Apicomplexa- Eimeria

Question 1

Name the three principal parasitic groups within Apicomplexa

Answer 1

Hematozoa
Coccidia
Cryptosporidia

Question 2

Do Eimeria show host-specificity?

Which hosts are they most important in?

Answer 2

Yes, although many species can affect the same host.

Poultry, ruminants, pigs, rabbits

Question 3

Does severity of host pathology depend on the level of infection, or does infection always create the same pathology?

Answer 3

Dependent on the level of infection

Question 4

By which route of transmission does Eimeria spread in poultry? How can you reduce spread?

Answer 4

Faecal-oral route.

• Put waterers and feeders at back level so birds cannot defecate or scratch litter into them
• Anti-roosting wire over the feeders
• Clean water and feeders frequently
• Add fresh litter/ rake to cover parasites
• Remove infected droppings
• Keep on wire so that birds have no contact with droppings (as in layer hens)

Question 5

What is the economical significance of Eimeria in poultry?

Answer 5

Affects 40billion chickens worldwide

UK cost of disease~ £42million/ annum

Question 6

Lifecycle of Eimeria in poultry

Answer 6

1) Sporulated oocyst is ingested, it ruptures to release SPOROZOITES that infect the gut epithelium
2) Maturation to SCHIZONT, which ruptures, releasing MEROZOITES into the gut lumen, each merozoite infects one new epithelial cell- this process is called Schizogeny
3) Gametogeny- sexual stage. Gut epithelial cell containing merozoites ruptures, each infects another new gut epithelial cell, where it matures into either a MACROGAMETE (female, unicellular) or MICROGAMETOCYTE (male, full of microgametes). 4) Microgametocyte ruptures, the microgametes fertilise the macrogamete to produce a ZYGOTE
5) Zygote passed in faeces onto the litter, where it develops into an OOCYST. Under correct conditions the oocyst will sporulate, ready for ingestion.

Question 7

What conditions are required for sporulation of oocysts? Temp/humidity

Answer 7

27˚C

80% humidity

Question 8

Which form of oocyst is infective?

Answer 8

Sporulated

Question 9

Name 4 features of a sporulated oocyst

Answer 9

Sporocysts
Sporozoite
Residual Body (material left over from sporulation)
Micropyle (susceptible to CO2 and enzymes, permits the entry of bile salts and trypsin that stimulate the release of sporozoites)

Question 10

In poultry Eimeria- In one sporulated oocyst, how many

a) sporocysts
b) sporozoites

Answer 10

a) 4

b) 8 (2 within each sporocyst)

Question 11

How would you identify a macrogamete?

Answer 11

Large, single nucleus, multiple food granules at the periphery

Question 12

There are 6 main species of Eimeria in poultry. Which 3 are the most pathogenic? 
E. tenella
E. maxima
E. acervulina
E. necatrix
E, mitis
E. brunetti

Answer 12

E. tenella
E. necatrix
E. brunetti

The others are less pathogenic

Question 13

What causes the pathogenesis associated with Eimeria in poultry?

Answer 13

Destruction of gut epithelial cells :
Cellular damage –> villus atrophy –> malabsorption of nutrients –> limited weight gain/weight loss, loss of egg production, blood loss with some species, death in severe cases

Question 14

Eimeria tenella

High or low pathogenicity?
Which age group does it affect?
How long for development?
What is the location of the epithelial cells it invades?
Do sporozoites remain in the epithelial cells of villi or do they migrate?
Which region of the gut do they localise in?
Diarrhoea?
Blood in faeces?

Answer 14

Highly pathogenic
Birds aged 3-7 weeks
6-7 days to develop
Epithelial cells in the Crypts of Lieberkuhn
They are carried in macrophages to the Lamina Propria
Caeca
Diarrhoae- yes
Blood in faeces- yes

Question 15

Eimeria tenella

3 features of PM

Answer 15

1) caeca filled with fresh or clotted blood
2) Haemorrhages can give a mottled appearance
3) Caecal content becomes thicker, mixed with fibrinous exudate and acquires a cheese-like appearance

Question 16

Eimeria brunetti

High or low pathogenicity? 
Which age group does it affect?
Mortality? 
How long for development? 
Which region of the gut do they localise in?
What is caused in the SI?

Answer 16

High pathogenicity 
Affects older birds than tenella
Variable mortality
Slower development
Localise in the terminal SI and rectum, sometimes caeca also
Causes haemorrhage in the SI

Question 17

Eimeria necatrix

Which of the other Eimeria does necatrix share many features with? What is the main difference between them?

Name the alternative mode of transport used by sporozoites of necatrix

Answer 17

Brunetti, necatrix is localised in the middle section of the SI with some involvement of the caeca whereas brunetti is more terminal

Some macrophage transport

Question 18

Eimeria maxima

Pathogenicity? 
Blood in faeces or not? 
Localised to which region? 
What gross lesions are seen? 
When does tissue damage occur? 
Which other eimeria is similar to maxima but with less severe lesions?

