Protozoa
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- Created by: fionnualamaire94
- Created on: 10-01-17 17:21
Protozoa
- unicellular - animal kingdom, eukaryotic with complex internal structures - many organelles and one or more nuclei
- locomotion - flagella, cilia, pseudopodia or others
- sexual reproduction
- conjugation, gametogony, syngamy
- asexual reproduction
- fission
- budding
- anchors to and penetrates host cells by apical complex - conoid, spirally arranged microtubules, secretory body, 2 polar rings
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3 phases of protozoal development
- schizogony - asexual
- sporozoites > trophozoite > schizont > merozoite > trophozoite (etc) > merozoite > gametocytes
- gametogony - sexual
- lots of microgametes (male), 1 macrogamete (female) > zygote
- sporogony - zygote (oocyst) > sporocysts > sporozoites - infective
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Coccidia - Chickens - Life Cycle/Symptoms
- Eimeria spp.
- direct life cycle
- oocysts passed in faeces, in high humidity and ~27C - sporulated oocycts - sporocysts (4) and sporozoites (2)
- sporulated oocysts ingested by host, sporozoite penetrates epithelial cell, forms trophozoite, division by multiple fission
- schizont, contains number of merozoites - invade neighbouring cells - gametogony - zygote, cyst wall, oocyst
- anorexia, sudden weight loss, diarrhoea, vomiting, dehydration, depression, huddled appearance, sudden death
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Eimeria tenella and Eimeria necatrix
- Eimeria tenella
- very pathogenic
- caecal coccidiosis, severe haemorrhagic enteritis
- mortality up to 90%
- blood 4-6 days post-infection, apathetic, drink and eat less
- PPP = 6 days
- Eimeria necatrix
- very pathogenic
- lower small intestine
- mucoid and haemorrhagic enteritis
- atony in small intestine
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Eimeria acervulina and Eimeria brunetti
- Eimeria acervulina
- high morbidity, low mortality, young stock
- catarrhal enteritis (mucous membranes)
- watery to mucoid faeces
- decreased egg production
- transverse ladder-like white streaks
- Eimeria brunetti
- very pathogenic, 4-9 week old chickens
- posterior small intestine, cloaca, rectum
- severe, gut wall is thickened
- haemorrhagic catarrhal exudate
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Eimeria maxima and Eimeria mitis
- Eimeria maxima
- moderately pathogenic, laying hens
- substantial mucus production, mucosa substantially and evenly thickened
- loss of tone, intestine flaccid and dilated
- mucosa, whitish with tiny petechiae, pinkish mucoid exudate
- immunity develops quickly
- Eimeria mitis
- relatively mild disease
- similar to E. acervulina
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Chicken coccidiosis - prevention and control
- environment - moisture control of litter - includes good ventilation
- prophylactic treatment - coccidostats, anticoccidial agents - target clinical signs, broiler chicks on lifetime medicated food - (amprolium, clopidol, diclazuril, halofuginone, lasalocid, monensin, nicarbazin, rovenidine, salinomycin)
- chemotherapeutic treatment - (amoprolium, sulphonamides, dinitolmide) - poor prognosis if clinical signs present already
- immunity - strain specific, each life cycle stage has different antigens, needs trickle dose or single moderate dose of exposure to induce effective immunity - drugs can interfere
- vaccination - precocious vaccine - Paracox
- broilers/breeders/layers
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Coccidiosis in Ruminants - Cattle
- cattle under 1 year of age, sometimes yearlings/adults
- 13 species - Eimeria zurni and Eimeria bovis are most pathogenic
- Eimeria zurni - schizonts in small intestine; sexual phase in terminal ileum, caecum and colon; acute infections - pass blood clots and mucous membrane strips, anaemia and wasting
- Eimeria bovis - asexual stages in small intestine; sexual stages in terminal ileum, caecum and colon - most pathogenic; majority of crypts in large intestine destroyed, epithelium lost and lumen filled with blood; very young calves
- clinical aspects - damage to mucosa of large bowel; acute - liquid faeces with blood; variable sloughed tissue and mucus; tenesmus - constantly wanting to evacuate bowels
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Coccidiosis in Ruminants - Sheep
- 15 different species - Eimeria ovinoidalis and E. crandallis associated with disease
- infection and clinical symptoms similar to cattle infection
- lambs most susceptible - 3 months and under 1x10^6 oocysts/gm faeces; 3-9 months 10,000 oocysts/gm faeces
- clinical signs about time of gametogony, 2.5-3 weeks after oocyst ingestion, liquid faeces with blood
- treat all calves/lambs; separate scouring animals; supportive therapy - fluids; treat concurrent infections with secondary bacteria; decoquinate in creep feed, diclazuril/toltrazuril 2-5wk -lambs, 1wk pre-expected disease - calves; hygeine - cover with straw remove 2-3wks regularly move feed/water points
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Coccidiosis in cats and dogs
- isospora mainly in carnivores - worldwide distribution
- controversy over pathogenicity of naturally occuring infections - clinical cases in young animals observed
- crowding, lack of sanitation, other intercurrent infectious diseases and stress promote spread - adult carriers
- 5 main species - oocyst sizes differ
- schizont stages in small intestine - catarrhal to haemorhagic enteritis
- diarrhoea, rapid emaciation and anaemia
- post-acute, dysentry replaced by mucous faeces for 2-4 days
- chronic - chronic diarrhoea alternated with stipsis - looks like parvo
- treatment - chlortetracycline, sulfametopyrazine, sulfadimethoxine
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Toxoplasma gondii
- only species in genus - toxoplasmosis is disease
