Definition
Contagious respiratory helminthosis, specific to Canidae, caused by the presence of Oslerus osleri "strongyle" in the trachea, and more precisely in the tracheobronchial branching.
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Synonyms
Canine filariasis caused by Filaroides osleri.
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Clinical importance
This parasitic disease has now been reported throughout France (first cases described in the region of Lyon) and above all in breeding facilities having imported dogs from England (Poodles, Greyhounds). It has also been described in many other countries (Canada, USA, Germany, Australia, New Zealand, South Africa, Russia).
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Predisposing factors
- Young kennel dogs (adult dogs are also equally receptive but the lifestyle of puppies is more prone to disease transmission).
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- Concomitant kennel cough (favouring expulsion of larvae).
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- Coprophagia (favouring ingestion L1 larva of of L1 larvae less commonly present in faeces).
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Transmission
- Direct transmission of infective L1 larvae by close contact, oronasal route (no intermediate host), cough or licking, or more rarely by faeco-oral route.
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- Larval migration from digestive tract to trachea via the thoracic duct, right heart and lungs.
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- No in utero transmission and long prepatence (approximately 10 weeks), hence the absence of clinical signs and symptoms before the age of 2 months.
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- Bitches may intermittently excrete infective larvae for several years.
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Oslerosis (tracheal nodules formed by Oslerus osleri).
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Diagnosis
- Chronic tracheobronchitis, usually starting before one year of age and not responsive to classical treatments.
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- Onset of the same symptoms in both puppies and their mothers should lead to suspect Oslerus osleri infestation.
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- Chest X-ray (in profile) to visualize possible nodules with liquid density.
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- Bronchoscopic examination to visualize whitish, greyish or pinkish nodules (a few millimetres to 1 centimetre long) in the tracheobronchial branching. Parasites can be seen through nodules. Nodules can then be biopsied to confirm this observation. This is the only reliable examination to confirm a presumptive diagnosis of oslerosis in case Baermann's collective examination of faeces from coughing dogs proves negative.
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- Determination of the degree of infestation with L1 larvae in faeces (Baermann's technique). This method is aleatory due to the irregular excretion of larvae.
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- Collection and examination of tracheal mucus samples, which is more delicate to perform but more sensitive than coprological examinations.
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- Post-mortem examination to detect bronchial nodules harbouring adult parasites.
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Differential diagnosis
- Infectious tracheobronchitis.
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- Kennel cough caused by Bordetella or Parainfluenza (see "Kennel cough").
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- Foreign bodies in the larynx or trachea.
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- Hereditary cardiac disorders.
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- Lung migration of Ancylostoma or Ascaris larvae in puppies.
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- Angiostrongylus vasorum infection.
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- Filaroides hirti infestation (parasite of alveoli and bronchioles).
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- C. Aerophila capillariasis (trachea, bronchi, nasal cavities).
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- Crenosoma vulpis infestation (rare and diagnosed by detection of larvae by tracheobronchial lavage).
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- Cardiopulmonary dirofilariasis.
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- Paragonimus sp. Pneumonia (rare).
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Treatment
- The efficacy of oxfendazole or fenbendazole at the rate of 50 mg/kg/day for 15 days has been mentioned in the literature.
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- A second possibility (because of low diffusion in the respiratory system): ivermectin at the rate of 400 µg/kg SC (off-label use, under the prescriber's responsibility) or, even better, by intranodular injection during tracheal endoscopy.
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Prognosis
- Prognosis is usually favourable.
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- Failing treatment, the infection may evolve towards asphyxia, pneumomediastin or pneumothorax.
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Prevention
- Parasitic coprological examination (including Baermann's method) on all coughing dogs in quarantine, above all when they come from infested areas.
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- Since larvae only survive a few hours in the environment, environmental control measures are limited (which is rare for parasitic diseases) to the regular cleaning of boxes to eliminate L1 larvae.
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