Chapter 7 Diseases of the Respiratory System

Paul J. Plummer, Cassandra L. Plummer, Kelly M. Still

Anatomy

Clinically significant upper airway structures in the small ruminant include the frontal and maxillary sinuses, pharynx, larynx, and trachea. The nasopharynx is the primary path for respiration, but oral respirations are anatomically possible, and “panting” occurs under some fairly normal conditions such as high ambient temperature. Laryngeal structure is similar to that in other species, with small V-shaped vocal folds just caudal and ventral to the arytenoid cartilages.^1,² The retropharyngeal lymph node is located dorsocaudal to the pharynx and can compress the larynx or trachea when enlarged or abscessed. The trachea runs down the ventromedial aspect of the neck from the larynx to the bronchial bifurcation in the thorax. It is composed of incomplete tracheal rings connected by a membranous wall. The tracheal diameter in small ruminants generally is smaller than might be expected and changes at the thoracic inlet: In goats the trachea narrows, whereas in sheep it enlarges.²

In the thorax, the trachea bifurcates into two main bronchi. Just cranial to this bifurcation a separate bronchus branches out to the right cranial lung lobe. The major lung divisions include left and right cranial lobes, each with a cranial and caudal part; the right middle (cardiac) lobe; the right accessory lobe; and the left and right caudal (diaphragmatic) lobes. When enlarged, the mediastinal lymph nodes and thymus may compress or shift the thoracic trachea or lung. The caudal lung border is demarcated by the sixth rib ventrally, by the seventh rib at the lateral midthorax, and by the eleventh rib dorsocaudally. The intercostal vessels and nerves run caudally along each rib, and care should be taken to avoid these structures during thoracocentesis or biopsy procedures.²

Physiology

The respiratory system permits reoxygenation of pulmonary venous blood and release of carbon dioxide formed by cellular respiration. Effective respiration requires both alveolar ventilation and gas diffusion across the respiratory membrane; together, these two processes can be quantified by the ventilation-perfusion ratio, which may be altered during disease. Alveolar ventilation occurs through movement of gas from the terminal bronchioles and depends on inspiratory tidal volume and expiratory functional reserve in addition to respiratory rate. Anatomic dead space (e.g., nasal passages, pharynx, trachea, bronchi) does not contribute to alveolar ventilation. Once in the alveolus, respiratory gases must diffuse between the lung and capillaries. Gas movement across membranes is affected by the diffusion coefficient of the gas, the thickness of the septum, and the surface area available for diffusion. Because carbon dioxide diffuses much more readily than oxygen and is the direct stimulus for respiration, hypoxia may occur without significant increases in respiratory rate. Alveolar septum thickness can be increased by edema and fibrosis. Surface area can be physically decreased by consolidation and emphysema or physiologically reduced by alteration in the ventilation-perfusion ratio stemming from increased physiologic dead space or shunting of blood away from ventilated alveoli.³

Significant innate immune defenses are present in the lung. The sneeze and cough reflexes forcibly expel large particles and irritants from the upper airway. Nasal hairs and air turbulence over the nasal concha will filter out airborne particles as small as 6 μm. Gravitational precipitation will filter smaller particles (1 to 5 μm) in the small bronchioles. Mucociliary clearance efficiently moves trapped particles to the pharynx, where they are either swallowed or coughed out. This system is formed by mucus-producing goblet cells and ciliated epithelial cells that line the respiratory tract from the nasal passages to the terminal bronchioles. Once in the alveoli, particles larger than 0.5 μm will come to lie against the alveolar wall and be cleared by alveolar macrophages or the lung lymphatic system. Particles less than 0.5 μm in size remain suspended and will be exhaled without consequence.⁴

Diagnostic Approaches

Physical Examination and Auscultation

A thorough and unbiased physical examination is the most important component of the diagnostic evaluation of small ruminants presented for abnormalities of the respiratory tract. Without a complete physical exam, important primary or secondary physiologic problems may be missed, and the diagnostic plan may be incomplete or result in failure to obtain a definitive diagnosis.

