Amebas; Sporozoa; Hemosporidians Flashcards by Morgan Hildebrand

Entamoeba histolytica

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

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Entamoeba histolytica (hosts)

Humans, dogs, pigs, monkeys

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Entamoeba histolytica (morphology)

trophozoite and cyst forms

Precyst, cyst, metacyst

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Entamoeba histolytica (life cycle)

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

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Entamoeba histolytica (pathology)

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

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Entamoeba histolytica (diagnosis, treatment, epidemiology)

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

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Family Vahlkamphidae

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

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Family Hartmannellidae

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

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Coccidia

Phylum Apicomplexa

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

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Toxoplasma gondii (final host)

cats

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Toxoplasma gondii (IH)

Many mammals, birds, humans

Humans most susceptible: Unborn fetus and immunosuppressed

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Toxoplasma gondii (life cycle)

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.

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Toxoplasma gondii (incidence and pathology)

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

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Toxoplasma gondii (pathology in animals)

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

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Toxoplasma gondii (diagnosis)

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

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Toxoplasma gondii (prevention)

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

Cryptosporidium sp (hosts)

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

Cryptosporidium sp (diagnosis, pathology, treatment)

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

Cryptosporidium sp (transmission)

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

Eimeria sp.

Hosts: Vertebrates – numerous host specific species

Isospora sp.

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

I. canis – dogs

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

Besnoitia sp.

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

Sarcocystis sp.

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

Equine Protozoal Myeloencephalitis

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

Pneumocystis carinii

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

Malarial Organisms

Plasmodium sp. Haemoproteus sp. Leukocytozoon

Plasmodium sp.

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

Haemoproteus sp.

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

Leukocytozoon

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

Piroplasms

Family Babesiidae | Cytauxzoon felis

Family Babesiidae

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

Babesia bigemina – Texas Cattle Fever

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.

Cytauxzoon felis

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