An updated description of bacterial pneumonia in adult horses and factors associated with death

BACKGROUND

Available descriptive studies on equine pneumonia are outdated or focus on specific horse or bacterial populations.

OBJECTIVES

To describe the clinical presentation and bacterial isolates of adult horses with bacterial pneumonia and identify factors associated with death.

ANIMALS

One hundred sixteen horses >2 years old with bacterial pneumonia.

METHODS

Retrospective case series. Data regarding history, physical examination, clinicopathologic features, treatment, bacterial culture and sensitivity, and outcome were collected and analyzed retrospectively.

RESULTS

Historical risk factors were present for 60% of cases, whereas abnormal vital signs on intake were present for <50%. Most horses (58%) underwent at least 1 change of antimicrobial treatment, and 67% received the highest-priority critically important antimicrobials. Streptococcus zooepidemicus was the most isolated bacteria (44%), followed by Escherichia coli (19%), Klebsiella spp. (18%), other Streptococcus species (17%), and Bacillus spp. (13%). Fusobacterium spp. were the most common anaerobic isolates (11%). Antimicrobial susceptibility varied widely. Survival to discharge was 73%. Heart rate at presentation (odds ratio [OR] 1.08, 95% confidence interval [CI] 1.008-1.17, P = .03) and higher creatinine (OR 14.1, 95% CI 1.56-127.6, P = .02) increased the risk of death. Higher lymphocyte count (OR 0.27, 95% CI 0.08-0.94, P = .04) reduced risk.

CONCLUSIONS AND CLINICAL IMPORTANCE

Contrasting older literature, Fusobacterium spp. were the most common anaerobes. Streptococcus zooepidemicus remained the most common isolate and was predictably susceptible to penicillin. Antimicrobial susceptibility was otherwise variable and broad applicability is limited as this was a single-center study. Increased risk of death associated with tachycardia and abnormally high serum creatinine concentration is consistent with previous studies.

Immunology of Physical Exercise: Is Equus caballus an Appropriate Animal Model for Human Athletes?

Domestic horses routinely participate in vigorous and various athletic activities. This enables the horse to serve as a model for studying athletic physiology and immunology in other species, including humans. For instance, as a model of physical efforts, such as endurance rides (long-distance running/aerobic exercise) and races (anaerobic exercise), the horse can be useful in evaluating post-exercise response. Currently, there has been significant interest in finding biomarkers, which characterize the advancement of training and adaptation to physical exercise in the horse. The parallels in cellular responses to physical exercises, such as changes in receptor expression and blood cell activity, improve our understanding of the mechanisms involved in the body's response to intense physical activity. This study focuses on the changes in levels of the pro- and anti-inflammatory cytokines and cellular response in the context of post-exercise immune response. Both the direction of changes in cytokine levels and cellular responses of the body, such as proliferation and expression of surface markers on lymphocytes, monocytes and neutrophils, show cross-functional similarities. This review reveals that horses are robust research models for studying the immune response to physical exercise in human athletes.

Pleural Empyema in Six Horses: A Retrospective Case Series

The clinical findings of pleural empyema in six horses were retrospectively studied using epidemiological, clinical pathology, microbiological, ultrasound, and post-mortem data. The clinical findings included tachycardia (n = 3/6), tachypnea (n = 6/6), cyanotic mucosa (n = 2/6), hyperthermia (n = 4/6), inspiratory or mixed dyspnea (n = 6/6), presence of fluid and/or pleural rubbing (n = 2/6) and coarse crackling on auscultation (n = 4/6). Horses demonstrated leukocytosis (16.22 × 103/µL) with neutrophilia (12.32 × 103/µL) and hyperfibrinogenemia (633.33 mg/dL) and an increase in urea (69.80 mg/kg) and globulins (5.22 g/dL). The pleural fluid exhibited exudate (n = 5/6). The pathogens isolated from transtracheal wash (TTW) and/or pleural effusion included Aspergillus fumigatus, Enterobacter cloacae, alpha and beta hemolytic Streptococcus, Pseudomonas aeruginosa, Salmonella sp., Streptococcus equi subsp. zooepidemicus, and beta hemolytic Staphylococcus. The in vitro tests of microbial sensitivity of the isolates revealed that ceftiofur (5/6) and penicillin (3/6) were the most effective drugs. The fatality rate was 83% (5/6). The main post-mortem finding was the presence of fibrin in the pleural cavity with adhesion between the parietal and visceral pleura. These results show that pleural empyema is a complex disease pathophysiology that is refractory to conventional treatment.

