Apicomplexa- Eimeria Flashcards
Name the three principal parasitic groups within Apicomplexa
Hematozoa
Coccidia
Cryptosporidia
Do Eimeria show host-specificity?
Which hosts are they most important in?
Yes, although many species can affect the same host.
Poultry, ruminants, pigs, rabbits
Does severity of host pathology depend on the level of infection, or does infection always create the same pathology?
Dependent on the level of infection
By which route of transmission does Eimeria spread in poultry? How can you reduce spread?
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)
What is the economical significance of Eimeria in poultry?
Affects 40billion chickens worldwide
UK cost of disease~ £42million/ annum
Lifecycle of Eimeria in poultry
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.
What conditions are required for sporulation of oocysts? Temp/humidity
27˚C
80% humidity
Which form of oocyst is infective?
Sporulated
Name 4 features of a sporulated oocyst
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)
In poultry Eimeria- In one sporulated oocyst, how many
a) sporocysts
b) sporozoites
a) 4
b) 8 (2 within each sporocyst)
How would you identify a macrogamete?
Large, single nucleus, multiple food granules at the periphery
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
E. tenella
E. necatrix
E. brunetti
The others are less pathogenic
What causes the pathogenesis associated with Eimeria in poultry?
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
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?
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
Eimeria tenella
3 features of PM
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
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?
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
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
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
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?
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
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
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
Name 4 diagnostic approaches to Eimeria
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
Epidemiology- what host factors can reduce susceptibility to disease?
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
Epidemiology- husbandry- which factors ought to be considered?
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
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?
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
Coccidiosis in laying hens
Do they develop good immunity? Why?
Are layers given live vaccines?
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
Name the four principal methods of coccidiosis control
Sanitation, Litter, Anticoccidials, Vaccination
Sanitation and control- methods?
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
It is important to keep litter dry, how?
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
Anticoccidials- how are they used? What is the difference between coccidiostatics and coccidiocidals?
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.
Vaccination
Name the Live virulent vaccine and the live attenuated vaccine
Why are they not often used in broilers?
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
