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Clinical Microbiology > Intro to parasitology > Flashcards

Intro to parasitology Flashcards

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1
Q

Parasitology

A

The study of parasites

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2
Q

Parasite

A

An organism living on or in, and at the expense, of another organism. This interaction is not always harmful, some are beneficial.

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3
Q

Parasitism

A

One organism is injured by activities of another.

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4
Q

Obligate parasite

A

A parasite that must always live in contact with a host. Malaria is a perfect example because it must be carrying out its life cycle either in the gut of a mosquito or in human cells

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5
Q

Facultative parasite

A

A parasite that can complete its life cycle in a free-living environment or, alternatively, that lives during part or all of its cycle within a host. Helminths are one example- they can mate in the intestinal tract

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6
Q

Endoparasite

A

Living within a host- tapeworms, chagas disease, malaria

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7
Q

Ectoparasite

A

Living outside the host (body surface)- fleas, lice, mites

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8
Q

Symbiosis

A

Member of different species of organisms living in close association with its host. You may not see any symptoms of infection. Usually, there is a nutritional benefit. An endosymbiont is a symbiont within the host. An ectosymbiont is a symbiont outside of the host

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9
Q

Commensalism

A

Beneficial to one partner and not problematic to the other (causes no harm). In a facultative association, both species live independently. In an obligatory association, one species must live in association of the partner

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10
Q

Mutualism

A

Beneficial relationship to both parasite and host organism. Some research suggests that having a parasite may reduce the inflammation caused by autoimmune diseases.

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11
Q

Protozoa

A

Single-celled eukaryote that are primarily unicellular, non photosynthetic and are further classified on their ability for movement (motility) – pseudopods, flagella, cilia

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12
Q

Sporozoa

A

A nonmotile protozoa

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13
Q

Trophozoites

A

The feeding, motile stage of protozoa

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14
Q

Cysts

A

Infectious stage of protozoa, highly condensed cytoplasm and thick cell wall

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15
Q

Karyosome

A

Concentrated clumps of chromatin material within the nucleus.

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16
Q

Peripheral chromatin

A

Non-active chromatin, providing the nucleus halo-like appearance.

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17
Q

Sporogony (microsporidia)

A

Productions of spores, asexual stage

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18
Q

Oocyst

A

A thick or thin-walled stage in the life cycle of coccidia, shed in feces in human infections

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19
Q

Proglottid

A

Tapeworm segments containing male and female reproductive systems; may be immature, mature or gravid. Proglottids can be around a half inch in length. Cestodes can have anywhere from one thousand to three thousand proglottids, and each proglottid is capable of producing eggs

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20
Q

Scolex

A

The head or attachment portion of a tapeworm; suckers or hooklets

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21
Q

Tachyzoite

A

Rapidly multiplying stage in development of tissue phase of Toxoplasma

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22
Q

Bradyzoite

A

Slowly multiplying trophozoite contained in the tissue cyst, chronic infection of Toxoplasma

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23
Q

Kinetoplast

A

Intensely staining rod or disk-shaped or spherical extranuclear DNA structure found in parasitic flagella near the base of the flagellum

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24
Q

Amastigote

A

Small round intracellular stage of Leishmania and Trypanosoma spp., base of flagella is anterior to the nucleus, no external flagellum

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25
Q

Promastigote

A

Development stage of Trypanosomes, the base of the flagellum is anterior to the nucleus, no undulating membrane

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26
Q

Trypanosome

A

A slender, flagellate protozoan found in the blood of humans; also called trypomastigote

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27
Q

How are protozoa classified?

A

Based on their ability to move

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28
Q

Sarcodina

A

Intestinal amebae

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29
Q

Mastigophora

A

Intestinal flagellates

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30
Q

Ciliophora

A

Intestinal ciliates

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31
Q

Plasmodium

A

Sporozoa from blood and tissue

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32
Q

Leishmania and Trypanosome

A

Flagellates from blood and tissue

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33
Q

Naegleria

A

Amebae from other body sites (outside the intestine)

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34
Q

Trichomonas

A

Flagellates from other body sites (outside the intestine and blood and tissue)

35
Q

Toxoplasma

A

Coccidia from other body sites (outside the intestine)

36
Q

Microsporidium

A

Microsporidia from other body sites (outside the intestine)

37
Q

Classification of human parasites (3)

A
  1. Nematodes (roundworms)
  2. Cestodes (tapeworms)
  3. Trematodes (flukes)
38
Q

Helminths

A

They are large, multicellular organisms (worms)- this term is broad and encompasses all worms. Includes nematode, cestode or trematode. Easily visible in adult stages (do not need microscope), although adults can’t multiply in humans due to their large size. Consuming a large ova burden can result in more worms being present in the body and more symptoms. Either free-living or parasitic in nature.

