Filaroides osleri

Synopsis

CAPC Recommends

• Filaroides osleri can be easily between dogs in kennels because larvae are immediately infectious and the life cycle is direct.
• Diagnose this parasite using feces or BAL fluid and fecal flotation or sedimentation.
• Larvae have a rounded anterior end and “kink” in their tail.

Species

Canine

Filaroides osleri – canine tracheal and bronchial nodular worm.

Filaroides osleri is a parasite that produces hemorrhagic or granular, wart-like nodules in the trachea and bronchi of the dog and other canids. It has been reported from many parts of the world. The infection is passed from dog to dog by first-stage larvae, and thus, infection follows the ingestion of fresh feces, vomitus, or respiratory secretions.

Overview of the Life Cycle

• The adults live in nodules in the trachea and bronchi, usually at bifurcations. Filaroides osleri has a direct life cycle, requiring no intermediate host, with the first stage larvae passed in the feces or in saliva and is immediately infective to another dog. Nodules in experimental F. osleri infections can be detected with the bronchoscope about 2 months after infection. The prepatent period is 6 to 7 months.

Stages

• Adult males are 5.6 to 7 mm long, and females are 10.0 to 13.5 mm long.
• The female is ovoviviparous; the uterus is filled with larvated eggs that measure 80 µm by 50 µm.
• The larvae hatch and are passed in the feces are about 300 µm long. The larvae of Filaroides osleri and Filaroides hirthi are virtually indistinguishable.
• Upon infection, all development from larva to adult is in the lung tissue.

Disease

• The major sign is the spasmodic attack of a hard, dry cough started by exercise or exposure to cold air. Attacks are not induced by pressure upon the larynx.
• Young dogs are most acutely affected and sometimes develop respiratory distress, anorexia, and emaciation.

Prevalence

• Low prevalence, worldwide distribution.

Host Associations – Transmission between Hosts

• This is a parasite dogs; domestic dogs and wild canids.
• Transmission occurs easily in kennels because the larvae are infectious when passed.
• Life cycle is direct, no intermediate host is necessary for transmission.
• Maternal grooming is a suspected method of transmission to young puppies.
• Infectious larvae can also be transmitted through ingestion of regurgitated food.

Prepatent Period – Environmental Factors

• Nodules can be detected at approximately 2 months post-infection, and larvae can be found in feces at approximately 6 to 7 months.

Site of Infection – Pathogenesis

• The worms live in nodules in the trachea and bronchi.
• The gray-white, wart-like submucosal nodules range in size, reported up to 18 mm in diameter, and commonly occur at the bifurcation of the trachea.
• The nodules are usually transparent, and the coiled worms inside are clearly visible.

Diagnosis

• The lesions observed by bronchoscope are pathognomonic.
• The infection can also be diagnosed by finding the larvae in fecal flotation using centrifugation. The larva has a constriction and a kink just posterior to the end of the tail. The larvae of Filaroides osleri are virtually indistinguishable from those of Filaroides hirthi.
• The first-stage larvae of Filaroides species lack the caudal spine present on the tail of the larvae of Angiostrongylus vasorum and have rounded anterior ends that differentiate them from the larvae of Crenosoma vulpis that has a conical anterior end and a tail that ends in a sharp point without a constriction.

Treatment

• Many anthelmintics have been used to treat F. osleri.
• Fenbendazole 50mg/kg for 10 days has been shown effective in recession of nodules and clinical symptoms (Yao et al., 2011).
• Oxfendazole 10mg/kg for 28 days has also been show effective in treating F. osleri (Kelly and Mason, 1985).
• Randolph and Rendano (1984) reported reduced nodules and clinical symptoms after treatment with thiabendazole 32mg/kg for 10 days and levamisole 7.5mg/kg for 9 weeks.
• Other anthelmintics used experimentally include ivermectin 0.2-0.3 mg/kg at 1-3 doses and doramectin 0.2mg/kg once.
• Some remove as many nodules as possible with the aid of the bronchoscope.

Control and Prevention

• Dogs that are infected should be isolated from other dogs because of the infectious nature of the larvae.

Public Health Considerations

• No reported infections in people.

Selected References

• Bowman DD. Georgis’ Parasitology for Veterinarians. 10ed. Elsevier. 2014.
• Dunsmore JD and Spratt DM. The life history of Filaroides osleri in wild and domestic canids in Australia. Vet Par. 1979; 5:275-286.
• Kelly PJ and Mason PR. Successful treatment of Filaroides osleri infection with oxfendazole. Vet Rec. 1985; 116:445-446.
• Randolph JF and Rendano VT. Treatment of Filaroides osleri infestation in a dog with thiabendazole and levamisole. JAAHA. 1984; 20:795-798.
• Yao C, O’Toole D, Driscoll M, McFarland W, Fox J, Cornish T, Jolley W. Filaroides osleri (Oslerus osleri): Two case reports and a review of canid infections in North America. Vet Par. 2011; 179:123-129.