Protozoa II - Toxoplasma, Neospora, Crypto, Giardia Flashcards
Name 5 genera to belong to Sarcocystidae.
Cystoisospora
Sarcocystis
Toxoplasma
Hammondia
Neospora
Cystoisospora
Sarcocystis
Toxoplasma
Hammondia
Neospora
The above all belong to which phylum, class, order and family?
Phylum Alveolata/Apicomplexa
Class Coccidea
Order Eimeriida
Family Sarcocystidae
What is TSAR?
Also known as phylum apicomplexa or alveolata. Previously, Sporozoa.
Definitive and intermediate hosts of T.gondii.
One species under Toxoplasma genus - that is, gondii (acultatively heteroxenous parasite).
Worldwide prevalence wherever cats are found.
Cats are definitive hosts.
Warm-blooded animals are intermediate hosts.
Able to infect most cells!
T.gondii transmission routes: (5)
- Fecal-oral (oocysts)
- Transplacental (tachyzoites)
- Lactogenic (tachyzoites)
- Organ transplantation (tachyzoites)
- Carnivorism (tissue cysts) through intermediate host ingestion.
Define Tachyzoite
Tachyzoite – form of toxoplasma gondii
Fast growing infective stage
- in neural and muscle tissues or in the blood
- Causes acute toxoplasmosis
- Eventually develops into bradyzoite in tissue cysts
Define Bradyzoite
Bradyzoite – form of Toxoplasma gondii
Slow growing infective stage
- cysts in tissues (also neurons and skeletal muscle cells)
- semi-dormant - causes chronic toxoplasmosis
T.gondii asexual stages are found in?
Facultative intermediate or paratenic hosts.
Not required for life cycle of the parasite.
In Accidental or “dead-end” hosts the parasite cannot complete the life cycle - nobody eats this host.
Describe When T.gondii undergoes a Direct/ homoxenous life cycle.
This would imply From cat to cat.
The intermediate host are not technically required but beneficial evolutionarily.
If t.gondii were to undergo Facultative indirect/ heteroxenous life cycle:
- From cat to paratenic host
- From paratenic host to cat
And a Life cycle without definitive host:
- From paratenic host to paratenic host
What is a Merogony in parasitology?
Also known as schizogony.
A form of asexual reproduction whereby a parasitic protozoan replicates its own nucleus inside its host’s cell and then induces cell segmentation.
Predilection site for T.gondii in the definitive host?
Intestinal cycle (only in cats)
Merogony/schizogony
- in intestinal epithelium
- invasion of enterocytes
- mild signs or none at all, mild diarrhea possible
Gametogony
- unsporulated oocysts shed with feces
- Usually once per life-time
- 2-5 days to sporulate
Patent period: shedding lasts 1-2 weeks.
Life cycle of Toxoplasma gondii In intermediate hosts? Predilection site etc.
Extraintestinal cycle occurs in intermediate hosts (which can also be cats).
● Formation of tachyzoites after infection with sporulated oocysts which hatch sporozoites (that develop into tachyzoites).
- Asexual reproduction by endodyogeny
- Tachys infect many different cell types!
- This is the Acute phase of toxoplasmosis!
Antibodies limit this phase.
● Then, formation of tissue cysts (bradyzoites) once the parasite has found tissue where it wants to stay. Stays there forever or until eaten by a cat.
- Asexual reproduction by endodyogeny
- Thousand of bradyzoites in microscopic cysts.
- Chronic/latent phase of toxoplasmosis!
define endodyogeny
a process of asexual reproduction, favoured by parasites such as Toxoplasma gondii.
It involves an unusual process in which two daughter cells are produced inside a mother cell, which is then consumed by the offspring prior to their separation.
This Acute phase of toxoplasmosis involves what life stage of T-gondii?
tachyzoites
● Formation of tachyzoites after infection with sporulated oocysts which hatch sporozoites (that develop into tachyzoites).
- Tachys infect many different cell types! Destroys host cells in the process and induces an acute immune response.
- This is the Acute phase of toxoplasmosis!
Antibodies limit this phase.
The Chronic/latent phase of toxoplasmosis involves what life stage of T-gondii?
bradyzoites in cysts
● Formation of tissue cysts (wih thousands of bradyzoites inside) once the parasite has found tissue where it wants to stay (after circulating the blood stream as tachyzoites).
These cause no symptoms typically.
Tissues that T. gondii favors: brain, liver, lungs and striated muscles.
Cysts stay there forever or until eaten by a cat.
In some instances, immunosuppression can cause reactivation of an old infection.
Describe Prenatal transmission = transplacental transmission of T.gondii.
Transplacental transmission of T.gondii can occur in humans, sheep, goats, cats and mice.
