M12: Medical Parasitology

Question 1

Parasitism is a type of symbiotic relationship where _.

Parasitology is the study of this relationship and includes the study of parasitic (3).

An important response of humans to the presence of most parasites is _.

However, many other aspects of a vigorous immune response do not occur in response to a parasitic infection. Parasites use _, in which a pathogen produces molecular structures that resemble molecular structures within the human host.

Answer 1

one organism depends on another organism for survival at some expense to the host organism

protozoa, helminths, and arthropods

eosinophilia

molecular mimicry

Question 2

How can parasites be distinguished from bacteria?

Parasites are (eukaryotic / prokaryotic) organisms belonging to the kingdoms of _, _(both previously classified under Protista) and _.

In contrast to bacteria, they

1. Possess a _ (bacteria do not)
2. Possess _ ribosomes (bacteria have _)
3. May possess _ (bacteria do not)
4. Do not possess a _ (bacteria have a _)
5. Reproduce _ (bacteria do not)

Answer 2

eukaryotic

Protozoa, Chromista, and Animalia

nucleus

80S (70S)

mitochondria

cell wall (peptidoglycan cell wall)

sexually

Question 3

What types of parasites exist?

_ are protozoa

_ include helminths and ectoparasites (insects and arachnids).

Answer 3

Protista

Animalia

Question 4

What types of parasites exist?

Endoparasites are parasites that live _.

They can be _ or _.

Answer 4

inside the body of the host

protozoa or helminths

Question 5

What types of parasites exist?

Protozoa are (simple / complex) organisms that are generally (unicellular / multicellular) and free living.

They are divided into four distinct groups on the basis of their methods of locomotion.

These means of locomotion include:

• _ (Giardia lamblia)
• _
• _ (Entamoeba histolytica)
• _ (Plasmodium falciparum)

Many protozoa have specific _ distributions – this is a key to considering the possibility of infection clinically.

Answer 5

simple
unicellular

• flagella
• cilia
• pseudopods
• apical microtubule complex

geographic

Question 6

What types of parasites exist?

Helminths are _.

The helminths can be divided into _ (_) and _.

The flatworms can further be divided into _ () and _ ().

As with the protozoa, many helminths have specific _ distributions.

Helminths cause disease by a variety of mechanisms such as _ (intestinal obstruction), competition for _, or _ of host tissues.

Answer 6

worms

roundworms (nematodes) and flatworms

tapeworms (cestodes) and flukes (trematodes)

geographic

mechanical effects
nutrients
invasion

Question 7

What types of parasites exist?

All medically important ectoparasites belong to the Phylum _ which include members of class _ (eg: lice and fleas) and class _ (eg: ticks, spiders).

They fulfill a life cycle requirement through interaction with the _ or _ of the host.

Examples include (3)

In some cases the manifestations of disease are purely the result of the ectoparasite _ (allergic reaction to the deposited feces of scabies causes severe itching).

In other cases, ectoparasites are vectors of _, _, or _ infection.

Answer 7

Arthropoda
Insecta
Arachnida

skin or hair

lice, scabies and ticks

being on the skin or hair

bacterial, viral, or protozoal

Question 8

What is a parasite’s life-cycle and what are the common modes of transmission?

The life-cycles are the different _ that parasites take, as they _ and _ in different hosts and different environments.

Many parasites require (#) host species to complete their life cycle.

The definitive host is where the parasite reaches _ whereas the intermediate host harbors the _ or _ stage of the parasite.

The number or type of hosts may be characteristic of a _ of parasites.

For example, _ (eg: Schistosoma) would always have mollusks as their first intermediate host.

Answer 8

forms
develop
reproduce

two or more

sexual maturity
asexual or larval

group

trematodes or flukes

Question 9

What is a parasite’s life-cycle and what are the common modes of transmission?

The _ is a common mode of transmission of parasites.

Raw or improperly cooked food may harbor the infective ova or larvae of parasites (_).

Other parasites such as hookworms and Schistosoma infect their hosts by _.

Parasites may also be transmitted through _ such as in the case of malaria and filariasis. Prevention of these infections may be done through _.

Other modes of transmission include _ (such as in Toxoplasma), inhalation of _ (Enterobius), and _ (Trichomonas).

Answer 9

fecal-oral route

cystercercosis

skin penetration

insect vectors
vector-control

vertical transmission
eggs
sexual intercourse

Question 10

What are some of the medically important protozoa?
Entamoeba histolytica:

_ is the most important amoeba to infect humans.

The amoebae, like other protozoa, are _ and (unicellular / multicellular).

They possess a _ and an _, within which the _ and _ exist.

