Parasitology (protazoa) Flashcards
Protozoa general characteristics
Unicellular, eukaryotic organisms
* Often host specific
* Asexual and maybe sexual reproduction in vertebrate host
* Numbers in vertebrate host may increase by reinfection or multiplication (microparasites)
* Individual can transform into new stage in final host and go on to infect new host (ex. Giardia)
* Diagnostic stages seen in fecal samples called oocysts or cysts
apicomplexa
protazoan
intracellular
divided into:
* Coccidia type organisms (based in the GI tract)
* Hemosporozoa (blood parasites - hemoparasites)
coccidia
apicomplexa
Sexual and asexual reproduction
Most are parasites of the GI tract
Both direct and indirect life cycles
Usually host specific for host where sexual reproduction occurs
Clinical disease primarily related to GI tract: diarrhea most common sign
Usually diagnosed by identification of stage specialized for transmission in feces: oocyst
Coccidiosis
GI disease caused by coccidia
Usually a disease of young animals in combination with environmental factors
* Heavy exposure to oocysts
* Stress
Disease caused by destruction of cells as coccidia stages emerge to continue their life cycle
Pathogenicity of each coccidia species affected by
* Cell type infected. (ex, infection of epithelial cells at tips of villi results in less damage than infection of regenerative cells at base of villi - each species uses specific cells)
* Number of generations of multiplication
Coccidia oocysts
- Passed in feces
- Thin shell with single cell inside – smaller than strongylid eggs (12-50 µm)
- Highly resistant to environmental conditions: may survive “≥” 1 year in protected locations (out of direct sun or desiccation)
- Undergo sporogony in the environment: sporulated oocyst
- Single cell undergoes division in environment to form sporocysts containing sporozoites
sporulated oocyst
infective stage of coccidia
Eimeria
genus of coccidia
Common intestinal parasite of Ruminants, Birds, Rodents, Pigs, Others
Very host specific
Eimeria life cycle
coccidia
sporogony
1. oocyst released in feces
2. sporulation occurs, becomes sporulated oocyst (infective)
3. host swallows sporolated oocyst
schiszogony
4. sporocysts released inside host and invade gut cells
5. schzogony inside cells (maturation)
6. merzoites released from cells
7. some merzoites reinfect cells
gametogony
8. some merzoites mature into male and female gametes then into oocyst
Ruminant coccidiosis
Ruminants infected with multiple host-specific Eimeria species worldwide
Cattle: Eimeria bovis and E. zuernii most pathogenic
Th1 immunity (intracellular)
All animals routinely exposed from an early age
* immunity gradually develops
* mainly affects young animals
Clinically:
* Mainly Subclinical
* can be mild to severe (Diarrhea, with blood if very severe, Fecal stained perianal area, Straining to defecate and subsequent rectal prolapse, Weight loss and/or stunting, Death)
Pathology influenced by:
* Eimeria species present
* Infection dose
* Inflammatory/immune response
* Related stress
ruminant coccidosis diagnosis and control
Diagnosis
* All young animals have oocysts in manure by a few months of age
* Presence of oocysts alone doesn’t provide diagnosis of coccidiosis
* Clinical judgement important
Control
* Fix environmental elements that disrupt balance
* Improve sanitation, feed off the ground
* Fix damp spots, good for oocysts
* Reduce stress
* Use of coccidial drugs
poultry coccidiosis
- Each type of bird host infected with multiple different Eimeria species
- One of the most important production diseases of confined poultry: several billion $ spent world wide annually for prevention in broilers
- Also can be a problem in backyard chicken flocks
- Coccidia species vary in pathogenicity
- Different sites of infection can produce different signs
Prevention
* Anticoccidial drugs
* Vaccine composed of live oocysts
* Backyard birds may have food containing drugs for prevention or be treated if disease develops
* Other domestic and wild birds have their own species that can be pathogenic
coccidia in dogs and cats
Enteric coccidiosis caused by coccidia in genus Cystoisospora
host specific
unsporulated large oocyst: l. canis, l. felis (40um)
unsporulated meduim oocyst: l. ohioensis-like (dog), l. rivolta (cat) (25um)
canine and feline coccidiosis life cycle
PPP 10-14 days
rodents can be paratenic hosts
rest is like emeria:
sporogony
1. oocyst released in feces
2. sporulation occurs, becomes sporulated oocyst (infective)
3. host swallows sporolated oocyst
schiszogony
4. sporocysts released inside host and invade gut cells
5. schzogony inside cells (maturation)
6. merzoites released from cells
7. some merzoites reinfect cells
gametogony
8. some merzoites mature into male and female gametes then into oocyst
Canine and feline coccidiosis clinical signs and diagnosis
diarrhea
young animals
diagnosis:
* Oocysts in the feces: large (“~”40 “μ”m) and small (“~”20 “μ”m) oocysts in both cats and dogs from different species
* Coprophagy in dogs leads to presence of Eimeria oocysts in canine feces: spurious parasites
Cystoisospora suis
coccidia of pigs
Neonatal diarrhea, stunting, death if compounded by other factors
Hepatic coccidiosis of rabbits
Eimeria stiedae: Parasites in the bile ducts, causes severe damage
Also have intestinal coccidiosis
patent infection in coccidia
can see oocysts in feces
when life cycle in host is completed
toxoplasma gondii
Important zoonotic parasite
Coccidian species with felid as DH
toxoplasma gondii life cycle
Felids are only definitive host
* Sexual stages only in cats
Can be direct or with intermediate host
Three infectious stages: the tachyzoites (in groups or clones), the bradyzoites (in tissue cysts), and the sporozoites (in sporulated oocysts).