The physical exam should be conducted in a systematic manner and must include all aspects of the respiratory system. Before restraining the animal, the clinician should spend a few minutes observing its attitude, stance, respiratory rate, and respiratory pattern from a distance, because significant elevations in respiratory rate and pattern can occur after capture and restraint, particularly in animals that are less socialized. In consequence of the flocking instincts of sheep and goats, animals observed to be standing apart from the rest of the flock or herd are likely to be significantly ill. Once the animal is caught and restrained, the practitioner should begin by evaluating the respiratory system starting at the head (see Chapter 1). The nares should be examined for evidence of serous, mucopurulent, or hemorrhagic discharge from one or both nostrils (Figure 7-1). Unilateral nasal discharge may provide significant localization of a lesion and should be noted on the examination form. Both nares should be accessed for patency by placing either a small cotton ball or a mirror in front of the nose and observing for movement or fogging, respectively. The remainder of the head should be evaluated for evidence of facial deformity or soft tissue swelling indicative of a localized lesion. The pharyngeal area should be palpated, with particular attention paid to the local lymph nodes. When possible, the palpation should include an attempt to feel the area lateral and dorsal to the pharynx by placing a hand alongside the trachea and palpating with gentle dorsal pressure. This area is a common site for retropharyngeal abscesses (often caused by Corynebacterium pseudotuberculosis), which may result in considerable respiratory stridor and effort. The extrathoracic trachea should be palpated from the pharynx down to the mediastinal entrance for any evidence of stricture, dilatation, or external compression. During this portion of the evaluation, occasional gentle squeezing pressure should be applied to the trachea, to determine how easily coughing can be induced. The mediastinal opening is another area that warrants palpation for evidence of space-occupying lesions or tracheal deviation associated with such findings.

Figure 7-1 The clinician is carefully examining the nares in this well-restrained ewe. (Note: Both a light source and saline are available to flush out any material that precludes proper evaluation.)

(Courtesy Dr. A.N. Baird, Purdue University.)

Attention should then turn to performing a complete auscultatory examination of the thorax, when possible. Owing to the heavy wool cover on the thorax of sheep, this exam may be of limited usefulness without adequate shearing. At a minimum, the cranioventral aspect of the thorax of sheep can be auscultated in the nonwooled area located immediately behind the elbow. In sheared or haired sheep and lambs and goats, the entire thorax generally can be auscultated without further removal of fiber or hair. Attention should be paid to the intensity, duration, and character of the breath sounds, as well as the stage of respiration (i.e., inhalation or exhalation, early or late) during which they occur. In comparison with those in cattle, the normal airway sounds heard in sheep and goats are much more obvious, owing to the thinner body wall. This perceived magnification often results in the erroneous impression of abnormal respiratory sounds.

Abnormal sounds should be classified as either of two different descriptive types: Wheezes are high-pitched, continuous musical sounds associated with altered airflow through larger airways. They are indicative of either fluid in the airway or increased velocity of air movement in the airway. Crackles are noncontinuous brief “popping” sounds associated with sudden opening of small airways or alveoli. They most commonly are heard during inspiration, particularly late inspiration, and previously were described as “rales.” If any abnormal breath sounds are auscultated, they should be localized and their anatomic location recorded on the examination form. In most instances, the use of a rebreathing bag, as is common in respiratory evaluation of horses, is not necessary for small ruminants, owing to their relatively thin body wall.

After completion of the auscultation exam, several additional pieces of information should be collected. The rectal temperature will reveal whether the animal is febrile, normothermic, or hypothermic. The presence of fever may provide additional evidence of an inflammatory process that may warrant additional diagnostic effort. Additionally, the nutritional status of the animal should be evaluated, because immune dysfunction is more common in young animals with less than adequate reserves of body fat. This assessment is perhaps best performed by body condition scoring of multiple animals in the same management group. Finally, the practitioner should spend some time evaluating the environment in which the diseased animal is housed. Environments with poor ventilation, drafts, dust, or high stocking densities may predispose resident animals to the development of respiratory disease; in such instances, appropriate treatment may require addressing the environmental conditions.

With respiratory disease in preweaned animals, it also is worthwhile to consider the role of colostrum management and failure of passive transfer in the disease process. When warranted, serum samples from several animals can be collected and assayed for failure of passive transfer status. Our own preference is to test a group of 10 animals between 24 and 72 hours of age; at least 8 of the 10 animals should demonstrate adequate evidence of passive transfer. If increased rates of failure of passive transfer are identified, then herd- or flock-level changes are needed to improve immunity of this at-risk group.

