Lower airway diseases of the adult horse

Experimentally Induced Open Pneumothorax in Horses

The objective of this study was to evaluate clinical and cardiovascular parameters and pleural and intra-abdominal pressures of horses after experimentally induced unilateral open pneumothorax. Prospective, experimental study-animals: seven healthy adult horses, 4 females and 3 males. Left hemithorax thoracotomy was carried out to create an open pneumothorax for 60 minutes. Pleural pressure (P_pl) was directly obtained at the midpoint of the left eighth intercostal space before thoracotomy. Esophageal pressure (P_es), arterial blood gas analysis, left ventricular function, and ultrasonographic assessment of pneumothorax extent/resolution were performed at the baseline, and 5, 10, 15, 30, 45, and 60 minutes after thoracotomy, and on the first, second, third, fifth, and seventh days postoperatively. Intra-abdominal pressure was only recorded while the pneumothorax was present. There was moderate correlation (Spearman's rs = 0.404; R² = 0.8; P < .00001; Bland-Altman bias = -2.59; s.d. = 2.11) between P_es and P_pl. Esophageal pressure increased (P < .05) after open pneumothorax until the fifth day postoperatively. Partial pressure of oxygen in arterial blood reduced (P < .05) until the third day postoperatively when it returned to the baseline. No significant variations in P_aCO₂, pH in arterial blood, and in left ventricular function were appreciated. The extent of the pneumothorax was assessed by thoracic ultrasonography. Esophageal pressure, in association with blood gas analysis and thoracic ultrasonography, could be used to aid diagnosis of pneumothorax in horses. Horses tolerate open pneumothorax, with minimum cardiovascular impairment, even without aspiration of free air from within pleural space to restore thoracic wall integrity.

Retrospective study of fatal pneumonia in racehorses

Respiratory diseases have a major impact on racehorses in training and are often cited as the second most common reason of horses failing to perform. Cases were submitted by the California Horse Racing Board to the California Animal Health and Food Safety laboratory for postmortem examination between January 1, 2005 and December 31, 2014. We determined the demographics of racehorses with fatal pneumonia, characterized the pathologic findings in animals with a postmortem diagnosis of respiratory infection, and determined the most significant pathogens associated with lower respiratory tract disease. We analyzed autopsy reports from 83 horses with a diagnosis of pneumonia, bronchopneumonia, and/or pleuropneumonia. The most common presentation was pleuropneumonia (71% of cases), with extensive areas of lytic necrosis and abscesses of the pulmonary parenchyma. Streptococcus equi ssp. zooepidemicus, a normal mucosal commensal of the upper respiratory tract of healthy horses, was the most commonly isolated organism (72% of cases), either in pure culture or accompanied by other aerobic or anaerobic bacteria. Its presence in the pulmonary parenchyma is associated with severe and extensive damage to the lung. Furthermore, this agent has zoonotic potential, which stresses the importance of early detection and proper management of cases of pneumonia in racehorses.

Pneumonia Caused by Klebsiella spp. in 46 Horses

BACKGROUND

Klebsiella spp. are implicated as a common cause of bacterial pneumonia in horses, but few reports describe clinical presentation and disease progression.

HYPOTHESIS/OBJECTIVES

To describe the signalment, clinicopathologic data, radiographic and ultrasonographic findings, antimicrobial susceptibility, outcome, and pathologic lesions associated with Klebsiella spp. pneumonia in horses.

ANIMALS

Forty-six horses from which Klebsiella spp. was isolated from the lower respiratory tract.

METHODS

Retrospective study. Medical records from 1993 to 2013 at the William R. Pritchard Veterinary Medical Teaching Hospital, University of California, Davis were reviewed. Exact logistic regression was performed to determine if any variables were associated with survival to hospital discharge.

RESULTS

Survival in horses <1 year old was 73%. Overall survival in adults was 63%. For adults in which Klebsiella pneumoniae was the primary isolate, survival was 52%. Mechanical ventilation preceded development of pneumonia in 11 horses. Complications occurred in 25/46 horses, with thrombophlebitis and laminitis occurring most frequently. Multi-drug resistance was found in 47% of bacterial isolates. Variables that significantly impacted survival included hemorrhagic nasal discharge, laminitis, and thoracic radiographs with a sharp demarcation between marked caudal pulmonary alveolar infiltration and more normal-appearing caudodorsal lung.

