Parasitology - Avian Coccidiosis Flashcards Preview

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Flashcards in Parasitology - Avian Coccidiosis Deck (22):
1

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

 

 

2

What is the pre-patent period of Eimeria spp that cause coccidiosis?

4-5 days for most species.

3

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.

4

When are Eimerian oocyts considered infective?

After they have undergone asexual division, aka sporogony, to form four sporocysts with two sporozoites inside each.

5

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. 

6

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

7

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

8

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.

 

9

Diagnosis:

1. 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. 

2. The presence of haemorrhage is also an indicator of Eimeria species in the Haemorrhagic group

3. Size of schizonts (after trophozoite stage enters schizogony) & oocysts found in mucosal scrapings also aids in diagnosis.

4. 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

 

10

Diagnosis:

1. 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.

2. The presence of haemorrhage is also an indicator of Eimeria species in the Haemorrhagic group.

3. Size of schizonts (after trophozoite stage enters schizogony) & oocysts found in mucosal scrapings also aids in diagnosis.

4. 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

11

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.

12

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.

13

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

14

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)

15

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.

16

What stages of Eimeria development are compared when diagnosing species with histopathology?

Merozoites and schizonts are compared across species.

Only E. maxima is the biggest oocysts and E. mitis the smallest, but everything else is in-between so there's no point just looking at oocyst size. 

17

The PPP of Eimeria spp is 3-4 days but the oocysts can survive, unsporulated, for months or years. 

What are the other features of Eimeria that make it IMPOSSIBLE to keep poultry-keeping buildings free of infection? 

1. Chicks get infected by pecking the ground as soon as they arrive there.

2. Biotic potential is enormous - thousands of oocysts are excreted in faeces for every oocyst ingested & PPP/generation time is very short

3. Immunity builds up slowly so high stocking densities worsen the situation

18

What is it about the chicken's immunity to Eimeria spp that  is good for vaccine usage and also bad for vaccine development/usage?

Chickens have no passive immunity to the protozoan antigens, but but infection DOES induce very strong immune response (good for vaccine).

However, the immune response is highly host specific (bad for vaccine).

19

In controlling coccidiosis in a boiler or hen house, you need to consider management & hygiene + drugs. Ie., Integrated Control.

Most important management & hygiene issues are ensuring high litter quality, then stocking density & ventilation.

What drugs would you use to control spread of coccidiosis for hens & broiler breeders bred to supply eggs? Broiler chicks? Broilers?

Replacement layers & broiler breeders:
- Paracox (multivalent attenuated live vaccine) contains live strains of 7 species; “precocious” strains because their PPP is shorter than normal; chicks vaccinated w/ single dose @ 1-9 days old by ingesting in water or feed or sprayed on feathers; vaccinated birds can have suboptimal growth rates; costly compared with chemotherapy ∴ NOT used for broilers

- some replacement layers & broiler breeders ares simply allowed to develop their own immunity as growth rate not important ∴ vaccinated or use “step down” medication regime that allows some infection to cycle through,
allowing them to develop immunity

Broiler chicks:
- Paracox 5 - for broiler chicks; similar to above w/ 5 strains representing 4 most important Eimeria species in broilers (E. acervulina, E. maxima, E. mitis & E. tenella)

Broilers:
- life-span less than 7 weeks ∴ must grow @ max. potential (too fast for immunity to develop)
- continuous use of in-feed prophylactic drugs; need to be withdrawn before slaughter

20

Aside from vaccines, what other prophylaxis (chemoprophylaxis) are available & used, especially in broilers that don't live long enough to develop immunity from vaccination? 

Chemoprophylaxis:

Toltrazuril: in drinking water, 21-day withdrawal period 

Ionophores: eg. Monensin, Narasin, Lasalocid, Salinomycin
85% of all anti-coccidials; have dose-related response
At high concentrations, ionophores are toxic, esp. to horses
Importantly, they don’t kill off all parasites so hosts can build up some immunity

 

21

85% of all anti-coccidials are ionophores, used especially for broilers who don't live long enough (seven weeks) to develop immunity against coccidiosis-causing Eimeria spp from vaccination. 

What are some ionophores and how do they work?

Ionophores:
 Monensin, Narasin, Lasalocid, Salinomycin

How ionophores work:

They don’t kill off all parasites so hosts can build up some immunity:

 In presence of Monensin, for example, Na+ enters sporozoite → osmotic pressure increases inside parasite as water flows in → parasite depletes energy store attempting to restore Na+:K+ ratio & osmotic balance → energy depletion + structural damage → death of organism

 

22

How do poultry breeders deal with resistance to chemoprophylactics such as ionophores? 

Producers tend to use “shuttle” programme of using different drugs in sequence during growing period to minimise risk of resistance, protect bird while vulnerable & ensure good immunity development before withdrawal period.

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