Overview

Coccidia are a devastating group of parasites that can be highly dangerous to most species in the animal kingdom. Livestock are known to suffer heavily from infections (known as coccidiosis) and as such there is a substantial pressure to keep this group of apicomplexans under control. These series of articles will aim to cover coccidia of the Eimeria genus, specifically those affecting the domestic turkey (Meleagris gallopavo domesticus). This particular article will detail the clinical pathology, identifying features and economic impact of Eimeria adenoides based on available research in industry.

If you were looking for a more general article on symptoms of coccidia and guidance for their control – you can access that here. However, feel free to read on if this interests you!

Pathogenicity

Eimeria adenoides was first described in 1951 [1]. Early literature also details a relative morbidity of 70% in 2-week inoculated poults (dosage = 20,000 oocysts (N = 10)), and morbidity of 100% (dosage = 80000 oocysts (N = 10)) [2]. Furthermore A later paper detailed a lower relative mortality rate of 33% for poults that had been inoculated at 3 weeks.  (N=8 (4F/4M) [3]. This instance involved a higher dosage of  approximately 100,000 oocysts per bird. Further to this, one study found a relatively low dosage of 200,000 oocysts would result in total mortality of a juvenile flock at 3 -weeks old [1] (Sample size N/A). This shows that the key period for a rise in innate immunity occurs between weeks 2-3. A further paper found the effect was found to be largely mitigated at 11 weeks of age, wherein they were dosed with 3,000,000 oocysts [1].

Weight Gain Depression

Any inoculation below the lethal limit was found to result in substantial weight gain depression [1], as would be expected from damage to the alimentary canal. . In terms of weight gain, six days of infection with E. adenoides resulted in an average weight gain of 66.3g for males (male control = 203.5g) and 68.3g for female birds (female control = 203.6g) [3]. This is vastly reduced weight gain by comparison to the controls. Vaccination would be beneficial in said instances to protect against production losses. [Breed = Broad-Breasted White turkey Age = 14 day olds].

Necropsy signs

This species typically infects the lower small intestine and caecum. This leads to the rectum, deep glands and villi experiencing damage. In addition, a key characteristic relating to identification and cataloguing of intensity whilst lesion scoring is the formation of caseous plugs in the caecum, as well as the periodic formation of petechiae in the caecum mucosa [4]. E. adenoides may also develop in the lower ileum, however current papers detail no lesions to be present in this area or in the rectum during sampling.

Malabsorption of glucose and methionine may occur in jejunum even with absence of parasite [10]; It is stated that the average size of the intestine decreases with infection, which would explain the WGD suffered from E. adenoides infections due to the reduction in diffusion capacity and subsequent poor uptake of glucose and methionine.

Summary of features as per [5]

  • Prepatent period: 112 hr (approximate)
  • Presence of a refractile body: Yes
  • Pathogenicity: Highly pathogenic

Oocysts:

  • Length range (µm): 18.95 – 31.26
  • Width range (µm): 12.60 – 20.94
  • Average (L x W): 25.60 x 16.59
  • Ratio (L/W) 1:1.54
  • Shape: Ellipsoidal, ovoid and smooth
  • One micropyle
  • 1-3 polar graules
  • No oocyst residuum – clear globule at the large end

Sporocysts:

  • Elongate stedia body and residuum with clear globule at the large end

Meronts (two generations):

  • 1st gen: 30 x 18um (mature) (700 merozoites)
  • 2nd gen: 10×10 um (12-24 merozoites)
  • Sporulation time: 24 hrs

(Pictures to follow!)

References

[1] Clarkson, M.J. (1958) “Life history and pathogenicity of Eimeria adenoeides (Moore & Brown, 1951), in the Turkey poult,” Parasitology, 48(1-2), pp. 70–88. Available at: https://doi.org/10.1017/s0031182000021065.

[2] Hein, H. (1969) “Eimeria adenoeides and E. meleagrimitis: Pathogenic effect in Turkey poults,” Experimental Parasitology, 24(2), pp. 163–170. Available at: https://doi.org/10.1016/0014-4894(69)90153-2.

[3] Anderson, W.I., Reid, W.M. and McDougald, L.R. (1976) “Efficacy of monensin against Turkey coccidiosis in laboratory and floor-pen experiments,” Avian Diseases, 20(2), p. 387. Available at: https://doi.org/10.2307/1589278.

[4] Gadde, U.D. et al. (2019) “Pathology caused by three species of eimeria that infect the turkey with a description of a scoring system for intestinal lesions,” Avian Pathology, 49(1), pp. 80–86. Available at: https://doi.org/10.1080/03079457.2019.1669767.

[5] Moore, E.N., Brown, J.A. and Carter, R.D. (1954) “A new coccidium of turkeys, Eimeria subrotunda n. sp. (protozoa: Eimeriidae),” Poultry Science, 33(5), pp. 925–929. Available at: https://doi.org/10.3382/ps.0330925.