Filaroides hirthi

Synopsis

CAPC Recommends:

• Filaroides hirthi 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 hirthi – canine lungworm.

Filaroides hirthi lives threaded through the lung parenchyma of dogs and other canids. The life cycle is direct with the first-stage larvae in the feces or respiratory secretions of a dog being infective to other dogs.

Overview of the Life Cycle

• The adults live threaded through the lung parenchyma. Larvae in the feces or in the respiratory secretions of infected animals are immediately infective. Transmission can occur from the bitch or between littermates from the ingestion of first-stage larvae in feces. Ingested larvae get to the lungs within 6 hours via the hepatic portal circulation or the mesenteric lymphatic draining. Larvae appear in the feces of experimentally infected animals within 5 weeks after infection.

Stages

• Adults of Filaroides hirthi are difficult to dissect out of fresh lung tissue. On the male, the spicules are short and stout, the cuticle appears inflated, but a bursa is not readily apparent. The vulva of the female is just anterior to the anus, and the uterus is full of eggs containing infective larvae.
• The larvae passed in the feces or recovered by bronchoalveolar lavage are 240 to 290 µm long.
• Larvae have a distinctive ‘kinky’ tail.

Disease

• Usually the infection is not associated with clinical signs.
• Severe infections may show radiographic changes.
• Fatal cases of hyperinfection have developed in severely stressed and immunodeficient animals

Prevalence

• Periodically appears in some kennels or in individual dogs.

Host Associations – Transmission between Hosts

• This is a parasite dogs.
• Transmission occurs easily in kennels because the larvae are infectious when passed.
• Filaroides hirthi has a direct lifecycle.
• Larvae shed in feces may be intermittent and auto-reinfections often occur.

Prepatent Period – Environmental Factors

• Larvae appear in the feces of experimentally infected animals within 5 weeks after infection.

Site of Infection – Pathogenesis

• The worms in the alveoli and bronchioles provoke a focal granulomatous reaction and other pulmonary changes, some of which suggest drug-induced and neoplastic lesions.
• Dogs often present with dry cough, rapid breathing, dyspnea along with decreased appetite and abdominal pain.
• In a clinical case, a dog infected with F. hirthi had complete blood counts indicating eosinophilia and thrombocytopenia and a chest X-ray revealing extensive bronchoalveolar infiltrate (Cervone et al., 2018).

Diagnosis

• Diagnosis is made by finding the characteristic larvae in the feces or bronchoalveolar lavage. The larvae have a constriction and a kink just posterior to the end of the tail. The larvae of Filaroides hirthi are virtually indistinguishable from those of Filaroides osleri.
• The first-stage larvae of Filaroides species lack the caudal spine present on the tail of the larvae of Angiostrongylus species and have rounded anterior ends. This differentiate them from the larvae of Crenosoma vulpis, which has a conical anterior end and a tail that ends in a sharp point without a constriction.
• Baermann techniques are not effective in recovering larvae from feces. Fecal flotation is best, followed by fecal sedimentation.

Treatment

• Treatment is difficult.
• Albendazole 25mg/kg twice daily for 5 days has been shown effective against F. hirthi infection (Georgi et al., 1978).
• Cervone et al. (2018) effectively treated a dog with fenbendazole (50mg/kg per os for 2 weeks) combined with 3 subcutaneous off-label injections of ivermectin (0.4 mg/kg once every 2 weeks).

Control and Prevention

• In breeding kennels that have a serious problem, it may be necessary to derive the puppies by caesarian section and foster mothers.

Public Health Considerations

• No human health hazard appears to be associated with Filaroides hirthi.

Selected References

• Bauer C and Bahnemann R. Control of Filaroides hirthi infections in Beagle dogs by ivermectin. Vet Par. 1996; 65:269-273.
• Bowman DD. Georgis’ Parasitology for Veterinarians. 10ed. Elsevier. 2014.
• Cervone M, Giannelli A, Rosenberg D, Perrucci S, Otranto D. Filaroidosis infection in an immunocompetent adult dog from France. Helminthologia. 2018; 55:77-83.
• Georgi JR, Slauson DO, Theodorides VJ. Anthelmintic activity of albendazole against Filaroides hirthi lungworms in dogs. Am J Vet Res. 1978; 39:803-806.