After the physical exam has been completed, the clinician should use the findings to develop a comprehensive problem list that will serve as a basis for development of a complete diagnostic plan and differential list. Although this step often is skipped in the interest of time, it is one of the few ways to ensure consideration of all possible clinical entities in the differential diagnosis.

Diagnostic Procedures

Once a complete list of diagnostic possibilities has been generated, the clinician can turn to the development of a useful and cost-effective diagnostic approach specific to the case. In this context, it is important to ascertain the expectations of the client with regard to desired outcome. For instance, the producer with 29 weaned kids in group housing of which 10 were lost to pneumonia in the past week may have very different expectations and motivations to pursue diagnostic investigation from those for a producer with a single animal showing clinical signs. Many of the usual procedures for such investigation, as described next, may not be economically feasible or desirable if the producer perceives that the cost does not justify the return on investment. By contrast, if the results can be used to prevent disease in multiple animals, the motivation to pay for the diagnostics may be increased.

Blood Gas Analysis

Blood gas analysis provides a rapid and useful assessment of hemoglobin oxygenation and alveolar diffusion of gases. Its usefulness is, however, limited by the need for rapid testing and appropriate sample handling to prevent erroneous results. The advent of portable blood gas analyzers that can be carried on the ambulatory care truck make this test feasible in the farm situation; in most instances, however, its application is limited to high-value cases in referral hospital settings. In our experience, an arterial blood gas sample is best collected from small ruminants using the brachial artery located on the medial aspect of the proximal portion of the front legs. Special blood gas syringes are commercially available and should be used if accurate assessment of partial pressures is required, as would be the case in respiratory disease. While the animal is lying in lateral recumbency, the lower limb is extended and the pulsation of the artery is palpated between the index and middle fingers while the needle is inserted at a 90-degree angle to the skin. Once the artery is penetrated, the syringe is held steady and should self-fill. Negative pressure should not be applied to the syringe, because this will alter gas partial pressures in the sample. Once the blood is collected, the needle should be rapidly sealed, typically with the rubber stopper supplied with blood gas syringes. Care should be taken to not introduce any bubbles into the syringe during this process. Arterial partial pressures of O₂ (Pao₂) should be above 70 to 80 mm Hg in an animal with normal oxygenation. Partial pressures below that level may be indicative of inappropriate ventilation, poor alveolar ventilation, or thickened alveolar walls that impair oxygen diffusion. Normal partial pressures of CO₂ in an arterial sample should be below 40 mm H, and if the sample yields a Pao₂ greater than that value in association with a very low oxygen partial pressure, the possibility that a venous sample has been obtained needs to be considered.

Radiography

Radiographs of the thorax, neck, or head often are required and can be of significant diagnostic benefit. Radiographs can easily be obtained using portable radiographic equipment commonly available to veterinary practitioners. When unilateral nasal discharge or facial deformities are observed during the physical exam, radiographic evaluation with both lateral and dorsoventral views of the head may elucidate the etiology. In many instances, nasal foreign bodies or sinusitis can be confirmed on the basis of the radiographic interpretation of the head views. Similarly, radiographs of the neck may provide additional evidence of tracheal compression or retropharyngeal masses that may be associated with coughing in affected animals. Thoracic radiographs can be obtained with the animal either standing or in lateral recumbency, depending on the facilities available to the practitioner (Figure 7-2, A and B).

Figure 7-2 Radiograph showing pulmonary edema related to a tracheal obstruction in a 6-year-old Suffolk ewe. A, Increased opacity is evident throughout the lungs, along with peribronchial cuffing and lack of visualization of the vascular markings. It is difficult to distinguish the borders of the caudal vena cava because of the increased interstitial opacity. Other considerations in the differential diagnosis for this pulmonary pattern would be pneumonia and pulmonary hemorrhage. B, Lateral view of the caudal thorax of the same patient 24 hours after treatment with a tracheotomy, diuretics, and antibiotics. The vascular margins are better delineated, as are the borders of the caudal vena cava. Interstitial opacity within the lungs is less than on the previous radiograph. Although mild interstitial opacity persists, the pulmonary edema is resolving.

(Courtesy Dr. Debra Baird, Purdue University.)

