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Parasitology Flashcards

1
Q

In what two groups do we separate the platyhelminthes? What are the pathogens in each group?

A

Flatworms are divided into cestodes (tapeworms) and trematodes (flukes).

The trematode pathogens include the Schistosoma spp.

The cestode pathogens include the Taenia spp.

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2
Q

What are immune escape mechanisms? Give examples.

A

They are ways in which parasites evade the immune system. Include antigenic variation of surface molecules, resistance to immune effector mechanisms, antigenic masking, intracellular location, and immunosuppression.

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3
Q

What are the groups of parasitic protozoa?

A

Amebas, ciliates, flagellates, and sporozoa.

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4
Q

Describe the body plan of nematodes. Name the pathogens in this group.

A

Nematodes are roundworms with cylindrical bodies. The pathogens are Ascaris lumbricoides, Strongyloides stercoralis, Enterobius vermicularis, the hookworms (Necator) and the filarias.

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5
Q

Describe the locomotion and reproduction of flagellates. Name the flagellate pathogens.

A

Flagellates move by using flagella. They reproduce asexually. The flagellate pathogens are Giardia lamblia, Trichomonas spiralis, Trypanosoma spp., and Leishmania spp.

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6
Q

Describe the locomotion of ciliates and their reproduction. What is the only ciliate pathogen?

A

Ciliates move by using cilia and reproduce asexually. The only pathogen is Balantidium coli.

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7
Q

What is the active form of Entamoeba histolytica called? What is the infectious form?

A

The active form is the trophozoite. The infectious form is the cyst.

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8
Q

Describe the mode of reproduction of the apicomplexa. What is another name for apicomplexa? What are the pathogens in this group?

A

Apicomplexa are also called Sporozoa and reproduce both sexually and asexually. The asexual cycle involves multiple fission.

The pathogens are Plasmodium, Cryptosporidium, and Toxoplasma.

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8
Q

What are the specific mechanisms that grant immunity to parasites?

A

Production of parasite specific IgE and eosinophilia following a T-helper 2 mediated response that depends on IL-4 and IL-5.

IgE mediated degranulation of mast cells and basophils.

Eosinophil mediated IgE dependent cytotoxicity.

Ab response if parasite is invasive (IgM to IgG).

Induction of granulomatous responses and fibrosis.

CD4+ cell activation and cytokine production.

CTL responses to intracellular protozoa.

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10
Q

Describe the life cycle of Entamoeba histolytica.

A
  1. Cysts are ingested in contaminated food or water. (Contaminated with human feces)
  2. Cysts excyst in the small intestine. Trophozoites colonize the large intestine.
  3. Trophozoites reproduce asexually by binary fission. May invade mucosa.
  4. Cysts are passed in feces.
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11
Q

Describe the locomotion of amebas and their mode of reproduction. What is the only true amebic human pathogen?

A

They move using pseudopodia and reproduce asexually by binary fission. Entamoeba histolytica is the only ameba that is a human pathogen.

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12
Q

Describe the epidemiology of Entamoeba histolytica: where is it common, how is it transmitted?

A

It is common in tropical and subtropical areas. Transmitted by the fecal-oral route.

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13
Q

How is amebiasis diagnosed?

A

Demonstration of trophozoites or cysts in fecal sample.

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14
Q

What are the commensal amebas?

A

Entamoeba coli

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15
Q

What is the active stage of Giardia lamblia? The infective stage? Describe their morphology.

A

The active stage of Giardia lamblia is the trophozoite. It is a pear shaped flagellate with two nuclei and four pairs of flagella. The cyst is the infective stage.

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16
Q

Describe the life cycle of Giardia lamblia.

A
  1. The cysts are ingested in contaminated food or water.
  2. Cysts excyst amd trophozoites colonize the small intestine.
  3. Cysts are passed in the feces.
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17
Q

Describe the epidemiology of Giardia lamblia.

A

Fecal-oral transmission.

Beavers are reservoir hosts.

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18
Q

How is girardiasis diagnosed?

A

Demonstration of trophozoites or cysts in the feces.

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19
Q

Describe the morphology of Trichomonas vaginalis?

A

Trichomonas vaginalis has a single nucleus, a short undulating membrane, and four flagella.

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20
Q

Describe the life cycle of Trichomonas vaginalis.

A

Trichomonas vaginalis has not been shown to make cysts. It lives in the vagina, urethra, and prostate gland/epididymis.

Infection is aquired as an STI.

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21
Q

What are the two forms of blood flagellates? Describe their morphologies.

