Pseudocapillaria tomentosa, Mycoplasma spp., and intestinal lesions in experimentally infected zebrafish Danio rerio

Intestinal neoplasms and preneoplastic lesions are common in zebrafish research facilities. Previous studies have demonstrated that the neoplasms are caused by a transmissible agent, and two candidate agents have been implicated: a Mycoplasma sp. related to M. penetrans and the intestinal parasitic nematode, Pseudocapillaria tomentosa, and both agents are common in zebrafish facilities. To elucidate the role of these two agents in the occurrence and severity of the neoplasm and other intestinal lesions, we conducted two experimental inoculation studies. Exposed fish were examined at various time points over an 8 mo. period for intestinal histpathologic changes and the burden of Mycoplasma and nematodes. Fish exposed to a Mycoplasma isolate from zebrafish were associated with preneoplastic lesions. Fish exposed to the nematode alone or with the Mycoplasma isolate developed severe lesions and neoplasms. Both inflammation and neoplasm scores were associated with an increase in Mycoplasma burden. These results support the conclusions that P. tomentosa is a strong promoter of intestinal neoplasms in zebrafish, and that Mycoplasma alone can also cause intestinal lesions and accelerate cancer development in the context of nematode infection.