Lecture 8 Flashcards
Another name for roundworms?
Nematodes
How many nematode species?
Estimated 1 million
Nematode apperance?
- Cylindrical worms with thick cuticle
- Separate sexes
Repeated moults during development of Nematodes
- Larval Stage 1 (L1)
- Larval Stage 2 (L2)
- Larval Stage 3 (L3)
- Larval Stage 4 (L4)
- Adult
Gastrointestinal Nematodes (GIN) of sheep, goats and cattle?
- Direct life cycle
- Larvae present on the grass cause infection
What is the infection with GIN called?
Parasitic Gastroenteritis (PGE)
Parasitic Gastroenteritis (PGE) results?
- Reduced feed intake
- Inefficient digestion of ingested protein
- Loss of protein due to damage to the epithelial barrier
- Diversion of available proteins to immune/inflammatory responses
PGE symptoms
- Diarrhoea
- Loss of appetite
- Dehydration
- Anaemia
- Bottle jaw
- Weight loss
Bovine PGE
- Ostertagia ostertagi and Cooperia spp.
- Calves, first grazing season most affected
- Older cattle may serve as a source of infection
- Disease mostly due to the presence of worms in the abomasum
Ovine PGE
- Many species
- Lambs generally more affected than adult sheep
- Peri-paturient rise in egg output
- Disease due to worms in the abomasum and the small intestine
Seasonality of PGE
- Eggs and larvae affected by environmental conditions
-> No development under 10 degrees, die off under 0 degrees
-> Mild winters = high survival on pasture = reservoir of infection
-Develop in Spring (warm and wet conditions)
-Gradual build-up of eggs/larvae on pasture during the grazing season (extent depending on stocking density)
- Hypobiosis in some spp:
-> Larvae on pasture that have been exposed to falling temperatures; more likely to undergo arrested development
-> Emergence of large numbers of larvae from glands/mucosa into limen in late winter/early spring can cause severe disease
-Build up of infective larvae on pasture during the summer
- Greatest disease risk mid-summer to autumn
When is PGE mostly observed?
- Spring born calves and lambs in their first grazing season (6-8 months old): Due to their exposure to large numbers of L3 on pasture
- Calves and lambs in late winter/early spring following first grazing season (yearlings): Due to mass emergence of hypobiotic larvae
What animals are less likely to get PGE?
- Older animals: Protected against clinical disease
- They can contribute to pasture contamination particularly ewes around parturition
Host Immunity against GIN
- Regular exposure to GIN results in the development of immunity
- Immunity to Teladorsagia circumcinta can take 10-12 months to develop while it develops more rapidly to Nematodirus battus
- Immune/ Resistant hosts can:
-Prevent worm migration and
establishment- Halt development at a less
harmful stage - Reduce the size and fecundity of
the worms
- Halt development at a less
- Adults that have developed immunity can ingest large amounts of larvae without developing clinical signs
- However, pregnant ewes can produce large numbers!
Nematodirus Battus
- Larvae develop to L3 stage inside the eggs
- Eggs are resistant to freezing
- Freezing temperatures followed by rise in temperatures (>10 degrees) stimulates synchronous hatching
- Mass hatching in Spring!
Parasitic Bronchitis (Hoose)
- Cattle lungworm (Dictyocaulus viviparus)
- Direct life cycle
- Eggs hatch before leaving the host
- Symbiotic relationship with fungus, Pilobolus
- Pilobolus (the hat tossing fungus)
D.viviparus: Clinical Signs
- Parasitic bronchitis
- Coughing
- Shortness of breath
- Nasal discharge
- Fever
- Weight loss
- Dehydration
- All ages are susceptible
- Calves usually acquire immunity following first grazing season
Parasitic Bronchitis: Epidemiology
- Source of infection at the start of grazing
-> Carrier animals (asymptomatic of hypobiotic)
-> Overwintering larvae - Infections peak in mid summer- late autumn
- In the past: mostly in calves during their 1st grazing season (immune therafter)
- More recently: Yearlings and replacement heifers most affected
Animals that are most at risk from PGE and parasitic bronchitis?
- Lambs
- Spring born dairy calves
- Autumn born dairy calves
- Beef calves
Use of Anthelmintics
- New class of anthelmintic drug almost every decade since the 1960’s
- Frequent use was recommended to maximise health, productivity and profitability
- Most recent = monepantel in 2008
Anthelmintic Resistance
- This approach of having a new drug every decade led to resistance every time
- Now, virtually all economically important helminth species are demostrating increasing levels of resistance
What do anthelmintic drugs control?
Helminths
Anthelmintic treatment failure in Ireland
Sample collection carried out by farmer:
- 15 lambs gathered in a pen, allowed to defecate
- Faecal samples taken from 10 faecal deposits and sent to approved labs
- Farmers uses drug of choice, and repeats sampling procedure in 7 or 14 days
Faecal Egg Count carried out by approved labs:
- Receive10 individual samples from farmer for both pre and post samples
- Combines proportionally to form one composite sample
- A composite pre and post treatment sample counted for each test
Anthelmintic treatment failure on Irish sheep farms
Overall treatment efficacy:
- Only 51% of anthelmintic treatments were considered effective
- No difference in treatment efficacy between each year
- No difference in treatment efficacy between regions
- No difference in treatment efficacy between sampling months
- Approximately half of all treatments failed in each year
- BZ least effective but most popular anthelmintic
- Fewer farmers using BZ and switching to ML by the end
- Resistance is likely the cause of much of the treatment failure observed
Characterisation of Ivermectin and Multi-Drug Resistance in Irish T.circumcincta
- 2014 (n=60) and 2015 (n=57) artificially reared lambs acquired.
- FEC on 3 consecutive days to ensure egg free
- Day 0, infected with 7,500 T.circumcinta
- Day 23, FEC to ensure infection worked
- Day 34, lambs assigned to BZ, LEV, IVM and Control groups
- Post treatment FEC’s on days 7,14 and 16 post treatment
Conclusion:
- Ivermectin resistance confirmed on two sheep farms
- Teladorsagia circumcincta was the only resistant species
- Both strains were also resistant to Benzimidazole and Levamisole
- First confirmed case of Multi-drug resistance in Ireland
- Moxidectin resistance not detected
Aims of controlling helminths in grazing ruminants?
- Minimise anthelmintic use
- Maximise non-chemical control methods
- Keep worm burdens below levels that affect welfare and production
- Use anthelmintics strategically: identify most at risk/heavily infected animals and focus treatment on those
- Leave a portion of the parasite population undosed (either in animals or in the environment)
- Never overdose
- Rotate drugs with different chemical classes
Controlling helminths in grazing ruminants
Good pasture management- Prevent the build up of parasite numbers over the grazing season and avoid overuse of the pasture
- Reduce stocking densities
- Alternative grazing (switching between different livestock species and crops)
- Mixed grazing (grazing different livestock species at the same time)
- Rotational grazing (young susceptible stock followed by older immune stock)
- Forecast systems
- Vaccination (parasitic bronchitis)
- Good surveillance (faecal egg counts, growth rates, body condItion scores)
- Monitoring for anthelmintic resistance (FECRT)
