Microbiology Chapter 12 #76-109

93. What are the two major categories of parasitic helminths?

platyhelminthes (flatworms) and Nematoda (roundworms)

100. Why is schistosomiasis important?

world problem

80. What are the intermediate and definitive hosts for malaria?

intermediate: human definitive: mosquito

94. What four generalizations distinguish parasitic from free-living helminths?

1. They may lack a digestive system. They can absorb nu- trients from the host's food, body fluids, and tissues. 2. Their nervous system is reduced. They do not need an extensive nervous system because they do not have to search for food or respond much to their environment. The environment within a host is fairly constant. 3. Their means of locomotion is occasionally reduced or com pletely lacking. Because they are transferred from host to host, they do not need to search actively for a suitable habitat. 4. Their reproductive system is often complex. An individual produces large numbers of eggs, by which a suitable host is infected.

96. What does dioecious and hermaphroditic mean?

Adult helminths may be dioecious; male reproductive or- gans are in one individual, and female reproductive organs are in another. In those species, reproduction occurs only when two adults of the opposite sex are in the same host. Adult helminths may also be monoecious, or hermaphroditic— one animal has both male and female reproductive organs. Two hermaphrodites may copulate and simultaneously fertilize each other. A few types of hermaphrodites fertilize themselves.

107. What are hookworms and why are they important?

Adult hookworms, Necator americanus (ne-kāʹtôr ä-me-ri-kaʹnus) and Ancylostoma duodenale (an-sil-osʹtoma düʹo-den-al-ē), live in the small intestine of humans (Figure 25.23, page 741); the eggs are excreted in feces. The larvae hatch in the soil, where they feed on bacteria. A larva enters its host by penetrating the host's skin. It then enters a blood or lymph vessel, which carries it to the lungs. It is coughed up in sputum, swallowed, and finally carried to the small intestine.

76. What does Plasmodium cause and why is that important?

Apicomplexans have a complex life cycle that involves trans- mission between several hosts. An example of an apicomplexan is Plasmodium (plaz-mōʹdē-um), the causative agent of malaria. Malaria affects 10% of the world's population, with 300 to 500 million new cases each year. The complex life cycle makes it dif- ficult to develop a vaccine against malaria.

106. Why is Ascaris important? What is their life cycle?

Ascaris lumbricoides (asʹkar-is lum-bri-koiʹdēz) is a large nematode (30 cm in length) that infects over 1 billion people worldwide (Figure 25.24, page 742). It is dioecious with sexual dimorphism; that is, the male and female worms look dis- tinctly different, the male being smaller with a curled tail. The adult Ascaris lives in the small intestines of humans exclu- sively; it feeds primarily on semidigested food. Eggs, excreted with feces, can survive in the soil for long periods until acci- dentally ingested by another host. The eggs hatch in the small intestine of the host. The larvae then burrow out of the intes- tine and enter the blood. They are carried to the lungs, where they grow. The larvae will then be coughed up, swallowed, and returned to the small intestine, where they mature into adults.

83. Name four other Apicomplexa that are human pathogens besides Plasmodium.

Babesia microti toxoplasma gondi cryptosporidium cyclospora

84. What diseases do they cause? (see pages 356, 668, 673, 737, 738 & 740)

Babesia microti: babesiosis toxoplasma gondi: toxoplasmosis cryptosporidium: diarrhea cyclospora: diarrhea

101. What are cestodes or tapeworms? Why are they medically important? (see pages 732-737 for information in this area & information to answer upcoming questions)

Cestodes, or tapeworms, are intestinal parasites

102. What are characteristics of tapeworms?

Cestodes, or tapeworms, are intestinal parasites. Their structure is shown in Figure 12.27. The head, or scolex (plural: scoleces), has suckers for attaching to the intestinal mucosa of the defini- tive host; some species also have small hooks for attachment. Tapeworms do not ingest the tissues of their hosts; in fact, they completely lack a digestive system. To obtain nutrients from the small intestine, they absorb food through their cuticle. The body consists of segments called proglottids. Proglottids are continu- ally produced by the neck region of the scolex, as long as the scolex is attached and alive. Each mature proglottid contains both male and female reproductive organs. The proglottids far- thest away from the scolex are the mature ones containing eggs. Mature proglottids are essentially bags of eggs, each of which is infective to the proper intermediate host.

89. What is Chagas' disease and why is it important? (see pages 356 and 666)

Chagas' disease, also known as American trypanosomiasis, is a protozoan disease of the cardiovascular system human pathogen: trypanosome cruzi source: bite of triatoma (kissing bug)

87. How are Cryptosporidium transmitted?

Cryptosporidium (krip-tō-spô-riʹdē-um) lives inside the cells lining the small intestine and can be transmitted to humans through the feces of cows, rodents, dogs, and cats

81. Why might malaria increase in the United States? (see pages 668-672)

In recent years, however, there has been an upward trend in the number of U.S. cases, reflecting a world- wide resurgence of malaria, increased travel to malarial areas, and an increase in immigration from malarial areas. Occasion- ally, malaria has been transmitted by unsterilized syringes used by drug addicts. Blood transfusions from people who have been in an endemic area are also a potential risk.

