2 Parasitology The study of eucaryotic parasites, protozoa and helminths Cause 20% of all infectious diseases Less prevalent in industrialized countries; increasingly common in AIDS patients
3 Typical Protozoan Pathogens Single-celled, animal-like microbes, most having some form of motility Estimated 100,000 species, approximately 25 are important pathogens Life cycles vary –Most propagate by simple asexual cell division of the active feeding cell (trophozoite). –Many undergo formation of a cyst. –Others have a complex life cycle that includes asexual and sexual phases.
5 Infective Amebas
6 Entamoeba histolytica and Amebiasis 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. Ingested Carried by 10% of world population
8 Entamoeba histolytica 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
9 Entamoeba histolytica Life-threatening manifestations are: hemorrhage, perforation, appendicitis, and tumorlike growths, amebomas. May invade liver and lung Severe forms of disease result in 10% fatality rate. Effective drugs are iodoquinol, metronidazole, and chloroquine.
10 Amebic Infections of the Brain Caused by Naegleria fowleri and Acanthamoeba Ordinarily inhabit standing water Primary acute meningoencephalitis is acquired though nasal contact with water or traumatic eye damage. Infiltration of brain is usually fatal.
11 An Intestinal Ciliate: Balantidium coli An occupant of the intestines of domestic animals such as pigs and cattle Acquired by ingesting cyst-containing food or water Trophozoite erodes intestine and elicits intestinal symptoms. Healthy humans are resistant. Rarely penetrates intestine or enters blood Treatment – tetracycline, iodoquinol, nitrimidazine or metronidazole
13 The Flagellates
14 Trichomonads: Trichomonas species Small, pear-shaped 4 anterior flagella and an undulating membrane Exist only in trophozoite form 3 infect humans: –T. vaginalis –T. tenax –T. hominis
16 Trichomonas vaginalis Causes an STD called trichomoniasis Reservoir is human urogenital tract 50% of infected are asymptomatic. Strict parasite, cannot survive long outside of host 3 million cases yearly, a top STD Female symptoms – foul-smelling, green-to-yellow discharge; vulvitis; cervicitis; urinary frequency and pain Male symptoms – urethritis, thin, milky discharge, occasionally prostate infection Metronidazole
17 Giardia lamblia and Giardiasis Pathogenic flagellate 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. Usually ingested with water and food ID 10 to 100 cysts
19 Cysts enter duodenum, germinate, travel to jejunum to feed and multiply Causes giardiasis – diarrhea, abdominal pain Diagnosis is difficult because organism is shed in feces intermittently. Treatment: quinacrine or metronidazole Agent is killed by boiling, ozone, and iodine.
20 Hemoflagellates: 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
22 Trypanosoma species and Tropanosomiasis Distinguished by their infective stage; trypomastigote is an elongate, spindle- shaped cell with tapered ends, eel-like motility 2 types of trypanosomiasis: –T. brucei – African sleeping sickness –T. cruzi – Chagas disease – endemic to Central and South America
23 Trypanosoma brucei and African Sleeping Sickness Spread by tsetse flies Harbored by reservoir mammals Two variants of disease caused by 2 subspecies: –T.b.gambiense – Gambian strain; West Africa –T.b. rhodesiense – Rhodesian strain; East Africa Biting of fly inoculates skin with trypomastigotes, which multiplies in blood and damages spleen, lymph nodes and brain.
24 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.
26 Trypanosoma cruzi Causes Chagas disease 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
28 Leishmania species and Leishmaniasis Leishmaniasis - zoonosis transmitted among mammalian hosts by female sand flies that require a blood meal to produce eggs Endemic to equatorial regions Promastigotes are injected with sand fly bite, convert to amastigote and multiply; if macrophage is fixed the infection is localized; systemic if macrophage migrates.
30 Cutaneous-oriental sore, Baghdad boil - localized ulcerated sore Espunda – 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.
31 Apicomplexan parasites Sporozoans Lack locomotor organelles in the 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. –Plasmodium –Toxoplasma –Cryptosporidium
32 Plasmodium: The Agent of Malaria 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 million new cases each year 2 million deaths each year
33 2 distinct phases of malarial parasite development: asexual phase – human host –Infected female mosquito injects asexual sporozoite which localizes in liver; it then undergoes schizogony generating 2,000-40,000 merozoites which enter circulation in 5-16 days depending on species. –Merozoites attach to and enter red blood cells, convert to trophozoites and multiply; red cell bursts releasing merozoites that differentiate into gametes.
34 Sexual phase – mosquito host –Mosquito draws infected RBCs; gametes fertilize forming diploid cell which forms sporozoites in stomach. –Sporozoites lodge in salivary glands; available to infect human host
36 Plasmodium Symptoms include episodes of chills-fever-sweating, anemia, and organ enlargement. Symptoms occur at 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, quinine, or primaquine.
