Coccidia

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Coccidiosis

Introduction

Coccidia - Joel Mills

The following refers specifically to the life cycle of Coccidia spp.

  • The oocyst is the resistant stage in the environment
  • The infective sporozoite is released from the oocyst
  • Inside the host, the sporozoites invade the intestinal epithelial tissue
    • Sporozoites feed and grow
  • As the sporozoite grows the nucleus divides forming a schizont
  • The schizont contains numerous elongated merozoites
  • The formation of merozoites is the first asexual reproductive stage called schizogony
  • The schizont ruptures releasing the merozoites which also invade the epithelial cells
  • Another generation of schizonts form which is the beginning of the sexual phase of reproduction called gametogony
  • The merozoites form male microgamonts or female macrogamonts
    • Collectively known as gamonts or gametocytes
  • The microgamonts released from the microgametocyte penetrate and fertilise the macrogamont (which is contained within the macrogametocyte)
  • Gametogony forms the zygote
    • Surrounded by a cyst wall
    • Forms the oocyst
  • The oocyst is passed in the faeces and is unsporulated
  • The oocyst becomes sporulated in the second asexual reproductive phase called sporogony
  • Once the oocyst is sporulated it is infective

Eimeria spp.


Isospora spp.


Coccidia of Poultry

Buff orpington - nabrown RVC
Sporulated Eimeria - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona
  • Direct life cycle
  • 1 week prepatent period
  • After oocysts are ingested, sporozoites are released which penetrate the intestinal epithelium
  • 2 asexual phases of multiplication called schizogony occur followed by a phase of sexual multiplication called gametogony
  • Zygote develops into an oocyst which is then shed in the faeces
    • Oocyst measures 20-30μm
  • For each oocyst ingested, thousands are shed
  • Life cycle is self-limiting
    • Organisms from a single infection go through the sequence of developmental stages synchronously
    • Organisms leave the body simultaneously as oocysts
  • Oocysts are only infective once they have sporulated
    • Sporulation requires warmth, moisture and oxygen
    • Takes 2-3 days in broiler houses
  • Oocysts contain 4 sporocysts each with 2 sporozoites

Pathogenesis

  • 7 important Eimeria species
  • 4 malabsorptive species
    • Eimeria acervulina which is moderately pathogenic
    • Eimeria maxima which is moderately pathogenic
    • Eimeria mitis which has low pathogenicity
    • Eimeria praecox which has low pathogenicity
  • 3 haemorrhagic species
    • Eimeria tenella
    • Eimeria necatrix
    • Eimeria brunetti
    • All highly pathogenic
    • Form large sub-epithelial second generation schizonts at the base of intestinal crypts
    • Deep eruptions form when cells rupture to release merozoites
    • Destruction of crypt stem cells and marked haemorrhage
    • Blood stained faeces
    • High morbidity and high mortality

Diagnosis

  • Post-mortem diagnosis of lesion severity
    • Region of intestine affected
    • Appearance of lesion
    • Presence or absence of haemorrhage
    • Size of schizonts and oocysts found in mucosal scrapings
  • Eimeria acervulina
    • Proximal gut
    • Thickening of walls
    • 'White ladder lesions' produced by dense foci of gamonts and oocysts
    • Watery exudate
  • Eimeria maxima
    • Mid-gut
    • Thickening of walls
    • Pink exudate
  • Eimeria tenella
    • Swollen caeca
    • Thickening of wall
    • Dark colouring containing a core of necrotic tissue and blood
  • Lesion scoring is the best method of diagnosing the severity of the lesions and therefore the causative Eimeria species
  • Eimeria necatrix
    • Mid-gut
    • Ballooning of wall
    • White spots and petechiae forming 'salt and pepper' lesions
    • Haemorrhage into lumen

Immunity

  • Different Eimeria species produce different levels of protective immunity
    • E.maxima -> E.brunetti and E.acervulina -> E.tenella and E.necatrix
  • There is no cross immunity between species
  • There is very little passive immunity
  • Evokes a cell-mediated response
  • All ages of poultry are susceptible

