Lungworm in horses (dictyocaulus
arnfieldi)
The lifecycle of
lungworms is different to other nematodes as adults settle in the lungs rather
than the intestine. Eggs are laid then travel up the trachea, are swallowed and
passed out in the faeces. Further development then takes place on the pasture,
infective larvae are swallowed by horses or donkeys to further develop into egg
laying adults.
It is extremely rare
for lungworm larvae to develop to full maturity in horses as the horse is not a
good host for that particular parasite.
Horses can be infected with lungworm but as they do not mature in to egg
laying larvae in any numbers to sustain a population on the pastures. Exceptions to this in horses can arise in
very young or old horses and seriously depilated horses whose immune systems
are impaired.
Up to 70% of donkeys carry lungworms often
showing no clinical signs of infestation and it is in donkeys where the
parasite reaches full maturity. Donkeys do not always develop the symptomatic
cough that is seen in horses but if horses are grazed along side donkeys then
particular care must be taken to treat for lungworms accordingly with
particular attention to foals as they can sustain permanent lung damage if
infected.
Diagnosis can be done
through the actual physical and clinical signs which might be moderate
coughing, a slightly increased
respiratory rate or even severe persistent coughing and respiratory distress.
Fecal egg counts can be used to determine lungworm levels but a sedimentation
test is required so at least 3 times the amount of fecal matter needs to be
supplied to the laboratory.
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