Lung field consolidation can be readily identified by observing radiographic opacities in the cranial ventral lung fields, and mediastinal masses, often associated with caseous lymphadenitis abscesses, generally are revealed as a line of masses of increased density coursing through the thorax at the level of the trachea. In rare instances, a thymoma may result in the appearance of a mass cranial to the heart that gives the appearance of the animal’s having two hearts.

Ultrasound Imaging

Portable ultrasound units are becoming standard equipment in many large animal clinics, affording easy access to this imaging modality. Many units used for reproductive practice are equipped with a linear, 5- to 7.5-MHz transducer. This type of machine can provide reasonably good-quality images of the thorax and adjacent soft tissues. When available, a curvilinear probe will provide a superior image but certainly is not required for diagnostic use. Appropriate patient preparation is paramount for obtaining a good-quality image. Wool or hair over the site of interest should be clipped, although the use of coupling agents (e.g., gel, vegetable oil, alcohol) can be helpful in some instances. Owing to the nature of the functioning, gas-filled lung, ultrasonography of the respiratory tract is more limited than that of other body systems. For example, ultrasound examination of the pharyngeal region may provide an easy means of identifying retropharyngeal abscesses when they are suspected from findings on palpation. In such cases the probe should be placed parallel to the lateral aspect of the trachea and directed dorsomedially towards the opposite ear. Abscesses typically have a hyperechoic wall, with variable echotexture of the contents.

Ultrasound imaging also can provide useful information in evaluation of the thorax. The clinician should become familiar with the appearance of normal aerated lung, allowing rapid identification of areas that lack the normal appearance. Normal lung is recognizable by the bright hyperechoic line of the visceral pleura above a classic reverberation artifact induced by the aerated lung. The reverberation artifact is typical of ultrasound waves hitting a gas interface and consists of sequential hyperechoic lines spaced at regular intervals. It is important to realize that any images appear on the screen deep to the start of the reverberation artifact are indeed artifacts and not images of the lung parenchyma (Figure 7-3). Once an appreciation for the normal appearance of lung has been achieved, the thoracic exam can be systematically performed. With use of a linear or a curvilinear probe, the probe should be oriented parallel to the ribs in the intercostal space. We prefer to start at the most dorsal aspect of each intercostal space and slowly move downwards to the ventral thorax observing the lung surface along the path. This is repeated in each intercostal space moving caudally. The image quality is maximized by following the natural “lay” of the wool or hair (in a dorsal-ventral direction). As the exam progresses caudally, the diaphragm will come into the image while moving ventrally, often with the adjacent liver filling the space below. With use of this method, the extent of the thoracic lung field can be determined. The three primary lesions that will be observed are parenchymal masses in the lung that are adjacent to the visceral pleura, lung consolidation, and the characteristic “comet tail” lesions associated with pleural thickening and inflammation. The first of these lesions is readily identified by the observation of echodense masses interrupting the normal reverberation artifact of the lung. Such masses can be measured to allow for sequential ultrasonographic examination as a means of assessing treatment success or resolution of the lesion. In our experience, these lesions most commonly are associated with parenchymal abscesses. Consolidated lung is recognized on deeper imaging, beyond the normal lung reverberation. In many instances, the consolidated lung may have an appearance similar to that of liver (“hepatized lung”) or may be seen to contain scattered gas shadows associated with presence of gas in the larger airways or in abscesses. “Comet tails” are recognizable as small, hyperechoic spots with a comet tail–shaped artifact located deep to the spot. These lesions are nonspecific but often are associated with thickening or inflammation of the pleura.

Figure 7-3 Ultrasound image of the right cranioventral thorax obtained at the sixth intercostal space in a 3-year-old LaMancha cross doe with normal lungs. The linear hyperechoic structure with reflective echoes represents the normal, aerated pleural surface. This ultrasound image was obtained using a 10-MHz linear array transducer. Dorsal is to the left of the image.

(Courtesy Dr. Karine Pader, Purdue University.)

If pleural fluid is present, it will be imaged as an anechoic or hypoechoic area in the ventral thorax, with normal lung reverberation noted at the lung-fluid interface. Because the mediastinum is not always easily imaged, radiographs remain the preferred imaging modality for identification of mediastinal masses.