39
Q

Nematodes (roundworms)

A

Unsegmented worms, bilateral symmetry, fully functioning digestive tract, long, cylindrical, mm to meter in length. They are very round and you may not see striations. Similar in morphology to an earthworm

40
Q

Cestodes (tapeworms)

A

Ribbon-like body with a chain of segments/proglottids, contains both male and female reproductive systems, scolex allows for worm attachment to intestinal tissue. Proglottids are immature, mature or may be gravid (full of eggs). This category of worms is the largest. Cestodes can have anywhere from one thousand to three thousand proglottids and may even be able to produce one million eggs per day

41
Q

Trematodes (flukes)

A

Flat, small worm with hooks (oral sucker), dorsoventrally flattened, all eggs are operculated (lid structure). Have a leaf-like morphology and are associated with biliary tract blockage. Adults worms have suckers that allow them to attach. Eggs are usually used for identification because they are found more easily in the stool- people generally do not purge the worms

42
Q

Classification of Nematodes (3)

A
  1. Intestinal - Ascaris, Enterobius (pinworm), Trichuris (Whipworm)
  2. Tissue – Trichinella, Toxocara
  3. Blood & tissue – Wucheria, Loa- these worms are small
43
Q

Classification of Cestodes (2)

A
  1. Intestinal – Diphyllobothrium, Taenia (associated with neurocysticercosis), Hymenolepis
  2. Tissue (larval form)– Taenia, Echinococcus
44
Q

Classification of Trematodes (3)

A
  1. Intestinal - Fasciolopsis, Heterophyes heterophyes, Metagonimus yokogawai.
  2. Liver & lung – Clonorchis (Opisthorchis), Paragonimus
  3. Blood - Schistosoma
45
Q

Common parasitic infections in the US (5)

A

Based on stool samples:
1. 3.8% Giardia (water contamination)
2. 2.7% Trichuris ova
3. 2.3% Ascaris ova
4. 1.6% Enterobius ova (probably higher as stool not best sample)
5. 0.6% Entamoeba

46
Q

How many people in the US have parasitic infections?

A

Definitive numbers not available – estimates ~64 million in the US are infected based on NPI data. Multiple parasites are commonly found in those infected.

47
Q

Problematic parasitic organisms outside of the US (4)

A
  1. Leishmaniasis
  2. Schistosomiasis (contaminated water)
  3. Helminths- ascaris is the most common- soil transmission
  4. Malaria- children most affected
    Total estimated infected individuals - ~2 billion infected, which is about 30% of the world population
48
Q

Notifiable parasitic disease in the US (6)

A
  1. Babesiosis (tick borne)
  2. Cryptosporidiosis (water associated)
  3. Cyclosporiasis (water and food associated)
  4. Giardiasis (water associated)
  5. Malaria (mosquito borne)
  6. Trichinellosis (Trichinosis- undercooked food)
49
Q

NPI

A

Neglected Parasitic Infections. The CDC is most concerned with chagas disease, neurocysticercosis (cause of seizures), toxocariasis (cats and dogs), toxoplasmosis (cats, venison, improperly treated meat), and trichomoniasis

50
Q

Risk factors for parasitic infections (4)

A
  1. Travel to or immigration from endemic areas
  2. Consumption of contaminated food or water- undercooked food or ice or water that was not appropriately heated
  3. Exposure to arthropod-mediated infection- protection by repellent products – DEET, mosquito netting, appropriate clothing.
  4. Swimming in fresh water, pools if inappropriate levels of chlorine.
51
Q

