Asymptomatic cysticercosis in wistar albino rats: A note of caution to all biomedical researchers

Sir, Rat is one of the most commonly used animals in biomedical research. It can spread various types of zoonotic diseases, most commonly, rat fever (caused by Streptobacillus moniliformis), ring worm infestation, rabies, tetanus, and salmonella.[1] Hence it is important to have a thorough knowledge regarding the common zoonotic diseases transmitted by the animal, the common modes of transmission to humans as well as necessary precautionary methods during handling of the animals. The researcher should not only keep in mind the possible zoonotic diseases that can affect him, but also the asymptomatic parasitic diseases common to the animals that can erroneously affect the results of the experiments. In our setting, we conducted an experiment involving Wistar albino rats, maintained according to the Committee for the Purpose of Control and Supervision on Experiments on Animals (CPCSEA) guidelines to observe the effects of fluoxetine on rat endometrium. At the end of the study, after sacrificing the animals, one of the rats of the control group (treated only with oral 0.9% normal saline) showed cyst formation on the liver. Histopathological examination confirmed the cyst to be of cestode origin as evidenced by the presence of an outer acellular eosinophilic cuticular layer and underlying subtentacular layer along with scolex-containing hooks and suckers [Figure 1]. Some giant cell reaction along with signs of inflammation was also evident in the adjoining tissue. Figure 1 HP examination shows outer acellular eosinophilic cuticular layer, subtentacular layer along with scolex containing hooks and suckers at 100× magnification Molecular techniques like PCR-linked mitochondrial DNA sequencing were not used to confirm the species of the tapeworm larva. But it is most likely due to the encysted larval form of Taenia taeniaeformis, i.e. Cysticercus fasciolaris, as it is one of the most common cestodes affecting the livers of the rats. Sometimes it has been found to be associated with hepatic fibrosarcomas.[2,3] Hence, animal experiments which particularly involve testing of liver functions can have erroneous results if asymptomatic rats harboring C. fasciolaris are used. Although our experimental protocol did not require measurements of liver function, it most likely did not affect the outcome. Besides Wistar albino rats, other commonly used laboratory animals can have asymptomatic parasitic infestations that can act as a restricting factor for attainment of experimental protocol. Therefore, the biomedical researchers should be aware of the asymptomatic spontaneous lesions to correctly interpret the outcome of their experiments.