Blood Metabolic and Hematology Parameters and Survivorship in Mice after Application of the Rabies Challenge Virus Standard in Vaccine Potency Test

Abstract

Background: Rabies virus can cause intensive and lethal infection of the central nervous system (CNS) in animals and humans. Metabolic examinations are conducted at the cerebrospinal fluid (CSF), and it has been found that many metabolic changes occur during RABV infection. However, although it is a neurotropic virus, it can cause damage to extraneural tissues - lungs, heart, kidneys and liver. This study aimed to determine differences in metabolic, endocrinology and hematologic parameters in blood of mice after application of rabies challenge with virus standard 27 strain (CVS-27).Materials, Methods & Results: This study included 30 survived, and 30 dead mice that were part of the standard procedure of NIH (National Institute of Health) test in Pasteur Institute in Novi Sad. Tests were performed in the following order: two groups of mice were vaccinated in a 7 day period with different dilutions of standard vaccine and the examined vaccine. Seven days after the last vaccination, immunized animals and animals in the control group received test virus CVS-27. Blood samples were collected from a heart puncture. Differences in hematologic and biochemical parameters were determined by t-test. Due to a high number of blood parameters, we performed a joint analysis of multiple dependent variables. Higher pH value and higher concentrations of glucose, cholesterol, lactate dehydrogenase (LDH), creatine kinase (CK), albumin, urea, creatinine, α-amylase, magnesium (Mg), nonesterified fatty acids (NEFA), beta-hydroxybutyrate (BHB) and lactate were noted in dead mice. Higher granulocytes and mean platelet volume (MPV) were noted in mice which died, but also reduced lymphocytes, erythrocytes, haemoglobin, hematocrit and platelets count. Higher values of insulin, cortisol and HOMA-IR (homeostatic model assessment insulin resistance) were noted in the group of dead mice compared to the surviving one. Reduced QUICKI (quantitative insulin sensitivity check index) value was noted in mice which died compared to the surviving group. Principal component analysis (PCA) showed that components 1 and 2 explain 38.7 of variance and that these two compounds are enough for the distinction between the animals which dies and those that survived. It was found that the cortisol, insulin, HOMAIR, NEFA, aspartate aminotransferase (AST), lactic acid, LDH and granulocyte could explain the variance of the first component, which highly correlated with the first principal component. Also, pH level, glucose, creatinine, albumin and BHB showed significant importance. A positive correlation was shown between those parameters.Discussion: Mice that died during NIH test after applying CVS-27 expressed more significant stress (higher cortisol level). Disturbances of energy metabolism were noted (more significant catabolism of lipids and insulin resistance), changes of protein metabolism caused by muscle load (urea, creatinine, AST and LDH) and general disturbances of acid-base status (higher pH) and dehydration (increased albumin) were also noted in mice that died. Values of hematologic parameters showed minor influence at total variability and are a bit correlated with metabolic changes. In factor analysis, component 1 was determined from numerous parameters. Correlations between component 1 and cortisol, HOMA-IR, lactates, insulin, AST and LDH were noted. It completely determines survived and dead animals after CVS-27 during NIH test. Disturbances in blood parameters showed an analogy with previous studies of CNS. Given parameters can be very useful in clinical-pathological analysis in RABV infection.