Symptoms of parasitic infections

A

The most common symptoms are diarrheal disease (bloody or watery diarrhea, abdominal pain, bowel obstructions, belching or flatulence, and steatorrhea). Other symptoms include eosinophilia, skin rash or itching, hepatosplenomegaly or lymphadenopathy, jaundice,
urinary tract associated symptoms (increased frequency, dysuria, hematuria), inflammation of the lungs (cough, pain, eosinophilia), and fever, chills, night sweats, malaise, muscle pain

52
Q

4 super-groups of human parasites

A
  1. Sar
  2. Excavata
  3. Amoebozoa
  4. Opisthokonta- contains all fungi, animals, and protists
53
Q

Cryptosporidium parvum

A

One of the intestinal protozoa that is associated with contaminated drinking water. Part of the Sar super-group

54
Q

Giardia duodenalis

A

Associated with contaminated freshwater. It is part of the normal flora of beavers and another animals. Part of the Excavata super-group

55
Q

Amoebozoa super-group

A

Includes Entamoeba coli, mana, histolyticum, and others. Very few of these species are pathogenic. They are all found in the same environment and can therefore be difficult to identify. Contains genera with amoeboid locomotion and ciliated microorganisms

56
Q

Transmission of disease (3 methods)

A
  1. No intermediate host- these infections are more problematic and are considered contagious as they spread from person to person
  2. One intermediate host- environmental exposures, like contaminated food
  3. Many intermediate hosts- these infections are more difficult to acquire
57
Q

DALY

A

Disability adjusted life years, associated with people who are sick due to a parasitic infection.

58
Q

Toxoplasmosis

A

The leading cause of foodborne illness and death. It can be associated with cats (cleaning the litter box) as well as venison or improperly treating meat. It can be very serious if a pregnant person is infected- associated with spontaneous abortion, neurological and birth defects in the fetus

59
Q

Trichomoniasis

A

One of the most common STIs in the US. It is actually more problematic than gonorrhea and chlamydia

60
Q

Most common laboratory method to detect parasites

A

A stool sample to do an ova (eggs of adult worms) and parasite examination. The sample are examined under the microscope using a wet mount. Preservatives are used to increase recovery of the parasites, since some organisms (like adult amoebas) may die or degrade quickly

61
Q

Preservatives used for an O&P (4)

A
  1. Formalin
  2. PVA – polyvinyl alcohol
  3. SAF – sodium acetate-acetic acid formalin
  4. Schaudinn’s Fluid – PVA & mercuric chloride
62
Q

Macroscopic analysis of stool

A

Visual determination of eggs, intact worms, proglottids (off white color), color determination

63
Q

Microscopic analysis of stool

A

Wet mount is done to view under the microscope– either done directly or after concentration of sample. You are looking for motile (swimming) trophozoites, cysts, or helminth eggs. Can use a trichrome stain or modified acid-fast stains

64
Q

Trichrome stains

A

Permanent stains, best for identification of protozoan trophozoites or cysts. Used for samples preserved with formalin or PVA

65
Q

Acid-fast stains

A

Used to view the acid-fast oocysts produced by Cryptosporidium, Microsporidia and others

66
Q

Specimens collected to diagnose parasites (6)

A
  1. Duodenal Aspirates & Sigmoidoscopy
  2. Cellophane Tape prep
  3. Urine, Vaginal, Urethral- especially done for trichomonas
  4. Blood
  5. CSF
  6. Others – tissues (look for worms), sputum, corneal scrapings, corneal biopsy, muscle
67
Q

Duodenal Aspirates & Sigmoidoscopy samples

A

A wash of fluid is collected and immediately brought to the lab. Some parasites have a characteristic motility and can be diagnosed using this test. An enterotest can be done to check for motile trophozoites, trichrome for others. Uses a gel capsule attached to a string which the patient then swallows. When the string is removed, it is put in a tube with a vortex of fluid. The fluid is then examined under the microscope to view parasites. This is mainly done for Giardia

68
Q

Cellophane tape prep

A

Done for Pinworm (Enterobius vermicularis) to collect the
1st morning collection of ova deposited in perianal area. Pinworm is the most common parasite found in children. At night, the adult female migrates out of the anus and deposits eggs in the perianal area. In the morning, the eggs hatch and the small worms migrate back into the anus and to the intestinal tract. This causes itching. Cellophane tape prep is a paddle with tape that is touched to the outside of the anus, ideally before the patient wakes up in the morning. The ova can be observed on the scotch tape in the lab

69
Q

When are blood samples collected?

