Protozoa

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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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