- important cause of abortion in sheep and humans
- oocysts - two sporocysts, four sporozoites
- tachyzoites develop in vacuoles - fibroblasts, hepatocytes, reticular cells and myocardial cells, 8-16 per cell
- tissue cysts - muscle, liver, brain, several thousand lancet-shaped bradyzoites
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Toxoplasma Life Cycle
- intestinal phase in definitive host, systemic in intermediate
- indirect life cycle
- definitive host - felid
- intermediate host - mammals and birds
- felids - bradyzoites/tachyzoites; cycle of schizogony, gametogony - oocysts 3-10 days, shed 1-2 weeks
- intermediate - oocysts ingested, life cycle is extra-intestinal, spread by haematogenous route, tachyzoite multiplies asexually - budding/endodyogeny, when 8-16 cells are accumulated, cell ruptures and new cells are infected - acute phase
- cysts containing bradyzoites - latent form held in check by acquired immunity of host
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Toxoplasma Epidemiology
- 60% of cats are serologically positive
- shed oocysts for 1-2 weeks - some carriers with reactivation in periparturient period or following corticosteroid therapy
- oocysts very resistant to environment
- risk of infection - concentrate feeding prior to tupping/lambing - contaminated with cat faeces; spread by coprophagous insects - contaminate veg, meat, animal fodder; milk of naturally infected goats - unpasteurised goats milk
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Toxoplasma Pathogenesis
- definitive host - asymptomatic
- intermediate host - digestive tract > disseminated by lymphatics and portal system > subsequent invasion of various organs and tissues - pathogenesis, tachyzoites > necrosis of vital organs, host pyrexic, lymphadenopathy can occur
- chronic phase is asymptomatic
- if pregnant animals experience for first time congenital disease is possible - predominantly CNS
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Toxoplasma Clinical Signs
- rare in cats
- sheep - abortion in ewes, perinatal mortality in lambs
- <55 days gestation - death and expulsion of fetus
- mid-gestation - abortion more easily detected or dead fetus is retained, mummified and expelled later or alive but stillborn/weak
- lamb normally in subsequent years
- dogs - fever with lassitude, anorexia and diarrhoea, pneumonia and neurological manifests
- cattle and horses - fairly resistant, no abortion
- pigs - not normally on modern farms - outdoor/organic systems in Europe
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Toxoplasma Diagnosis/Control
- cats - detection in faeces (rare), serological testing - latex agglutination (LAT)/ELISA
- others - sections brain/placenta, immunohistochemistry - PCR in DNA tissues, dye test (DT)/indirect fluorescent antibody test (IFAT) - direct agglutination (DAT)/LAT/ELISA
- live vaccine sheep - toxovac, 2yr protection
- control is difficult, cover feedstuffs, mixing infected stock with replacements
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Neospora caninum
- fatal protozoan parasite of dogs (and cattle)
- neosporosis - often misdiagnosed as T. gondii
- hindlimb paresis in dogs, neonatal mortality in cattle and sheep
- transmitted transplacentally
- very similar life cycle to T. gondii, primarily a disease of cattle
- definitive host - dogs
- intermediate hosts - tachyzoites and tissue cysts, intracellular cysts - CNS, oocysts excreted in faeces dogs/coyotes - sporulate in env. 24hrs
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Neospora caninum - Pathogenesis/Treatment
- abortion in cows, 3 months to full term - mostly 5-6 months
- neurological symptoms in surviving calves
- transplacentally infected calves - transmit infection
- most severe if transplacentally infected puppies, progressive ascending paralysis esp. hindlimbs; poss. polymyositis and hepatitis ~1-6 months
- trimethoprim/sulphadiazine/pyrimethamine/clindamycin
- dont let dogs eat aborted foetuses
- faeces prevented from contaminating bovine feed
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Sarcocystis spp. (Sarcocystosis) - Life Cycle
- indirect life cycle
- intermediate host - prey animal
- definitive host - predator
- schizogony in intermediate host - vascular epithelium cells, cyst formation in striated muscle - multiplication by endodyogeny
- gametogony - intracellularly in intestine of definitive host
- sporogony - definitive host - lamina propria mucosae - sporocysts released in faeces - infective only to intermediate host
- PPP = 7-14 days - variable between species
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Sarcocystis spp. - Epidemiology
- ingestion of sporocysts in food or water - to intermediate host, transplacental is rare
- prevalence factors - sarcocystis oocysts and sporocysts in lamina propria - discharged for many months
- sporocysts - remain viable for many months may be spread/protected by invertebrates
- large numbers of sporocysts shed by definitive host - from small quantities in meat
- little or no immunity in definitive host to reshedding of sporocysts
- passed in faeces in infective form
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Sarcocystis spp. - Clinical Signs
- definitive - rare symptoms, mild diarrhoea
- intermediate - acute - due to merogony, haemorrhage and anoxia in tissues with ruptured meronts - endothelial cells, brain, spinal cord and kidney
- non-suppurative encephalitis in lambs and calves - ataxia, paresis, muscle tremors
- older animals - pneumonia, hepatitis and abortion
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Sarcocystis spp. - Prevention
- no vaccine
- carnivores excluded from animal houses and feed/water/bedding
- uncooked meat/offal not fed to carnivores - freezing kills infection
- dead livestock - incinerated
- prophylactic anticoccidials - halofuginone, amprolium, salinomycin
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