Answer 10

Entamoeba histolytica

microscopic
unicellular

cytoplasmic membrane
endoplasm
nuclei and mitochondria

Question 11

What are some of the medically important protozoa?
Entamoeba histolytica:

Life cycle:

A _ that is excreted into the environment by another person is ingested by a person through _.

The cyst undergoes _ in the gut, becoming a _.

This attaches to the colonic mucosa, and can sometimes penetrate allowing it to reach the portal circulation causing an _.

Various triggers can initiate formation of new _ in the gut, which can then be shed into the environment, thereby completing the life cycle.

Geographic distribution:
(Commonly / Rarely) acquired in the United States (occasionally in institutions for the cognitively impaired and in gay men). Many cases arise in _.

Clinical manifestations (2)

Most common treatment:
_ and subsequent _ or _ to eradicate intraluminal cysts.

Answer 11

cyst
fecally contaminated food or water

excystation
trophozoite

amebic liver abscess

cysts

Rarely
Mexico

Bloody diarrhea (amebic dysentery) 
liver abscess

Metronidazole
paromomycin or diloxanide

Question 12

What are some of the medically important protozoa?
Acanthamoeba:

_ can get infection of the _ with this amoeba, particularly if they use “homemade saline” for lens disinfection or if they wear their lens while swimming in surface water.

Answer 12

Contact lens wearers

cornea

Question 13

What are some of the medically important protozoa?
Naegleria fowleri:

This organism also nicknamed “brain-eating ameba” is commonly found in _ and _.

It infects people by entering through the nose when _ or _.

Once the ameba reaches the brain through the cribriform plate it causes a usually fatal _.

Recent cases occurred in the _ USA. There is no effective treatment.

Answer 13

warm freshwater (lakes, hot springs) and soil

swimming or diving

meningo-encephalitis

Southern

Question 14

What are some of the medically important protozoa?
Giardia lamblia:

Clinical manifestations: _.

Most common treatment: _.

Answer 14

Diarrhea

Metronidazole

Question 15

What are some of the medically important protozoa?
Cryptosporidium spp.:

Clinical manifestations: _.

Answer 15

Diarrhea

Question 16

What are some of the medically important protozoa?
Microsporidia:

Microsporidia is a designation encompassing more than 100 genera and 1000 species of organisms.

Microsporidiosis is an infection which, like cryptosporidiosis, mainly causes _ and is predominantly a problem in _ people with human immunodeficiency virus (HIV) infection.

_ may be useful as therapy, but even more important is the restoration of immune function by use of _ medications.

Answer 16

diarrhea

immunosuppressed

Albendazole
anti-HIV

Question 17

What are some of the medically important protozoa?
Trichomonas vaginalis:

Trichomoniasis is among the most common sexually transmitted infections (STI) in women. Its incidence is highest in _ and in _. Rates among newly incarcerated women approach 50%.

Most men who carry T. vaginalis are _.

Life cycle:
T. vaginalis is highly _. No _ is needed for transmission. Infected vaginal discharge contains 10-100,000 protozoa per mL. The organism is mechanically passed from _ to _ and then to another _. Although the organisms can survive on damp towels and clothes for hours, there has been no documented transmission through this means.

Geographic distribution: _

Clinical manifestations:
Infected women note _ and _ or _. Physical examination reveals a copious discharge, often with bubbles, giving it a frothy appearance. There is a characteristic _ odor.

Diagnosis:
A _ specimen, examined microscopically, will reveal _-shaped, _ organisms with a characteristic _ motility.

Most common treatment: _ (treat sexual partner as well!)

Answer 17

women with multiple sexual partners and in groups at risk for other sexually transmitted diseases

asymptomatic

site-specific
vector
female to male
female

Worldwide

vaginal discharge
vulvovaginal soreness
irritation
fish-like

wet mount
pear
flagellated
twitching

Metronidazole

Question 18

What are some of the medically important protozoa?
Babesia:

_ is an infection caused by the protozoa Babesia which, like Plasmodium spp, infects _ but is very different from malaria. The classic microscopic diagnosis is made when an _ is visualized.

Risk factor for severe disease and relapses is functional _.

Life cycle:
Part of the life-cycle occurs in _ (deer and white-footed mice), while _ (not mosquitoes) are the vectors of infection.

Geographic distribution:
_ United States (especially in Nantucket Island, Martha’s Vineyard and Cape Cod but also seen in Pennsylvania),

Most common treatment:
_ and _ or _ and _

Answer 18

Babesiosis
erythrocytes
intra-erythrocytric “Maltezer cross”

asplenia

non-human vertebrates
ticks

Northeastern

clindamycin and quinine
atovaquone and azithromycin

Question 19

What are some of the medically important protozoa?
Leishmania spp.:

The Leishmania spp. that infect humans are found as intracellular _ in macrophages in humans and extracellular _ in the gut of sandflies. There are numerous species, none of which are endemic in the United States.