- Usually only by first infection during pregnancy.
- But in mice, intrauterine infection also possible during chronic toxoplasmosis.
Describe Lactogenic transmission of T.gondii.
Occurs during the acute phase of toxoplasmosis, with tachyzoites.
identify
Toxoplasma gondii unsporulated oocyst and sporulated oocyst (right).
Clinical signs of toxoplasmosis in cats.
Mostly in immunosuppressed cats: FIV, FeLV, therapy with glucocorticosteroid.
Non-specific symptoms: fever, loss of appetite, lethargy.
Depends on where the parasite replicates:
Respiratory, lymphadenopathy, hepatic, pancreatic, skeletal muscle, reproductive tract, neurological signs.
Ocular signs: uveitis, enlarged pupil, light sensitivity, blindness.
Prenatal infections: abortion, acute infection in kittens
Clinical signs of toxoplasmosis in dogs.
Dogs: Clinical signs uncommon
Pneumonia, fever, neurological and ocular signs .
Important: differential diagnosis for neosporosis.
Clinical signs of toxoplasmosis in ruminants.
Sheep and goats very susceptible to T. gondii. Cattle, horses less susceptible.
Usually inapparent infections - enlarged lymph nodes, no appetite, pneumonia.
Primary infections of pregnant animals are important because:
● I trimester: embryonic abortion - mummification or reabsorption
● II trimester: abortion, stillbirth
● III trimester: infected lamb
Prevention of toxoplasmosis.
Avoid infection in farm cats:
- No raw or undercooked meat
- No raw milk
- No hunting
- Clean cat litter box daily
No cats in farms
No oocyst transmission to farm animals via:
* feed
* water
* pasture
Rodent control
Free range vs. intensive farming
Toxoplasmosis in humans.
Transmission through:
- Oocysts (cats) (and contaminted vegetables)
- Tissue cysts (from Raw meat from farm animals)
“Flu-like” symptoms from the tachyzoite phase.
Chronic disease from the bradyzoite phase.
Immunodeficient person may have:
- Severe disease
- Respiratory, CNS, ocular, etc.
Human newborns can be infected transplacentally and suffer severe defects.
Diagnosis of toxoplasmosis
Acute systemic disease in cats via:
- Fecal flotation methods - oocysts in feces which are similar to Hammondia and Besnoitia oocysts! Thus, PCR for species identification.
- Cerebrospinal fluid, BAL, tissue aspirates, necropsy for detection of tachyzoites or bradyzoites.
- Serological testing - IgG and IgM antibodies (rule out seronegative patients).
If IgM high - active infection (but also seen in healthy cats).
If IgG high - latent infection (chronic).
Definitive diagnosis via the detection of tachyzoites in cytology or PCR.
Treatment of toxoplasmosis
There is no treatment for tissue cysts.
Clinical toxoplasmosis in dogs and cats:
- Clindamycin for at least 4 weeks
- If clindamycin not indicated: sulfadiazine plus trimethoprim several weeks.
- In case of uveitis: parenteral glucocorticoids.
In sheep: attenuated vaccine, Toxovac®
Describe Hammondia spp.
A protozoan, coccidian parasite to affect mostly mammals (but also birds). Hammondia are similar to Toxoplasma but they are NOT zoonotic.
H. hammondi:
Obligate heteroxenous life cycle.
Not zoonotic.
- final host: cat
- intermediate hosts: pigs, mouse, goats, hamsters, dogs
Usually not pathogenic to cats.
H. heydorni:
Also Not zoonotic.
- final host: dog, fox, coyote
- intermediate hosts: bovine, sheep,goats, camels, dogs
Usually not pathogenic to dogs.
Genus more similar to Neospora caninum than to Toxoplasma.
How to differentiate coccidian oocysts.
Hammondia oocysts are morphologically indistinguishable from one
another as well as from Toxoplasma and Neospora.
Describe Neospora caninum.
Only 1 species under the genus Neospora - G.caninum. NOT zoonotic. Found worldwide.
N.caninum is an important cause of abortion in cattle and cause of neurological signs in dogs!
Final hosts: dog and wolf
Intermediate hosts: cattle, sheep, goats, horse, dog, fox, chicken, wild birds.
Possible transmission ways:
* fecal-oral
* transplacental
* lactogenic
Transmission routes for neospora caninum. (3)
- fecal-oral
- transplacental
- lactogenic
Life cycle of Neospora caninum
Heteroxenous life cycle
- Definitive dog host contaminates environment with oocyst-carrying feces.
- Oocysts sporulate quickly in the environment.
- Infective oocysts ingested by intermediate host.
- N.neospora spread hematogenously as tachyzoites.
