Lecture 7

Question 1

What is a parasite?

Answer 1

• 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

Question 2

What makes something a parasite?

Answer 2

• Metabolic dependence (nutrition, developmental stimuli, control of maturation)
  -Genetic complementation
  -Population dynamics (reproductive rate, lethal level, over-dispersion)

Question 3

Important parasite groups- Microparasites

Answer 3

• Unicellular organisms
• Examples: Cryptosporidium, toxoplasma, coccidia

Question 4

Important parasite group- Macroparasites

Answer 4

• Multicellular animals
• Examples: Roundworms (fluke), flatworms (ascaris) and arthropods (insects and mites)

Question 5

Direct Life Cycle of coccidia

Answer 5

-Slide 9
- Only one host species is required for the parasite to complete its life cycle

Question 6

Definitive/Final host

Answer 6

The host animal in which the parasite sexually reproduces

Question 7

Coccidiosis

Answer 7

• The disease caused by Coccidia infections
• Common in young livestock
• Degree of damage to intestinal epithelium dependent on:
  ->Parasite numbers
  ->Location
  ->Depth of penetration

Question 8

Coccidiosis in Poultry

Answer 8

• 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

Question 9

Coccidiosis in calves and lambs

Answer 9

• 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

Question 10

Treatment for Coccidiosis

Answer 10

• Culling (poultry)
• Isolation
• Anticoccidials
• Supportive treatment: oral/intravenous rehydration

Question 11

Control of coccidiosis

Answer 11

• 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

Question 12

Cryptosporidium

Answer 12

• 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

Question 13

Crytosporidium in animals

Answer 13

• 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

Question 14

Crytosporidiosis in Ireland

Answer 14

• 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

Question 15

Control of Crypto on farm

Answer 15

• Reduce exposure to oocysts
  -> Hygiene and biosafety
  -> Raised feed and water troughs
• Colostrum
• Calves in individual pens/separate age groups
• Avoid overcrowding

Question 16

Control of municipal supplies

Answer 16

• Reduce exposure to oocysts
  -> Catchment protection
  -> Regular testing
  -> UV, ozone treatment
  -> Boil water notices

Question 17

Toxoplasma

Answer 17

• 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

Question 18

Toxoplasma gondii life cycle

Answer 18

1. 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
2. Sporozoites, hatch out from oocysts and invade cells of the body
3. Tachyzoites, fast driving and present in lots of host cells
4. Bradyzoites, more slowly developing and become incapsulated in tissues such as muscle, lung and the CNS

Look at slides 29-33 for more notes

Question 19

Definitive host

Answer 19

The animal in which an adult parasite can reproduce sexually

Question 20

Intermediate host

Answer 20

Supports the immature or non-reproductive stages of a parasite

Question 21

Vartical transmission

Answer 21

When an infective agent passes from mother to offspring

Question 22

Oocysts

Answer 22

Are disseminated in the environment

Question 23

Tachyzoites

Answer 23

Responsible for rapid spread of the parasite between cells and tissues and for clinical manifestations

Question 24

Bradyzoites

Answer 24

Within tissue cysts; remain dormant for the life of the host unless the individual becomes severely immunocompromised

Question 25

Toxoplasmosis in cats

Answer 25

• 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

Question 26

Toxoplasmosis in sheep and goats

Answer 26

• 2nd most common cause for abortion in sheep
• Result of primary infection during pregnancy
• Transplacental transmission of tachyzoites
• Abortion and perinatal mortality in lambs