Epidemiology

  • Oocysts are ubiquitous and robust
    • Able to survive several months to years
  • It is impossible to keep buildings free from infection
    • Chicks become infected by pecking the ground shortly after being placed in the poultry house
  • Biotic potential is enormous
    • Generation time is short
    • Massive infections can build up rapidly
  • Immunity develops relatively slowly
    • With high stocking densities the situation is explosive

Control

  • Chemical
    • Intensive poultry production is largely dependent on the use of anticoccidial drugs
    • For more information see here
  • Vaccines
    • Paracox
      • Multivalent attenuated live vaccine for replacement layers and broilers
      • Contains 7 live strains of Eimeria
      • Lack the most pathogenic life cycle stage making the prepatent period shorter
      • Known as precocious strains
      • Chicks vaccinated on a single occasion when 1-9 days old through oocyst suspension in the feed or water
      • Vaccinated birds have sub-optimal growth rates so is not used for broilers
    • Paracox 5
      • Contains 5 strains of the most pathogenic Eimeria
      • Used for broilers
      • Sprayed onto the first feed offered to new batches of chicks
  • Integrated control
    • Careful management is needed so in-feed prophylaxis and vaccination do not fail
    • Remove litter and thoroughly clean houses in between crops
      • Optimum turn-around time is 10 days
    • Use the lowest stocking density which is compatible with economic production
    • Water bowls, roofs and walls should be well maintained to prevent litter becoming damp
    • Stress factors should be avoided and adequate nutrition provided

Other Avian Coccidia

Coccidia of Turkeys

  • 5 Eimeria species
    • 2 important pathogenically
  • Eimeria in caeca causes petechial haemorrhages and caseous caecal cores
  • Eimeria in the anterior and mid-intestine causes necrotic enteritis and petechial haemorrhages
  • Causes watery diarrhoea in young poults and some mortality

Coccidia of Geese

  • 3 Eimeria species
  • 2 intestinal species causing macroscopic lesions in kidney tubules
    • Oocysts carried in urine and pass out with faeces
  • Renal species cause severe disease in goslings
    • Depression, emaciation, diarrhoea and sometimes death

Coccidia of Ducks

Crested duck - nabrown RVC
  • Several Eimeria species
  • Another coccidia species which produces 8 sporozoites but these are not enclosed in a sporocyst
  • Causes severe enteritis and mortality in ducklings

Coccidia of Game Birds

  • 3 main species

Coccidia of Cattle

Eimeria sp. of ruminants - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona
Coccidia oocyst from ruminant faeces - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona
  • Many species affect cattle
  • Cattle under a year old are usually infected sporadically
  • 2-3 week prepatent period
  • Eimeria bovis
    • Endogenous stages in central lacteal of villi and epithelial cells of caecum and colon
    • Causes diarrhoea and enteritis
    • Oocysts are 28x20μm
    • Moderately pathogenic
  • Eimeria zuernii
    • Endogenous stages in connective tissue of lamina propria of the lower small intestine and in the epithelial cells of the caecum and colon
    • More pathogenic than Eimeria bovis
    • Causes blood stained dysentery, tenesmus and sloughed mucosa
    • Oocysts are spherical and measure 16μm
  • Mainly occurs in calves in poor conditions and bought-in calves
    • Also occurs in suckler calves turned out in spring
  • Eimeria alabamensis associated with diarrhoea in calves after spring turnout
  • Can be concurrent with cryptosporidium, viral and bacterial agents

Diagnosis

  • History, clinical signs, diarrhoea (often with blood) and a decrease in weight gain
  • Post-mortem
    • Diffuse inflammation and thickening of caecal mucosa (and sometimes ileal and colonic mucosa)
    • Masses of gamonts and oocysts in scrapings
  • High faecal oocyst count
    • However, healthy animals can pass millions of oocysts from mixed species infections which have no pathogenic significance
    • Animals may die before oocysts are shed

