Page 729 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

704 CHAPTER 3

VetBooks.ir PARASITIC CONDITIONS

Diagnosis
LUNGWORMS
Clinical examination is not diagnostic, although a
Definition/overview heaves-like disease in one or more horses in a group
Dictyocaulus arnfieldi causes parasitic pneumonia in at pasture in the late summer that have been graz-
horses. Donkeys and foals are the patent hosts; in ing with donkeys should raise suspicion. In donkeys
horses the infection is usually non-patent. Infection and foals only, faecal examination using the modi-
in donkeys is usually subclinical. Clinical signs are fied Baermann technique will reveal larvae. This is
due to the presence of adult worms and late-stage not a useful investigation in older horses because
larvae in the bronchi and bronchioles. Clinical signs patent infections are not established. In horses, air-
closely resemble those of RAO. Lungworm infection way lavage samples will reveal eosinophilia with L5
can be successfully treated with anthelmintics. larvae and/or adult nematodes (Fig. 3.164a,b). Note
that airway eosinophilia is not pathognomonic for
Aetiology/pathophysiology pulmonary parasitism.
D. arnfieldi is a nematode and has a typical lifecycle
with a migratory larval phase. Donkeys and foals Management
with patent infections shed eggs containing first- D. arnfieldi can be successfully treated with a vari-
stage (L1) larvae or hatched L1 larvae onto pasture. ety of anthelmintics including benzimidazoles,
Within days, these mature to the infective L3 stage. ivermectin and moxidectin. Benzimidazoles are
On ingestion, L3 larvae mature into migratory L4 given for 5 consecutive days, whereas single doses
larvae, which enter mesenteric lymphatics, then the of ivermectin and moxidectin are highly effec-
circulation via the thoracic duct and reach the lung tive. Regular anthelmintic treatment of donkeys
haematogenously. L4 larvae migrate into the alveoli will control shedding of eggs and L1 larvae and
and develop into L5 and then adults in the airway reduce pasture contamination. Picking up drop-
(bronchi and especially bronchioles). In donkeys and pings and sweeping also help to reduce pasture
foals, but not usually in adult horses, patent infec- contamination.
tion develops. Adult females lay eggs containing L1
larvae that are coughed into the pharynx and swal- Prognosis
lowed. Eggs containing L1 larvae may be passed in The prognosis is good.
faeces or eggs may hatch in the gut, releasing L1 lar-
vae into the faeces. PARASCARIS EQUORUM

Clinical presentation Definition/overview
There are usually no (obvious) clinical signs in don- Parascaris equorum causes parasitic pneumonia in
keys. Foals similarly show few, if any, clinical signs. foals and yearlings, typically towards the end of
In adult horses the clinical disease closely resembles their first summer at pasture. Adult parasites live in
heaves. Affected horses are bright, presenting with a the small intestine and clinical signs are caused by
history of coughing and decreased exercise capacity. larvae migrating through the lung. Solid immunity
There may be moderate tachypnoea and dyspnoea at develops after infection so that disease is uncommon
rest, and wheezes and crackles are audible on lung in foals older than 12–18 months. Infection can be
auscultation. treated successfully with anthelmintics. The prog-
nosis is good.
Differential diagnosis
Other causes of pulmonary disease should be con- Aetiology/pathophysiology
sidered, especially heaves and primary eosinophilic P. equorum is a large ascarid (roundworm). Adult
pulmonary disease. females can reach 50 cm in length, whereas males are