CONCLUSIONS AND CLINICAL IMPORTANCE

Klebsiella spp. should be considered as a differential diagnosis for horses presenting with hemorrhagic pneumonia and for horses developing pneumonia after mechanical ventilation. Multi-drug resistance is common. Prognosis for survival generally is fair, but is guarded for adult horses in which K. pneumoniae is isolated as the primary organism.

Antimicrobial use in critically ill horses

OBJECTIVE

To discuss controversies surrounding antimicrobial use in critically ill horses.

DATA SOURCES

PubMed searches from 1970-present for terms including, but not limited to: "horse," "foal," "antimicrobial," "prophylaxis," "infection," "surgery," "sepsis," and "antimicrobial resistance."

HUMAN DATA SYNTHESIS

Increasing bacterial antimicrobial resistance has changed first-line antimicrobial choices and prompted shortening of the duration of prophylactic and therapeutic treatment. The need to decrease bacterial resistance development to critically important antimicrobials has been highlighted.

VETERINARY DATA SYNTHESIS

Veterinary medicine has followed a similar trend but often without a high-level evidence. Common dilemmas include diseases in which the theoretically most effective drug is a reserved antimicrobial, the inability to differentiate infectious from noninfectious disease, the duration and necessity of prophylactic antimicrobials and use of antimicrobials in primary gastrointestinal disease. These problems are illustrated using examples of purulent infections, neonatal sepsis, colic surgery, and treatment of colitis. Although enrofloxacin, cephalosporins, and doxycycline, in contrast to gentamicin, reach therapeutic concentrations within the lungs of healthy horses, the first two should not be used as first line treatment due to their reserved status. Due to the high risk of bacterial sepsis, antimicrobial treatment remains indispensable in compromised neonatal foals but shortening the length of antimicrobial treatment might be prudent. One prospective randomized study demonstrated no difference between 3 and 5 days of perioperative antimicrobial treatment in colic surgery but shorter durations were not evaluated. High-level evidence to recommend antimicrobial treatment of adult horses with undifferentiated diarrhea does not exist.

CONCLUSIONS

Few evidence-based recommendations can be made. Commonly used antimicrobial combinations remain the mainstay for treating purulent infections. Antimicrobial treatment for compromised foals should not extend beyond recovery. Continuation of prophylactic antimicrobials >3 days is likely unnecessary after colic surgery; shorter durations might be equally effective. Antimicrobial prophylaxis in adult horses with diarrhea is unlikely to be beneficial.

Diagnostic equine serology

This article is presented with two main goals: (1) to provide equine clinicians with a resource for identifying types of serum tests available and (2) to outline briefly the necessary sample type, assay principle, and relative strengths and weakness of the various methods. Specific etiologies are presented and grouped by clinical diagnosis categories, along with brief comments concerning each disorder and its relevant diagnostic assays. This organization provides an abstracted list of infectious disorders commonly considered for the various clinical presentations and a summary of available serologic tests for narrowing the differential diagnosis list. The reader is also provided with a list of specific laboratories that perform the diagnostic assay for the mentioned disorders.

Lung inflammatory responses

Inflammation is an important manifestation of respiratory disease in domestic animals. The respiratory system is mucosal in nature and has specific defense mechanisms used to control invasion by microbes and environmental elements. Inflammation can be beneficial or detrimental to the host. This article broadly discusses the primary mediators and mechanisms of inflammation within the respiratory tract of domestic animals. The role of cells, chemokines, cytokines and mediators in both acute and chronic inflammation are addressed. The pathogenesis of the initial insult determines the type of inflammation that will be induced, whether it is acute, chronic or allergic in origin. Maintenance of the microenvironment of cytokines and chemokines is critical for pulmonary homeostasis. Uncontrolled inflammation in the respiratory tract can be life threatening to the animal. The understanding of the mechanisms of inflammation, whether due to microbes or through inappropriate immune activation such as those occurring with allergies, is required to develop successful intervention strategies and control respiratory disease in animals.