Control

  • Improve husbandry
    • Improve sanitation
    • Increase bedding
    • Raise food and water troughs to avoid faecal contamination
  • Preventative in-feed medication
    • E.g. Decoquinate
  • Injectable antiprotozoals may limit oocyst production but animals should still be moved to a clean environment
    • E.g. Sulphamethoxypyridazine

Coccidia of Sheep

Isospora felis sporulated - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine
Isospora felis unsporulated - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine
  • 11 different Coccidia species although only two are of clinical significance
    • Giant schizonts visible as white spots
  • 2 week prepatent period
  • Disease frequently seen in lambs under 6 months old
    • More often in twins and triplets when single lambs
  • Oocyts from ewes (immune carriers) accumulate in poorly managed litter or around feed and water troughs
  • Lambs born early in the year amplify the parasite problem increasing the parasite risk to lambs born later in the year
  • Affected lambs may die before oocysts are found in the faeces
    • Post-mortem diagnosis difficult
  • Different species of Eimeria occurs in sheep and goats
  • Infection may be coincident with Neospora or Cryptosporidium infections
    • Mixed infections complicate the diagnosis as oocyst differentiation is difficult
  • Other non-pathogenic species can cause papillomatous mucosal growths

Control

  • Improve husbandry
    • Avoid overcrowding
    • Decrease stress
  • Improve hygiene by dagging ewes
  • Avoid mixing lambs of different ages
  • Preventative measures include creep feeding lambs with decoquinate or oral dosing with diclazuril when lambs are 4-6 weeks
    • A second dose can be given after 3 weeks

Coccidia of Goats

Goats - nabrown RVC
Eimeria leukarti - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona
Isospora suis oocyst from pig faeces - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona
Isospora canis - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona
Coccidia in Cat Faeces - Joel Mills
Isospora felis - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona
  • Many Eimeria species
  • 2 Eimeria are pathogenic
  • Different species of Eimeria occurs in sheep and goats

Coccidia of Horses

  • Only one atypical Eimeria
  • Forms large subepithelial gametocytes in villi
  • Large, dark coloured oocysts
    • Approximately 12μm
  • Besnoitia bennetti in larynx of horses

Coccidia of Pigs

  • Many species of Eimeria and Isospora
  • Only Isospora suis is of clinical pathogenic importance
  • Causes sporadic, serious and sometimes fatal disease in unweaned piglets
  • Very short 1 week prepatent period
  • Diarrhoea starts before oocysts are shed in faeces
    • Ante-mortem diagnosis is difficult
  • Death usually occurs after parasites have left the host
    • Post-mortem diagnosis difficult
    • Isospora infections are self-limiting

Coccidia of Dogs

  • 2 common and 2 less common Isospora species
  • Occasionally can cause disease
  • Little pathogenicity
  • Even if faecal oocyst count is high, other causes of diarrhoea should be looked for
  • Hepatozoon americanum and subclinical H. canis in periosteal bone formation
    • Both are Tick borne diseases
      • H. canisRhipicephalus sanguineus
      • Ticks become infected by ingesting a blood meal containing macrophages and neutrophils infected with the parasite gamonts -> sexual replication in the gut of the tick -> oocysts containing infective sporozoites -> dogs ingest the tick  schizogony occurs in numerous tissues

Coccidia of Cats

  • 2 common Isospora species with little clinical significance
  • Oocysts in faeces have to be distinguised from those of Toxoplasma (smaller) and Sarcocytis (sporulated or naked sporocyts in faeces)

Coccidia of Rabbits

  • 3 pathogenic Eimeria species
    • 2 in the caecum
    • 1 in the bile duct
  • Eimeria steidae
    • Parasitises the bile duct epithelium
    • Travels via the bile duct to the liver where it forms large white nodules
    • Oocysts travel in the bile and are passed out in the faeces
    • Causes ascites, diarrhoea, weight loss and polyuria
  • Serious disease of both pet and farmed rabbits
  • Treatment is by administration of drugs in drinking water
    • E.g. Toltrazuril
  • Hygiene is the best method of prevention to prevent sporocysts from sporulating
  • Medicated feed can be used in commercial units
    • E.g. Rabenidine

Coccidia Flashcards