Necrotic Laryngitis
(Calf diphtheria, Laryngeal necrobacillosis) |  |
| Necrotic laryngitis is a disease of young cattle characterized by fever, toxemia, inspiratory dyspnea, and stridor. Inflammation of the pharynx, or the laryngeal mucosa and its cartilage, caused by invasion of
F
necrophorum
into existing lesions is responsible for the clinical signs. Necrotic laryngitis primarily affects feedlot cattle 3-18 mo of age; however, cases in calves as young as 5 wk and in cattle as old as 24 mo have been documented. It has a worldwide distribution. |
| Etiology: |
| The primary etiologic agent is uncertain because
F
necrophorum
, which is commonly isolated from lesions of affected cattle, is unable to penetrate intact mucous membranes. Contact ulcers on the mucous membranes of the vocal processes and medial angles of the arytenoid cartilages are thought to be the initial lesions; concurrent disease, inhaled irritants, vitamin A deficiency, and poor hygiene in confined animals have all been incriminated as predisposing factors. |
|  |
| Transmission, Epidemiology, and Pathogenesis: |
| Necrotic laryngitis is most common where cattle are closely confined under unsanitary conditions or in feedlots. The prevalence in feedlot calves is estimated to be 1-2%. Most cases are sporadic and occur year round, but disease peaks in the fall and winter. Mixed upper respiratory infections (viruses such as infectious bovine rhinotracheitis and parainfluenza-3;
Mycoplasma
spp
; and bacteria, including
Pasteurella
and
Haemophilus
), and the coughing and swallowing associated with these infections, may predispose feedlot cattle to develop erosions involving the vocal processes and medial angles of arytenoid cartilages. These ulcerative laryngeal lesions then provide a portal of entry for
F
necrophorum
. |
| Once it has invaded the mucosa of the pharynx and larynx,
F
necrophorum
causes inflammation and necrosis. Edema of the laryngeal mucosa results in variable narrowing of the rima glottidis accompanied by inspiratory dyspnea and stridor. If infection extends into the laryngeal cartilage, laryngeal chondritis develops, which delays healing and inhibits recovery. Pharyngeal lesions cause discomfort and result in painful swallowing motions. The exotoxin produced by
F
necrophorum
also causes systemic signs of illness. |
| |
| Clinical Findings: |
| Initially, a moist, painful cough is noticed. Severe inspiratory dyspnea, characterized by open-mouth breathing with the head and neck extended and loud inspiratory stridor are common findings. Ptyalism; frequent, painful swallowing motions; bilateral, purulent nasal discharge; and a fetid odor to the breath may also be present. Systemic signs may include fever (106°F [41.1°C]), anorexia, depression, and hyperemia of the mucous membranes. Untreated calves die in 2-7 days from
toxemia and upper airway obstruction. Longterm sequelae include aspiration pneumonia and permanent distortion of the larynx. |
Lesions:
| Lesions are typically located over the vocal processes and medial angles of arytenoid cartilages. Acute lesions are characterized by edema and hyperemia surrounding a necrotic ulcer in the laryngeal mucosa; lesions may spread along the vocal folds and processes to involve the cricoarytenoideus dorsalis muscle. In chronic cases, lesions consist of necrotic cartilage associated with a draining tract surrounded by granulation tissue. |
| |
| Diagnosis: |
| Clinical signs are usually sufficient to establish a diagnosis. However, because numerous other conditions can cause signs of upper airway obstruction, the larynx should be visually inspected to confirm a diagnosis. This can be accomplished by means of an orally inserted speculum, laryngoscopy, endoscopy, or radiography, but care must be exercised to avoid further respiratory embarrassment. A tracheostomy should be performed before laryngoscopic or endoscopic examination in
cattle with severe inspiratory dyspnea. Differential diagnoses include pharyngeal trauma; severe viral laryngitis (eg, infectious bovine rhinotracheitis); actinobacillosis; and laryngeal edema, abscesses, trauma, paralysis, or tumors. |
| |
| Treatment and Control: |
| Sulfonamides (an initial dose of 140 mg/kg, IV, followed by 70 mg/kg, IV, sid) or procaine penicillin (22,000 U/kg, IM, bid) are the drugs of choice. NSAID (aspirin, 100 mg/kg, PO, bid, or ketoprofen, 3 mg/kg, IM or IV, sid for up to 3 days) can be used to decrease the degree of laryngeal inflammation and edema. A tracheostomy is indicated in cattle with severe inspiratory dyspnea. The prognosis is good for early cases
that are treated aggressively; chronic cases will require surgery under general anesthesia to remove necrotic or granulation tissue and to drain laryngeal abscesses. A 60% success rate has been reported for surgical intervention in advanced cases. |
| There are no specific control measures for necrotic laryngitis; however, the proposed pathogenesis suggests that control measures for common respiratory pathogens may be beneficial. |
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