There are many internal and external parasites that can cause diseases of canine respiratory system. These parasites occur in the lungs, nares, nose and throat of dogs. Most canine internal parasite infections are caused by roundworms. Eucoleus boehmi is a roundworm that occurs both in dogs and cats. Dogs and cats can be infected through accidental ingestion of earthworms infected with this parasite. Aelurostrongylus abstrusus is a roundworm that is most commonly found in the form of worm larva in snails, a common food source for birds and rodents. Animals with mild infection often have only a few signs, while heavy infection can cause severe pneumonia marked by rapid, open-mouth breathing. Filaroides hirthi is a roundworm that occurs in the lungs of dogs. Puppies may be infected during the nursing period. There have been cases of this infection in dogs receiving corticosteroid therapy for arthritis. Animals with mild infection may develop a nonproductive cough, rapid and labored breathing, and exercise intolerance.
Respiratory infections can also be caused by flatworms. Paragonimus kellicotti is a flatworm that occurs in the lungs of cats and dogs. The main natural hosts of the adult Paragonimus kellicotti are badger, mink, otter and weasel, which get infected through ingestion of snails. Dogs and cats commonly become infected by eating fresh-water crabs, crayfish, or rodents and begin to shed eggs 5 to 7 weeks after the infection. Kittens may be infected by their mother. Signs are usually mild and usually include occasional coughing. In case of severe infection, infected animals can have labored breathing, a sudden attack of coughing and pneumothorax (an abnormal collection of air or gas in the pleural space separating the lung from the chest wall). Occasionally, sudden death may occur as a result of breaking of pleura (the membrane that envelops the lung).
Toxoplasma gondii is a microscopic protozoan that causes toxoplasmosis. Cats are the only hosts to this parasite. Infected animals may not show any signs of the infection, but when their immune system fails, cats may develop a systemic disease that most often reveals itself as respiratory disease. Cats with pneumonic toxoplasmosis usually have labored breathing, fever, lethargy, abdominal tenderness, and loss of appetite. Pneumonic toxoplasmosis often develops in cats that have other diseases such as feline immunodeficiency virus (FIV) infection.
Cuterebra is a large larva that is often found in the skin of dogs and cats. Signs of the infection may include persistent sneezing, clear or bloody nasal discharge, swelling over the nose, mouth or throat, and labored breathing. Animals get infected through contact with rodents, mainly in the spring time. Young kittens and puppies may be infected by the larva carried on the fur of their mother.
Pneumonyssoides caninum is a canine nasal mite Pneumonyssoides caninum. Dogs are infected through direct contact with other infected dogs. Signs may include sneezing, snuffling, snorting, itching of the face, and nasal discharge.