protozoan parasites with indirect life cycles

Question 1

what is a sarcicystidae?

Answer 1

○ Phylum apicomplexa
○ Similar to eimeria but have indirect life cycles
○ Asexual stages occur in intermediate hosts
○ Asexual and sexual stages occur in definitive hosts
-Examples- toxoplasma, neospora, sarcocystitis

Question 2

what is toxoplasma gondii?

Answer 2

-Apicomplexan protozoan parasite that infects most species of warm blooded animals, including humans, causing the disease toxoplasmosis
-Cat family (felidae) are the only known definitive hosts for the sexual stages to T.gondii and thus are the main reservoirs of infection
-toxoplasmosis in an important cause of abortion and foetal abnormality in humans, sheep and goats
-Also causes significant infections in immunocompromised humans e.g. In HIV/AIDs
-Important zoonosis

Question 3

what is the definitive and Intermediate hosts of toxoplasma gondii life cycle?

Answer 3

Definitive hosts
-domestic cat
-other felids

Intermediate Hosts
-rodents
-birds

Question 4

what happens in the life cycle of toxoplasma gondii?

Answer 4

-The parasite multiplies within the intestine of difinitive host cats and following the sexual cycle of gametology, oocysts are shed in the cats faeces
-Oocysts sporelate in and contaminate the environment and infect intermediate hosts which inadvertantly consumed them
-Within these intermediate hosts, the parasites migrate widely and form tissue cysts which are infective for cats which predate the intermediate hosts

Question 5

what are the accidental hosts of toxoplasma gondii?

Answer 5

-sheep
-pigs
-other mammals
-humans

Question 6

how can humans be accidental hosts?

Answer 6

-inadvertently consume oocysts contaminating food or drinking water or by handling litter trays with insufficient hand hygiene
-may be infected by consuming cysts in tissues of raw or undercooked meat of sheep and pigs

Question 7

what is the life cycle of cats, the definitive hosts of toxoplasma gondii?

Answer 7

-generally become infected by ingesting infected mammals or birds
-shed oocysts which become infectious to most mammals or birds
-most commonly infected as kittens
-shed large numbers of oocysts
-but only for 1-2 weeks
-develop immunity

Question 8

immediate and accidental hosts are infected by?

Answer 8

-sporulated oocysts- sporulate in 1-5 days
-carnivorism/omnivorism or
-transplacentally- most important in humans, sheep and goats

Question 9

what are tachyzoites?

Answer 9

-rapidly multiplying crescent shaped in the development of an acute tissue phase of infection

Question 10

what are bradyzoites?

Answer 10

-slow-growing, comma-shaped forms
-found in clusters with cysts in the tissues
-chiefly muscles and th brain, in chronic (latent) toxoplasmosis

Question 11

how do tachyzoites move?

Answer 11

-Gliding, flexing, undulating and rotating
-no externally visible means of locomotion such as cilia, flagella or pseudopodia
-motion affected by apical complex

Question 12

what is the lytic cycle of tachyzoites?

Answer 12

-enter host cells by actively penetrating cell membrane, or by phagocytosis
-multiply asexually repeatedly within host cells
-two progeny form within and consume the parent parasite: endodyogeny
-host cell ruptures when it can no longer support the growth of tachyzoites

Question 13

What is the endodyogeny cycle??

Answer 13

1. two inner membrane complexes develop in middle of cell from rudimentary conoid and microtubule organising centre
2. nucleus and mitochondria divide into membranous outlines
3. nascent apical organelles divide and inner membrane complex from mother dissociated
4. cleavage furrow
5. division continues to posterior end

Question 14

what occurs in the development of bradyzoites?

Answer 14

-multiply asexually within host cells by repeated endodyogeny
-tissue cysts appear 7-10 days post-infection
-contain hundreds of brazyzoites
-within host cell cytoplasm
-cyst wall
-quiescence

Question 15

what is the cyst (pseudocyst) wall?

Answer 15

-composed of host cell and parasite materials
-resistance to digestion by gastric juice
–> protection from host immune response

Question 16

what does the immune response normally prevent?

Answer 16

dissemination of tachyzoites

Question 17

how do cats acquire toxoplasma by ingesting infected intermediate hosts?

Answer 17

-ingest quiescent bradyzoites occupying tissue cysts
-ingest rapidly multiplying tachyzoites in recently infected intermediate hosts

Question 18

what happens to oocysts once ingested by the feline definitive host?

Answer 18

-excreted unsporulated in the faeces
-sporulates to become infectious 1-5 days after excretion

Question 19

what is toxoplasmosis like in sheep and goats?

