Definition

Helminths, arthropods, and protozoa that reside in the respiratory tract or pulmonary vessels of dogs and cats.

Pathophysiology

Infestation with parasites causes rhinitis, bronchitis, pneumonitis, or arteritis, depending on the location of the organism within the respiratory system. Eosinophilic inflammation usually results from invasion of the parasite.

Systems Affected

• Respiratory.
• Cardiovascular.
• Hepatic-with hepatopulmonary migration of some parasites (Toxocara spp.).
• Neurologic-with migration of parasites to the brain (Cuterebra) or cerebral hemorrhage (Angiostrongylus).

Genetics

There is no genetic basis.

Incidence/Prevalence

Depends on parasite

Geographic Distribution

• Pneumonyssoides caninum, Aelurostrongylus abstrusus, Linguatula serrata, Oslerus (Filaroides) osleri, Crenosoma vulpis, Eucoleus (Capillaria) aerophilus, Toxoplasma gondii, Toxocara spp.-worldwide.
• Eucoleus boehmi, Cuterebra spp., Filaroides hirthi, Paragonimus kellicotti-primarily North America.
• Andersonstrongylus (Filaroides) milksi-North America; Europe.
• Angiostrongylus vasorum-various countries of Europe, Africa, South America, North America.

Signalment

Signs

Causes

• Upper respiratory (nasal cavity and sinuses)-Pneumonyssoides caninum, Eucoleus boehmi, Linguatula serrata, Cuterebra spp.
• Lower airway (trachea and bronchi)-dogs and cats: Eucoleus (Capillaria) aerophilus (rare in cats); dogs: Oslerus osleri, Filaroides hirthi, Andersonstrongylus milksi, Crenosoma vulpis. Cuterebra spp. in the trachea.
• Pulmonary parenchyma-dogs and cats: Paragonimus kellicotti, Toxoplasma gondii; dogs: Filaroides hirthi, Andersonstrongylus milksi; cats: Aelurostrongylus abstrusus, Troglostrongylus brevior, Troglostrongylus subcrenatus.
• Vascular-dogs and cats: Dirofilaria immitis, larval migration of Toxocara canis and cati; dogs: Angiostrongylus vasorum.

Risk Factors

• Depends on the specific parasite-some have intermediate or paratenic hosts that must be ingested by the definitive host, putting hunting or scavenging animals at higher risk.
• Crenosoma vulpis-snails.
• Paragonimus kellicotti-snails; crabs; shellfish.
• Aelurostrongylus abstrusus-snails and slugs; transport hosts: rodents, frogs, lizards, birds.
• Linguatula serrata-ingestion of sheep offal.
• Toxoplasma gondii-ingestion of infected small mammals and birds or less commonly by ingesting sporulated oocysts in soil or water.
• Multi-animal households with unhygienic living conditions-allows fecal-oral or direct-contact transmission.
• Angiostronhylus vasorum-gastropod (slug/snail) or frogs are the intermediate host. Frogs can also serve as paratenic hosts.

Differential Diagnosis

• Upper respiratory-other causes of epistaxis, rhinitis, or sinusitis (see specific chapters).
• Lower respiratory-acute bronchitis (non-parasitic); chronic bronchitis; infectious tracheobronchitis.
• Pulmonary parenchyma-eosinophilic lung disease; bronchopneumonia; granulomatous pneumonia; pulmonary granulomatosis.
• Vascular-other causes of coagulopathy, right-sided heart failure, or pulmonary artery disease.

CBC/Biochemistry/Urinalysis

• CBC-variable; may note eosinophilia, basophilia, neutrophilia, and monocytosis; can see anemia with Angiostrongylus vasorum.
• Biochemistry-often normal; high liver enzyme activity with some parasites during early stages as a result of hepatic migration if burden is substantial.
• Urinalysis-normal.

Other Laboratory Tests

Coagulopathy with Angiostrongylus vasorum or severe cases of heartworm disease (DIC).

Imaging

Diagnostic Procedures

Pathologic Findings

• Upper respiratory-may find nasal mites or worms in epithelium of sinuses and nasal cavity.
• Lower respiratory and parenchyma-can see pulmonary nodules containing parasites throughout the parenchyma or within bronchi.
• Vascular-changes include thrombi and intimal proliferation of the vascular walls.
• Cuterebra spp. can be found in brain sections when associated with neurologic signs.

Appropriate Health Care

Most commonly outpatient-upper and lower respiratory parasites; may need repeated examinations to monitor response.

Nursing Care

Supportive care and oxygen therapy can be needed depending on the severity of disease.

Activity

Strict cage rest if severe pulmonary dysfunction occurs with upper or lower respiratory parasites; also with vascular parasite infection or bullous lung disease associated with Paragonimus.

Diet

No special restrictions

Client Education

• Explain that treatment duration and response depend on the type of parasite.
• Warn client of the risk of recurrence in animals that maintain lifestyles conducive to transmission of the parasites (e.g., hunting, sporting dogs, multidog households, outdoor cats).

