Documented and Potential Research Impacts of Subclinical Diseases in Zebrafish

Abstract

The zebrafish (Danio rerio) has become a very important animal model in biomedical research. In contrast to other models, such as mice, there has been relatively little documentation or control of subclinical disease in zebrafish research facilities. Several infectious and non-infectious conditions are consistently detected by histopathology in apparently healthy D. rerio. The most commonly observed infectious agent in zebrafish is Pseudoloma neurophilia, which is a microsporidian organism that targets the central nervous system, peripheral nerves, and occasionally other tissues. Mycobacteriosis, caused by M. chelonae and other species, is also a frequent finding. Less commonly encountered agents include Pseudocapillaria tomentosa, which can cause extensive proliferative enteritis, and a myxozoan (Myxidium sp.) that inhabits the urinary tract, but appears to cause few if any pathological changes. Non-infectious diseases that are often clinically unapparent in zebrafish include hepatic megalocytosis, bile and pancreatic ductal proliferation, and neoplasms of the ultimobranchial gland, gastrointestinal tract, and testis. To date there is little information on the degree to which these conditions may impact research in subclinically affected fish, but there is reason to believe that they should be considered as potentially significant causes of non-protocol variation in experiments. Therefore, it is imperative that research facilities monitor their stocks for the presence of these occult diseases, and be aware of their existence when interpreting study results. Furthermore, for underlying disease conditions that cannot be readily eradicated, it is essential to determine the physiological and immunological changes that they elicit in zebrafish. Understanding the cause, modes of transmission, and distribution of the pathogens would provide useful information for the development of control and prevention strategies.

Tolerance and Efficacy of Emamectin Benzoate and Ivermectin for the Treatment of Pseudocapillaria tomentosa in Laboratory Zebrafish (Danio rerio)

“…2 Infected fish are often asymptomatic; however, emaciation and skin darkening may also be evident. 3 On histopathological examination, cross sections of nematodes embedded in the mucosal epithelium may be observed as well as severe inflammatory changes in the intestine and coelomic cavity. 3 Characteristic double-operculated barrel-shaped eggs may also be visualized in the gut lumen.…”

Recommendations for Health Monitoring and Reporting for Zebrafish Research Facilities

“…The presence of granulomas confounds histopathology data in a number of studies. 3 Parikka et al showed that M. marinum upregulates various inflammatory cytokines that may confound immunological research. 29 Infection with this species has been documented to alter gene expression in several studies.…”

“…When reporting results from a study utilizing an animal research model, it is important to describe the health status of the animals, including the presence or absence of clinical or subclinical infection. 1 Failure to report presence of disease can lead to misinterpretation of research results from zebrafish 2,3 and mammalian models [4][5][6] and result in published studies becoming unusable or nonreplicable. 7 Subclinical infections in zebrafish can result in confounded experimental results, misinterpretation of experimental data, poor reproducibility, and the unnecessary utilization of more animals to demonstrate statistical significance.…”

Expansion of the Known Host Range of the Microsporidium, Pseudoloma neurophilia

“…2 As a result, there is increasing awareness of the importance of chronic infections of laboratory zebrafish. 3 Zebrafish are a very popular tropical fish for home aquariums and there are numerous reports of zebrafish being obtained from retail pet stores and used in research. 4,5 Indeed, virtually all zebrafish lines, even those currently maintained in laboratory fish facilities, were originally derived from retail pet store fish.…”

“…3,7 As P. neurophilia has only been described from one fish species since its initial report in 1980, it may be assumed that this parasite has very narrow host specificity. However, the observation of P. neurophilia infecting a moribund Betta splendens that was cohabitating with zebrafish in a personal home aquarium for several months led us to realize that this assumption was incorrect, and thus, we were interested in investigating the ability of this parasite to infect other laboratory fishes.…”