Retrospective study of pneumonia in non-racing horses in California

Pneumonia is a significant disease of horses. Although pneumonia has traditionally been studied in racehorses, little information is available for non-racing horses. Non-racing horses that died with pulmonary lesions (n = 156) were available from cases submitted for autopsy from January 2015 to June 2020. Bronchopneumonia (35%), interstitial pneumonia (29%), embolic pneumonia (21%), granulomatous pneumonia (13%), and pleuritis (2%) were observed in the examined horses. Seventy-four horses died or were euthanized because of pulmonary diseases, and 82 horses died or were euthanized because of non-pulmonary causes but had lung lesions. Of the horses that died from pulmonary causes, the most common finding was bronchopneumonia, with abscesses and/or necrosis in the cranioventral aspect of the lung. Bacteria isolated from cases of bronchopneumonia were Streptococcus equi subsp. zooepidemicus (48.5%), Klebsiella pneumoniae (12.1%), and Actinobacillus equuli subsp. haemolyticus (9.1%). The most common extrapulmonary lesions responsible for death in horses that also had lesions in the lung were mainly in the gastrointestinal system (30%), multiple systems (septicemia and/or toxemia; 27%), and musculoskeletal system (12%). The main postmortem findings in cases of bronchopneumonia of non-racing horses were similar to those reported previously in racehorses. However, some non-racing horses also had interstitial and granulomatous pneumonia, patterns not described previously in racehorses in California, likely as a result of the inclusion of extended age categories for non-racing horses. We also found that the equine lung was frequently affected in cases of sepsis and gastrointestinal problems of infectious origin.

Bilateral thoracic radiographs increase lesion detection in horses with pneumonia or pulmonary neoplasia but do not bring any additional benefit for inflammatory or diffuse pulmonary disease

Published studies describing the effects of bilateral radiographic projections on the detection of equine pulmonary lesions are currently lacking. The objectives of this retrospective, single center, observational study were to compare unilateral and bilateral thoracic radiographic projections for the detection of pulmonary lesions in a group of horses. Based on their clinical diagnosis, 167 adults and foals with bilateral thoracic radiographs were classified as having pneumonia (n = 88), inflammatory or diffuse pulmonary disease (n = 72), and pulmonary masses (n = 7). After an initial interrater repeatability test, right-to-left and left-to-right projections were anonymized and independently interpreted by a radiologist blinded to the clinical diagnosis. Scores were attributed for each pattern/lesion (alveolar, interstitial, bronchial, nodules/masses, cavitary lesions) and each quadrant. Agreement between scores from each projection was evaluated with Bland-Altman plots. Lesions identified on one side but not on the contralateral projection were considered discordant. There was no preferential lateralization of pulmonary lesions. The prevalence of discordance was 14.4%, 9.0%, and 4.2% for alveolar pattern, nodules/masses, and cavitary lesions, respectively. Up to nine horses (10.2%) with pneumonia could have been misdiagnosed. A pulmonary mass would have been missed in one case. For inflammatory or diffuse disease, discordance was slight, and the addition of contralateral projections had no impact on radiographic interpretation. In conclusion, in horses with pneumonia or neoplasia, bilateral projections, or adding at least one contralateral caudoventral view, increased the probability of identifying pulmonary lesions. In horses with inflammatory or diffuse disease, bilateral thoracic radiography provided no additional benefit.

Interstitial pneumonia and diffuse alveolar damage in domestic animals

Classification of pneumonia in animals has been controversial, and the most problematic pattern is interstitial pneumonia. This is true from the gross and histologic perspectives, and also from a mechanistic point of view. Multiple infectious and noninfectious diseases are associated with interstitial pneumonia, all of them converging in the release of inflammatory mediators that generate local damage and attract inflammatory cells that inevitably trigger a second wave of damage. Diffuse alveolar damage is one of the more frequently identified histologic types of interstitial pneumonia and involves injury to alveolar epithelial and/or endothelial cells, with 3 distinct stages. The first is the “exudative” stage, with alveolar edema and hyaline membranes. The second is the “proliferative” stage, with hyperplasia and reactive atypia of type II pneumocytes, infiltration of lymphocytes, plasma cells, and macrophages in the interstitium and early proliferation of fibroblasts. These stages are reversible and often nonfatal. If damage persists, there is a third “fibrosing” stage, characterized by fibrosis of the interstitium due to proliferation of fibroblasts/myofibroblasts, persistence of type II pneumocytes, segments of squamous metaplasia of alveolar epithelium, plus inflammation. Understanding the lesion patterns associated with interstitial pneumonias, their causes, and the underlying mechanisms aid in accurate diagnosis that involves an interdisciplinary collaborative approach involving pathologists, clinicians, and radiologists.

Antimicrobial Selection for the Equine Practitioner

Antimicrobial drugs play an important, often central, role in the therapeutic management of mature horses and foals with a variety of illnesses, including those requiring critical care. Antimicrobial use must be based on rational principles involving thorough patient evaluation and sound clinical judgment that indicate a high likelihood that the patient has a bacterial infection and that antimicrobials are indicated to promote recovery. The aim of antimicrobial treatment is to inflict an insult on infecting bacteria sufficient to kill the organism or render it susceptible to inactivation by natural host defenses or the local microenvironment without adversely affecting the patient.

Causes and Pathology of Equine Pneumonia and Pleuritis in Southern Brazil

We document the causes and pathological findings in 50 cases of equine pneumonia and pleuritis in Southern Brazil. Suppurative (17/50), pyogranulomatous (14/50), aspiration (5/50), mycotic (4/50), bronchointerstitial (3/50), embolic (3/50) and eosinophilic granulomatous pneumonia (1/50) and pleuritis (3/50) were the main conditions identified. Streptococcus spp. were identified in 11 cases of suppurative pneumonia. Suppurative pneumonia was further divided into acute (8/17), subacute (6/17) and chronic (3/17) based on the morphological pattern of lesions. Rhodococcus equi was identified in all cases of pyogranulomatous pneumonia and exclusively affected young foals.