The animal should be standing and adequately restrained for this procedure. Sedation may be warranted. If a fiberoptic endoscope is available (8 to 9 mm diameter), it may be inserted through the nasal passage in some adult sheep or goats. If this is not possible, the endoscope can be passed through an oral speculum. An endoscopic examination may allow visualization of the respiratory tract, identify exudates, and enhance sample collection. If an endoscope is unavailable, a percutaneous transtracheal wash (TTW) procedure can be performed. Use of a commercially available presterilized, complete kit designed for foals, when available, will enhance the ease of this procedure (Figure 7-4, A and B). Alternatively, a hypodermic needle of appropriate size to allow a sterile tube catheter (220 polyethylene) to pass through the bore may be used. On the ventral aspect of the neck, the hair or fiber should be removed over at least a 6-inch square of skin centered on the midline and located roughly one third of the way down the neck from the throatlatch. The trachea should be identified and easily palpated at this level. The site should be disinfected using a standard surgical preparation, and a small bleb can be raised with lidocaine placed under the skin directly over the midline of the trachea in the center of the site. A stab incision should be made through the skin using a scalpel blade. The procedure should be performed using sterile technique. If a commercial kit is to be used, the blunt-tipped needle and associated placement trochar should be identified in the kit, and the clinician should become familiar with their design and use before performing the procedure. The unit should be placed through the skin incision and the tip of the trocar used to palpate the tracheal rings while the operator’s opposite hand is used to stabilize the trachea. The tip of the trocar should be positioned on midline between the tracheal rings and firm pressure applied to facilitate passage of the trochar into the trachea. A slight “pop” may be felt as the tip of the stylet enters the cavity. The trocar should be advanced until it can be felt to fully penetrate the trachea and can be slightly advanced in a ventral direction (Figure 7-5, A). The stylet should be removed and the aspiration catheter passed (using sterile gloves) through the trocar to roughly the level of the tracheal bifurcation. Twelve to 15 mL of sterile saline should be infused into the trachea and a sterile syringe used to apply gentle suction as the catheter is moved back and forth in the trachea (see Figure 7-5, B). The goal is to move the catheter so that its tip is in the pool of fluid created just cranial to the tracheal carina. Although this cannot be visualized, it can be located with practice in a majority of cases. If needed, additional normal saline (another 5 to 10 mL as indicated) can be given to increase the recovery volume. The catheter should be removed, followed by the trocar. In cases in which a needle and polypropylene catheter are used, the needle should be removed from the trachea before the catheter, to minimize the risk of cutting off the distal tip of the catheter during its withdrawal.

Figure 7-4 Transtracheal wash. A, Site of access for transtracheal wash on the ventral midline in the midcervical region. B, Supplies for transtracheal wash procedure: 18-inch flexible wash catheter (1), sample vial (2), trochar removed from cannula for visualization (3), and wash cannula (4).

Figure 7-5 A, The middle third of the neck is aseptically scrubbed, the skin and subcutaneous tissue are anesthetized, a stab incision is made through the skin and subcutaneous tissue, a 14-gauge needle or trocar is passed through the incision and into the trachea, and tubing is passed using sterile technique just beyond the tracheal bifurcation. B, The clinician injects sterile isotonic solution (12 to 30 mL) through the tubing and then immediately performs fluid retrieval by aspiration with the syringe. (Note: With this method, caution should be taken to avoid cutting off the tube in the trachea with the sharp needle.)

Thoracocentesis

Thoracocentesis provides a reliable means of collecting a sample of pleural fluid for diagnostic submission. This is best performed in the cranial-ventral portion of the chest, where pleural fluid pools in the most dependent part of the thorax. While the animal is standing, this area can be evaluated by ultrasound imaging and an appropriate site selected as indicated by presence of fluid and absence of other viscera. The body wall thickness can be measured to assist in determining how deep to advance the needle to acquire the sample. Once collected, the sample should be evaluated for appearance, odor, and turbidity, in addition to being submitted for bacterial culture and cytologic study. The presence of a pungent foul odor often is associated with anaerobic infection, and treatment decisions should consider this possibility.

Upper Airway Disease

Stertor and stridor, sneezing, and nasal discharge are hallmark signs that suggest upper airway disease over pneumonia.

Rhinitis

Possible causes of rhinitis in sheep and goats include foreign material such as from regurgitation, parasites, tumor, and other respiratory infections.

