TRANSMISSION OF Pseudoloma neurophilia IN ZEBRAFISH Danio rerio WHEN USING A MASS SPANWING CHAMBER

Pseudoloma neurophilia, a microsporidium that primarily infects neural tissues, is one of the most common pathogens in laboratory zebrafish. Infected fish can transmit P. neurophilia vertically; however, horizontal transmission during spawning is more common. It is unclear if risk of parasite transmission is different when spawning zebrafish in individual spawning tanks as compared to mass spawning chambers, and if this risk is correlated to the number of spawning events. In addition, disinfection protocols have not been evaluated to determine if any could decrease or eliminate the risk of transmission following spawning.

The present study was conducted to evaluate P. neurophilia transmission from a known infected colony (prevalence = 52%) to uninfected fish and their offspring when using 2 different spawning apparatuses (n = 30 per group). Infected and uninfected fish were allowed to spawn in either a mass spawning chamber or breeding tanks for 1 or 3 spawning events.  Uninfected fish and offspring were evaluated for infection 15-weeks later by histopathology and Luna stain. In addition, we sought to develop an effective protocol for disinfecting the mass spawning chamber between uses to eliminate P. neurophilia spores. Devices were either allowed to dry for 1 hour or were disinfected with one of the following  protocols  for  10 minutes after  infected zebrafish spawned for 1 hour (n=5 per method): reverse-osmosis water, 90-110 ppm bleach (pH = 6.8 - 7.5), 1.0% Virkon Aquatics, 75 ppm Wescodyne, or 175 ppm Wescodyne Plus spray.

Results demonstrated increased risk for transmission to uninfected fish when spawning occurs in a mass spawning chamber (100% infected after 3 spawning events), as compared to the other groups (0-7% infected). The parasite was not detected in offspring from these spawning events regardless of spawning device or number of spawning events. The Wescodyne Plus spray, bleach soak, and Wescodyne soak were 100% effective at eliminating P. neurophilia spores as determined by PCR following spawning (Table 1). It is important to prevent or minimize spread of this pathogen as there is no treatment and infections can cause morbidity and mortality with the potential to confound research results.