Coccidosis Flashcards
1
Q
Coccidia
A
- Coccidiosis: name of the disease produced
- All need to have at leasr one lifecycle
- Protosomes: single celled organisms
- Toxoplasma spp. (cyst)
- Eimeria spp. (Non-Cyst)
2
Q
Eimeria spp.
A
Eimeria Species
- Broad range but are completely species specific (only affects cattle, birds, sheep or reptiles etc)
- Can affect almost all livestock but are HOST SPECIFIC!
One kind can only infect sheep
One kind can only infect chicken
So on…..
- Not zoonotic, not transferrable between species & none affect humans
- ↑ prevalence in chickens due to ↑ stocking densities large economic impact (>£2billion/year)
- 62 billion born a year–> CAN INFECT VAST NUMBER OF POULTRY
3
Q
Chickens and Eimeria spp.
A
Problem:
- The settings that chicken are in are cramped and in close quarters
- One host will host the replication ofthe parasite and then the poultry surrounding will get sick from infection
- Backyard system would probably get an infection, but you wouldn’t see disease
- Vaccines can include all 7 but there is a cost issue, with broilers you would want to include the 3-5 species of coccidia that you would see
- A third of antimicrobials sold for use in UK agriculture arecoccidiostats!! –> becoming a big issue
- ranked in top 20 veterinary disease/pathogens globally based upon impact on the poor –> If you cant afford to have cattle/pigs and only can get chickens, large impact
4
Q
Life Cycles of Coccidia
A
- Direct: goes from host to host of same host type e.g. Eimeria
- Indirect: has a definitive/ intermediate host, e.g. Sarcocystis
- Facultative: can do either, e.g. Toxoplasma
5
Q
Eimeria Life Cycle
A
- Sporulation occurs outside the host (requires several days and oxyfgen
- Must go through sporulation process to be infectious! It is a metabolic process
- In one egg (oocyst) you are looking at 8 parasites (sporozoites)- 2 sporozoites per sporocyst
- After sporocysts have been released from the oocyst in the gut through excytation, sporocysts will pass into intestines and the sporozoites will emerge
6
Q
Excystation
A
- Sporocyst excysting from oocyst, sporozoite emerging from sporocyst
7
Q
Sporozoite
(Eimeria)
A
- 1st motile stage of parasites life cycle will move around until it finds a cell to invade to initiate infection (in the intestine)
- Apical Complex: Shared by other parasites of the phylum
- Series of organelles that secrete proteins that allow that parasite to attach and invade
- when the sporozoite comes out of the sporocyst it will glide along the intestine until it finds a cell to invade
- at that point stands on its head and drives itself into the cell
- depending on parasite actinomyosin is a pretty quick process (about 10-15 seconds)
- parasite basically holds on a pulls itself into the cell
- once it is in the cell it become a Trophozoite and undergoes a round of asexual replication to form a Schizont
- within the schizont it produces merozoites and those are the second motile stage of the parasites life cycle
8
Q
Schizogany
A
- asexual reproduction by multiple fission, found in some protozoa, especially parasitic sporozoans
- The parasite undergoes asexual replication in the schizont
- the schizont will end up being packed with merozoites, those will invade neighboring cells and continue the infection process
- They have several rounds of this asexual replication, the amount of rounds depends on the species! (either 3 or 4 rounds)
- After 3 or 4 rounds they differentiate into gametes (the sexual stage of replication) -male gamete packed with sperm and female macrogametes that are like ova
- male gametes will emerge and fertilize the female macrogamete
- from the zygote, secretes an oocyst wall and it is released into the environment through faeces!!
9
Q
Eimeria
Sporulation
A
- Non-infectious egg (oocyst) is excreted environment
- Oocyst sporulates (20-30um) outside of host & becomes infectious
- Conditions: temps >2 degrees, humidity and oxygen, takes several days (>2)
- –>a round of meiosis then mitosis –> 4 sporocysts (each containing 2 sporozoites)- so one oocyte contains 8 parasites & can survive environment for long periods of time (6 months- >1 year)
10
Q
Eimeria Spp.
