Evidence of Sex Influenced Severity of Mycobacterial Lesions in Zebrafish

Investigation of the pathogenesis of infectious microorganisms is important for understanding disease processes and for development of therapies to maintain human and animal health. Some pathogens are similar across species and generate similar lesions upon infection, and these similarities have made use of model organisms (e.g., zebrafish Danio rerio) especially useful in research aimed at understanding particular disease processes. An example is Mycobacteria, among which are species responsible for tuberculosis in humans and other species that are important fish pathogens. The lesions (tubercles) generated in the lungs of human patients are morphologically similar to lesions generated in kidneys of infected zebrafish. We looked for histological lesions in 26 (13 females, 13 males) adult zebrafish from a population chronically infected with Mycobacteria, after imbedding kidneys in paraffin and staining with hematoxylin and eosin.  If lesions were present, we ranked the severity on a four-point scale. The frequency of fish with lesions was similar between sexes with lesions present in 54% of the females and 46% of the males. However, in fish with lesions, severity in female zebrafish averaged 2.6 on our 1-4 scale while males averaged only 2.