http://www.nadis.org.uk/Nematodirosis/NEMATO_1.HTM

NADIS disease bulletins are written specifically for farmers, to
increase awareness of prevalent conditions and promote disease
prevention and control, in order to benefit animal health and welfare.
Farmers are advised to discuss their individual farm circumstances
with their veterinary surgeon.


Nematodirosis
Nematodirosis is usually seen in young lambs and is characterised by
acute onset profuse watery diarrhoea, lethargy, abdominal pain rapid
weight loss, dehydration and sudden deaths.




SCOUR AND DEATH IN A WELL GROWN 8 WEEK OLD LAMB DUE TO NEMATODIROSIS






SCOUR AND RAPID WEIGHT LOSS IN 8 – 10 WEEK-OLD LAMBS



The clinical signs of nematodirosis are associated with severe
catarrhal inflammation of the small intestine caused by the presence
of 2000 or more immature or adult Nematodirus battus worms.




SEVERE CATARRHAL INFLAMMATION OF THE SMALL INTESTINE ASSOCIATED WITH
TANGLED KNOTS OF N. BATTUS WORMS



Risk assessment

The life cycle and transmission of nematodirosis differs from that of
the other important sheep worms. Infective larvae develop within the
N. battus egg and can survive freezing and very low temperatures on
pasture for up to two years. Hatching and release of infective larvae
only occurs after a period of cold exposure followed by a period of
daily maximum temperatures above 10oC. Infective N. battus larvae
generally don’t survive for long on pasture when weather conditions
are warm and dry, but can survive for several months during cool and
damp weather. Disease outbreaks are seen when the presence of large
numbers of larvae on pasture coincides with the grazing of susceptible
lambs. Most nematodirosis outbreaks are therefore seen in May and
June, the precise timing being influenced by local weather conditions
and sheep grazing management. While the warm weather during March
this year would have encouraged an early hatch of N. battus eggs,
subsequent cool and wet weather will have enabled prolonged larval
survival on pasture, which April-born lambs are now beginning to eat.



The life cycle of N. battus essentially involves transmission from one
season’s lamb crop to the next and the accumulation of infection on
pasture takes place over a period of grazing by susceptible lambs (and
occasionally dairy calves). Typically, lambs which are grazed on
pastures used for young lambs during previous years are at greatest
risk. However, during recent years, nematodirosis has also been seen
in older lambs during late summer. This is probably associated with
the effect of cold and wet summers on larval survival and means that
some pastures may now be heavily contaminated as a result of grazing
by older scouring lambs during the previous summer.




IN RECENT YEARS NEMATODIROSIS OUTBREAKS HAVE BEEN SEEN IN OLDER LAMBS
DURING LATE SUMMER



Very young lambs are at low risk because they do not graze significant
amounts of pasture, while older lambs develop some degree of immunity,
which is partly dependent on previous exposure.



Diagnosis of nematodirosis

The diagnosis of nematodirosis is based on knowledge of the local
disease pattern, history of susceptible lambs grazing pasture used by
young lambs in previous years (or pasture where nematodirosis was
identified in older lambs during the previous summer) and clinical
signs of scour, weight loss, or sudden death. The diagnosis is
supported by the identification of Nematodirus sp. eggs in faeces,
although the absence of eggs in faecal samples does not exclude a
diagnosis of nematodirosis, because disease can occur during the
prepatent period of infection.



The diagnosis of nematodirosis can be confirmed by post mortem
findings of catarrhal enteritis and the presence of slender 2 cm long
white worms in the lumen of the intestine. N. battus worms are
sometimes seen in tangled knots with a characteristic ‘cotton wool
ball’ appearance, although in acute cases these may have been expelled
before death.




TANGLED KNOTS OF N. BATTUS WORMS



Most of the modern anthelmintics are effective against N. battus
although none afford persistent protection. During high risk seasons
two or three anthelmintic treatments may be required before weaning.
While anthelmintic resistance by N. battus is not currently recognised
as a problem in the UK, its appearance is inevitable and should be
monitored.



Spring teladorsagiosis

During recent years there have been several reports of teladorsagiosis
in 8 – 10 week-old lambs, associated with the overwinter survival of
high burdens of Teladorsagia circumcincta (brown stomach worm) larvae
on pasture. Most spring teladorsagisois outbreaks have occurred on
pastures which were grazed by older lambs during the previous winter
months.



In several of the nematodirosis outbreaks which have been investigated
this year, both T. circumcincta and N. battus infections have occurred
concurrently. Unfortunately, benzimidazole (white drench) resistant
T. circumcincta are present in many UK flocks. Therefore, white
drenches should be avoided for nematodirosis control where
benzimidazole resistance has been identified and the risk of spring
teladorsagiosis exists. Irrespective of the anthelmintic used,
checking the faecal egg counts of about 7 lambs, 7 – 10 days after
treatment can provide useful reassurance about the efficacy of the
drug.




NEMATODIRUS EGG (LEFT) AND TELADORSAGIA EGG (RIGHT)



Your vet can provide advice about the nematodirosis risk in your
flock, monitoring for resistance and most appropriate choice of
wormer.

Neil Sargison BA VetMB DSHP FRCVS

Copyright © NADIS 2004






"As I was walkin' - I saw a sign there
And that sign said - no tress passin'
But on the other side .... it didn't say nothin!
Now that side was made for you and me!"
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