Nematodirus

A nasty worm which is found in the small intestine and affects lambs. A diagnostic feature of this worm is that the eggs are twice the size of any other trichostrongyle family worm. 

Life Cycle

1. The unembryonated egg is shed in the faeces. Unlike ostertagia where the worms develops free living on the pasture, this worm develops to the L3 still inside the egg. I guess its similar to the cuticle of ostertagia- designed to survive the winter and overwinters as a larvated egg. 
2. The L3 hatches under specific requirements!

• A prolonged period of chill followed by.
• Exposure to a mean temperature of 10 degrees (similar to the optimum conditions for ostertagia development on pasture). 

3. The L3 is the infective stage. Ingested, and moults to the L4 stage in the intestinal lumen. The L4 then burrows into the mucosa before moulting to the L5. Adults reside in the Lumen.

PPP= 15 days (shorter than oestertagia). 

Pathogenesis & Disease

• The developing L5 destroy the mucosa (was the developing L4 and emerging L5 in oestertagiosis). 
• This leads to catharral (serous fluidy) enteritis & villous (absorption of stuff) atrophy.
• As you can imagine this leads to nutrient and fluid disruption being absorbed. 

This disease can cause around 20% mortality and 100% morbidity. Poor lambs :(. 

Only 2000 worms are needed to cause clinical signs. Much smaller when compared to ostertagia (40,000). 

Clinical Signs:

• Sudden outbreaks of acute, watery diarrhoea (eat a lot of worms in spring). 
• Inappetance & abdominal pain (yes.. you'd feel some pain too). 
• Dehydration and weight loss due to fluid and nutrients not being absorbed. 

Epidemiology

Disease appears in 4-12 week old lambs before they gain immunity A mean worm count of >500epg would signify a heavy infection. 

• En mass emergence of L3 in spring- similar to oestertagia (but happens in July). 
• Hatching must coincide with susceptible lambs- May-June. 
• Ewes have acquired immunity- unaffected.
• Lamb to lamb cycle. 
• Due to hatching requirements- the disease may not appear every year. 

Control

• Grazing management.
• Treatment- from April  after March turn out to June. 
• Not susceptible to injectable moxidectin. 
• Disease forecast- disease may not appear each year but recent autumn outbreaks as the period of chill is not needed.