Answer 19

-acute phase rarely observed
-affects non immune pregnant females
-clinical signs are dependent on the stage of pregnancy

Question 20

what are the signs of toxoplasmosis in sheeps and goats in the early, mid and late stage of gestation
abortion- barren ewe
abortion, lesions in cotyledons of placenta and foetus or mummification of dead foetus
still born or weak lambs

Answer 20

Early - abortion- barren ewe
Mid - abortion, lesions in cotyledons of placenta and foetus or mummification of dead foetus
Late - still born or weak lambs

Question 21

what are the appearances of toxoplasmosis in sheep and goats?

Answer 21

-grossly the placental cotyledons have characteristic 1-2mm white or yellow focal lesions

Question 22

what is infection of toxoplasmosis in humans acquired by?

Answer 22

-Eating raw or undercooked meat
-Unpateruased dairy products
-ingestion of occysts

Question 23

what does infection of toxoplasmosis in humans result in?

Answer 23

-Acute phase–>flu-like illness
-Congeintal infection–> risk of abortion, foetal abnormality
-Reactivation of cysts possible in highly immunosuppressed individuals

Question 24

what are the signs of severe toxoplasmosis?

Answer 24

-Acute or reactivated toxoplasma infection
-Damage to brain, eyes or other organs
-More likely in immunocompromised individuals
-Very young, very old, HIV/AIDS, immunosuppressive therapy

Question 25

what is neospora canium?

Answer 25

○ An emerging and now widepread cause of abortion in cattle, that has many similarities to toxoplasmosis, but with a canine definitive host
Identifies in 1984 as a cause of bovine abortion and neonatal death in cattle which acts as intermediate hosts

Question 26

what are the definitive hosts of neospora canium?

Answer 26

dogs, producing oocysts

Question 27

how does neosporosis present in the dog?

Answer 27

-Puppies and dogs <1 year old
-Myositis
-Encephalomyelitis- Paralysis

Question 28

how does neosporosis cause abortions in cattle?

Answer 28

Repeat abortions
Returns to service

Question 29

what are congenitally infected claves with neosporosis like?

Answer 29

-Still born, weak or apparently normal
-Vertical transmission: heifers may abort during first pregnancy

Question 30

what is the life cycle of neospora cranium in cows?

Answer 30

-Canines infected by consuming tissues from cattle especially placenta
-After asexual and sexual development cycles, dogs pass oocysts in faeces which sporulate and contaminate environment, exposing cattle to risk of ingesting
-Other animals may also act as intermediate hosts
-Cattle may abort hteir calves and release placentas that may be eaten by dogs, completing the life cycle

Question 31

what is the exogenous transplacental transmission of neospora in cattle?

Answer 31

-infections resulting from ingestion of sporulated oocysts
-involved dog defintive host
-new infection of naive herds

Question 32

what is the endogenous transplacental transmission of neospora in cattle?

Answer 32

-infections resulting frmo reactivation of bradyzoites during pregnancy
-principle route of infection of cattle
-does not involve dog definitive host
-maintenance of infection in endemic herds

Question 33

what is sarcocystitis?

Answer 33

-A genus of protozoa with indirect life-cycles, infecting mammals, birds and reptiles
-The carnivore definitive hosts have asymptomatic gut infections while their herbivore prey, the intermediate hosts, have cysts in muscle and other tissues that may lead to clinical signs

Question 34

what is the sarcocystis life cycle?

Answer 34

1. Definitive host carnivores are infected by ingestion of bradyzoites within sarcoses, which penetrate lamina propria of small intestine
2. Immediately undergo gametogeny to produce oocysts which sporulate before being passed in faeces
3. Sporulated oocysts are more fragile than those of eimeria, toxoplasma or neospora
4. Sporocysts released into environment where may be ingested by intermediate hosts
5. Initial asexual multiplication takes place within endothelial cells of intermediate hosts followed by development of tissue cysts in striated muscle cells which contain bradyzoites surrounded by thick outer wall known as sarcocysts
6. These are consumed by definitive host carnivores

Question 35

what is equine protozoal myeloencephalitis?

Answer 35

-First recognised in 1995
-Neurological problem in horses in USA
-Caudal ataxia and weakness
-Sarcocystitis neurona
-Sarcocysts develop in equine CNS
Natural cycle= Opossum<–>birds/racoon/skunk/armadillo
-Horse is accidental or ‘dead end’ host

Question 36

What is Besnoitia besnoiti features

Answer 36

• Widespread in africa but spreading into europe
• Clinically affects cattle, goats

Question 37

What is Besnoitia bennetti features

Answer 37

Affects IH horses, donkeys, mules and zebras
- reported in UK donkeys

Question 38

What are clinical signs of Besnoitia

Answer 38

causes subcutaneous oedema with tachyzite replication in vascular endothelial cells
Brasyzoites form firm nodules - sclera of eye can dx

Question 39

What are clinical signs of Besnoitia in cattle

Answer 39

Skin and hoof lesions
Vulvitis, vaginitis, orchitis causing infertility