Other warm blooded animals act as “intermediate” hosts
When any warm-blooded animal eats sporulated oocysts:
* Sporozoites emerge
* Penetrate intestine
* Undergo rapid multiplication in cell: tachyzoites, which spread to all other tissues
* Eventually conversion occurs to cysts containing bradyzoites (infective stage as well)
Rest same as before:
sporogony
1. oocyst released in feces
2. sporulation occurs, becomes sporulated oocyst (infective)
3. host swallows sporolated oocyst
schiszogony
4. sporocysts released inside host and invade gut cells
5. schzogony inside cells (maturation)
6. merzoites released from cells
7. some merzoites reinfect cells
gametogony
8. some merzoites mature into male and female gametes then into oocyst
Bradyzoite
zoite of Apicomplexa with slow multiplication in cysts (slow, less dz)
infective
in tissue cysts
rapidly multiplying tissue stage, pathogenic stage
slowly dividing stage in cysts
Tachyzoite
zoite of Apicomplexa undergoing quick asexual multiplication in a host cell (fast, more dz)
in groups or clones
infective
rapidly multiplying tissue stage, pathogenic stage
sporozoites
in sporolated oocyst of toxoplasma gondii
infective
toxoplasma gondii in cat infections
Ingesting bradyzoites in cysts
* Most common and efficient route
* Get intestinal stages with multiplication and gametogony
* Also leads to tachyzoites and bradyzoites (tissue cysts)
Ingesting sporulated oocysts or tachyzoites
* Less efficient, may not lead to patent infection
* Tissue multiplication with tachyzoites and bradyzoites
* Some may go back to GI and complete cycle
non felid toxoplasma gondii infections
Several ways:
* Ingesting oocysts (sporozoites)
* Ingesting bradyzoites in cysts
* Congenitally (pregnant women)
* Rare tachyzoite transmission
Result of all these routes: tachyzoite multiplication and then bradyzoites in cysts
Neospora caninum
like toxoplasma but in dogs
May not use direct transmission at all – dogs must ingest bradyzoites in cysts in intermediate hosts
Intestinal cycle in dog – no clinical signs
Infection during pregnancy can produce infected litters, puppies develop paralysis – rare
Not known to be a zoonosis
Greatest importance in cattle
* Initial infection can cause abortion, or lead to persistent infection that can infect subsequent pregnancies and may lead to abortion
* Calves can be born live with persistent infection and later abort
Sarcocystis spp.
coccidia
Obligate indirect life cycle
Many species, often host specific for both intermediate and definitive host
Cyst in intermediate host called a sarcocyst (usually in muscle)
Sarcocystis spp. diagnosis
Sporulated oocysts (arrow) passed in feces but wall breaks down releasing individual sporocysts (infective stage) with sporozoites
Immediately infective (not like regular coccidia)
Sporocysts are small (~12 μm) so often missed in fecal exams of definitive hosts
Sarcocystis neurona
It’s the most important species of the genus Sarcocystis
It’s the primary cause of equine protozoal myeloencephalitis (EPM)
Horse is an dead-end host
Opossum definitive host, horses ingest sporocysts in feces
cryptosporidium
Very tiny (about 5 μm)
No sporogony in environment: immediately infective
Location in cells is immediately under the cell membrane of the microvilli: intracellular, extracytoplasmic (does not look intracellular on histopathology)
zoonotic
Cryptosporidium spp. lifecycle
sporogony in intestine (not environemnt)
schiszogony
4. sporocysts released inside host and invade gut cells
5. schzogony inside cells (maturation)
6. merzoites released from cells
7. some merzoites reinfect cells
gametogony
8. some merzoites mature into male and female gametes then into oocyst
Cryptosporidium spp. lifecycle
sporogony in intestine (not environemnt)
schiszogony
4. sporocysts released inside host and invade gut cells
5. schzogony inside cells (maturation)
6. merzoites released from cells
7. some merzoites reinfect cells
gametogony
8. some merzoites mature into male and female gametes then into oocyst
Babesia life cycle
MUST be transmitted vertically in ticks (infected female lays eggs), can be transmitted between tick life stages
rest is the same:
sporogony
1. oocyst released in feces
2. sporulation occurs, becomes sporulated oocyst (infective)
3. host swallows sporolated oocyst
schiszogony
4. sporocysts released inside host and invade gut cells
5. schzogony inside cells (maturation)
6. merzoites released from cells
7. some merzoites reinfect cells
gametogony
8. some merzoites mature into male and female gametes then into oocyst
babesia pathogenesis and diagnosis
Only infect RBCs (intracellular)
Destruction of RBC when merozoites released
Antigens released absorbed onto other cells which then are removed by host
Result is anemia (hemolytic most important, but also autoimmune)
Diagnosis
* Detection of organisms in Giemsa stained smears in acute infection
* Serology
* PCR
Giardia duodenalis life cycle
- Following ingestion, organism excysts, releasing trophozoites
- Trophozoite (teardrop shaped) has two nuclei, multiple flagella and sucking disc, relocates as needed
- Asexual multiplication
- Organisms in posterior small intestine encyst
- Cysts have 4 nuclei (2 per trophozoite), pass out with feces
Giardia diagnosis
Diarrhea, vomiting
cysts in fecal samples, antigen tests
Trypanosoma cruzi
intermediate host: Triatomine bug, kissing bug
Zoonotic
Blood feeding
Kissing bug feeds on dog, deposits organism near bite site, trypanosomes rubbed into opening
Other routes of infection
* Ingestion of infected animal or bug
* Direct blood contact
* Vertical transmission
Clinical signs
* Infection can be asymptomatic
* Some dogs develop chronic myocarditis
* In humans also cause heart disease
