into a cutaneous portal ; Local lesion, fever, and swelling of lymph nodes, spleen, and liver; Heart muscle and large intestine harbor masses of amastigotes; Chronic inflammation occurs in the organs (especially heart and brain); Treatment nifurtimox and benzonidazole |
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| Leishmania sp. and Leishmaniasis |
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| Leishmaniasis – zoonosis transmitted among mammalian hosts by female sand flies that require a blood meal to produce eggs; Endemic to equatorial regions ;1. Promastigotes - injected by sand fly bite, , 2. converts to amastigote and multiplies, 3. Infections: 3a)if macrophage does not migrate –localized infection 3b)if macrophage migrates, systemic infection;; Cutaneous – localized ulcerated sore; Baghdad boil ; Espundia – skin and mucous membrane infection of the head; chronic infection ; Systemic (visceral) – high intermittent fever; weight loss, enlarged spleen, liver, and lymph nodes --Kala azar is the most severe and fatal form if untreated |
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| Apicomplexan Parasites |
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| Sporozoans - No motile trophozoite state; Alternate between sexual and asexual phases and between different animal hosts; Most form specialized infective bodies that are transmitted by arthropod vectors, food, water, or other means a) Plasmodium; b) Toxoplasma c) Cryptosporidium; |
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| Plasmodium: The Agent of Malaria |
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| Dominant protozoan disease ; Obligate intracellular sporozoan; 4 species: P. malariae, P. vivax, P. falciparum, and P. ovale ; Female Anopheles mosquito is the primary vector; blood transfusions, mother to fetus ; 300-500 million new cases each year and 2 million deaths each year ; Sexual phase – mosquito host a) Mosquito takes a blood meal from an infected person or animal, b) In the mosquito stomach: gametes from the blood fertilize and form diploid cells which mature into sporozoites , c) Sporozoites travel to the salivary glands of the mosquito where they are available to get injected into the next animal or human host ;;; Asexual phase – human host, a) Infected female mosquito takes a blood meal and injects asexual sporozoite that travel to the liver; b) They then undergo schizogony a merozoites, c) Merozoites infect other liver cells and move into blood stream, d) Merozoites infect red blood cells and convert to trophozoites , e)Trophozoites multiply inside the RBC , f) Once mature, RBC bursts releasing merozoites that infect other RBCs. Some merozoites differentiate into gametes.;;; Symptoms: episodes of chills-fever-sweating, anemia, and organ enlargement; Symptoms occur at 48-72 hour intervals as RBCs rupture; interval depends on species;; P. falciparum most malignant type; highest death rate in children ; Diagnosis by presence of trophozoite in RBCs, symptoms ; Increasing drug resistance; Therapy is chloroquine, mefloquine; |
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| Toxoplasma gondii and Toxoplasmosis |
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| Intracellular apicomplexan parasite with extensive distribution ; Lives naturally in cats that harbor oocysts in the GI tract ; Acquired by ingesting raw meats or substances contaminated by cat feces ; Symptoms: Most cases of toxoplasmosis go unnoticed , Others: flu-likes symptoms with swollen lymph glands; may last up to one month, Severe infection seen in fetus and AIDS patients who can suffer brain, eye, and heart damage, Fetal damage often not observed at birth, but present with symptoms later; Treatment: pyrimethamine and sulfadiazine |
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| A Survey of Helminth Parasites |
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| Adults are large, multicellular animals with specialized tissues and organs ; Adult worms mate and produce fertilized eggs that hatch; larvae then mature in several stages to adults ; The sexes may separate or hermaphroditic ; Adulthood and mating occur in the definitive host ; Larval develop occurs in the intermediate host ; A transport host experiences no parasitic development ; Four basic patterns of life and transmission (fig 23.17) |
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| Parasitic Helminths |
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| : multiceullular animals, organs for reproduction, digestion, movement, protection; parasitize host tissues; Have mouthparts for attachement to or digestion of host tissues: Most have well-developed sex organs that produce eggs and sperm; fertilized eggs go through larval period in or our of the host body |
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| Helminth Pathogens |
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| Pathology arises from worms feeding on and migrating through tissues, accumulation of worms, and worm products ; Diagnosis based on blood cell count (eosinophilia), serological tests; eggs, larvae, or adult worms in feces; sputum, urine, blood, or tissue biopsies ; Antihelminthic drugs suppress a helminthic metabolic process that differs from the human process, inhibit the worm’s movement, prevent it from holding position, and act locally in the intestine |
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| Nematode (Roundworm) Infestations |
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| Most abundant animal groups; 50 species that affect humans ; Elongated, cylindrical worms with protective cuticles, circular muscles, a complete digestive tract, and separate sexes ; Divided into intestinal nematodes, and tissue nematodes |
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| Ascaris lumbricoides |
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| A large intestinal roundworm; Indigenous to humans ; Most cases in the U.S. occur in the southeastern states ; Ascaris spends its larval and adult stages in humans; release embryonic eggs in feces, and are spread to other humans; food, drink, or contaminated objects ; Ingested eggs hatch into larvae and burrow through the intestine into circulation and travel to the lungs and pharynx and are swallowed ; Adult worms complete cycle in intestines and reproduce – 200,000 eggs/day ; Worms retain motility, do not attach ; Severe inflammatory reactions mark the migratory route ; Allergic reactions can occur; Heavy worm loads can retard physical and mental development |
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| Trichuris trichiura and Whipworm Infection |
