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Molecular typing of BLV samples isolated from Holsteinized Russian Black Pied cattle was carried out, and various cytofluorometric and morphological blood indices were examined. We performed the total count of white blood cells (WBC), lymphocyte (lymf), granulocyte (gran), monocyte (mon), red blood cell (RBC), hemoglobin (HGB), hematocrit (HTC), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), red blood cell distribution width (RDW), platelet count (PLT), mean platelet volume (MPV), platelet distribution width (PDW), and platelet crit count (PCT). The LTR-region of BLV was haplotyped. Only viruses of haplotypes I (0.33±0.03) and III (0.67±0.03) of the eight possible were detected. The ratio of hematologically sick, healthy, and suspected carriers of BLV of haplotypes I and II was comparable with the results of other researchers. The numbers of leukocytes, erythrocytes and platelets in the blood of carriers of haplotype III exceeded the corresponding parameters of cattle affected by the virus of haplotype I. It is interesting to note that the difference in the hemolytic status of animals was manifested not only by the concentration of leukocytes as direct immune agents but also by the count of erythrocytes and platelets, which are not directly involved in the immune response. The number of particles of haplotype III of the BLV circulating in the blood of infected individuals exceeded that of the carriers of haplotype I. In this connection, an assumption was made about the evolutionary advantage of the more virulent haplotype III. However, the results of our own research in conjunction with the data of other scientists indicate that the high virulence of individual virus strains is a consequence of the tendency to implement the maximum possible intensity of the synthesis of virus particles but not of the high damaging effect alone. It is shown that high lethality is evolutionarily disadvantageous for viruses, since the extinction of the carrier as a biological species is fraught with the disappearance of the virus itself.

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The insect integument (exoskeleton) is an effective physiochemical barrier that limits disease-causing agents to a few portals of entry, including the gastrointestinal and reproductive tracts. The bacterial biopesticide Bacillus thuringiensis (Bt) enters the insect host via the mouth and must thwart gut-based defences to make its way into the body cavity (haemocoel) and establish infection. We sought to uncover the main antibacterial defences of the midgut and the pathophysiological features of Bt in a notable insect pest, the Colorado potato beetle Leptinotarsa decemlineata (CPB). Exposing the beetles to both Bt spores and their Cry3A toxins (crystalline δ-endotoxins) via oral inoculation led to higher mortality levels when compared to either spores or Cry3A toxins alone. Within 12 h post-exposure, Cry3A toxins caused a 1.5-fold increase in the levels of reactive oxygen species (ROS) and malondialdehyde (lipid peroxidation) within the midgut – key indicators of tissue damage. When Cry3A toxins are combined with spores, gross redox imbalance and ‘oxidation stress’ is apparent in beetle larvae. The insect detoxification system is activated when Bt spores and Cry3A toxins are administered alone or in combination to mitigate toxicosis, in addition to elevated mRNA levels of candidate defence genes (pattern-recognition receptor, stress-regulation, serine proteases, and prosaposin-like protein). The presence of bacterial spores and/or Cry3A toxins coincides with subtle changes in microbial community composition of the midgut, such as decreased Pseudomonas abundance at 48 h post inoculation. Both Bt spores and Cry3A toxins have negative impacts on larval health, and when combined, likely cause metabolic derangement, due to multiple tissue targets being compromised.

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