Oestrus ovis Infestation

Pathogenesis

Nasal bot infestation is more common in sheep than in goats, and infected goats have a lower larval burden than that typical for sheep.⁵ Clinical signs during the first spring infestation generally are mild, but disease severity markedly increases during subsequent infestations, probably owing to hypersensitization; goats may acquire immunity after repeated infections.⁵ The adult Oestrus ovis fly deposits larvae at the animal’s nostrils. The first instar larvae migrate up the nasal passages into the dorsal turbinates and sinuses. There they develop over a 2- to 10-month period to the third instar stage,^1,6 return to the nostril, and are sneezed out to pupate in the soil.⁶ Both first instar larvae and pupae may overwinter.⁶

Clinical Signs

Irritation from the adult flies will induce avoidance activities such as head shaking, head rubbing, and feet stomping; if the animal’s distress level is severe, grazing activity will decrease.⁶ Larval passage and development can cause inflammatory rhinitis characterized by sneezing, mucopurulent discharge, and decreased airflow through the nares. Sequelae can include bacterial rhinitis or sinusitis and, infrequently, interstitial pneumonia secondary to antigen aspiration.⁵

Diagnosis

O. ovis infection is associated with a profuse nasal discharge containing numerous eosinophils and mast cells.^5,⁷ Direct visualization of the bots or mineralized remains may be possible with endoscopic or radiographic imaging. In commercial herds, clinical signs, cytologic examination of the discharge, and response to therapy usually are sufficient to make the diagnosis.

Therapy

Treatment usually is administered for heavy late summer infestations or to kill overwintering bots. Ivermectin (0.2 mg/kg SC) is effective in killing the O. ovis larvae ^1,^6,⁷ but requires an extended milk withdrawal period: 40 days if administered subcutaneously and 6 days if administered orally (if administered at a higher oral dose of 0.4 mg/kg, an 11-day milk withdrawal is recommended).⁸ Pour-on eprinomectin (0.5 mg/kg) may be a better choice for commercial dairies because it has been shown to be effective in sheep against nasal bot infestation and has a zero-day milk withdrawal period.^9,¹⁰

Once the bots are killed, secondary bacterial infections usually will resolve without further intervention. If indicated, however, treatment is with broad-spectrum antimicrobials.⁷

Other Parasites

In the Himalayas, a nasal leech from standing water pools can cause similar clinical signs. Systemic ivermectin is ineffective, but direct application of ivermectin solution (0.1 mg/mL) to the leech will kill it within a few hours. Wetting the animal’s muzzle will encourage the leech to migrate down to the nostril opening so that the ivermectin can be applied.¹

On the Indian subcontinent, Schistosoma nasale infection (“snoring disease”) has been reported as a cause of nasal obstruction from parasite-associated inflammation and tissue proliferation.^1,¹¹

Enzootic Nasal Tumor

Pathogenesis

Enzootic nasal tumors are transmissible, sporadically occurring tumors of the nasal passages of sheep and goats.^12,¹³ This condition has been reported in animals as young as 15 and 7 months, respectively,^14,¹⁵ and is believed to be caused by type D or B retrovirus infection.^12,^16,¹⁷ These tumors can occur unilaterally or bilaterally and are locally invasive but not usually metastatic.^13,¹⁵ They originate from the olfactory mucosa and ethmoid or nasal turbinates and usually are classified as adenomas, adenopapillomas, and adenocarcinomas.¹³^–¹⁵ Other conditions on a differential diagnosis list for nasal masses include lymphosarcoma and fungal granuloma.¹

Clinical Signs

The tumor starts as small nodules that grow to form large nodular cystic masses, causing progressive inspiratory dyspnea and secondary emaciation.^13,¹⁵ Inflammatory polyps may be present near the tumor.^15,¹⁷ Primary clinical signs include unilateral or bilateral copious seromucous to mucopurulent nasal discharge with inspiratory stridor. Additional signs may include exercise intolerance, decreased airflow and open-mouth breathing, anorexia, head shaking and sneezing, exophthalmos, and bony facial asymmetry.¹³^–¹⁵

Diagnosis

A preliminary diagnosis can be made from the clinical signs and findings on sinus percussion. Radiographic or endoscopic imaging may be indicated. Definitive diagnosis requires surgical excisional biopsy.¹⁴

