Chapter 23: Parasitic protozoans and helminths

Question 1

Protozoan and helminth

Answer 1

-these parasites exist worldwide but they most often occur among people living in rural, underdeveloped, or overcrowded places.
-they are emerging as serious threats in developed nations, infections often involve a definite host and one or more intermediate hosts as well
-most protozoans that enter the body via ingestion have two morphological forms trophozoite and cyst
-protozoans parasites are based primarily on their mode of locomotion or in the nonmotile group (?)

Question 2

trophozoite

Answer 2

-active, feeding state

Question 3

cyst

Answer 3

dormant (protected state)

Question 4

Trophozoite life cycle

Answer 4

1. vegetative state when conditions are poor for growth goes through encystment
2. then goes into dormant cyst
3. leaves cyst and go back because good growth conditions then repeats

Question 5

Types of protozoa

Answer 5

1. flagellates
2. ciliates
3. ameba
4. sporozoan

Question 6

Balantidium coli

Answer 6

the only ciliate known to cause disease in humans and it is commonly found only in animal intestinal tracts, especially in pigs
-humans become infected by consuming food or water contaminated with feces containing the cysts

Question 7

What disease results from balantidium coli

Answer 7

Balantidial dysentery

Question 8

how do you treat balantidial dysentery?

Answer 8

treatment with tetracycline which doesn’t directly kill parasite but rather alters the normal flora environment making it unsuitable for the balantidium

Question 9

How do we prevent enteric protozoan infections?

Answer 9

-good personal hygiene (degerming) and efficient water sanitation as in other enteric infections

Question 10

amoebae (sarcodines)

Answer 10

-have no truly defined shape
-they move and acquire food through the use of pseudopods
-they are found in water sources throughout the world
-infections occur by drinking water contaminated with feces that contain cysts as in other enteric so prevent by degerming, clean water, and good hygiene

Question 11

entamoeba hislytics

Answer 11

maintaining clean water is important in prevention
-trophozoites migrate to the large intestine where they multiply and sometimes cause dysentery

Question 12

What are two brain eating amoebaes

Answer 12

1. acanthamoeba and naegleria and they can cause deadly form of amoebic encephalitis via nasal cavity

Question 13

flagellates

Answer 13

protozoa that possess at last one flagellum or more
-the number or arrangement of the flagella are important in determining the species

Question 14

What are common flagellates

Answer 14

1.trypanosoma
2. giardia
3. trichomonas
4.leishmania

Question 15

Trypanosoma

Answer 15

causes Africans sleeping sickness and chagas disease depending on species

Question 16

giardia

Answer 16

causes giardiasis (beaver fever)

Question 17

trichomonas

Answer 17

causes an STD

Question 18

Leishmania

Answer 18

causes leishmaniasis which is usually self resolving but it is a growing concern in immunocompromised people
-vector transmitted by the sand fly

Question 19

Trypanosoma brucei (gambiense and rhodesiense)

Answer 19

-causes African sleeping sickness
-the insect vector is the tsete fly
-humans are usually infected when bitten by tsete flies that were first infected while feeding on infected animals
-it progresses through three stages if left untreated

Question 20

What are the three stages trypanosoma brucei goes through if left untreated

Answer 20

1. wound created at the site of the fly bite becomes a lesion with dead tissue
2. the presence of the parasites in the blood triggers fever, lymph node swelling, and headaches
   3.invasions of the central nervous system causes meningoencephalitis resulting in headaches, extreme tiredness, neurological dysfunction and eventually coma leading to death

Question 21

Trypanosoma cruzi: chagas disease

Answer 21

-endemic to central and south America, some southwest USA cases
-opossums and armadillos are the primary resrvoirs
-transmission occurs through the bite of of insects in the genus triatomas called kissing bugs<—- (the vector)

Question 22

What four stages does chagas’ disease progress through

Answer 22

1.acute stage: swelling at the site of the bites
2. generalized stage: fever, swollen lymph nodes, myocarditis, and enlargement of the spleen, esophagus, and colon
3. chronic stage: asymptomatic and can last for years
4. symptomatic stage: congestive heart failure following the formation of pseudocysts which are clusters of amastigotes (non-flagellates) in heart muscle tissue

Question 23

What is the leading cause of deaths in Latin America

Answer 23

-parasite-induced heart disease

Question 24

Giardiases “bever fever”