Geographic distribution:
Leishmaniasis is common in _ and _ America and in the _ and _.

Clinical manifestations:
Dependent on the host’s cell-mediated immune responses. _ is most often seen in American troops who were infected in Iraq or Afghanistan. _ (kala azar) will manifest as _ and _.

Answer 19

amastigotes
promastigotes

Central and South
Middle East and Africa

Cutaneous leishmaniasis
Visceral leishmaniasis
fevers
hepatosplenomegaly (enlarged liver and spleen)

Question 20

What are some of the medically important protozoa?
Trypanosoma spp.:

There are two distinct forms of trypanosomiasis (2)

American trypanosomiasis is found throughout _ and _ America. It is transmitted by “_” and causes _ disease with esophageal and colon _ as well as _. Due to immigration there are carriers in the USA who can propagate the infection through blood transfusions and through mother to child transmission. 1:5000 blood donations in south California and south Florida are positive by serology.

African trypanosomiasis is transmitted by the _ and causes _, an often fatal _.

Answer 20

American and African

Central and South
kissing bugs
Chagas'
dysmotility 
cardiomyopathy

tsetse fly
sleeping sickness
meningo-encephalitis

Question 21

What are some of the medically important protozoa?
Toxoplasma gondii:

Clinical manifestations:
_ through perinatal transmission and reactivation _ in T-cell immunocompromized patients.

Answer 21

Eye infections (retinitis) 
encephalitis

Question 22

Helminths:
Intestinal Roundworms:
- Ascaris lumbricoides 
- Hookworm (Necator americanus, Ancylostoma duodenale) 
- Pinworm (Enterobius vermicularis) 
- Strongyloides stercoralis 
- Whipworm (Trichuris trichiura) 

Typical life-cycle:

Female worms in the _ of a human produce eggs. The eggs embryonate and infect humans by _ (Ascaris, Enterobius, whipworm) or by _ by larval forms (hookworm and Strongyloides).

The infections are most prevalent in _ areas where children play on contaminated soil around homes or where farmers use human excrement (“night soil”) for fertilizing crops. The one exception is _ which occurs commonly in the United States and is not associated with any specific socioeconomic level. It is common in siblings within the same family.

Clinical manifestations:
Ranges from _ (pinworm) to _ (strongyloidiasis). Soil-transmitted helminth infection (such as with Ascaris or Trichuris) usually present with non-specific _ and/or _.

Treatment:

_ or _

_ may also be used for E. vermicularis. In high prevalence countries periodic mass-treatment is provided since _ is so common.

Answer 22

gut
ingestion of infective eggs
penetration of the skin

impoverished rural
pinworm

perianal itch
disseminated infection
abdominal discomfort and/or microcytic anemia

Albendazole/mebendazole or ivermectin

pyrantel
re-infection

Question 23

Helminths:
Intestinal Roundworms (5)

Answer 23

Ascaris lumbricoides

Hookworm (Necator americanus, Ancylostoma duodenale)

Pinworm (Enterobius vermicularis)

Strongyloides stercoralis

Whipworm (Trichuris trichiura)

Question 24

Helminths:
Tissue Nematodes (filaria) (4)

Answer 24

Onchocerca

Wuchereria

Brugia

Trichinella

Question 25

Helminths:
Tissue Nematodes (filaria):
- Onchocerca 
- Wuchereria 
- Brugia

_ is a disease whereby larvae of roundworms are transmitted by mosquitoes or other insects.

Life cycle:
After the bite of the mosquito they pass into the _ where they mature into adult worms. From there, fertilized females may discharge _ into the _.

Clinical manifestations:
_ and _ are clinical manifestations, the latter resulting from lymphatic destruction.

Answer 25

Filariasis

lymphatics
microfilariae
blood

River blindness (onchocerciasis) 
elephantiasis

Question 26

Helminths:
Tissue Nematodes (filaria):
- Trichinella

Trichinellosis or trichinosis is caused by ingestion of _.

Life cycle:

The parasite larvae are released in the _ after digestion of the meat, and migrate through the _.

Larvae mature into _ producing larvae that migrate into _ of the host, causing diffuse _, _, and _ as a consequence of the immune-mediated inflammatory reaction.

Answer 26

raw or undercooked contaminated meats (pigs, boar, bear)

stomach
intestinal mucosa

worms
muscles
myalgias, facial edema, and fevers

Question 27

Helminths:

Trematodes (flukes) (3)

Answer 27

Schistosoma hematobium

Schistosoma japonicum

Schistosoma mansoni

Question 28

Helminths:
Trematodes (flukes):
- Schistosoma hematobium 
- Schistosoma japonicum 
- Schistosoma mansoni

Approximately 200 million people are infected with schistosomiasis worldwide.

