Coccidiosis - Poultry

Coccidia - Poultry

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