- Encystment of Neospora in the intermediate host’s neural or skeletal tissues (cysts contain bradyzoites).
- Carnivore host ingests meat with encysted Neospora bradyzoites.
Pre patent period: ≥ 5 days
Patent period: 2-3 weeks
Three infectious forms of Neospora caninum:
● Tachyzoites in the intermediate host (IH)
● Bradyzoites in tissue cysts (neural or skeletal muscles)
● Sporozoites in oocysts in final host feces
The final host of Neospora caninum gets the infection from the tissue cysts in an intermediate host. What happens next?
N.caninum undergoes gametogony in the final host and oocyst shedding comes next.
Oocysts are unsporulated upon excretion but sporulation outside is fast.
N.caninum Intermediate host gets infection from: (3)
1) Oocysts
- haematogenous spread of tachyzoites
- asexual development by endodyogeny
2) transplacental infection
- Seen in cattle, sheep, horses, dogs, cervids
- exogenous (new infection) and endogenous (reactivation of an old infection)
3) Lactation
- Seen in cattle and dogs
- Occurs also in later pregnancies
Pathogenesis and clinical signs of neosporosis in intermediate hosts when infection is from oocysts.
Infection from oocysts:
- Acute (tachyzoites) and chronic phase (tissue cysts).
- Destruction of host cells and tissue damage.
- Necrosis and inflammation of the placenta if animal is pregnant.
- Formation of cysts in neural and muscle tissues.
+ Transmission through lactation causes Neurological signs.
Pathogenesis and clinical signs of neosporosis in intermediate hosts when infection is from transplacental infection.
Transplacental infection:
a) mummified or absorbed fetus - abortion
beginning 3rd week (common in 5-6 week).
b) prenatally infected calves with neurological signs, weak, ataxia, exophthalmia, decreased reflexes.
c) healthy calf technically possible, but can develop disease later (2 months) and abort when an adult.
d) uninfected calf also possible but lucky.
+ Transmission through lactation causes Neurological signs.
Neospora caninum oocyst from dog.
Small, sub-spherical, smooth coat, no polar cap. When sporulated: 1: 2 :4 = 8 sporozoites
Describe Cryptosporidium spp.
Prevalent worldwide - affect at least in 200 different vertebrate species. Many spp. of Crypto with slight differences for host and predilection site.
Monoxenous or facultatively heteroxenous parasite.
Common symptom – long lasting watery diarrhea / dysentery.
Important pathogen in young calves, sheep and dogs.
Important zoonosis!
Oocysts very resistant outside, immediately sporulated when shed – so infectious!
Which species of Cryptosporidium affect humans?
C.parvum & C.hominis
Cryptosporidium spp. life cycle.
Infection by thick-walled oocysts which produce 4 sporozoites.
Sporozoite release in the small intestine.
Sporozoites attach to enterocytes – parasitophorous vacuole. They remain outside host cell cytoplasm, but inside a plasma membrane.
Trophozoite undergoes schizogony reproduction into type I meront (with 8 Type I merozoites inside).
Another round of schizogony in new enterocytes to produce type II meront (with 4 Type II merozoites inside).
The released merozoites become microgamont-microgametes (males) &
macrogamonts (females) which come together to form zygotes (gametogony, sexual repro).
The produced oocysts can be of 2 types: thick-walled (excreted) or thin walled (rupture for autoinfection).
Giardia belongs to what
phylum
class
order
family
phylum Excavata
class Trepomonadea
order Diplomonadida
family Hexamitidae
genus Giardia
giardiosis/giardiasis is caused by?
Giardia duodenalis (as its known today)
Used to be called G.lamblia and G.intestinalis.
In recent years, efforts have been made to standardize the naming of the organism to avoid confusion.
Morphology of Giardia duodenalis
4 pairs flagellae arise from the kinetosome complex (base of the flagellum, consisting of a circular arrangement of microtubules).
2 nuclei (=>Diplomonadida order!)
2 thin axostyles (microtubule sheets)
1 pair of curved median (parabasal) bodies
No mitochondria ja No Golgi apparatus.
Giardia duodenalis life cycle.
Min. infective dose:
- 10-25 cysts in humans
- 1-10 cysts in animals
Inside hosts, trophozoites emeerge from cysts and are active right away.
Trophozoites undergo asexual replication.
Progeny encyst on their way out the host body but both cysts and trophzoites are excreted.
The shed cysts are immediately infective! Can survive months outside.
Infection lasts a few days to a few months at which point shedding is intermittent.
giardia cysts and trophozoite
giardia cysts are smaller than isospora cysts
the more solid the poop, the more cysts.
the more runny the poop, the more trophozoites.