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| Whipworm; Humans sole host ; Trichuriasis has its highest incidence in the tropics ; Eggs hatch in intestines, larvae attach, penetrate the outer wall and develop into adults ; Females lay 3,000-5,000 eggs daily ; Worms can pierce capillaries, cause localized hemorrhage ; Heavy infestations can cause dysentery, rectal prolapse – can be fatal in children |
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| Enterobius vermicularis and Pinworm Infection |
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| Pinworm or seatworm ; Enterobiasis most common worm disease of children in temperate zones ; Eggs are picked up from surroundings and swallowed ; After hatching in the small intestine, they develop into adults ; Anal itching occurs when mature females emerge from intestine to release eggs ; Self-inoculation is common ; Tape test |
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| Trichinella spiralis and Trichinellosis |
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| Life cycle entirely within mammalian host ; Acquired from eating undercooked pork or bear meat ; Larvae migrate from intestine to blood vessels, muscle, heart, and brain, where it forms cysts ; First symptoms – flulike, diarrhea ; Second symptoms – muscle and joint pain, shortness of breath, pronounced eosinophilia ; No cure after larva have encysted |
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| Tissue Nematodes |
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| Complete their life cycle in human blood, lymphatics, or skin ; Filarial worms; elongate, filamentous bodies, spread by biting arthropods ; Cause chronic, deforming disease ; Wuchereria bancrofti – elephantiasis ; Onchocerca volvulus – river blindness ; Loa loa – eye worm |
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| Wucherereia bancrofti and Bancroftian Filariasis |
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| Tropical infection spread by mosquitoes ; Vector deposits larvae which move into lymphatics and develop into adults ; Chronic infection causes blockage of lymphatic circulation and elephantiasis, massive swelling in the extremities |
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| Onchocerca volvulus and River Blindness |
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| Transmitted by biting black flies; Larvae develop into adults in subcutaneous tissues ; Adult females migrate via the blood to the eyes, provoking inflammatory reactions ; Coinfection with Wolbachia bacteria causes river blindness ; Treatment: tetracycline and ivermectin |
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| Loa loa: The African Eye Worm |
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| Spread by bite of small flies ; Temperature-sensitive worm migrates around/under the skin and may enter the eye ; Treatment – pull worm from a small hole in conjunctiva or diethylcarbamazine |
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| Trematodes or Flukes |
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| Flatworms with ovoid leaflike bodies; Have digestive, excretory, neuromuscular, and reproductive systems ; Lack circulatory and respiratory systems ; Animals such as snails or fish are usually the intermediate hosts and humans are the definitive hosts |
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| Blood Flukes: Schistosomes |
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| Schistosomiasis – prominent parasitic disease ; Schistosoma mansoni, S. japonicum, S. haematobium ; Adult flukes live in humans who release eggs into water; early larva (miracidium) develops in freshwater snail into a 2nd larva (cercaria) ; This larva penetrates human skin and moves into the liver to mature; adults migrate to intestine or bladder and shed eggs, giving rise to chronic organ enlargement |
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| Liver Flukes |
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| Zoonotic ; Opisthorchis (Clonorchis) sinensis – cycles between mammals and snails and fish; humans are infected by eating inadequately cooked fish containing cercariae, larvae crawl into bile duct, mature, and shed eggs into feces; snail are infected ; Fasciola hepatica – cycles between herbivores, snails, and aquatic plants; humans are infected by eating raw aquatic plants; fluke lodges in liver |
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| Lung Flukes |
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| Paragonimus westermani – cycles between carnivorous animals, snails, and crustaceans; humans infected by eating undercooked crustaceans; intestinal worms migrate to lungs |
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| Cestode (Tapeworm) Infestations |
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| latworms ; Long, very thin, ribbonlike bodies composed of sacs (proglottids) and a scolex that grips the intestine ; Each proglottid is an independent unit adapted to absorbing food and making and releasing eggs ; Taenia saginata ; Taenia solium ; |
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| Taenia saginata |
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| Pork tapeworm; Infects humans through ingesting cysts or eggs ; Eggs hatch in intestine, releasing tapeworm larva that migrate to all tissues and encyst ; Most damaging if they lodge in the heart, eye, or brain ; May cause seizures, psychiatric disturbances ; |
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| The Arthropod Vectors of Infectious Disease |
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| Arthropods – exoskeleton and jointed legs; includes arachnids and crustaceans; many must feed on blood and tissue fluid of host during life cycle; ectoparasites ; Those of medical importance transmit infectious microbes in the process of feeding – biological vectors |
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| Arthropod Vectors - Insects |
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| Mosquitoes – require an aquatic habitat; females take blood meal transmitting disease: malaria, filariasis, Dengue fever ; Fleas – highly motile, flattened bodies; feed on warm-blooded animals; carry zoonotic diseases: plague, murine typhus ; Lice – small, soft; attach to head and body hair feeding inconspicuously on blood and tissue fluid; release feces that contaminate wound; epidemic typhus, relapsing fever |
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| Anthropod Vectors- Arachnids ; |
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| Ticks – cling on vegetation and attach to host on contact; larvae, nymph, and adults get blood meal by piercing skin of host ; Hard or ixodid ticks – small compact, rigid bodies; transmit bacterial, rickettsial, and viral diseases ; Soft or argasid ticks – flexible outer bodies; transmit relapsing fever |