Answer 24

-is a common GI disease in the US and elsewhere
- is found in the intestinal tracts of animals and humans worldwide but also in the environment
-infections usually result from ingestion of cysts in contaminated drinking water or while swimming
-giardiasis can range from an asymptomatic infection to significant gastrointestinal disease
-prevention of infections in endemic areas requires the use of filtered water and patients recovering from infection must use good hygiene to prevent transmission

Question 25

Trichomonas vaginalis

Answer 25

-the most common protozoan disease of humans in industrialized nations
-the parasite lives on the vulvas and vagina of women and in the urethras, bladders, and prostates of men, it is transmitted exclusively via sex so considered an STD
-occurs in people with a preexisting STD (chlamydia) or in people with multiple sex partners as with other STDs
-infection in women result in vaginosis
-infection in men is asymptomatic
-prevention is safe sex

Question 26

Plasmodium (apicomplexans)

Answer 26

-causative agent of malaria
-malaria is endemic throughout the tropics and subtropics but not necessarily limited to those areas
-mosquitoes act as the vector for plasmodium

Question 27

The four well defined species can cause malaria

Answer 27

1. P vivax
2. P. falciparum
3. P.ovale
4. P. malariae

Question 28

Which specific mosquito is the vector for plasmodium?

Answer 28

-it is a female and called Anopheles

Question 29

How can you be resistant to malaria

Answer 29

-various genetic traits increase resistance to malaria in endemic populations
1. sickle-cell trait (sickle-shaped cells somehow resist penetration by plasmodium)
2. homozygous for hemoglobin C (humans with two genes for hemoglobin C are invulnerable to malaria)
3. glucose-6-phosphates-dehydrogenase deficiency (needs trophozoites to synthesize DNA)
4. Duffy antigen absence (lack of Duffy antigen on red blood cells)

Question 30

Malaria Pathology

Answer 30

-symptoms of malaria are associated with synchronous cycles of erythrocyte lysis which produce fever cycles
-immunity gradually develops if the victim survives the acute stage of malaria (periodic episodes become less severe over time)
-prevention requires limiting contact with the mosquitoes carrying plasmodium

Question 31

What causes blackwater fever

Answer 31

p. falciparum
-cause extreme fever, large scale erythrocyte lysis, renal failure, and dark urine

Question 32

toxoplasma (apicomplexans)

Answer 32

toxoplasma gondii causes toxoplasmosis which results in fever, headaches, myalgia, sore throat, and enlarged lymph nodes in the head and neck
-although 25% of the worlds population is infected the majority of people are asymptomatic
-high risk populations are people with AIDS and the fetus of a pregnant women
-antibiotic treatment of pregnant women usually prevents transplacental infections but more aggressive treatments may be used for AIDS cases
-mammals and birds are reservoirs while cate are the definitive host but most infections are acquired by consuming undercooked meat

Question 33

cyptosporidium parvum (ampicomplexans)

Answer 33

-it causes zoonotic diseases cryptosporidiosis, which can result in severe diarrhea that can last up to two weeks
-the infection usually results from drinking contaminated water
-fecal-to-oral routes transmission can occur especially in day care facilities
-oral rehydration is used to treat the disease as drugs are ineffective against parasites

Question 34

helminths

Answer 34

-macroscopic, multicellular, eukaryotic worms
-their life cycles are complex as intermediate host are often needed to support the larval stages

Question 35

What are three groups of helminths

Answer 35

1. cestodes (tapeworms)
2. trematodes (flukes)
3. nematodes (roundworms)

Question 36

cestodes (tapeworms )

Answer 36

segmented flatworms with no digestive system belonging to phylum Platyhelminthes
-they have a scolex which allows it to attach to their host but it is not used for feeding
-their body segments are called proglottids which become filled with eggs and shed from the end
-the strobili are a string of proglottids
-they belong to the genus taenia (worm)

Question 37

trematodes (flukes)

Answer 37

flatworms with a partial digestive system that has ventral suckers which enable them to attach to the host tissues to obtain nutrients
-includes Platyhelminthes such as the blood fluke Schistosoma and the river fluke Clonorchis
-the snail is an intermediate host so schistosoman infections are often called snail fever

Question 38

nematodes (roundworms)

Answer 38

long cylindrical worms that taper at each end with a complete digestive system
-ex: ascaris, ancylostoma, and necator (both hookworms)

Question 39

What is the most common nematode infection worlwide?

Answer 39

ascariasis