Objective—To compare serum amyloid A (SAA) concentration, plasma fibrinogen concentration, total WBC count, and serum albumin-to-globulin concentration ratio (A:G ratio) in clinically normal (CN) and clinically abnormal (CA) horses.
Design—Prospective cohort study.
Animals—111 CN horses and 101 CA horses hospitalized at a specialty clinical practice.
Procedures—Shortly after admission, a blood sample (20 mL) was collected from each horse for a CBC, serum protein electrophoresis, and determination of plasma fibrinogen concentration; SAA concentration was assessed with a previously validated immunoturbi-dometric assay. Similar testing of a subset of CA horses was conducted at various points during treatment.
Results—Total WBC count, A:G ratio, and SAA concentration were determined for all 212 horses; data regarding plasma fibrinogen concentration were available for 127 horses (of which 47 were CN and 80 were CA). Median SAA concentration, total WBC count, and plasma fibrinogen concentration and mean A:G ratio differed significantly between CN horses and CA horses. Correlations between these variables were poor to weak. For discrimination of CN horses from CA horses, the SAA assay had sensitivity of 53% and specificity of 94% (diagnostic accuracy, 75%); for the other assessments, accuracy ranged from 59% to 62%. Repeated assessment of SAA concentration in some CA horses revealed a gradual return to normal concentrations.
Conclusions and Clinical Relevance—Results indicated that assessment of SAA concentration can provide valuable information regarding the clinical state of horses and may be more useful for patient monitoring and as a prognostic indicator than are traditional markers of inflammation.
Case Description—5 horses were evaluated because of decreased appetite, weight loss, fever, cough, tachypnea, and respiratory distress.
Clinical Findings—Tachycardia, tachypnea, increased respiratory effort, lethargy, fever, poor body condition, and nasal discharge were detected in various combinations on initial physical examination. Evaluation of the lower portion of the respiratory tract via radiography and ultrasonography revealed a severe nodular interstitial pattern. Histologic examination of lung tissue revealed interstitial expansion of alveolar parenchyma with collagen, intraluminal accumulation of neutrophils and macrophages within the alveoli, and occasional intranuclear inclusion bodies within alveolar macrophages. Equine herpesvirus type 5 was detected in samples of lung tissue, bronchoalveolar lavage fluid, or both via polymerase chain reaction assay in all cases. A diagnosis of equine multinodular pulmonary fibrosis (EMPF) was established.
Treatment and Outcome—Horses were provided supportive treatment and were administered a variety of medications including corticosteroids and acyclovir. Two horses survived and returned to their previous level of activity. Three horses were euthanized because of either deterioration of clinical condition (n = 2) or failure to improve within 4 weeks of initiation of treatment (1).
Clinical Relevance—EMPF should be considered as a differential diagnosis for adult horses with interstitial pneumonia and should be suspected on the basis of characteristic radiographic, ultrasonographic, and histopathologic findings. Equine herpesvirus type 5 is found in association with EMPF; although the exact pathogenic role this virus plays in EMPF is unknown, equine herpesvirus type 5 may be an etiologic agent or cofactor in the development of EMPF.