Reference Work Entry

Encyclopedia of Parasitology

pp 1241-1243

Respiratory System Diseases, Ruminants

The common clinical signs and pathology of parasitic infections of the respiratory system of ruminants are summarized in Table 1.
Table 1

Parasites affecting the respiratory system of ruminants (according to Vercruysse and De Bont)





Clinical presentation

Principal lesions


Sarcocystis spp.



Vascular endothelium

Anorexia, fever, weight loss, anemia and dyspnea

Lungs: mild interstitial pneumonitis and vasculitis


Schistosoma nasale



Nasal mucosal veins

Muco-purulent discharge, dyspnea, snoring

Granulomas in nasal mucosa



Strongyloïdes spp.



Small intestine, larvae migrate through lungs

Light coughing

Transitory eosinophilic alveolitis and bronchiolitis





Small intestine, larvae migrate through lungs

Soft cough

Petechial hemorrhages on the lungs with transistory alveolitis and bronchiolitis

Dictyocaulus filaria


Sheep, goat

Small bronchi

Coughing, hyperpnea, and dyspnea

Bronchitis, bronchiolitis, pneumonitis

D. viviparus



Bronchi, bronchioles

Coughing, hyperpnea, and dyspnea

Bronchitis, bronchiolitis, pneumonitis, pulmonary edema, emphysema

Mammomonogamus spp.



Nasal cavities, larynx, trachea, and bronchi

Light coughing

Chronic inflammation with small ulcerations of the mucosa of upper airways

Muellerius capillaris


Sheep, goat

Alveoli, pulmonary parenchyma, subpleural tissue

Usually no clinical evidence, sometimes persistent coughing, dyspnea

Bronchiolitis, pneumonitis with nodular lesions

Protostrongylus spp.


Sheep, goat


Usually no definite clinical signs

Bronchiolitis, lobular pneumonitis


Toxocara vitulorum



Small intestine, transit of larvae through lung parenchyma


Transitory eosinophilic alveolitis and bronchiolitis, lesions more marked in repeated infections




Oestrus ovis


Sheep, goat

Nasal passages, sinuses

Nasal discharge, frequently sneezing, nasal rubbing

Catarrhal rhinitis and sinusitis

1, A primary parasite of the respiratory system. 2, Affects the lungs through normal migration or proliferation. 3, Parasites of another organ system that produces respiratory symptoms

Nasal Cavity and Sinuses

The larvae of a number of flies of the family Oestridae are parasites of nasal cavities and sinuses of ruminants. The most ubiquitous is the nasal botfly of sheep and goats, Oestrus ovis . The flies cause great stress when they attack the sheep to deposit larvae near the nostrils of the host, a process which significantly interferes with grazing and rumination. The larvae which develop in the nasal cavities may get up to 3 cm in length and cause severe discomfort, partly because of the damage caused by the oral hooks and cuticular spines of the larvae, but also because of hypersensitivity​ phenomena. Nasal discharge and sneezing are common features in affected sheep, with caked dust obstructing the nostrils. Head shaking and nose rubbing may sometimes be seen. Extension to the cranial cavity via the ethmoid causes nervous symptoms and is usually fatal, but is also very rare.

Schistosoma nasale lives in the nasal veins of a variety of domesticated animals on the Indian subcontinent, including cattle, water buffalo, sheep, goat, and rarely horse. The lesions which are granulomatous in nature are caused by the passage of eggs through the wall of the nasal cavity. The condition is associated with cauliflower-like growths on the nasal mucosa causing partial obstruction of the cavity and snoring sounds when breathing. The lesions tend to get more severe in older animals and may become very spectacular in cattle, leading to “ snoring disease”.

Leeches such as Dinobdella ferox commonly enter the nasal cavities of domestic animals, mainly in southern Asia. They suck blood, generally induce inflammation, and may impede breathing.