Treatment

If enzootic nasal tumor is untreated, death will occur within 90 days of appearance of clinical signs.^13,¹⁴ Surgical debulking is a palliative option¹⁴ but may not be curative.¹⁸ The mass can be accessed for excision by creating an I-shaped incision in the skin and then the nasal bones along the dorsal facial midline axis, reflecting the cutaneous and bony flaps, and removing the nasal septum. Profuse hemorrhage is to be expected; epinephrine (1:100,000)-soaked gauze pads can help with hemostasis, and a blood donor should be readily available.¹⁸ A temporary tracheostomy may be needed during the surgical procedure and the postsurgical period.¹⁴ Herd or flock control of enzootic tumor is difficult in the absence of a serologic test to identify animals with preclinical disease. Enzootic nasal tumors can be spread by nasal discharge; infected animals should be isolated and culled.¹⁷

Other Respiratory Infections

Other respiratory infections involved in small ruminant rhinitis include herpesvirus and Pasteurella multocida infections. Herpesvirus infection causes fibronecrotic ulceration of the nasal septum with a marked catarrhal rhinitis, usually accompanied by additional severe systemic signs.¹ P. multocida infection causes nasal turbinate atrophy, which can be identified at necropsy by cross-sectioning the head at the level of the first premolar.¹ In tropical and subtropical regions, an important consideration in the differential diagnosis for bacterial rhinitis is nasal melioidosis (caused by Burkholderia pseudomallei).¹ Respiratory involvement is particularly common in small ruminant species and may include oculonasal discharge, coughing, lymphadenopathy, and pulmonary disease, all characterized by multiple caseous abscesses. Melioidosis is zoonotic and reportable in many parts of the world.¹⁹

Sinusitis

Pathogenesis

Sinusitis is a relatively rare condition in sheep and goats, usually related to dehorning infections (with consequent involvement of the frontal sinus) or dental abnormalities (with maxillary sinus involvement). Signs of frontal sinus infection may appear weeks to months after the dehorning process. Multisinus infection can result from nasal bot infestation, neoplasia, facial fractures, and horn injuries.⁷

Clinical Signs

Indications of sinusitis include drainage from dehorning sites as well as swelling, softening, or deformities of the overlying facial bones. Malodor, unequal airflow, head shaking and rubbing, extension of the head and neck, or head resting or pressing also may be noted. Systemic signs such as pyrexia, anorexia, and lethargy may develop as well, and chronic sinusitis may lead to neurologic symptoms.⁷

Diagnosis

A presumptive diagnosis can be made from the clinical presentation and findings on percussion. Radiographic imaging is indicated for investigation of recurring or refractory cases. In one instance of chronic sinusitis in a pet goat, computed tomography was used to accurately characterize the lesion.²⁰ An oral exam with the animal under light sedation should be performed if dental abnormalities are suspected. Culture and sensitivity testing of the sinus exudate can help direct antimicrobial selection.

Treatment

Basic therapy involves daily lavage of the dehorning site and sinus with a dilute antiseptic such as 0.1% chlorhexidine. Lavage solution can be introduced through a teat cannula or 16-18 French catheter. Multiple trephination sites may be needed, especially in the highly compartmentalized ovine frontal sinus.⁷ Trephine holes need to be large enough to establish drainage; 14-gauge needles commonly are used for diagnostic sampling but are too small for lavage. Placement and ease of trephination are facilitated by the softer bone and the bone deformity found in typical chronic sinusitis cases.²¹ The caudal frontal sinus can be accessed 5 mm from the base of the horn while avoiding the frontal vein in the supraorbital groove; the rostral frontal sinus lies medial to the orbit. Trephination borders for the maxillary sinus are cranial to the orbit, caudal and dorsal to the facial tuberosity, and ventral to the infraorbital foramen.²²

Complete resolution may require a couple weeks of daily treatment, because the sinus structure is complex and biofilm development is common. Sheep have been used in experimental models for antibiofilm approaches to sinusitis; early results are promising.²³ Animals showing systemic signs should be treated with antibiotics (penicillin, 22,000 IU/kg twice daily) and nonsteroidal antiinflammatories (e.g., flunixin meglumine, 1.1 mg/kg IV twice daily, or ketoprofen, 3.0 mg/kg IV or IM once a day).

