6.4 Protists 1 Flashcards
Protists; overview; basic body structure, movement, repro
*all are single‐celled, eukaryotic organisms
*ancient group of organisms
*may or may not have a sexual process
*some use flagella or cilia for locomotion
Parasitic Protists; general overview; where they infect; life strategies
- parasitic protists infect virtually all sites in the body either intracellularly or extracellularly
- both simple and highly complex life cycle strategies
- some possess resistant stages to pass from host to
host - others use intermediate and/or paratenic hosts to move from one definitive host to the next
Parasitic Protists; Major Groups (6)
- Apicomplexa
(enteric and ‘tissue’ coccidia, malaria, piroplasms) - flagellates
(kinetoplastids and trichomonads) - ciliates
- amoebae
- Microsporidia
- Myxosporidia
Phylum Apicomplexa; General Life Cycle
Oocysts containing sporozoites
> Merogony >
Meronts (=schizont) containing merozoites
> Gametogony >
Gametes
-macrogametes: female
-microgametes: male
-fuse to form a zygote
> Sporogony >
Oocysys containing sporozoites
Eimeriorina is a suborder of phylum:
Apicomplexa
Eimeriorina ‘True’ Coccidia; families and their members
Family Eimeriidae
* Eimeria, Isospora, Caryospora spp.
Family Sarcocystidae
* Sarcocystis, Toxoplasma, Neospora, Cystoisospora
Eimeriorina also known as
‘True’ Coccidia
Eimeriorina ‘True’ Coccidia; which are primarily enteric parasites?
Family Eimeriidae
* Eimeria, Isospora, Caryospora spp.
Family Sarcocystidae
* Cystoisospora
Eimeriorina ‘True’ Coccidia; which are primarily ‘tissue coccidia’?
Family Sarcocystidae
* Sarcocystis, Toxoplasma, Neospora
Eimeriorina; General Characteristics; where it lives, types of life cycle, site of infection
- obligate intracellular parasites
- both monoxenous (Eimeria, Cystoisospora, etc.) and heteroxenous (Toxoplasma, Sarcocystis, etc.) life cycles
- parasites of the digestive tract of the definitive host but many other tissues of the intermediate host
Apicomplexan parasites; do what to host cells
actively penetrate host cells
-pull cell membrane around themselves, form parasitophorous vacuole
Eimeria spp.; develop where
- intestinal development in specific vertebrates
Eimeria spp.; oocyst appearance
Sporulated oocysts have:
* sporocysts with Stieda bodies
* sporozoites with refractile bodies
Eimeria species ‐ Life Cycle
Endogenous Stages 1
* sporozoites invade epithelial cells
* merogony (=schizogony) gives rise to multinucleate meronts (=schizonts) within host cells which finally produce merozoites
* merozoites usually reinvade cells to start a second (or more) round(s) of merogony
Endogenous Stages 2
* merozoites eventually enter cells and begin gametogony (formation of gametes)
* microgamonts each give rise to many microgametes (males)
* macrogamonts give rise to a single macrogamete (female) ‐ macrogametes possess characteristic wall‐forming bodies
Endogenous Stages 3
* biflagellate microgametes (males) are motile and search out macrogametes (female) which they fertilize
* the resulting zygote is an unsporulated oocyst
* the unsporulated oocyst passes from the host in the feces to begin the cycle again
Exogenous Stages
* the unsporulated oocyst undergoes sporulation
* requires oxygen, moisture and warmth
* meiosis and then asexual division gives mature (sporulated) oocyst
* ONLY sporulated oocyst is infective to next host.
only form of the Eimeria life cycle that is infective to the next host
- ONLY sporulated oocyst is infective to next host.
Eimeria species; Pathogenesis/Lesions/Clinical Signs
- enteritis, may be bloody depending on species
- inflamed, congested mucosa with mucosal sloughing in serious cases
- villar atrophy results from death of enterocytes
- malabsorptive diarrhea
- decreased production parameters
(increased water intake and reduced feed conversion efficiency)
