Amebas; Sporozoa; Hemosporidians

Question 1

Entamoeba histolytica

Answer 1

Amoebic dysentery of man, Third most common cause of parasitic death in the world; pathogenic and harmless strains

Question 2

Entamoeba histolytica (hosts)

Answer 2

Humans, dogs, pigs, monkeys

Question 3

Entamoeba histolytica (morphology)

Answer 3

trophozoite and cyst forms

Precyst, cyst, metacyst

Question 4

Entamoeba histolytica (life cycle)

Answer 4

Trophozoites in large intestine begin encystment in firming stools
Trophozoite form found in stool of dysentery patients; cyst in semisolid stools; metacyst in formed stools
Metacysts infective to new host

Question 5

Entamoeba histolytica (pathology)

Answer 5

Pathogenic strains may ulcerate colon lining and invade bloodstream  skin, liver, lungs, etc. – dead end course – abscesses, etc.
Mildly affected hosts  lg. # cysts in feces (resistant to chlorine levels used to treat H2O; many serve as asymptomatic carriers

Question 6

Entamoeba histolytica (diagnosis, treatment, epidemiology)

Answer 6

Diagnosis:
Trophs or cysts in fecal sample – serial direct smears

Treatment:
Several drugs work – metronidazole drug of choice

Epidemiology:  
Prevalence 5% in U.S.
Prevalence 40% - tropical
Incidence higher among gay men
Oral-anal contact

Question 7

Family Vahlkamphidae

Answer 7

Naegleria fowleri – facultative
Causes rare condition called
Primary Amebic Meningoencephalitis (PAM), otherwise known as “Brain Eating Ameba”

Rapidly fatal – transmitted through water entering nasal passages (especially hot pools, or stagnant water in the summer)

Found in the municipal water supply in three parishes of Louisiana in the last few years

Question 8

Family Hartmannellidae

Answer 8

Acanthamoeba sp. – Facultative
Rarely causes keratitis
The most common ameba of water and soil

Question 9

Coccidia

Answer 9

Phylum Apicomplexa

1-2 hosts required; reproduce by phases of asexual & sexual reproduction

Question 10

Toxoplasma gondii (final host)

Answer 10

cats

Question 11

Toxoplasma gondii (IH)

Answer 11

Many mammals, birds, humans

Humans most susceptible: Unborn fetus and immunosuppressed

Question 12

Toxoplasma gondii (life cycle)

Answer 12

Cat infected by ingestion of sporulated oocysts or tissue cysts  intestinal stages  sexual repro  pass oocysts in3-8 days; oocysts sporulate in 1-5 days to become infective. May also have extra-intestinal stages tissues infected – brain, muscle, retina, etc. (this occurs in IH). IH infected by ingestion of sporulated oocysts or tissues cysts as well.

Question 13

Toxoplasma gondii (incidence and pathology)

Answer 13

Incidence:
Transplacental - ̴3500 congenitally infected babies/year – U.S. – early embryonic death, stillbirth, retardation, blindness, etc.

Pathology:
Most humans – asymptomatic – mild cold/flu-like symptoms
Fetus – as above
Immunosuppressed – may be fatal

Question 14

Toxoplasma gondii (pathology in animals)

Answer 14

Pathology in Animals
Cat: usually no illness with intestinal stages; if serving as IH, may develop serious muscle or nervous disorders
Most other mammals may develop muscle inflammation or CNS disease
Sheep: especially prone to stillbirths/abortions

Question 15

Toxoplasma gondii (diagnosis)

Answer 15

Diagnosis
Human/Other IHs
demonstrate organism in biopsy or autopsy study of tissues
ELISA to demonstrate antibody titer
Women contemplating pregnancy may want to have testing prior to conceiving; if has + antibody titers, not generally susceptible

Cat
Oocysts on fecal exam – direct smear or flotation
Antibody titers
Organism in tissue samples if IH

Question 16

Toxoplasma gondii (prevention)

Answer 16

Avoid eating undercooked meat or unpasteurized milk
Freezing kills most cysts
Wash hands/utensils well after handling meat; do not cross- contaminate fresh foods
Wash raw fruits/vegetables well
Wear gloves when gardening
Cover sandboxes when not in use
Maintain sanitary conditions – flies or cockroaches can carry toxo oocysts from cat feces to food

Question 17

Cryptosporidium sp (hosts)

