The impact 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 lack 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 that is closely related to another retrovirus that induces a tumor in the lungs of sheep and goats (see Pulmonary Adenomatosis in Sheep and Goats). This type of tumor generally affects mature animals (2–4 yr old), although it has been reported in animals as young as 4 mo old. There is no known sex or breed predilection. The lesion may be unilateral or bilateral, resulting in either unilateral or bilateral serous, mucoid, or mucopurulent nasal discharge. Advanced unilateral tumors may cause deviation of the nasal septum resulting in bilateral nasal discharge. Affected animals show progressive signs of dyspnea (inspiratory), including open-mouth breathing, decreased airflow as measured at the nares, dullness on auscultation and percussion over the turbinates, sneezing, and head-shaking. With advancing tumor growth, exophthalmos and facial deformity may occur. 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, 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, Pasteurella multocida, Mannheimia haemolytica, and Fusobacterium.
Corynebacterium pseudotuberculosis, the causative agent of caseous lymphadenitis (see Caseous Lymphadenitis) 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), adeno-virus, and respiratory syncytial virus. These viral pneumonias most often affect lambs and kids.
PI-3 is an enveloped RNA virus (family Paramyxoviridae) that induces a mild interstitial pneumonia. Clinical signs may include coughing, serous nasal and/or ocular discharge, fever (104–106ºF [40–41ºC]), and an increased respiratory rate. The single PI-3 serotype for sheep that has been identified is distinct from the bovine PI-3 serotype. Infection with this virus can be confirmed by its isolation from nasal swabs from affected animals, or by comparison of acute and convalescent serum antibody levels. Treatment is usually not warranted in mildly affected animals. In severely affected animals in which secondary pathogens are suspected, antimicrobial therapy is recommended using drugs with efficacy against those organisms that are the most likely, such as Pasteurella multocida, Mannheimia haemolytica, Arcanobacterium pyogenes, Bordetella parapertussis, and Mycoplasma sp. There are no PI-3 vaccines specifically designed for use in small ruminants.
Adenoviruses are nonenveloped, double-stranded DNA viruses (family Adenoviridae). Two caprine and 6 ovine adenovirus antigenic types have been identified in association with pneumonia. It is likely that adenovirus-induced pneumonias are widespread, especially in young stock. Clinical signs are usually mild and include coughing, increased respiratory rate, anorexia, and fever. Treatment recommendations are the same as for PI-3 infection. No vaccines are available.
Respiratory syncytial virus is an enveloped RNA virus (family Paramyxoviridae) that has been isolated from both sheep and goats with pneumonia. Its importance as a major cause of respiratory disease in small ruminants is not well known.
Chronic, progressive viral pneumonia is most common in adults and includes progressive interstitial retroviral pneumonia (in sheep, ovine progressive pneumonia or maedi [see Progressive Pneumonia in Sheep and Goats]; in goats, pneumonia induced by arthritis encephalitis virus [see Caprine Arthritis and Encephalitis]) and pulmonary adenomatosis (see Pulmonary Adenomatosis in Sheep and Goats), 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 abnormal cellular proliferation. In affected sheep, the loss of functional lung tissue results in progressive dyspnea, anorexia, and weight loss.
M haemolytica, P multocida, Mycoplasma spp, Chlamydophila pneumoniae, 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 can alter the protective mechanisms in the respiratory tract so that certain bacteria may invade lung tissue, multiply, and cause serious disease. An initial infection with PI-3 virus, adenovirus, or Bordetella parapertussis may predispose an animal to infection with pathogenic M haemolytica. Also, Mycoplasma ovipneumoniae alone can cause a mild bronchopneumonia; however, it 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 (see Caseous Lymphadenitis) 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. (Also see Lungworm Infection). 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. In the USA, these drugs or recommended routes of administration may constitute extra-label use, requiring a valid veterinary-client relationship and an appropriate withdrawal time for slaughter purposes.
Last full review/revision March 2012 by Michelle Kopcha, DVM, MS