Parasitology - Avian Coccidiosis Flashcards
Coccidiosis in poultry can follow three complex life cycles but we are mostly concerned with that of the Eimeria species.
That is a DIRECT life protozoan life cycle. What are the key stages, starting with unsporulated oocyst excreted by chicken in faeces?
Unsporulated oocyst (excreted by host)
(sporogony)
**Sporulated oocyst with four sporocysts containing two sporozoites each **(eaten by host)
(each sporozoite seen as refractile body invades an epithelial cell)
Trophozoites (motile)
(schizogony)
Schizont filled with merozoites
(merozoites invade more epithelial cells)
Gametogony
Macrogamete & Microgamete
Zygote
Unsporulated oocyst
What is the pre-patent period of Eimeria spp that cause coccidiosis?
4-5 days for most species.
What does it mean that the Eimerian life-cycle is “self-limiting”?
The organisims from a single infection go through the sequence of developmental stages synchronously and leave the body simultaneously as oocysts. They don’t have about to parasitize the host over and over.
When are Eimerian oocyts considered infective?
After they have undergone asexual division, aka sporogony, to form four sporocysts with two sporozoites inside each.
What environmental conditions are required for oocytsts to become infected in the usual 2-3 days in a broiler house?
Warmth, up to 25°C, humidity and oxygen.
There are seven Emeria species that affect chickens. They are split into two different groups depending on what?
What are these two groups?
The pathology of the coccidiosis they cause:
Malabsorption group
Haemhorrhagic group
Eimeria spp are divided into Malabsorptive and Haemhorragic groups, based on their pathology.
The Malabsorptive is further divided into two groups based on their pathogenicity. What are they?
Moderately pathogenic:
- Eimeria avervulina*
- E. maxima*
Low pathogenicity:
- E. mitis*
- E. praecox*
What are the characteristics of coccidiosis in the Malabsorptive group? What happens to the chicken?
The malabsorptive type of coccidiosis is characterised by villous atrophy, mucoid enteritis but little haemhorrage caused by the protozoan parasites that invade the superficial layers (mucosal, submucosal) of the gut wall.
Diagnosis:
- Eimeria species that cause coccidiosis in chickens is diagnosed by post-mortem examination of the bird’s intestines. The region of the intestine affected indicates the species of Eimeria responsible.
- The presence of haemorrhage is also an indicator of Eimeria species in the Haemorrhagic group.
- Size of schizonts (after trophozoite stage enters schizogony) & oocysts found in mucosal scrapings also aids in diagnosis.
- The appearance of lesions.
Which regions of the gut are affected by the *Eimeria species *of the Malabsorptive group that cause moderately pathogenic coccidiosis & what type of lesions would you expect to see?
Malabsorptive, moderately pathogenic Eimeria species invade the upper-half of the intestines.
- E. acervulina - invades proximal GIT to duodenal loop; characteristic lesions are white “ladder” lesions ie., dense foci of gamonts & oocysts as well as watery exudate;
- E. maxima - named for its very large oocysts; found mid-gut, jejunal junction to the ileum; lesions are thickened walls with pink exudate
Diagnosis:
- Eimeria species that cause coccidiosis in chickens is diagnosed by post-mortem examination of the bird’s intestines. The region of the intestine affected indicates the species of Eimeria responsible.
- The presence of haemorrhage is also an indicator of Eimeria species in the Haemorrhagic group.
- Size of schizonts (after trophozoite stage enters schizogony) & oocysts found in mucosal scrapings also aids in diagnosis.
- The appearance of lesions.
Which regions of the gut are affected by the Eimeria species of the Haemorrhagic group that cause highly pathogenic coccidiosis & what type of lesions would you expect to see?
- E. necatrix - midgut
- E. tenella - invades deep into the caecal mucosa, causing the caecum to swell, become dark and thickened. Upon PM exam, a core of necrotic tissue and blood clots is evident.
**E. brunetti - **found much further down in the system, in the rectal wall
What are the characteristics of coccidiosis caused by Eimeria spp in the Haemorrhagic group?
What would you expect to see clinically?
The haemorrhagic type of coccidiosis is characterised in post-mortem exam by deep erosions in the epithelium when the cells rupture to release merozoites; destruction of crypt stem cells and marked haemorrhage.
The key difference from species of the Malabsorptive group is these Eimeria invade much deeper in the intestinal mucosal layer, replicating below the cells’ nuclei, causing detachment of the intestinal epithelial cells from the gut lining, and thus bleeding.
Clinically, blood-stained faeces, high morbidity & high mortality are presented by seriously affected animals.
Why is diagnosis using the morphology of oocysts not enough to identify the species of Eimeria?
E. maxima oocysts are the largest and E. mitis the smallest, but the rest are somewhere in
between.
Thus oocysts morphology can only help you identify between two malabsorptive species.
Explain the principles behind “lesion scoring” for diagnosis of Eimeria in poultry.
Lesion scoring is the most widely used method for identifying presence of Eimeria and coccidial species.
0 = no lesions
+1 = mild lesions
+2 = moderate lesions
+3 = severe lesions
+4 = extremely severe lesions or death
What can the colour of poultry faeces tell you about the type of Eimeria species that affected it to cause coccidiosis?
Bloody faeces indicates haemorrhagic coccidiosis (E. tenella);
Orange mucus + some blood & blood clots in faeces indicates the moderately pathogenic malabsorptive coccidian species, E. maxima;
Thickened intestinal wall, distended jejunum & ileum, lots of blood, brown mucus indicate *E. necatrix *(haemorrhagic)
Why would using PCR not be a very practical way to determine the Eimeria species causing coccidiosis in a boiler house?
It’s difficult get DNA from an unsporulated oocyst, so you would have to wait until it sporulates.