Sinusitis may be prevented by bandaging open dehorning sites for 5 to 7 days after the procedure and by gauze-packing extracted tooth sockets.⁷

Pharyngitis

Pathogenesis

In sheep and goats, pharyngitis typically develops secondary to traumatic injury, with subsequent bacterial colonization. Inciting trauma usually is caused by dosing equipment, rough feeds, or foreign objects. Plastic animal health devices (e.g., dosing and balling guns, stomach tubes, speculum), especially older devices that have been roughened from chewing, are notorious for traumatizing the pharynx. Commonly involved pathogens include Arcanobacterium pyogene, Fusobacterium necrophorum, and C. pseudotuberculosis.⁷

Clinical Signs

Coughing, painful swallowing, anorexia, and drooling are typical for pharyngitis. Oral malodor and dyspnea or stridor may be present, and the animal may stand with an extended head and neck. Systemic signs may include fever, dehydration, and aspiration pneumonia. Hyperemia, swelling, exudate, and foreign material may be identified on oral exam. Mild lesions may resolve spontaneously, but more severe infections can lead to cellulitis and formation of abscesses or granulomas.

Diagnosis

Cough and a pain response will occur on palpation of the pharyngeal region. An oral exam should be performed; light xylazine sedation will facilitate this process. Radiographic and endoscopic imaging may be indicated in some cases. Bacterial culture and sensitivity testing may help with antimicrobial selection if uncontaminated samples can be obtained.

Treatment

Pharyngitis should be treated with parenteral broad-spectrum antibiotics and NSAIDs. Oral medications and forced tube feeding are contraindicated; a temporary rumen fistula can be placed if nutritional support is needed. Abscesses can be drained into the pharyngeal cavity and flushed with a dilute antiseptic, such as 0.1% or 0.2% povidone-iodine (Betadine).⁷

Retropharyngeal Abscesses

Although retropharyngeal abscesses can develop in association with pharyngitis, they more commonly are due to C. pseudotuberculosis infection. Clinical signs result from pressure on the pharynx and trachea and include stridor, cough, and difficulty swallowing. Diagnosis is based on clinical signs, palpation, and possibly radiographic imaging. To avoid contamination of the environment, C. pseudotuberculosis abscesses should not be lanced. Surgical removal of the retropharyngeal lymph node is technically possible but difficult owing to the presence of vital anatomic structures in the region. Closed-system lavage along with either intralesional or subcutaneous tulathromycin (2.5 mg/kg) is as effective as traditional methods of lancing, draining, and flushing subcutaneous caseous lymphadenitis abscesses ²⁴; this approach may be an option if the retropharyngeal abscess can be accessed percutaneously.

Laryngitis and Tracheitis

Necrotic laryngitis (necrobacillosis, “calf diphtheria”) is caused by invasion by the opportunistic anaerobe F. necrophorum through breaks or ulcers in the laryngeal mucosa. This condition is rare in sheep and goats but is seen more commonly with indoor housing systems and in feedlot environments. Clinical signs include a moist-sounding painful cough, inspiratory dyspnea, difficulty swallowing, and salivation. A presumptive diagnosis usually can be made on the basis of clinical signs; laryngoscopic and endoscopic examinations are warranted with recurring or refractory cases. In cattle, most early cases respond well to broad-spectrum antimicrobial therapy ²⁵ and NSAIDs. A temporary tracheostomy may be needed until medical therapy takes effect.

Laryngeal chondritis is characterized by edema, suppuration, necrosis, and abscessation of the arytenoid cartilages. This disease has been described in Texel sheep as well as in cattle and horses.²⁵^–²⁷ Breed predilections have been documented, but mode of inheritance is unknown.²⁷ Clinical signs may resemble those of necrotic laryngitis and include increased upper airway noise, dyspnea, cyanosis, and possibly halitosis; if the condition goes untreated, clinical progression and death are expected.^26,²⁷ Diagnosis in the live animal requires endoscopic evaluation of the arytenoids. Partial arytenoidectomy has been suggested as a treatment,^7,²⁶ but subsequent aspiration pneumonia has been observed in cattle.²⁷ Goulding and associates reported a successful standing permanent tracheostomy in a heifer; the surgery was intended as a salvage procedure, but the heifer was retained and bred successfully.²⁵ If laryngeal chondritis is caught before cartilage necrosis, abscess formation, or granulation, early ovine and bovine cases have been successfully treated with broad-spectrum antibiotics (lincomycin) and dexamethasone.^26,²⁷