104. Why are nematode or roundworms medically important?

Members of the Phylum Nematoda, the roundworms, are cy- lindrical and tapered at each end. Roundworms have a complete digestive system, consisting of a mouth, an intestine, and an anus. Most species are dioecious. Males are smaller than females and have one or two hardened spicules on their posterior ends. Spicules are used to guide sperm to the female's genital pore.

92. Know the definition of obligate intracellular parasite.

Obligate intracellular parasites cannot reproduce outside their host cell, meaning that the parasite's reproduction is entirely reliant on intracellular resources. Certain bacteria, including: Chlamydia, and closely related species. Rickettsia

108. What are whipworms and why are they important?

One billion people worldwide are infected with Trichuris trichiura, or whipworm. The worms are spread from person to person by fecal-oral transmission or through feces-contaminated food. The disease occurs most often in areas with tropical weather and poor sanitation practices and among children.

78. What is a sporozoite?

Plasmodium grows by sexual reproduction in the Anopheles (an-ofʹel-ēz) mosquito (Figure 12.20). When an Anopheles car- rying the infective stage of Plasmodium, called a sporozoite, bites a human, sporozoites can be injected into the human. The sporozoites undergo schizogony in liver cells and produce thousands of progeny called merozoites, which infect red blood cells.

103. What is the life cycle of the beef tapeworm? the pork tapeworm?

The adults of Taenia sagi nata (teʹnē-ä sa-ji-näʹtä), the beef tapeworm, live in humans and can reach a length of 6 m. The scolex is about 2 mm long and is followed by a thousand or more proglottids. The feces of an infected human contain mature proglottids, each of which contains thousands of eggs. As the proglottids wriggle away from the fecal material, they increase their chances of being ingested by an animal that is grazing. Upon ingestion by cattle, the larvae hatch from the eggs and bore through the intestinal wall. The larvae migrate to muscle (meat), in which they encyst as cysticerci. When the cysticerci are in- gested by humans, all but the scolex is digested. The scolex anchors itself in the small intestine and begins producing proglottids. Diagnosis of tapeworm infection in humans is based on the presence of mature proglottids and eggs in feces. Cysticerci can be seen macroscopically in meat; their presence is referred to as "measly beef." Inspecting beef that is intended for human con- sumption for "measly" appearance is one way to prevent infections by beef tapeworm. Another method of prevention is to avoid the use of untreated human sewage as fertilizer in grazing pastures. Humans are the only known definitive host of the pork tape- worm, Taenia solium. Adult worms living in the human intestine produce eggs, which are passed out in feces. When eggs are eaten by pigs, the larval helminth encysts in the pig's muscles; humans become infected when they eat undercooked pork. The human- pig-human cycle of T. solium is common in Latin America, Asia, andAfrica.IntheUnitedStates,however,T.soliumisvirtually nonexistent in pigs; the parasite is transmitted from human to human. Eggs shed by one person and ingested by another person hatch, and the larvae encyst in the brain and other parts of the body, causing cysticercosis (see Figure 25.21, page 739). The human hosting T.solium's larvae is serving as an intermediate host. Approximately 7% of the few hundred cases reported in recent years were acquired by people who had never been out- side the United States. They may have become infected through household contact with people who were born in or had traveled in other countries.

99. What is the life cycle of the blood fluke Schistosoma? (see pages 666-667)

The cercariae of the blood fluke Schistosoma (shis-tō-sōʹma) are not ingested. Instead, they burrow through the skin of the human host and enter the circulatory system. The adults are found in certain abdominal and pelvic veins. The disease schis- tosomiasis is a major world health problem

91. What are hemoflagellates?

The hemoflagellates (blood parasites) are transmitted by the bites of blood-feeding insects and are found in the circula- tory system of the bitten host. To survive in this viscous fluid, hemoflagellates usually have long, slender bodies and an undu- lating membrane. The genus Trypanosoma (tri-paʹnō-sō-mä) includes the species that causes African sleeping sickness, T. brucei (brüsʹē), which is transmitted by the tsetse fly. T. cruzi (kruzʹē; see Figure 23.23, page 667), the causative agent of Chagas' disease, is transmitted by the "kissing bug," so named because it bites on the face (see Figure 12.33d on page 363). After entering the insect, the trypanosome rapidly multi- plies by schizogony. If the insect then defecates while biting a human, it can release trypanosomes that can contaminate the bite wound.

What are some defining characteristics of the life cycle of parasitic helminths?

The life cycle of parasitic helminths can be extremely complex, involving a succession of intermediate hosts for completion of each larval (developmental) stage of the parasite and a definitive host for the adult parasite. Adult helminths may be dioecious; male reproductive or- gans are in one individual, and female reproductive organs are in another. In those species, reproduction occurs only when two adults of the opposite sex are in the same host. Adult helminths may also be monoecious, or hermaphroditic— one animal has both male and female reproductive organs. Two hermaphrodites may copulate and simultaneously fertilize each other. A few types of hermaphrodites fertilize themselves.