Answer 17

Hosts:
Lack of host specificity – animals serve as reservoir hosts for human infection
Opportunistic parasite of humans, esp. children and immunosuppressed
Live in GI or respiratory epithelial cells

Question 18

Cryptosporidium sp (diagnosis, pathology, treatment)

Answer 18

Diagnosis
Oocysts in feces – special flotation/stain

Pathology
AIDS patients – profuse watery diarrhea of several months duration
Immunocompetent – varies – no signs to self-limiting diarrhea up to 10 days duration

Treatment (Tx)
None effective

Question 19

Cryptosporidium sp (transmission)

Answer 19

Fecal-oral contamination
Municipal water supplies
Swimming pools – chlorination doesn’t kill

Question 20

Eimeria sp.

Answer 20

Hosts: Vertebrates – numerous host specific species

Question 21

Isospora sp.

Answer 21

Gastrointestinal disease in young
Hosts:
I. felis, I. rivolta – cats

I. canis – dogs

I. belli – humans in tropics – severe disease in AIDS patients

Question 22

Besnoitia sp.

Answer 22

Final Host: Cat
IH: Cattle/related animals
Pathology: In cattle, various signs, infertility, even death

Question 23

Sarcocystis sp.

Answer 23

Final Hosts: Carnivores (humans for some species)
IH: Herbivores
Life Cycle: FH infected by eating tissue cyst in herbivores (very prevalent) – herbivores infected by ingesting sporocysts from carnivore feces.
Pathology: Non-pathogenic to signs like anorexia, fever, lameness, anemia, wt. loss, abortion, death

Question 24

Equine Protozoal Myeloencephalitis

Answer 24

(EPM) Sarcocystis neurona
IH: Horses, birds
FH: Opossums (shed oocysts in stool)
Severe neurologic disease

Question 25

Pneumocystis carinii

Answer 25

Classification – Fungal or protozoan??
Hosts: Many mammals
Importance: Interstitial pneumonia in immunosuppressed – important cause of death in AIDS patients

Question 26

Malarial Organisms

Answer 26

Plasmodium sp.
Haemoproteus sp.
Leukocytozoon

Question 27

Plasmodium sp.

Answer 27

Hosts: Humans (4 species), primates, rodents, reptiles, birds, etc.
IH: Mammalian – Anopheles mosquitoes
Avian – Culicoides sp.
Life Cycle: Stages in RBCs/hepatocytes of vertebrate  transmitted to mosquito during blood meal  development in mosquito  to vertebrate during feeding
Pathology: generalized
Cyclic bouts of chills/fever with sometimes other complications from hemolysis of RBCs – also cerebral signs, pulmonary edema, shock, etc.
Considered the most important human disease worldwide
Eradicated in U. S. in 1950s – mosquito control

Question 28

Haemoproteus sp.

Answer 28

IH: Birds, reptiles
FH: flies
Pathology: slight to none
Morphology: Elongate, horseshoe-shaped cells embracing RBC nucleus

Question 29

Leukocytozoon

Answer 29

IH: Birds
FH: Flies
L. simondi – acute fatal disease of ducks/geese
L. smithi – turkeys
Morphology: Invade RBCs, lymphocytes, monocytes – greatly distort cell shape

Question 30

Piroplasms

Answer 30

Family Babesiidae

Cytauxzoon felis

Question 31

Family Babesiidae

Answer 31

Pyriform, round, or oval parasites of blood cells of mammals and various tissues of ticks.

Question 32

Babesia bigemina – Texas Cattle Fever

Answer 32

Host: Cattle
IH/Vector: tick, Boophilus annulatus – very host specific 1-host tick; transovarian transmission of B. bigemina occurs
Pathology: Hemolysis  Severe anemia
Adults more severely affected
History: Smith/Kilbourne – TA&M researchers discovered life cycle in 1880s; disease eradicated in U.S. about 1940 by requiring cattle be dipped for ticks
Tx: Tetracyclines, quinicrine, etc.

Question 33

Cytauxzoon felis

Answer 33

Cytauxzoonosis
Rapidly fatal disease of cats – rural wooded areas of Gulf Coast states
Hemolytic anemia – death within a few days
Blood smear: Organisms with light blue cytoplasm and dark red nucleus within RBCs
Bobcat or American Lynx – gets parasitemia but no disease; may be reservoir host