Answer 18

Moderate-low pathogenicity, depending on the strain
Can produce blood in the faeces
Localised to SI
Gross lesions- oedema and gut swelling with haemorrhage, of the whole SI
Gametogeny is when tissue damage occurs, due to the large gametes developing in a sub-epithelial location
Eimeria mitis

Question 19

Eimeria acervulina- most widespread species

Pathogenicity?
What stage causes the pathogenicity?
Blood and haemorrhage?
What fluid is seen in the intestine?
Localisation?
Which disease of chickens is associated with this?
Describe the appearance of the intestine when infected

Answer 19

Moderate to low pathogenicity
Pathogenicity is caused by the superficial development of schizonts and gametocytes
No blood or haemorrhage
A watery exudate in the intestine
Duodenal localisation
Bacterial enteritis in chickens
Intestine has normal mucosa, thick and orange coloured, with white spots that indicate the location of developing gametes and oocysts

Question 20

Name 4 diagnostic approaches to Eimeria

Answer 20

Appearance of bird- huddled, ball posture, closed eyes, dirty ruffled feathers, drooping wings, failure to thrive

Abnormal faeces- liquid +/- blood and mucus

Laboratory detection of oocysts in faeces using a semi-quantitative method

PM the bird- anaemic internal organs with pallor; consider the gut appearance and location of lesions; identification of schizonts on slide

Question 21

Epidemiology- what host factors can reduce susceptibility to disease?

Answer 21

Age- disease of young birds so older birds are less susceptible

Previous exposure can create species-specific immunity

Genetics- some breeds/strains appear to be less susceptible to coccidia

Diet- good nutrition strengthens the immune system

Question 22

Epidemiology- husbandry- which factors ought to be considered?

Answer 22

Rearing system- raising on wire reduces contact with infected litter, lower the stock density, monitor temperature and humidity

Hygiene- oocysts persist in the litter

Prophylactic drugs- underdosing may occur if given in feed

Question 23

Coccidiosis in broilers

Self limiting? Why?
How many oocysts can be found per gram of litter in very cramped conditions?
Severity of disease?
Why might some birds still be susceptible to disease at 3-5 weeks?
Why might it cause reduced profit?

Answer 23

It is self-limiting, as natural immunity develops with exposure to infected litter
100-300k oocysts/gram litter
Can be fatal
Not all young birds have the same exposure to infected litter so may not develop immunity, hence prolonged susceptibility at a time that corresponds to the highest concentration of oocysts
Reduced profit- reduced weight gain, longer time to slaughter and loss of birds

Question 24

Coccidiosis in laying hens

Do they develop good immunity? Why?
Are layers given live vaccines?

Answer 24

No, because they are often caged on wire so have little access to infected litter. This is good and bad, good as chance of infection is reduced but bad as immunity won’t develop.

Not given live vaccines as they don’t have the prolonged exposure required to maintain immunity

Question 25

Name the four principal methods of coccidiosis control

Answer 25

Sanitation, Litter, Anticoccidials, Vaccination

Question 26

Sanitation and control- methods?

Answer 26

Disinfectants don’t work, remove droppings and practice good hygiene

Put waterers and feeders at back level so chickens can’t shit in them

Put anti-roosting wire over the feeders

Clean water and feeders frequently

Keep different age groups seperately

Add fresh litter or rake litter frequently to cover the parasites

Question 27

It is important to keep litter dry, how?

Answer 27

Remove any wet or crusted litter, use a propane radiant brooder to dry out litter, good ventilation, prevent water leaks, insulate building to prevent condensation, don’t feed rations with excessive protein or salt

Question 28

Anticoccidials- how are they used? What is the difference between coccidiostatics and coccidiocidals?

Answer 28

Primarily as a prophylaxis, feed continuously but change the drug every 4-6 weeks to prevent resistance developing.
Theraputic use is in water, often combined with vitamins A and K and antibiotics to prevent secondary infections and improve recovery rate

Coccidiostats arrest intracellular growth, growth resumes if drug is withdrawn

Coccidiocidals kill the coccidia during development. Some can be static in the short term then cidal long term.

Question 29

Vaccination

Name the Live virulent vaccine and the live attenuated vaccine

Why are they not often used in broilers?

Answer 29

Coccivac is live, virulent. Used for low dose infections and is combined with chemotherapy. Pathogenicity can occur.

Paracox is attenuated, contains a mixture of oocysts. Sprays or gels for use in day old chicks, protection starts from 14-21 days post vaccination.

High cost prevents their use in broilers, shuttle programmes that rotate between vaccines and coccidiostats were developed to reduce the cost