A

Thick and thin smears are done to diagnose malaria, babesia, or trypanosomes

70
Q

When are CSF samples collected?

A

Samples are observed for amebic mobility in encephalitis patients. However, if an amoeba is present in the CSF, the patient will have almost no chance of survival

71
Q

When are muscle biopsies done?

A

Biopsies can be done, typically of the large muscles of the calves or leg, to view encysted parasites. However, this is typically a last resort as serology or another method can be used first

72
Q

Laboratory methods (4)

A
  1. Serology
  2. ELISA
  3. Molecular testing
  4. Direct fluorescent antibody (DFA) Techniques
73
Q

Serology testing

A

IgM (acute phase) and IgG (recovery). Not helpful in populations with endemic exposures since everyone has been exposed and will test positive. This type of testing is
helpful for travelers

74
Q

ELISA

A

FDA has given approval of malaria ELISA kit (whole blood), and ELISA is becoming a more popular method of diagnosis. Used for detection of parasitic antigens, which confirms current infection. It is the preferred method for commonly isolated parasites in the US, like Giardia, Cryptosporidium, and Entamoeba histolytica. Also utilized for Toxoplasmosis, Chaga’s Disease, Leishmaniasis, Schitosomiasis, Echinococcosis, Trichinellosis, Filariasis

75
Q

Molecular testing

A

This method has become more common over time in order to diagnose the common parasitic organisms. NAAT - Cryptosporidium, Giardia, Trichimonas, E. histolytica – FDA approved. BioFire parasite detection identifies Cryptosporidium, Cyclospora, Entamoeba histolytica, Giardia

76
Q

Direct fluorescent antibody (DFA) Techniques

A

Becoming outdated but still used for Cryptosporidium or Giardia sometimes. However, there are better and faster ways to diagnose these parasites

77
Q

Antihelminthic treatment

A

2/3 of world population live in conditions where parasite exposure and infection avoidance is impossible, so drugs are necessary. Most common target of these drugs is the helminth neuromuscular system. 3 groups of drugs cover all human infections – albendazole, praziquantel, ivermectin. There are few treatment options available
due to poor efficacy and safety, and some infections are untreatable. Giardia may also be able to be treated with an antibacterial agent

78
Q

Benzimidazoles

A

Includes Albendazole, mebendazole. Only administered orally. These drugs are well tolerated but may cause nausea or vomiting. Main mechanisms are stopping cell division and reducing ATP stores of the organism

79
Q

Benzimidazoles mode of action

A

Binds to nematode ß-tubulin, inhibiting polymerization of the tubulin and preventing the formation of microtubules. This causes the inhibition of cell division. These drugs also cause impaired uptake of glucose, leading to depletion of glycogen and reduced stores of ATP. Can stimulate Ascaris worms to emerge from mouth and nostrils, patients should be forewarned.

80
Q

Pyrazinoisoquinolones

A

Includes Praziquantel, delivered orally only. This drug is well tolerated

81
Q

Pyrazinoisoquinolones mode of action

A

Disrupts calcium ion homeostasis in the worm, antagonizing voltage-gated calcium channels. This results in uncontrolled calcium ion influx, leading to uncontrolled muscle contraction and paralysis- can cause the worm to detach from the tissue. Exposes schistosome antigens at the parasite surface. The binding site for the drug remains to be identified

82
Q

Macrocyclic lactones

A

Includes Ivermectin and doramectin. Delivery can be topical, oral (most common), or even IV. These drugs are generally well tolerated but may cause neurotoxicity (confusion, ataxia, coma)

83
Q

Macrocyclic lactones mode of action

A

Binds to glutamate-activated chloride channels existing in nerve or muscle cells of nematode causing hyperpolarization of nerve or muscle cells by increasing permeability of chloride ion through the cell membrane, parasites are paralyzed to death.

Clinical Microbiology (19 decks)

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