79. What is an intermediate host and what is a definitive host?

The mosquito is the definitive host because it harbors the sexually reproducing stage of Plasmodium. The host in which the parasite undergoes asexual reproduction (in this case, the human) is the intermediate host.

82. Compare Plasmodium vivax to Plasmodium falciparum. Why is the latter so much more dangerous? (see page 670)

The most dangerous malaria is that caused by P. falciparum. Perhaps one reason for the virulence of this type of malaria is that humans and the parasite have had less time to become adapted to each other. It is believed that humans have been exposed to this parasite (through contact with birds) only in relatively recent history. Referred to as "malignant" malaria, untreated it eventu- ally kills about half of those infected. The highest mortality rates occur in young children. More red blood cells (RBCs) are infected and destroyed than in other forms of malaria. The resulting ane- mia severely weakens the victim. Furthermore, the RBCs develop surface knobs that cause them to stick to the walls of the capil- lary vessels, which become clogged. This clogging prevents the infected RBCs from reaching the spleen, where phagocytic cells would eliminate them. The blocked capillaries and subsequent loss of blood supply leads to death of the tissues. Kidney and liver damage is caused in this fashion. The brain is frequently affected, and P. falciparum is the usual cause of cerebral malaria.

105. What is the life cycle of pinworms? How are they detected?

The pinworm Enterobius vermicularis (en-te-rōʹbē-us ver-mi-kū-larʹis) spends its entire life in a human host (Fig- ure 12.29). Adult pinworms are found in the large intestine. From there, the female pinworm migrates to the anus to de- posit her eggs on the perianal skin. The eggs can be ingested by the host or by another person exposed through contami- nated clothing or bedding.

98. What is the life cycle of the lung fluke?

To exemplify a fluke's life cycle, let's look at the lung fluke, Paragonimus, spp (pãr-ä-gōnʹe-mus). Paragonimus species oc- cur throughout the world. P. kellicotti (kel ́li-kot-tē), endemic in the United States, has been associated with eating rawcrayfish on river raft trips. The adult lung fluke lives in the bronchioles of humans and other mammals and is approxi- mately 6 mm wide and 12 mm long. The hermaphroditic adults liberate eggs into the bronchi. Because sputum that contains eggs is frequently swallowed, the eggs are usually excreted in feces of the definitive host. If the life cycle is to continue, the eggs must reach a body of water. A series of steps occurs that ensure adult flukes can mature in the lungs of a new host

86. What is the life cycle of Toxoplasma gondii?

Toxoplasma gondii (toks-ō-plazʹmä gonʹdē-ē) is another api- complexan intracellular parasite of humans. The life cycle of this parasite involves domestic cats. The trophozoites, called tachyzoites, reproduce sexually and asexually in an infected cat, and oocysts, each containing eight sporozoites, are excreted with feces. If the oocysts are ingested by humans or other animals, the sporozoites emerge as trophozoites, which can reproduce in the tissues of the new host (see Figure 23.24, page 669). T. gondii is dangerous to pregnant women because it can cause congenital in- fections in utero. Tissue examination and observation of T. gondii are used for diagnosis. Antibodies may be detected by ELISA and by indirect fluorescent-antibody tests (see Chapter 18).

97. What are trematodes or flukes?

Trematodes, or flukes, often have flat, leaf-shaped bodies with a ven- tral sucker and an oral sucker (Figure 12.25). The suckers hold the organism in place. Flukes obtain food by absorbing it through their nonliving outer covering, called the cuticle. Flukes are given common names according to the tissue of the definitive host in which the adults live

109. What is trichinellosis and why is it important?

Trichinellosis is caused by a nematode that the host ac- quires by eating encysted larvae in undercooked meat of infected animals (see page 743). The nematode, Dirofilaria immitis (dirʹō-fi-lãr-ē-ä imʹmi-tis), is spread from host to hostthrough the bites of Aedes mosquitoes. It primarily affects dogs and cats, but it can infest human skin, conjunctiva, or lungs. Larvae injected by the mosquito migrate to various organs, where they mature into adults. The parasitic worm is called a heartworm because the adult stage is often in the animal host's heart, where it can kill its host through conges- tive heart failure (Figure 12.30). The disease occurs on every continent except Antarctica. Wolbachia bacteria appear to be essential to development of the worm embryos (see the box in Chapter 11 on page 308.)

88. What is Leishmaniasis and why is it important? (see pages 356 and 672)

a disease its human pathogen is leishmania the source is a bite of a sand fly. contact with contaminated blood from transfusions or shared needles can also lead to infection.

85. Which one is associated with ticks & has been found in Minnesota & Wisconsin?

babesia microti

77. What is the life cycle of Plasmodium vivax?

figure 12.20

90. What is African trypanosomiasis and why is it important? (see pages 354 & 629)

human pathogen: t. brucei gambiense. t.b. rhodesiense source:bite of tsetse fly African trypanosomiasis, or sleeping sickness, is a protozoan dis- ease that affects the nervous system.