37 Coccidian Parasites Zoonotic in domestic animals and birds
38 Toxoplasma gondii and Toxoplasmosis Intracelllular 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 Most cases of toxoplasmosis go unnoticed except in fetus and AIDS patients who can suffer brain and heart damage. Treatment: pyrimethamine and sulfadiazine
40 Sarcocystis and Sarcocystosis Sarcocystis – parasites of cattle, swine, and sheep Domestic animals are intermediate hosts; they pick up infective cysts while grazing on grass contaminated with human feces. Humans are infected when the meat is consumed. Symptoms include diarrhea, nausea, and abdominal pain. No specific treatment
41 Cryptosporidium: A Newly Recognized Intestinal Pathogen An intestinal pathogen Infects a variety of mammals, birds, and reptiles Exists in tissue and oocyst phases 1990s – 370,000 cases in Milwaukee, WI due to contaminated water; filtration required for removal Ingestion of oocysts which give rise to sporozoites that penetrate intestinal cells Causes gastroenteritis, headache, sweating, vomiting, abdominal cramps, diarrhea AIDS patients may suffer chronic persistent diarrhea. No effective drugs
42 Isospora belli and Coccidiosis Intracellular intestinal parasite with oocyst stage Transmitted in fecally contaminated food or drink Infection usually asymptomatic or self-limited Symptoms include malaise, nausea and vomiting, diarrhea, fatty stools, abdominal cramping, and weight loss. Treat with sulfadiazine and pyrimethamine, when required
43 Cyclospora cayetanensis and Cyclosporiasis Emerging protozoan pathogen; causes cyclosporiasis Oral-fecal transmission; fresh produce and water Oocysts enter small intestine and invade the mucosa. Symptoms of watery diarrhea, stomach cramps, bloating, fever, muscles aches Diagnosis can be complicated. Treatment: trimethoprim and sulfamethoxazole
44 Babesia species and Babesiosis First protozoan found to cause a disease – redwater fever of cattle First protozoan found to be associated with a vector - tick Human babesiosis - relatively rare zoonosis Associated with infected rodents Infection resembles malaria.
45 A Survey of Helminth Parasites 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 are hermaphroditic. Adults live in the definitive host. Eggs and larvae may develop in the same host, the external environment of the intermediate host. A transport host experiences no parasitic development. Four basic patterns of life and transmission
47 Helminths 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.
49 Nematode (Roundworm) Infestations Most abundant animal groups; 50 species that affect humans Enlongated, cylindrical worms with protective cuticles, circular muscles, a complete digestive tract, and separate sexes Ascaris lumbricoides, Trichuris trichiura, Enterobius vermicularis, hookworms, Strongyloides stercoralis, Trichinella spiralis, filarial worms
50 Ascaris lumbricoides A large intestinal roundworm Most cases in the U.S. occur in the southeastern states Indigenous to humans 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.
51 Ascaris lumbricoides 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.
52 Trichuris trichiura and Whipworm Infection 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, and allow bacteria to leave intestine. Heavy infestations can cause dysentery, rectal prolapse – can be fatal in children.
53 Enterobius vermicularis and Pinworm Infection 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
54 Hookworms Characteristic curved ends and hooked mouths Necator americanus and Ancylostoma duodenale Humans shed eggs in feces, which hatch into filariform larvae and burrow into the skin of the lower legs. Larvae travel from blood to lungs, proceed up bronchi and throat and are swallowed. Worms mature and reproduce in small intestine and complete, the cycle. May cause pneumonia, nausea, vomiting, cramps and bloody diarrhea Blood loss is significant – anemia.
56 Strongyloides stercoralis and Strongyloidiasis Threadworm Tiny roundworms completes life cycle in humans or moist soil. Larvae penetrate skin and migrate to lungs, are swallowed and complete development in the intestine. Can reinfect the same host without leaving the body Heavy worm loads can cause pneumonitis and eosinophilia, bloody diarrhea, liver enlargement, bowel obstruction and malabsorption.
57 Trichinella spiralis and Trichinosis 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
59 Tissue Nematodes 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
60 Wucherereia bancrofti and Bancroftian Filariasis 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.
61 Onchocerca volvulus and River Blindness 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
62 Loa loa: The African Eye Worm 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
63 Trematodes or Flukes 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.
64 Blood Flukes: Schistosomes 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.
65 Liver and Lung Flukes Zoonotic Liver flukes: Opisthorchis (Chlonorchis) sinesis - cycles between mammals and snails and fish; humans are infected by eating inadequately cooked fish containing cercaria, 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.
66 Lung fluke: Paragonimus westermani – cycles between carnivorous animals, snails, and crustaceans; humans infected by eating undercooked crustaceans; intestinal worms migrate to lungs.
67 Cestode (Tapeworm) Infestations Flatworms 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
68 Taenia saginata Beef tapeworm Very large, up to 2,000 proglottids Humans are the definitive host. Animals are infected by grazing on land contaminated with human feces. Infection occurs from eating raw beef in which the larval form has encysted. In humans, larva attaches to the small intestine and becomes an adult. Causes few symptoms; vague abdominal pain and nausea; proglottids in stool
70 Taenia solium 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 heart muscle, eye, or brain May cause seizures, psychiatric disturbances
71 The Arthropod Vectors of Infectious Disease 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
72 Insects Mosquitoes – require an aquatic habitat; females take blood meal transmitting disease: malaria, filariasis, zoonoses 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 Flies – tsetse fly, sand fly
73 Arachnids Ticks – cling on vegetation and attach to host on contact; larvae, nymph and adults get blood meal by piercing skin of host –hard ticks – Dermacentor, Ixodes – small compact, rigid bodies; transmit rickettsial, borrelial, and viral diseases –soft or argasid ticks – Ornithodoros- flexible outer bodies; transmit relapsing fever