Eimeria spp.; which domestic animals do they infect
-cattle
-sheep
-goats
-poultry
-horses
Eimeria spp. of cattle
E. bovis *
E. zuernii*
E. auburnensis
E. alabamensis, etc.
Eimeria spp. of sheep
E. ahsata*
E. ovina
Eimeria spp. of goats
E. ninakohlyakimovae*
E. arloingi
Eimeria spp. of poultry
Many Eimeria spp.*
Eimeria spp. of horses
E. leukarti
Eimeria spp of Cattle; most pathogenic and life cycle character
- Eimeria bovis and E. zuernii most pathogenic
- Life cycles have two generations of merogony followed by gametogony
- First generation meronts are huge
Bovine Coccidiosis in Canada; general; source of infection, who gets infected, outcomes, disease geography
- environmental oocysts source of infection
- infection of immunologically naïve animals (usually calves)
- infected animals develop immunity to further infection (do not shed parasites)
- distinctly different diseases in eastern Canada (e.g. Ontario) and western Canada (e.g. Saskatchewan)
Bovine Coccidiosis in Canada; Eastern Canada; summer and winter environment, consequences
SUMMER
* Environment: lush, wet, warm pastures
* Host: susceptible calves on pasture
* Agent: high reproductive potential
Consequences
‐ relatively high stocking density (productive pasture)
‐ good oocyst survival (wet, warm, protected)
‐ high parasite density (good survival and many susceptible hosts in a confined area)
>Disease: Coccidiosis in naïve calves
WINTER
* Environment: confined barn environment
* Host: most calves immune now
* Agent: high reproductive potential
Consequences
‐ hosts are numerous and crowded
‐ good oocyst survival (wet, protected)
‐ low parasite density (good survival but most hosts are immune to infection)
>Disease: No Coccidiosis in immune calves
Bovine Coccidiosis in Canada; Western Canada; summer and winter environment, consequences
SUMMER
* Environment: dry, hot, sparse pastures
* Host: susceptible calves on pasture
* Agent: high reproductive potential
Consequences
‐ relatively low stocking density (pasture not very productive)
‐ very poor oocyst survival (dry, hot, UV radiation)
‐ low parasite density (combination of poor survival and few susceptible hosts spread over a large and inhospitable area)
>Disease: Little or no coccidiosis in naïve calves
WINTER
* Environment: confined barn environment
* Host: most calves susceptible
* Agent: high reproductive potential
Consequences
‐ hosts are numerous and crowded
‐ good oocyst survival (wet, protected)
‐ high parasite density (good survival and most calves are susceptible to infection)
>Disease: Coccidiosis in naïve calves
Eimeria spp of domestic poultry
Apicomplexa: Coccidia
In chickens
-E. acervulina
-E. maxima
-E. necatrix
-E. tenella
In turkeys
-E. adenoeides
-E. meleagrimitis
Hosts: species‐specific coccidia
Eimeria spp of domestic poultry; site of infection
Site: throughout intestinal tract, species‐specific
Eimeria spp of domestic poultry; Pathogenesis
- each species infects a particular region of the intestinal tract
- all species can be pathogenic IF sufficient numbers of oocysts are ingested by a susceptible host
- immune status of host with respect to that particular species is a critical determining factor if animal is going to become clinically ill
Eimeria spp of domestic poultry; Treatment/Prevention:
- numerous licensed compounds
- continual prophylactic anticoccidial usage the norm
- management (litter) supplements prophylaxis
- live vaccines useful for breeders/layers and being used increasingly in broiler flocks or in operations wishing “organic” (e.g. RWA) product
Eimeria spp of domestic poultry; Anticoccidial Usage considerations
- Anticoccidial resistance is a widespread problem
-continuous and shuttle programs; within a flock
-rotation programs; between flocks - Rarely are these compounds used therapeutically and most do not have label claim against these parasites for treatment
Cystoisospora spp.; General Characteristics; who they infect, hosts, site
- Infect – carnivorous/omnivorous mammals, or birds of prey
- infections in young dogs, cats and particularly swine of regional interest
- each Cystoisospora sp. is host‐specific
(humans have their own species, Cystoisospora belli) - infect cells of the intestinal mucosa (Note: exceptions)
Cystoisospora spp.; life cycle
- unsporulated oocysts occur in feces
- sporulation occurs to form sporulated oocysts
- sporulated oocysts each contain 2 sporocysts with 4 sporozoites within each sporocyst
- sporulated oocysts are infective to the next host
> ingestion and digestion of sporulated oocyst cyst
excystation
endodyogeny
merogony
gametogony
fertilization
unsporulated oocyst
sporulated oocyst (Infective)
OPTION for Cystoisospora only:
>ingestion of sporulated oocyst by paratenic host
>excystation
>sporozoites leave intestine
>monozoic cyst in extraintestinal tissue
>digestion of cyst….
Cystoisospora spp.; sporulated oocysts each contain
2 sporocysts with 4 sporozoites within each sporocyst
Cystoisospora spp.; Pathogenesis and Clinical Signs
- like most coccidia, Cystoisospora spp. causes disease in young (neonatal) animals
- direct damage to epithelial cells
(destroyed as the parasites leave the cells after dividing) - immune‐mediated enteritis
- results in diarrhea as the main clinical sign
Cystoisospora spp.; Diagnosis
- 4 species infect dogs and 2 infect cats
‐ these vary in their ability to cause disease - distinguish species on the basis of:
a) location and cells infected in gut
b) details of endogenous development c) size of oocyst and sporocysts within
(Note: little clinical relevance, ID to genus only)
Cystoisospora spp.; Treatment
- usually self‐limiting disease if small numbers of oocysts caused the infection
- control of oocyst numbers is preventative
(surface disinfection in a timely manner – remember sporulation time) - watch for dehydration because of diarrhea
- can treat with sulfa drugs (inhibit folic acid biosynthesis) or off‐label toltrazuril (Baycox )
Cystoisospora suis; disease; when/where is it seen, PPP, sporulation time, pathogenesis
Neonatal coccidiosis in swine
* Almost always seen clinically in pigs less than 4 weeks of age
* PPP = 4‐6 days; sporulation time = 3‐5 days
* Destruction of villar epithelium principal cause of diarrhea – may lead to sloughing of entire epithelium
* Extensive destruction may occur during PPP
Prepatent period
the period between infection with a parasite and the demonstration of the parasite in the body especially as determined by the recovery of an infective form (as oocysts or eggs) from the blood or feces.
Cystoisospora suis; clinical signs
- Clinical signs include profuse pale yellow diarrhea, failure to gain weight, runting, death
