Parasitology (protazoa)

Question 1

Protozoa general characteristics

Answer 1

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

Question 2

apicomplexa

Answer 2

protazoan
intracellular
divided into:
* Coccidia type organisms (based in the GI tract)
* Hemosporozoa (blood parasites - hemoparasites)

Question 3

coccidia

Answer 3

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

Question 4

Coccidiosis

Answer 4

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

Question 5

Coccidia oocysts

Answer 5

• 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

Question 6

sporulated oocyst

Answer 6

infective stage of coccidia

Question 7

Eimeria

Answer 7

genus of coccidia
Common intestinal parasite of Ruminants, Birds, Rodents, Pigs, Others
Very host specific

Question 8

Eimeria life cycle

Answer 8

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

Question 9

Ruminant coccidiosis

Answer 9

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

Question 10

ruminant coccidosis diagnosis and control

Answer 10

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

Question 11

poultry coccidiosis

Answer 11

• 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

Question 12

coccidia in dogs and cats

Answer 12

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)

Question 13

canine and feline coccidiosis life cycle

Answer 13

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

Question 14

Canine and feline coccidiosis clinical signs and diagnosis

Answer 14

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

Question 15

Cystoisospora suis

Answer 15

coccidia of pigs
Neonatal diarrhea, stunting, death if compounded by other factors

Question 16

Hepatic coccidiosis of rabbits

Answer 16

Eimeria stiedae: Parasites in the bile ducts, causes severe damage
Also have intestinal coccidiosis

Question 17

patent infection in coccidia

Answer 17

can see oocysts in feces
when life cycle in host is completed

Question 18

toxoplasma gondii

Answer 18

Important zoonotic parasite
Coccidian species with felid as DH

Question 19

toxoplasma gondii life cycle

Answer 19

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

Question 20

Bradyzoite

Answer 20

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

Question 21

Tachyzoite

Answer 21

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

Question 22

sporozoites

Answer 22

in sporolated oocyst of toxoplasma gondii
infective

Question 23

toxoplasma gondii in cat infections

Answer 23

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

Question 24

non felid toxoplasma gondii infections

Answer 24

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

Question 25

toxoplasma gondii clinically in cats

Answer 25

**High prevalence of antibodies** in cats, 50% or more Most infections in cats probably occur in **young cats** * **Immunity develops**, prevents recurrence of oocyst shedding Only about 1% oocyst prevalence in feline fecal samples * Cats **shed oocysts for just a few weeks, reshedding unlikely** **Disease in cats is rare** * Disease caused by tissue tachyzoites

Question 26

toxoplasma gondii dz in other animals

Answer 26

Common cause of **abortion in small ruminants** * Occurs when first infection takes place during pregnancy * **Immunity develops** and protects subsequent pregnancies * tachyzoites is pathogenic stage **Cattle less susceptible** to infection, abortion not seen Sporadic disease in some circumstances * Exotic animals in zoos, otters, marine mammals, birds, animals that are immunosuppressed

Question 27

toxoplasma gondii public health

Answer 27

human infections by: * **cysts in meat, food, water contaminated w cat feces** * blood transfusion, organ transplant * transplacentally Possible outcomes of infection in humans: Immunocompetent adults: * **Asymptomatic** * Flu-like illness, **ocular lesions** Immunosuppressed individuals * First infection or disease from reactivation of tissue cysts * Encephalitis Congenital infection, initial infection of **woman during pregnancy** * **Abortion, Stillbirth** * Mental deficit, visual lesions, deafness

Question 28

Neospora caninum

Answer 28

**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

Question 29

Sarcocystis spp.

Answer 29

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)

Question 30

sarcocyst

Answer 30

Cyst in intermediate host of sarcocystis

Question 31

Sarcocystis spp. diagnosis

Answer 31

**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

Question 32

Sarcocystis spp. clinically

Answer 32

Lots of species in vertebrates **Carnivore definitive host** **Prey intermediate host** In **definitive host clinically unimportant** Disease may occur in heavy **infections of domestic animal intermediate host but usually uncommon or rare** One major exception: Sarcocystis neurona

Question 33

Sarcocystis neurona

Answer 33

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

Question 34

Sarcocystis neurona clinically

Answer 34

**Most infections asymptomatic** In some horses parasites in the **CNS** produce disease: * Lameness * Stumbling * Muscle atrophy * Paresis Definitive diagnosis and treatment are difficult Neospora hughesi can also cause EPM, but S. neurona more common

Question 35

cryptosporidium

Answer 35

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

Question 36

Cryptosporidium spp. lifecycle

Answer 36

**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

Question 37

Cryptosporidium spp. lifecycle

Answer 37

**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

Question 38

What dz does Cryptosporidium cause?

Answer 38

Common cause of **diarrhea in neonatal dairy calves** * Not often fatal unless other stressors also present * No treatment available, will resolve as immunity develops * Control through sanitation

Question 39

Cryptosporidium parvum

Answer 39

bovine cryptosporidium zoonotic, causes diarrhea

Question 40

Cryptosporidium hominis

Answer 40

human dz causes diarrhea can be fatal in immunocompromised

Question 41

Babesia spp.

