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Title: CLINICAL PATHOLOGY AND HEMOSTATIC ABNORMALITIES IN EXPERIMENTAL AFRICAN HORSESICKNESS

Author
item SKOWRONEK, A - FORMER USDA EMPLOYEE
item LA FRANCO, L - FORMER USDA EMPLOYEE
item Stone Marschat, Melissa
item Burrage, Thomas
item REBAR, A - PURDUE UNIVERSITY
item LAEGREID, WILLIAM - USDA ARS NAP, CLAY CENTER

Submitted to: Veterinary Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: African horsesickness (AHS) is a fatal disease of horses which is carried by certain insects (midges). The disease is found in Africa and there have been recent outbreaks in Spain. The final stages of the disease have been described in experimental and field cases, however, the changes that occur in the blood and affected tissue which lead to death of the animal are unknown. Knowledge of these changes in the blood and tissues is critical for designing strategies for caring for infected animals, to help stop the spread of the disease, and aid in the design of vaccine-based and other preventative measures. This study uses three different types of AHS virus which cause three distinctive forms of the disease; a lung disease, a heart disease and a mild, fever-only disease. Sixteen serum chemicals and six blood cell parameters were determined for each group of infected animals. Since the end stage of the disease always involved edema and/or hemorrhage, ,the coagulation properties of the blood were also evaluated. This study i the most comprehensive blood analysis of AHS virus infection and it found significant alterations in some but not all of the serum enzymes and chemical ions, activation of the coagulation system, and major alterations in the umber of circulating blood cells. This study concludes that AHS virus damages blood vessels which, in turn, leads to coagulation in those blood vessels and the eventual death of the infected animal.

Technical Abstract: Infection of naive North American horses with 10(4) cell culture infectious doses of virulence variants of AHSV, designated AHSV/4SP, AHSV/9PI, and AHSV/4PI, reproduced three classical forms of AHS: acute, subacute and febrile, respectively. Distinct clinicopathologic and hemostatic abnormalities were associated with each form of disease. Hemostatic abnormalities included increased concentration of fibrin degradation products and prolongation of prothrombin, activated partial thromboplastin, and thrombin clotting times. Hemostatic findings indicate activation of the coagulation and fibrinolytic systems with clotting factor consumption in acute and subacute cases of AHS. Hematologic abnormalities in acute and subacute cases of AHS included leukopenia, decreased platelet counts, elevated hematocrit, and increased erythrocyte counts and hemoglobin concentration. Leukopenia was characterized by lymphopenia, neutropenia, and a left shift. Increased levels of serum creatine kinase, lactate dehydrogenase, aspartate aminotransferase, and alkaline phosphatase, hypocalcemia, hypoalbuminemia, hypoproteinemia and elevated creatinine, phosphorus, and total bilirubin levels were present in some but not all horses. Metabolic acidosis, indicated by decreased total bicarbonate and increased lactate and anion gap, was present in horses with the acute form of disease. Mild thrombocytopenia and leukopenia were occasionally associated with the febrile form of disease.