Besnoitia besnoiti occurs in cattle in Southern Europe, Africa and Southeast Asia. The parasite multiplies mainly in the skin, but may also alter the mucosa of the upper respiratory tract and the lung may appear edematous. The large cysts are identifiably with the naked eye in the nasal mucosa and at necropsy at the respective predilection sites.

Larynx and Trachea

Mammomonogamus laryngeus occurs in the larynx and the trachea of cattle and humans in Southeast Asia and South America, and M. nasicola is found in nasal cavities, trachea, larynx, and bronchi of sheep, goats, and cattle in Africa and South America. In animals there are no apparent symptoms except for a light coughing. There is one record of a fatal infection in sheep believed to be due to a respiratory obstruction initiated by M. nasicola.

Lower Respiratory Tract

Parasitic infections of the lower respiratory tract of ruminants are very common and important. Some species such as the lungworms use the lower air passages and more rarely the lung parenchyma as final habitat. Other species just pass through the lungs during their migration, causing various degrees of damage according to the nature and intensity of the host–parasite interaction.


Protozoa that are spread across tissues by parasitemia or induce generalized disease may also affect the respiratory system. For instance, lung edema is often observed during babesiosis, mucosal bleedings occur during theileriosis, coughing and dyspnea may develop during toxoplasmosis in small ruminats. Sarcocystis may occasionally cause dyspnea. A multifocal interstitial pneumonitis and vasculitis are responsible for the respiratory signs.


Dictyocaulus viviparus is certainly the most important lungworm of cattle in temperate areas. The severity of the clinical signs depends on the susceptibility of the host and on the number of invading larvae. Cattle are most susceptible to infection when they are first exposed to contaminated pastures. Since the occurrence of the primoinfection varies, dictyocaulosis (husk) can be seen in all age classes. In early infections lesions are mainly found in the alveoli, which the larvae penetrate from lymphatics and blood vessels. An eosinophilic exudate accumulates in the alveoli and the terminal bronchioles. Hyperpnea and coughing may become noticeable as soon as 10–14 days after heavy infections. Occasionally, fatal pulmonary edema and emphysema develop at this stage, probably as a result of hypersensitivity reactions. During the patent period (25–55 days after infection), adults reside and lay eggs in the bronchi where they induce a hyperplasia of the mucosa. Eosinophilic exudate obstructs the lumen of the bronchi, which result in atelectasis of the alveoli distal to the plugs. In addition, eggs aspirated into the alveoli initiate foreign body reactions. The overall consequence of dictyocaulosis is a diffuse consolidation of the lungs. The animals show dyspnea and coughing, with rapid loss of condition. Harsh respiratory sounds with emphysemaous crackling can be heard. The post-patent phase of the disease is often one of gradual recovery in that the respiratory rate decreases, weight gain is resumed, and the coughing abates.

D. filaria causes outbreaks of pulmonary nematodosis in sheep and goats in most temperate areas of the world, often with high mortality rates. The pathogenesis and clinical signs appear to be similar to those of D. viviparus infections in cattle.

The Protostrongylidae are common lungworms of sheep and goats. They include Muellerius capillaris, Protostrongylus rufescens, P. brevispiculum, P. kochi, and Cystocaulus ocreatus. These parasites are of minor pathogenic importance. Infections with Muellerius and Cystocaulus are generally associated with small, spherical nodular lesions in the lung tissue, whereas Protostrongylus causes irritation and local inflammatory reactions in the bronchioles resulting in small foci of lobular pneumonitis. Generally animals show no clear symptoms although in the rare heavy infections, and especially with Protostrongylus in sheep and Muellerius in goats, there may be severe and even fatal disease.

Other Parasites

Larvae of Ascaris suum may be responsible for an atypical interstitial pneumonia in grazing cattle. Signs of acute respiratory distress such as severe dyspnea, expiratory grunt, hyperpnea and moist cough appear about 10 days after application of contaminated pig manure as a slurry to the pasture.


Chemotherapy, Drugs.

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