Answer 41

* Each species is quite **host specific** for both IH and DH * Organism can be transmitted **from one tick stage to another** (transstadial or horizontal) and **from female tick to eggs** (transovarial or vertical) * **Immunity** limits parasitemia, but animal may remain persistently infected without clinical disease

Question 42

Babesia life cycle

Answer 42

**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

Question 43

babesia pathogenesis and diagnosis

Answer 43

**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

Question 44

Babesia spp. in dogs

Answer 44

most important: **B. canis** (3 subspecies, maybe species) * **Anemia, splenomegaly, fever** * Not common, except in far south * **Tick-transmitted** species (brown dog tick or Rhipicephalus sanguineus) Another species (**B. gibsoni**) occurs more widely, also **transmitted by fighting** Dogs can be **treated but may remain carriers**

Question 45

Babesia spp. in cattle

Answer 45

Bovine babesiosis (Texas Cattle Fever) was **eradicated from the US** in the early 20th century through mandated dipping cattle It’s a very **serious livestock disease**. So, the US got rid of the tick (Rhipicephalus microplus, former known as Boophilus microplus)

Question 46

Cytauxzoon felis life cycle

Answer 46

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

Question 47

flagellate parasites

Answer 47

Have **flagellum/flagella in at least one stage** of the life cycle Some extracellular, some have both **intracellular and extracellular** stages

Question 48

Giardia duodenalis

Answer 48

flagellate Cause of **diarrhea in animals and humans** Parasite of the **small intestine** Exits in two forms: **trophozoite and cyst** Trophozoite: general term, active feeding stage of protozoa Direct life cycle affects all domestic, wild animals, birds, reptiles

Question 49

Giardia duodenalis life cycle

Answer 49

1. Following ingestion, **organism excysts, releasing trophozoites** 2. Trophozoite (teardrop shaped) has two nuclei, multiple flagella and sucking disc, relocates as needed 3. **Asexual multiplication** 4. Organisms in **posterior small intestine encyst** 5. Cysts have 4 nuclei (2 per trophozoite), pass out with feces

Question 50

Giardia duodenalis pathogenesis

Answer 50

Most infections **asymptomatic but can produce diarrhea** Pathogenesis * Pathology caused by **trophozoites** * Trophozoites attach to the surface of enterocytes in the small intestine, usually in the proximal portion. * Attachment causes **damage to enterocytes**, resulting in functional changes and blunting of intestinal villi, which leads to maldigestion, malabsorption, and diarrhea. * **Malabsorptive diarrhea—fatty stool**

Question 51

Giardia duodenalis cysts

Answer 51

Cysts **survive for awhile in the environment ** Survive a **few months in cool water**, less time out of water probably * Has led to idea that is a waterborne parasite but it doesn’t have to be in water Susceptible to desiccation, harsh weather conditions **Susceptible to disinfectants** but not to level of bleach in water supplies

Question 52

Giardia diagnosis

Answer 52

Diarrhea, vomiting cysts in fecal samples, antigen tests

Question 53

Is giardia zoonotic?

Answer 53

Kind of. Giardia divided into categories. Most dogs infected with different type than human. More likely human to dog than dog to human.

Question 54

Trichomonad parasites

Answer 54

**Flagellates of the GI tract and reproductive tract** Undulating membrane (recurved flagellum that is attached) and tuft of anterior flagella **No cyst stage, only trophozoites**

Question 55

Tritrichomonas foetus

Answer 55

**Flagellate of cattle** Inhabits the **uterus of cows and preputial cavity of bulls** * Can produce **infertility, early embryonic death, pyometra**, fetal death at 60-120 days * Causes early **embryonic death, not abortion** because it makes the **endometrium inhospitable to implantation** **Only exists as trophozoite, no cyst** Only **venereal transmission** Diagnosis: * collecting a preputial scraping sample from bull * PCR most sensitive test **No effective approved treatment** * Cull infected bulls * Rest infected cows

Question 56

Hemoflagellates (Trypanosomes)

Answer 56

Very important group of animal and human parasites worldwide Transmitted by **insects vectors** Found in mammals in 2 forms: * **Trypomastigote: extracellular in blood** * **Amastigote: intracellular**

Question 57

Trypanosoma cruzi

Answer 57

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

Question 58

Leishmania spp.

Answer 58

flagellate, **Zoonotic** **Intracellular in the monocyte-macrophage** phagocytic system of the host **Human and canine** parasite Cutaneous and visceral forms of disease but both involve **skin lesions** Route of infection * Transmission from the bite of an **infected sand fly** * Possible transmission from **skin lesions from FIGHTING** * Vertical transmission Visceral leishmaniasis: **organisms generalized** * Non pruritic dermatitis and alopecia * Generalized lymphadenopathy * **Chronic wasting** * Once disease develops leads to death if untreated **Cutaneous** leishmaniasis: organisms **localized to lesion** * Dogs present with single lesion * Better prognosis | know TRANSMISSION THROUGH FIGHTING

Question 59

Visceral leishmaniasis

Answer 59

organisms **generalized** Non pruritic dermatitis and alopecia Generalized **lymphadenopathy** **Chronic wasting** Once disease develops leads to **death** if untreated

Question 60

Cutaneous leishmaniasis

Answer 60

organisms **localized to lesion** Dogs present with **single lesion** Better prognosis