Lung lesions of slaughtered horses in southern Brazil

ABSTRACT: Respiratory diseases cause significant veterinary costs, reduce performance and require withdrawal of horses. Yet, studies of the causes of pneumonia in horses are scant. This study aimed to describe the pathological and microbiological features of lung lesions in slaughtered horses in southern Brazil. In this study, 84 samples of lungs were examined, and a conclusive diagnosis was obtained in 74 cases. These were composed of bronchopneumonia in 50 cases, followed by granulomatous eosinophilic pneumonia (9/74), recurrent airway obstruction (7/74), lung fibrosis (4/74), lung hemorrhage (3/74) and pulmonary pythiosis (1/74). Bronchopneumonia had grossly firm focally extensive yellow to dark-red areas, which consisted microscopically of multifocal to coalescing infiltrate of degenerate neutrophils. Streptococcus equi subsp. zooepidemicus was identified in 21 of the 50 cases. Granulomatous eosinophilic pneumonia had multifocal pinpoint firm-hard yellow areas, which microscopically were composed of granulomas with a mineralized center surrounded by collagen fibers and severe infiltrate of eosinophils. Recurrent airway obstruction had mild multifocal pinpoint firm white areas that consisted microscopically of large amounts of mucus inside bronchi and bronchiole. Lung fibrosis had two patterns: focally extensive areas of consolidation and firm nodular areas. Microscopically, the first pattern had interstitial to peribronchial fibrosis, while the second had, in addition to the interstitial fibrosis, a severe pneumocyte hyperplasia and an alveolar infiltrate of neutrophils and macrophages with rare intranuclear inclusion bodies (equine herpesvirus 5, EHV-5). Pulmonary pythiosis presented a focal firm nodular area, with multiple kunkers observed in the cut surface, which corresponded microscopically to areas of necrosis surrounded by a mixed inflammatory infiltrate. At the periphery of the necrotic areas, multiple negatively stained hyphae were observed, which were evidenced through Grocott’s stain and immunohistochemistry anti-Pythium insidiosum.

A prospective study on the microbiological examination of secretions from the paranasal sinuses in horses in health and disease

BACKGROUND

Diagnostics in equine sinusitis can be challenging and often require a combination of different imaging tools to ascertain its underlying aetiology. The bacterial flora of healthy and diseased paranasal sinuses, respectively, has only sporadically been assessed in horses. The objectives of this study were to determine whether assessment of microbiological features of secretions from the paranasal sinuses displays a useful diagnostic tool in equine sinusitis to distinguish between different aetiologies. Secretion samples from 50 horses with sinusitis and from 10 healthy horses were taken transendoscopically from the drainage angle of the nasomaxillary aperture using a guidable Swing Tip catheter. Bacteria found in healthy and diseased equine sinuses were compared. Endoscopic samples in all healthy and 19 diseased horses were compared with samples taken directly from the affected sinus after trephination.

RESULTS

Eleven of the 14 horses with primary sinusitis revealed growth of Streptococcus equi ssp. zooepidemicus, with three samples yielding pure cultures. Anaerobes were found in 15 out of 26 samples from horses with dental sinusitis. Healthy sinuses revealed mainly α-haemolytic streptococci and coagulase-negative staphylococci or showed no growth. Enterobacteriaceae were found more frequently in secondary sinusitis. There were significant differences in the bacterial composition and diversity (P < 0.05) between primary sinusitis, dental sinusitis and healthy controls. The correlation between endoscopic and trephination samples was satisfying.

CONCLUSIONS

Microbiological examination of secretions from horses with sinusitis collected transendoscopically can help to distinguish between primary and dental sinusitis. Therefore, it may display a feasible ancillary diagnostic tool, but does not replace a meticulous examination procedure including diagnostic imaging.

Streptococcus equi subspecies zooepidemicus septicemia in alpacas: three cases and review of the literature

Streptococcus equi subspecies zooepidemicus septicemia of alpacas and llamas, also called alpaca fever, is characterized clinically by fever, depression, recumbency, and death, and pathologically by polyserositis. Although a few natural and experimental cases of the disease have been reported, very little information about the pathology of spontaneous cases has been published. We present a detailed gross and microscopic description of 3 spontaneous cases of alpaca fever and review the literature on this condition. Typical of spontaneous and experimental infections with S. equi ssp. zooepidemicus, the 3 animals had disseminated fibrinosuppurative polyserositis with vascular thrombosis and intralesional gram-positive cocci. In addition, 2 of the animals had severe fibrinosuppurative pneumonia, endocarditis, and myocardial necrosis; the third animal had transmural pleocellular enteritis with prominent lymphangitis. The enteric lymphangitis observed in the latter suggests that dissemination of S. equi ssp. zooepidemicus occurred through lymphatic circulation and that, at least in this animal, the portal of entry of infection was the alimentary system.