MULTI-STATE OCCUPANCY MODEL ESTIMATES PROBABILITY OF DETECTION OF AN AQUATIC PARASITE USING ENVIRONMENTAL DNA: PSEUDOLOMA NEUROPHILIA IN ZEBRAFISH AQUARIA

Review of Pseudoloma neurophilia (Microsporidia): A common neural parasite of laboratory zebrafish (Danio rerio)

Zebrafish (Danio rerio) is now the second most used animal model in biomedical research. As with other vertebrate models, underlying diseases and infections often impact research. Beyond mortality and morbidity, these conditions can compromise research end points by producing nonprotocol induced variation within experiments. Pseudoloma neurophilia, a microsporidium that targets the central nervous system, is the most frequently diagnosed pathogen in zebrafish facilities. The parasite undergoes direct, horizontal transmission within populations, and is also maternally transmitted with spores in ovarian fluid and occasionally within eggs. This transmission explains the wide distribution among research laboratories as new lines are generally introduced as embryos. The infection is chronic, and fish apparently never recover following the initial infection. However, most fish do not exhibit outward clinical signs. Histologically, the parasite occurs as aggregates of spores throughout the midbrain and spinal cord and extends to nerve roots. It often elicits meninxitis, myositis, and myodegeneration when it infects the muscle. There are currently no described therapies for the parasite, thus the infection is best avoided by screening with PCR-based tests and removal of infected fish from a facility. Examples of research impacts include reduced fecundity, behavioral changes, transcriptome alterations, and autofluorescent lesions.

Assessment of Oral Albendazole and Fumagillin in the Treatment of Pseudoloma neurophilia in Adult Zebrafish

Pseudoloma neurophilia ( Pn ), the causative agent of the most commonly reported disease of zebrafish, is a microsporidian parasite that confounds research by inducing behavioral and physiologic changes in zebrafish. Although a treatment for P. neurophilia has not been documented in zebrafish, albendazole (ALB) and fumagillin (FUM) have been used to treat microsporidian infections of other fish species. To investigate the efficacy of oral ALB and FUM in the treatment of Pn, we performed a pilot study that demonstrated the safety and palatability of novel gel-based diets containing FUM or ALB in adult AB zebrafish. In a subsequent study, approximately 250 adult AB zebrafish (previously infected with Pn ) were treated with these medicated diets for 4 wk. At 4 different time points (weeks 0, 5, 10, and 16 of the study), fish were euthanized and whole-body qPCR was performed to assess Pn prevalence across treatment and control groups. There was no statistically significant association between treatment group and Pn prevalence at any time point, although potential biologically relevant reductions in Pn prevalence occurred in the combination therapy group at weeks 5 and 16 and in the ALB group at week 5. Based on high-performance liquid chromatography analyses, the medicated diets contained less ALB and more FUM than expected, highlighting the importance of validating medicated feed concentrations to ensure safety, efficacy, and consistency. While Pn remains challenging to eradicate and control, results of this study warrant further investigation into the utility of ALB and FUM as potential treatments for this pathogen.

Application of an eDNA assay for the detection of Pseudoloma neurophilia (Microsporidia) in zebrafish (Danio rerio) facilities

Environmental DNA (eDNA) water assays are beginning to be implemented for many important pathogens in confined aquaculture systems. Recirculating systems are rapidly being developed for fin fish aquaculture. Zebrafish (Danio rerio) are reared in these systems, and Pseudoloma neurophilia (Microsporidia) represents a serious challenge for zebrafish research facilities. Diagnosis of the pathogen has traditionally used histology or PCR of tissues with lethal sampling. However, with the development of a nonlethal assay to detect P. neurophilia in tank water, facilities will be able to integrate the assay into routine surveillance efforts to couple with their established protocols. Here, we first describe a modified protocol to extract and quantify parasite DNA from the environment for nonlethal detection of P. neurophilia in adult zebrafish populations. Using this modified assay, we then evaluated water samples from a longitudinal experimental infection study, targeting timepoints during initial infection. The parasite was detectable in the water immediately after initial exposure until week 4 post exposure (pe), when the parasite was undetectable until 7 weeks pe. After that time, the parasite was sporadically detected in the water for the 10-month study, likely correlating with the lifecycle of the parasite. Using water samples from the Zebrafish International Resource Center, we also validated the clinical relevance of the assay in a large zebrafish facility. The integration of this assay at ZIRC will significantly compliment surveillance and control efforts for the microsporidian parasite.