Respiratory Diseases of Sheep and Goats: Introduction

The importance of respiratory diseases in sheep and goats depends on their prevalence, their effect on productivity, the value of the animal (commercial stock versus purebred animals or pets), and for some diseases, their international spread (the effects on the import/export market).

Upper Respiratory Tract:

Diseases of the upper respiratory tract of sheep and goats include sinusitis caused by the larvae of Oestrus ovis , nasal foreign bodies, and nasal tumors. Clinical signs associated with sinusitis may include some or all of the following: unilateral or bilateral, serous to mucopurulent nasal discharge; decreased or absence of airflow through one or both nostrils; coughing; sneezing; and mild to severe respiratory distress. Although tumors in general are rare in sheep and goats, the nasal cavity is one of the more common sites for their occurrence. The types of nasal neoplasms that have been reported include adenopapillomas (nasal polyps), adenomas, adenocarcinomas, lymphosarcomas (goats), and squamous cell carcinomas (sheep). An enzootic adenoma/adenocarcinoma has been described in goats and sheep. The tumor histologically appears to be benign or of low malignancy and is caused by a retrovirus. A closely related retrovirus induces tumor formation in the lungs of sheep and goats (see pulmonary adenomatosis, Pulmonary Adenomatosis). Surgical exploration of the nasal cavity with removal of the tumor mass has been described. Outcome depends on the tumor type, condition of the animal, and extent of the lesion. Surgical removal of a noninvasive tumor in an otherwise healthy animal can be rewarding.

The most common problems associated with the pharynx and larynx are trauma and abscessation. Pharyngeal trauma usually results from overly aggressive use of equipment used to administer oral medication (eg, balling guns, dose syringes, oral speculums, and stomach tubes). Injuries may result in the formation of discrete abscesses or extensive and diffuse cellulitis, both of which can interfere with swallowing and possibly lead to respiratory difficulty or distress. Bacteria commonly isolated after an incident of pharyngeal trauma include Arcanobacterium (Actinomyces) , Pasteurella multocida , Mannheimia (Pasteurella) haemolytica , and Fusobacterium .

Corynebacterium pseudotuberculosis , the causative agent of caseous lymphadenitis ( Caseous Lymphadenitis of Sheep and Goats) in sheep and goats may localize in the regional lymph nodes of the head, especially the pharyngeal lymph nodes. Lymph node enlargement may cause clinical signs similar to those described for traumatic pharyngitis.

Lower Respiratory Tract:

The most common problem associated with the lower respiratory tract is pneumonia. Pneumonias can be caused by viruses, bacteria, or parasites. They can be acute, chronic, or progressive.

Viruses associated with acute pneumonia include parainfluenza-type 3 (PI-3), adenovirus, and respiratory syncytial virus. These viral pneumonias most often affect lambs and kids. Chronic, progressive viral pneumonia is most common in adults and includes progressive interstitial retroviral pneumonia (in sheep, ovine progressive pneumonia or maedi [ Progressive Pneumonia]; in goats, pneumonia induced by arthritis encephalitis virus [ Caprine Arthritis and Encephalitis: Introduction ]) and pulmonary adenomatosis ( Pulmonary Adenomatosis), also known as jaagsiekte or the contagious lung tumor of sheep and, infrequently, of goats.

Chronic, progressive, proliferative changes in the lungs are usually associated with the lentiviruses (family Retroviridae), or so-called slow-virus infections. In both progressive pneumonia and pulmonary adenomatosis, the entire lung can change in a gradual process of cellular proliferation, which results in progressive weight loss and dyspnea.

M haemolytica , P multocida , Mycoplasma spp , Chlamydia spp , Haemophilus spp , and Salmonella spp are associated with either primary or secondary bronchopneumonia in sheep and goats. Both P multocida and M haemolytica can be cultured from the upper respiratory tract of normal sheep and goats. Not all factors predisposing to acute respiratory diseases are known, but acute viral infections in a susceptible population of sheep can alter the protective mechanisms in the respiratory tract so that certain bacteria may invade lung tissue, multiply, and cause serious disease. A confirmed synergism is an initial infection with PI-3 virus or adenovirus followed by invasion of M haemolytica , biotype A. Also, Mycoplasma ovipneumoniae alone can cause a mild bronchopneumonia and is often isolated along with M haemolytica from sheep and goats with severe pneumonia, suggesting that the Mycoplasma may predispose the lung to invasion by this organism. Additionally, introduction of new animals, high-density stocking, poor ventilation, and a low plane of nutrition can act as stress factors that predispose to development of pneumonia.

Caseous lymphadenitis ( Caseous Lymphadenitis of Sheep and Goats) caused by Corynebacterium pseudotuberculosis may result in abscessation of the lungs and mediastinal lymph nodes. This can result in a progressive debilitation in sheep and goats with or without obvious clinical signs of respiratory disease.

Parasitic or verminous pneumonias of sheep and goats most commonly are caused by infection with Dictyocaulus filaria , Muellerius capillaris , or Protostrongylus rufescens . (See also lungworm infection, Lungworm Infection: Introduction). In contrast to the acute viral and bacterial pneumonias, which result in a bronchopneumonia affecting the anterior ventral portion of the lungs, verminous pneumonia affects the diaphragmatic lung lobes. Dictyocaulus has a direct life cycle, whereas Protostrongylus and Muellerius have indirect life cycles and rely on a variety of snails and slugs to serve as intermediate hosts. Adult forms of Dictyocaulus and Protostrongylus live in bronchi and produce clinical signs of coughing, mild to moderate dyspnea, anorexia, depressed milk production, and loss of condition. Adult Muellerius live in alveoli and lung parenchymal tissue and are considered the least pathogenic of the 3 lungworms. Muellerius appears to cause more problems for goats than for sheep.

Diagnosis of lungworm infection requires Baermann examination of fecal material. Dictyocaulus and Protostrongylus can be treated effectively with levamisole (8 mg/kg, SC or PO), ivermectin (0.2 mg/kg, SC or PO), fenbendazole (5-10 mg/kg, PO), moxidectin (0.2 mg/kg, PO or SC), or febantel (5 mg/kg, PO). Ivermectin (0.3 mg/kg, SC or PO), fenbendazole (15 mg/kg, PO, administered twice, 3 wk apart), and albendazole (10 mg/kg, PO) have been reported to be effective in treatment of Muellerius .