Lecture 7 Flashcards
What is a parasite?
- An organism that lives on or in another organism causing some harm
-However, the term ‘parasite’ is also a collective term for the eukaryotic parasite species
What makes something a parasite?
- Metabolic dependence (nutrition, developmental stimuli, control of maturation)
-Genetic complementation
-Population dynamics (reproductive rate, lethal level, over-dispersion)
Important parasite groups- Microparasites
- Unicellular organisms
- Examples: Cryptosporidium, toxoplasma, coccidia
Important parasite group- Macroparasites
- Multicellular animals
- Examples: Roundworms (fluke), flatworms (ascaris) and arthropods (insects and mites)
Direct Life Cycle of coccidia
-Slide 9
- Only one host species is required for the parasite to complete its life cycle
Definitive/Final host
The host animal in which the parasite sexually reproduces
Coccidiosis
- The disease caused by Coccidia infections
- Common in young livestock
- Degree of damage to intestinal epithelium dependent on:
->Parasite numbers
->Location
->Depth of penetration
Coccidiosis in Poultry
- All production systems at risk
- Particularly deep litter systems
- Optimal conditions for oocyst development
- Overcrowded, unhygienic housing
- Poor ventilation
- Stress, malnutrition
- Mixed age groups
- High mortality rates
Coccidiosis in calves and lambs
- Mild infections well tolerated
- May cause diarrhoea in very young calves/lambs
- Outbreaks especially in (late) calves/lambs
- Outbreaks due to stress, poor hygiene, insufficient colostrum
- Adults act as carriers - Contribute to oocysts
Treatment for Coccidiosis
- Culling (poultry)
- Isolation
- Anticoccidials
- Supportive treatment: oral/intravenous rehydration
Control of coccidiosis
- Good hygiene (especially around feed and water troughs) and biosafety measures (restricted access)
- Avoidance of overcrowding
- Separate age classes
- Vaccination (only available for poultry eg paracox)
- Prophylactic anticoccidial treatment
Cryptosporidium
- Direct life cycle, faecal oral transmission
- Infectious to humans (zoonosis)
- Disease (cryptosporidiousis) mostly in:
-> Young calves, lambs and humans
-> Concurrent GIT infections
-> Immunocompromised hosts - Damage of enterocytes causes:
-> Diarrhoea, malabsorption and dehydration
-Oocysts very resilient to environmental stress (including regular drinking water treatment measures)
- Waterborne outbreaks common in Ireland
Crytosporidium in animals
- Persistent yellowish, watery, mucoid diarrhoea and lethargy
- Infected calves usually have mild to moderate diarrhoea that persists for several days regardless of treatment
- Age of onset tends to be later and lasts longer than common viral and bacterial infections
- Villous atrophy in the small intestine
- Large numbers of parasites embedded in the microvilli
- Symptomatic treatment in form of oral or parenteral fluid and electrolyte replacement
Crytosporidiosis in Ireland
- 82% of drinking water is derived from surface water- prone to contamination:
-> Agricultural run-off (slurry spreading, high stocking densities, livestock grazing)
-> Leaking septic tanks
-> Discharge from wastewater treatment plans - Water treatment with chlorine is not effective against Cryptosporidium
Control of Crypto on farm
- Reduce exposure to oocysts
-> Hygiene and biosafety
-> Raised feed and water troughs - Colostrum
- Calves in individual pens/separate age groups
- Avoid overcrowding
Control of municipal supplies
- Reduce exposure to oocysts
-> Catchment protection
-> Regular testing
-> UV, ozone treatment
-> Boil water notices
Toxoplasma
- Unicellular, apicomplexan, microparasite
- Cats (domestic and wild) are the definitive host
- Toxoplasmosis= infection caused by toxoplasma
- A classic zoonosis- infective agent passed from animals to humans
- 1/3 of the worlds population is exposed
Toxoplasma gondii life cycle
- Adult parasites in the intestinal cells of cats release oocysts into the environment that take up to 5 days to become infective. These can reinfect cats to complete the life cycle
- Sporozoites, hatch out from oocysts and invade cells of the body
- Tachyzoites, fast driving and present in lots of host cells
- Bradyzoites, more slowly developing and become incapsulated in tissues such as muscle, lung and the CNS
Look at slides 29-33 for more notes
Definitive host
The animal in which an adult parasite can reproduce sexually
Intermediate host
Supports the immature or non-reproductive stages of a parasite
Vartical transmission
When an infective agent passes from mother to offspring
Oocysts
Are disseminated in the environment
Tachyzoites
Responsible for rapid spread of the parasite between cells and tissues and for clinical manifestations
Bradyzoites
Within tissue cysts; remain dormant for the life of the host unless the individual becomes severely immunocompromised
Toxoplasmosis in cats
- Site of infection in the cat: small intestine
- Infections usually aclinical
- Most (all) cats with outdoor access become exposed
- First infection: short but high oocyst output
- Oocysts: highly resistant to adverse environmental conditions
Toxoplasmosis in sheep and goats
- 2nd most common cause for abortion in sheep
- Result of primary infection during pregnancy
- Transplacental transmission of tachyzoites
- Abortion and perinatal mortality in lambs