What tissues do they infect?

A

The two forms are the trypomastigote and the amastigote.

Trypomastigotes are elongated, motile with an undulating membrane. They live in the blood and the CSF.

Amastigotes are flatter, round, lack flagella and live intracellularly and in tissues.

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22
Q

Describe the life cycle of trypanosomes.

A

Trypanosomes have a two host cycle. They are transmitted by vectors: the tse-tse flies and the kissing bug (reduviid bugs).

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23
Q

Which are the two species known as African trypanosomes? Which vector transmits these parasites?

How do these organisms evade the immune system?

A

Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense.

The vector is the tse-tse flies.

They exhibit antigenic variation of surface antigens. They also induce polyclonal B cell activation with elevated serum IgM.

24
Q

What organism is known as the American trypanosome? Which vector transmits these parasites?

A

The species is Trypanosoma cruzi.

They are transmitted by reduviid bugs.

25
Q

What cells do Leishmania spp. infect? What receptor do they use to enter? What is the vector?

A

Leishmania uses the C3 receptor to infect macrophages and monocytes. The vector is th sandfly.

26
Q

Describe the morphology of Leishmania spp. Describe the life cycle.

A

The infective stage is the flagellated promastigote. The amastigote is a small oval non-flagellate intracellular stage. The amastigote reproduces asexually in humans.

27
Q

Describe the role of the immune system in determining the severity of Leishmaniasis

A

?

28
Q

What are the apicomplexa? Describe their reproductive cycle.

A

The apicomplexa are Cryptosporidium parvum, Toxoplasma gondii, Plasmodium spp., and Pneumocystis spp.

In general, sporozoans invade their target cells as sporozoites to carry out multiple fission and produce a schizont that releases merozoites in a cycle of asexual reproduction.

In the sexual cycle, merozoites invade a target cell to produce gametes, which upon fusion produce an oocyst. The oocyst releases sporozoites upon excystation.

29
Q

Which cells does Cryptospiridium parvum invade?

Which is the infective stage? What are the hosts?

A

Cryptosporidium parvum invades the epithelial cells of the small intestine.

C. parvum only has one host. The infective stage is the oocyst, which is passed in the feces.

30
Q

Describe the epidemiology of Cryptosporidium parvum.

A

It is an opportunistic infection, with wide distribution. Associated with immunosuppressed patients. Carried in infected water.

31
Q

Describe the life cycle of Toxoplasma gondii.

A

T. gondii is an obligate intracellular parasite that infects epithelial, muscle, and neural cells. It has a two host life cycle.

The asexual cycle happens in the human host (schizogony - produces schizonts).

The sexual cycle occurs in felines (housecats) - produces sporozoites (tachyzoites) which come from infective oocysts.

32
Q

Describe the epidemiology of Toxoplasma gondii

A

T. gondii is cosmopolitan and ubiquitous. Infections may be chronic and asymptomatic. Opportunistic in the immunocompromised. Related to cats.

Transmission is from ingestion of cysts from infected meat or oocysts from material contaminated with cat feces.

33
Q

Describe the morphology of Plasmodium spp.

A

Plasmodium trophozoites present in RBCs as ring-like discs with a dot of chromatin (ring form).

Schizont has multiple merozoites.

34
Q

Describe the life cycle of Plasmodium.

A

Plasmodium are obligate two host parasites. The sexual cycle occurs in female anopheline mosquitoes.

The asexual cycle occurs in the human host, specifically in erythrocytes and hepatocytes. The sporozoites invade hepatocytes to produce schizonts that release merozoites. Merozoites invade RBCs to produce trophozoites (ring forms) and release more merozoites.

35
Q

Which intestinal nematodes have infective larvae?

A

Strongyloides stercolaris (threadworm) , Necator americanus and Ancylostoma duodenale (hookworms).

36
Q

Which intestinal roundworms have infective eggs?

A

Ascaris lumbricoides (ascariasis) , Trichuris trichuria (whipworm) , Enterobius vermicularis (pinworm)

37
Q

Which roundworms are vector-borne?

A

Filarias - Wuchereria bancrofti

38
Q

Describe the morphology of the Enterobius vermicularis egg.

A

Oval, flattened on one side. This is the infective stage.

39
Q

Describe the morphology of the adult and egg in Trichuris trichuria.

A

The adult is has a lash-like (whip) thin anterior. The egg is barrel shaped (football shaped) with characteristic polar plugs.

40
Q

Describe the adult and egg of Ascaris lumbricoides.