(Key Facts)
A
- Many Species (hundreds of thousands)
- Direct Life Cycle (no intermediate hosts or vectors)
- Faecal- oral transmission
- Sporulated oocyst 20-30 um (very small, stongyle is 80um) has 4 sporocysts each containing 2 sporozoites
- Host specific
- Self- Limiting:
3 or 4 rounds of replication
- then sexual replication before leaving the host
- not driven by the host immune response , parasite life cycle terminates!
- “hit and run” parasites, get in and replicate quickly
11
Q
Pathogenecity
A
- Some are more pathogenic than others
- But some effect is dose dependent (amt of parasite)
- 2 groups:
- Malabsorptive Group (Biggest issue in U.S. -E. maxima) - E. acervulina and E. maxima (low pathogenicity: E. mitis & E. praecox) - malabsorptive because later stages of the lifecycle (gametes, zygotes, oocysts) will actually cause problems in the gut). Form a physcial barrier that disrupts gut function and absorption of nutrients.
- also stimulate the production of mucus
- result in villous atrophy and mucoid enteritis–> decreased weight gain & increased feed conversion ratio
- these are located more at the top of the cells they invade (above nuclei)
- Haemorrhagic group E. tenella, E. necatrix & E. brunetti
- these cause much more damage in the gut
- will see haemorrhage, not just damage
- earlier stages of the lifecycle cause problems here (asexual)
- cells rupture to release merozoites causing deep erosions and haemorrhage –> bloody faeces, high morbidity, high mortality
- these go much deeper, even below the nuclei –> when they rupture tehy cause much more damage!!
12
Q
Invasion
A
Invasion
- Once in the gut, the Eimeria drive their way into the epithelial cells- fairly quick process (10-15secs)
- Dependent on parasite actionmyosin
13
Q
Schizogony (asexual reproduction)
A
Schizogony (asexual reproduction)
- Sporozoites–> trophozoites and undergo schizogony
- Schizonts produce large numbers of merozoites- which are released & invade other parts of the gut
- Number of times this cycle occurs is hardwired- different species have different numbers of rounds of
- asexual replication, its normally 3/4, after that they differentiate into male/ female gametes
14
Q
Gametology
A
Gametology
- ♂ gametes have 2 flagella
- fuse with ♀ –> zygote
- –> oocyst which is shed–> environment
15
Q
Summary of Eimeria Life Cycle
A
Summary
Eimeria replicate in intestine, are excreted into environment (oocyst) undergo rounds of sporulation and are the ingested and start life cycle again
- Direct life cycle
- Self-limiting- leave host once gamete
stage is reached so no residual infection
- Faecal-oral transmission
- PPP= 138hours (E. tenella)
20
Q
Chemoprophylaxis
A
- Ionophores= dominant (most important)- dose related response: suppress infection but don’t completely stop it so inclusion rate is important, ‘leaky’ so allows chickens to develop immunity
- Forms molecular pore on parasite–> Na+ enters–> parasite must pump the Na+ out, but it requires energy, once they have run out they try & balance out the concentration by absorbing water instead –> swollen parasite- much harder to invade cells/ replicate. the parasite life cycle can’t really continue, but the host can still build up an immune response by recogntion of the parasite
- How we include in diets is important as they are toxic
- Highly toxic particularly to species such as horses (very susceptible!)- safety precautions regarding litter
- Classed as antibiotics (ZFAs-zootechnical feed additives/MFS- medicated feed supplements)- so there’s a big drive to ↓ their use
- Withdrawal period: 3-5 days
- “leaky” –> ISSUE
- Other chemicals = (anticoccidials) all or nothing (kill parasite or don’t) so can select for resistance
- chemical drugs are a kill or no kill method
-Most commonly give a mix of an ionophore and a chemical (Maxiban)
Not really any new coccidial drugs, problem as we see new forms of parasite
Resistance develops very fast
24
Q
GIT of a chicken
A