Life-cycle: Transmission of schistosomiasis requires:

1) An appropriate _ intermediate host (where part of the life-cycle occurs)
2) Slowly moving _ (where _ have been released from the snail)
3) Human entry into the _ (the cercariae penetrate the _)

After penetrating the skin, there is migration to the _ and _ with maturation into the adult worms. The worms then migrate via the _ to their final destination (through either the veins of the gastrointestinal tract or the veins of the bladder). From here, eggs can be released into the _ or the _, thus completing the life-cycle.

Geographic distribution:
Everywhere except _, _, and _.

Clinical manifestations: 
Acute schistosomiasis (_) and chronic schistosomiasis (_, _, _, or _). 

Diagnosis:
Finding characteristic _ in the urine () or feces (, _)

Treatment:
_ which affects membrane permeability in the worm.

Answer 28

snail

fresh water
cercariae

snail-infested water
skin

lungs and liver
veins
feces or the urine

North America, Europe and Australia

Katayama fever
chronic liver disease, hematuria, bladder cancer or neurologic disease

eggs
S.hematobium
S.japonicum, S.mansoni

Praziquantel

Question 29

Helminths:

Cestodes (tapeworms) (3)

Answer 29

Taenia solium
Taenia saginata
Echinococcus

Question 30

Helminths:
Cestodes (tapeworms):
- Taenia solium

The _ tapeworm is the most important tapeworm.

Humans may acquire the infection by either ingesting _ eggs or by consuming undercooked pork containing _ (_). This results in _.

Humans who are infected with ova obtained from fecally contaminated food will develop _.

The most critical location is the brain, an infection called _. The inflammation around the cysterci in the brain can cause _, which is a common manifestation in Latin America and Asia.

Answer 30

pork

T. solium
infectious larval cysts (cysticerci)
taeniasis

cysticercosis

neurocysticercosis
seizures

Question 31

Helminths:
Cestodes (tapeworms):
- Taenia saginata

The _ tapeworm can give abdominal symptoms but does not disseminate as T. solium does.

Answer 31

beef

Question 32

Helminths:
Cestodes (tapeworms):
- Echinococcus

Hydatid disease is another important cestode infection due to _.

This tapeworm is carried by _; ingestion of the eggs by humans (after contact with dogs or by food contaminated by dog feces) results in human infection.

Once in the _, the eggs hatch to form _ which penetrate the intestinal mucosa and enter the circulation.

These then _ in human organs, especially the liver where it can cause multiloculated large _.

Answer 32

Echinococcus granulosus

dogs

gastrointestinal tract
oncospheres

encyst
cysts

Question 33

What are the common ectoparasites infesting humans?

Lice are small insects which can infest the

1) _ (: “nits”),
2) _ (: “body lice”)
3) _ (“crabs”)

Scabies is caused by an arachnid, _. It produces an extremely _ infestation of the skin due to an allergic reaction with a _.

Myiasis is infestation of the _ by the larvae of flies (maggots)

Answer 33

Scalp hair (pediculosis capitis)
Body hair (pediculosis corporis)
Pubic hair

Sarcoptes scabei
itchy
scaly rash

subcutaneous tissue

Question 34

Drugs for malaria treatment:
Chloroquine:

• active against the erythrocytic stages of _
• its effectiveness has been eliminated in most parts of the world (both for prophylaxis and treatment) because of _.
• Chloroquine-resistant _ transport chloroquine out of the cell

Answer 34

Plasmodium spp.

resistance

Plasmodia

Question 35

Drugs for malaria treatment:
Quinine:

• also acts against the asexual erythrocytic stages of _
• retains activity against most _ resistant strains
• intravenous formulation (is / is not) available in the USA and often substituted by _
• Often combined with _

Answer 35

Plasmodium spp.

chloroquine

is not
quinidine

doxycycline

Question 36

Drugs for malaria treatment:
Primaquine:

• is the only drug available that has activity against the exoerythrocytic, hypnozoite forms of _ and _ that reside in the liver

Answer 36

P. vivax and P. ovale

Question 37

Drugs for malaria treatment:
Artemisinin derivatives:

• mode of action is not well understood
• act against _ resistant and _ resistant strains
• should only be used as combination therapy such as _ with _, or _ to prevent emergence of resistance

Answer 37

chloroquine
quinine

coformulated artemether with lumefantrine (coartem)
amodiaquine with artesunate

Question 38

Drugs for malaria treatment:
Mefloquine (Lariam):

• used as _ and _
• some resistance has been reported in _

Answer 38

prophylaxis and treatment

SE Asia

Question 39

Drugs for malaria treatment:
Atovaquone/proguanil (Malarone):

• used as _ and _

Answer 39

prophylaxis and treatment