Disease progression is better understood by revealing the pathophysiological mechanisms underlying the clinical infections. Blood indices are highly correlated to the health status of the fish as the organism tries to maintain a steady physiological response to stimuli and disrupts homeostasis. Cell lysis, following tissue damage associated with the disease condition, can result in the release of enzymes into the bloodstream leading to elevated serum enzyme activity. Evaluation of haemato-biochemical indices can be useful in predicting metabolic alterations and timely prognosis. Viral infections are accompanied by extensive degeneration and necrosis of hematopoietic tissues such as the kidney and spleen. Blood-biochemical anomalies in diseased fish have been evaluated and provide insight into specific responses in the pathophysiology of many viral infections. Ictavirus ictaluridallo1 (Ictalurid herpesvirus 1, IcHV1 commonly called channel catfish virus, CCV) is a significant pathogen infecting fry and fingerling stages of channel catfish that poses a serious threat to commercial hatchery operations. A better understanding of IcHV1-associated pathophysiological alteration in ictalurid catfish is warranted to unravel why infected fish fail to maintain homeostasis and how the physiologically relevant tissues contribute towards mass mortality.
Naïve channel catfish (average weight ~40g) were exposed to IcHV1 at a dose <LD50 via immersion. An equivalent amount of serum-free media was added to control tanks. Six tanks, each containing twenty fish were allocated for treatment or control groups. Three fish per tank were arbitrarily sampled at days 1, 2, 3, 5, 7, and 14 post-infection, euthanized with excess MS-222, and the blood was collected from the caudal vein using lithium-heparinized syringes. Blood gas values (pH, pCO2, pO2), oximetry values (Hb, osmolality, Hct), electrolytes (K+, Na+, Ca2+, Cl-), and metabolites (glucose, lactate) of the whole blood were tested using a blood-gas analyzer (ABL-90, Radiometer America Inc). Plasma was separated by centrifuging the whole blood at 5000 x g for 3 min. Fifteen plasma biochemical markers were also examined using a clinical chemistry analyzer. The results were statistically analyzed and compared between the IcHV1-infected and non-infected control groups.
Hematological analysis showed significant alterations in circulating metabolites of diseased fish. These changes may represent underlying mechanisms leading to the severe gross clinical signs associated with IcHV1 infection, such as lethargy, ascites, and abnormal swimming patterns. The findings from this study are useful to provide detailed insight into the pathophysiological changes associated with IcHV1 infection, which may possibly cause damage to any off-target organs such as brain, liver, or heart, critically involved in major physiological functions.