A

The adult is white, long, with a smooth cuticle.

The eggs are oval, with a thick smooth inner shell. They are decorticated (lack covering)

41
Q

Describe the life cycle of Ascaris.

A

Eggs are ingested by host and they hatch in the small intestine. The juveniles migrate to the lungs and molt. Third stage juveniles migrate from lung capillaries into alveoli. They are coughed up and swallowed. The juveniles complete their development in the small intestine. The adult females and males in the small intestine produce eggs that are passed in the feces.

42
Q

Distinguish between rhabditiform and filariform larvae.

A

Rhabditiform are not infectious. Filariform are the infective stage.

43
Q

Name the human hookworms. How are the eggs distinguished? What is the infective stage?

A

The human hookworms are Necator americanus and Ancylostoma duodenale.

The eggs are oval, and have a single thin hyaline shell.

Larvae can be rhabditiform or filariform. The filariform larvae are infective.

44
Q

Describe the life cycle of hookworms.

A

Filariform larvae are free living in the soil. They penetrate the skin of the host and migrate to the lungs. They penetrate the pulmonary capillaries, enter the alveoli, are coughed up and swallowed. They enter the small intestine and attach to the surface where they mature into adult forms. Adults feed on blood and release eggs into the feces.

45
Q

What is the diagnostic stage of Strongyloides stercolaris?

A

The diagnostic stage is the larvae, which is hookworm-like.

46
Q

Describe the life cycle of Strongyloides stercolaris.

A

Stromgyloides has a free living cycle and a parasitic cycle. The parasitic infection begins with filariform larvae in the soil which penetrate the skin of the host and migrate to the lungs. They are coughed up and swallowed. In the small intestine they mature and the females release eggs. The eggs hatch in the small intestine. Juveniles are passed in the hosts feces. Autoinfection can occur if the juveniles are of the filariform type.

47
Q

Describe the morphology of Trichinella spiralis. What tissue does it invsde? What are the eggs like?

A

T. spiralis is a short, spiral worm that invades and encysts in muscle. There are no eggs, the female produces larvae.

48
Q

Describe the life cycle of Trichinella spiralis.

A

Humans are dead end hosts. Humans are infected by eating contaminated meat with the infective juvenile stage.

49
Q

Describe the general characteristics of the filarial parasites.

A

They are nematodes; are obligate parasites of blood lymph, muscle, ct, and sct.

Are transmitted by arthropod vectors; mosquitoes: Anopheles, Culex, Aedes

50
Q

Describe the life cycle of Wuchereria bancrofti.

A

Mosquito injects juvenile when it feeds. The juveniles migrate to lymph nodes where they grow to sexual maturity. The females produce microfiliriae larvae which end up in bloodstream. The vector feeds on blood with microfiliriae and these develop into infective juveniles in the mosquito.

51
Q

Describe the general morphology of cestodes.

A

The adult cestode features a scolex, or head, that mediates attachment to the intestinal mucosa via suckers and hooks. The neck is the region of growth from which the individual proglottid units stem. Proglottids are hermaphroditic. They have a cuticle.

Larvae are solid (cysticercus) or vesicular (hydatid cyst)

52
Q

Which are the intestinal cestodes?

A

Taenia saginata and Taenia solium

53
Q

Describe the life cycle of Taenia spp.

A

Eggs are ingested by an intermediate host (T. solium - pork; T. saginata - beef). Eggs hatch in small intestine of intermediate host and larvae migrate to muscle to grow as a cysticercus. Humans are infected when they ingest a cysticercus in contaminated meat. Cysticercus grows to adult sexually reproducing worm in the small intestine. Eggs are passed in the feces.

Humans can also be infected by cysticercus of T solium - cysticercosis

54
Q

Describe the morphology of Schistosoma adults and larvae.

A

Schistosoma adults are sexually dimorphic. The female is smaller than the male and they live together.

They are flatworms

55
Q

Describe the eggs of Schistosoma mansoni, Schistosoma japonicum, and Schistosoma haematobium.

A

S. mansoni - oval eggs with lateral spine
S. japonicum - oval eggs with lateral knob
S. haematobium - oval eggs with terminal spine

56
Q

Describe the life cycle of Schistosoma spp.

A

Cercariae in the water penetrate skin of human. Immature worm enter bloodstream and migrate to veins near intestine or bladder. Females release eggs to intestinal lumen or bladder. Eggs are passed into urine or feces. Miracidium hatches from egg to infect intermediate host (snails). Cercariae leave snails.

Micro (3 decks)

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