Respiratory Parasites
Respiratory Parasites – 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
SIGNALMENT
Species
Dog and cat
SIGNS
General Comments
Four basic categories—upper airway (nasal cavity and sinuses), lower respiratory (trachea and bronchi), pulmonary parenchyma, and vascular; based on location and lifestyle of parasite.
Often insidious and chronic, with few clinical signs.
Respiratory compromise often not severe.
Historical Findings
Upper respiratory—sneezing; nasal discharge (serous, sanguinous); reverse sneezing; nasal irritation or rubbing; neurologic signs with Cuterebra spp.
Lower respiratory and parenchyma—may have no clinical signs, variable coughing, tachypnea, or altered respiratory pattern.
Vascular—can have weight loss, lethargy, coughing, exercise intolerance. Acute onset of respiratory distress if embolization or hemorrhage occurs.
Physical Examination Findings
Upper respiratory—similar to historical findings; variable.
Lower respiratory and parenchyma—cough elicited on tracheal palpation; occasionally harsh lung sounds.
Vascular—may present with signs of pulmonary disease, right-sided heart failure, anemia, coagulopathy, neurologic 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.
DIAGNOSIS
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
Thoracic Radiography
Often nonspecific findings—generalized interstitial pattern; peribronchiolar infiltrates, nodular to alveolar pattern.
Oslerus—soft tissue nodular densities within the trachea at the level of the carina.
Paragonimus—can see bullae, cystic lesions or pneumothorax due to bulla or cyst rupture.
Dirofilaria—right-sided heart enlargement, tortuous and truncated pulmonary arteries, pulmonary infiltrates (dogs). Few cardiac changes in cats, large pulmonary arteries possible.
DIAGNOSTIC PROCEDURES
Sputum examination
May reveal eggs or larvae (L-1).
Fecal Examination
Multiple examinations often necessary; negative results do not rule out infection.
Direct fecal smear: Angiostrongylus (larvae).
Standard fecal flotation: Eucoleus aerophilus (eggs), Eucoleus boehmi (eggs).
Zinc sulfate centrifugation: Aelurostrongylus (larvae), Oslerus osleri, Andersonstrongylus milksi, Filaroides hirthi (larvae, larvated eggs), Angiostrongylus vasorum (larvae).
Baermann: Aelurostrongylus (larvae), Oslerus osleri, Andersonstrongylus milksi, Filaroides hirthi (larvae, eggs), Crenosoma (larvae, larvated eggs), Angiostrongylus (larvae).
Sedimentation: Paragonimus (eggs).
Rhinoscopy
Upper respiratory—examination via retrograde pharyngoscopy or rhinoscopy with antegrade flushing of anesthetic gas can allow visualization of nasal mites; retrograde nasal lavage and cytologic examination of fluid can be helpful.
Eucoleus boehmi—histopathology can reveal eggs deep within the epithelium.
Linguatula serrata—diagnosis made by observation of eggs in nasal secretions or around the nares.
Bronchoscopy
Lower respiratory and parenchyma—rarely can see tracheal and bronchial parasites and parasitic nodules; occasionally can be removed for definitive identification.
Tracheal wash or bronchoalveolar lavage can allow identification of larvae (Oslerus osleri, Aelurostrongylus, Crenosoma, Filaroides hirthi, Andersonstrongylus milksi, Angiostrongylus); eggs (Eucoleus aerophilus, Paragonimus); organisms (Toxoplasma).
Oslerus osleri—can also be diagnosed by brushings or histopathology of nodules at the carina.
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.
TREATMENT
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.
FOLLOW-UP
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.
MISCELLANEOUS
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.
Visit your veterinarian as early recognition, diagnosis, and treatment are essential.