Page 174 - The Veterinary Laboratory and Field Manual 3rd Edition

Parasitology 143

beyond the scope of this book but in cases where Specific nematodes of veterinary
a population of animals has a heavy worm infes- significance
tation despite having been treated this needs
to be reported to the veterinarian in charge so The next section is a brief summary of some of
that a suitable parasite management plan can be the important nematode parasites that are com-
developed and alternative treatment provided. monly seen in tropical and temperate climates.
It is generally best to alternate the products The examples selected illustrate key concepts
used. Advice on which products will work best in that should be taken into account when dealing
an area can be obtained from the regional animal with parasite problems. We have provided the
health authorities. Worm count (at necropsy) or ‘common’ name where appropriate but have also
faecal egg count examination after treatment used the scientific (Latin) name as the ‘common
(Faecal Egg Count Reduction Test – FECRT) names’ vary from region to region. For additional
are used to determine the efficacy of anthelmin- information, there are a good range of reference
tic treatment. In the laboratory, other tests can texts available that provide a more comprehen-
also be used to identify possible anthelmintic sive coverage of helminthology (see references
resistance, for example, the egg hatch assay and at the end of the chapter).
larval development assays.
Nematodes found in the stomach

It should be noted that helminth infections or abomasum
in a normal flock or herd usually follows a • Wire worms (Haemonchus spp.) are also called
binomial distribution; wherein, ~20% are ‘barbers pole’ worms and are red in colour,
heavily infected and a similar percentage the males are 10–20 mm long and the females
are infected with very few to no parasites. are 18–30 mm long, red striped and are eas-
The rest of the flock or herd will have a ily seen at necropsy. In sheep, the worms (in
moderate to low level helminth infection. sufficient numbers) can suck a significant
This suggests that we only need to treat amount of blood resulting in anaemia and
a proportion of the flock or herd, for exam- eventually oedema, due to fluid leakage asso-
ple, the heavy egg shedders, and leave the ciated with protein loss and debility. Fluid
more resistant animals (that is, moderate may specifically collect under the jaw, hence
and low shedders) so they form a refugia the term ‘bottle jaw’ for haemonchosis in
of ‘anthelmintic susceptible’ helminths in some areas. Acute disease may result from
pasture and slow down the development heavy infestation (2000–20,000 worms) in
of anthelmintic resistance in the flock/herd. young sheep (Haemonchus contortus), adult
An overall assessment of the whole flock/ sheep may develop a degree of immunity. The
herd to identify the heavy egg shedders and life cycle is illustrated in Figure 3.23.
targeting them for subsequent anthelmintic • Brown ‘stomach worm’ (Ostertagia spp.).
treatment and monitoring drug efficacy by These are smaller than wire worms but can
FECRT is a reasonable way to move forward cause severe clinical disease in ruminants.
in tackling anthelmintic resistance. Ostertagia (Teladorsagia) circumcincta and O. tri-
furcata cause inflammation of the abomasum
in sheep and goats. O. ostertagia is responsible
for significant losses in cattle causing aboma-
sitis, diarrhoea and weight loss. Ruminants

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