Coccidia

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
  • Haemorrhages and pale focal lesions in small intestine

Coccidia of Game Birds

• 3 main species

• Caecal species most pathogenic causing white caecal cores

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

• Passive immunity is sufficient during the neonatal period

• 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

• Eimeria ovinoidalis
  • Highly pathogenic
  • Diarrhoea
  • Parasitises the caecum and colon

• Eimeria crandalis
  • Varying pathogenicity
  • Scours, grey, foul-smelling faeces
  • Parasitises the small intestine, caecum and colon

• 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
  • Cause diarrhoea and a decreased growth rate

• 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

• Occasionally causes diarrhoea

• 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
  • Causes profuse diarrhoea

• 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. canis – Rhipicephalus 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