Surgical Considerations

Ruptured Paragonimus cysts generally require surgical excision.

Drug(s) Of Choice

• Anthelmintics-few studies confirm efficacy; most data anecdotal. For treatment of Dirofilaria, see chapters on Heartworm Disease.
• Pneumonyssoides caninum-selamectin at 6–24 mg/kg applied every 2 weeks for three treatments. milbemycin oxime at 0.5–1 mg/kg PO weekly for 3 weeks, ivermectin at 200 µg/kg SC or PO for two treatments 3 weeks apart; note: not labeled for use in dogs at this dosage.
• Cuterebra-ivermectin at 300 µg/kg SC or PO every other day for three doses combined with a tapering dose of corticosteroids.
• Linguatula serrata-physical removal of organisms from the sinuses.
• Eucoleus aerophilus, Eucoleus boehmi-ivermectin 200 µg/kg PO once; fenbendazole 25–50 mg/kg q12h for 10–14 days, very difficult to clear.
• Oslerus osleri-efficacious therapy not fully determined. Consider ivermectin at 400 µg/kg SC or PO q3 weeks for four doses.
• Crenosoma vulpis-levamisole 7.5 mg/kg SC q48h (two doses); fenbendazole at 50 mg/kg PO q24h for 7 days; milbemycin oxime 0.5 mg/kg PO once.
• Aelurostrongylus abstrusus-fenbendazole at 25–50 mg/kg PO q24h for 10 days; ivermectin 400 µg/kg SC, selamectin spot-on formula 45 mg/cat, two doses, 23 days apart.
• Filaroides hirthi, Andersonstrongylus milksi-fenbendazole 50 mg/kg PO q24h for 14 days; albendazole 50 mg/kg PO q12h for 5 days, repeat in 3 weeks.
• Paragonimus kellicotti-praziquantel at 25 mg/kg PO, SC q8h for 3 days; fenbendazole at 25–50 mg/kg PO q12h for 14 days.
• Toxoplasma-clindamycin 12.5 mg/kg PO q12h for 28 days.
• Angiostrongylus vasorum-fenbendazole at 20–50 mg/kg PO q24h for 5–21 days; milbemycin oxime 0.5 mg/kg PO weekly for 4 weeks; single topical application of moxidectin at 2.5 mL/kg.
• Toxocara spp. larval migration-fenbendazole 50 mg/kg PO q24h for 10 days.
• Anti-inflammatory agents-recommendations for concurrent use of steroids vary.

Contraindications

Ivermectin-not labeled for use in dogs or cats other than for heartworm prophylaxis; contraindicated at dosages >100 µg/kg in breeds with known sensitivity (collies, collie breeds, and Australian shepherds).

Precautions

None

Alternative Drugs

None

Patient Monitoring

• Serial fecal Baermann larval extractions or examination for eggs-some anthelmintics can suppress egg or larval production in some species and intermittent shedding reduces value of repeated fecal exams.
• Resolution of clinical signs-suggests response to treatment; does not indicate complete clearance of parasites.
• Peripheral eosinophilia, if noted initially, may subside with treatment.
• Repeat bronchoscopic examination-can help assess efficacy of treatment for Oslerus osleri.

Prevention/Avoidance

• Avoid activity that predisposes to infestations (often not practical).
• Avoid contact with wildlife reservoirs (especially wild canids and felids).
• Consider prophylactic treatment for heartworm.

Possible Complications

• Chronic pulmonary damage-possible with persistent and heavy lower respiratory parasite burdens.
• Infestations generally not fatal; however, severe pulmonary damage can result with some species; Cuterebra spp. and Angiostrongylus can cause fatal neurologic complications.
• Pneumonyssoides caninum has been associated with gastric dilation and volvulus.

Expected Course and Prognosis

• With aggressive management-prognosis usually fair to excellent; variable.
• Return to performance-depends on chronicity of disease and level of chronic pulmonary damage by lower respiratory parasites.
• Recurrence possible.

Zonotic Potential

None

Synonyms

• Lungworm infestation-Aelurostrongylus, Eucoleus (Capillaria) aerophilus, Crenosoma, Oslerus osleri, Filaroides hirthi, Andersonstrongylus milksi.
• Nasal mite infestation-Pneumonyssoides caninum, Pneumonyssus caninum.
• French heartworm-Angiostrongylus vasorum.

See Also

• Heartworm Disease-Cats
• Heartworm Disease-Dogs
• Pneumonia, Eosinophilic

Internet Resources

• Bowman DD. Respiratory System Parasites of the Dog and Cat (Part I): Nasal Mucosa and Sinuses, and Respiratory Parenchyma: http://www.ivis.org/advances/Parasit_Bowman/ddb_resp/ivis.pdf.
• Bowman DD. Respiratory System Parasites of the Dog and Cat (Part II): Trachea and Bronchi, and Pulmonary Vessels: http://www.ivis.org/advances/ParasitBowman/ddb_resp2/ivis.pdf.

Client Education Handout Available Online