The behavioral teratogenic potential of fenbendazole: a medication for pinworm infestation

Experience of eradicating parasites of laboratory rats in conventional vivarium

The purpose of the research is to test different dehelminthization schemes of laboratory rats infected with cestodes Rodentolepis nana and nematodes Syphacia muris and evaluate the significance of combined environment disinfection measures. The practical experience of eradication (helminth eradication) in animals in a conventional vivarium was described.Materials and methods. Experiments were conducted to study the efficacy of anthelmintics and administration schemes against cestode and nematode infections in laboratory rats. In the first experiment, praziquantel was used at a dose of 10 mg/kg to treat rats infected with R. nana. In the second experiment, the comparative efficacy of fenbendazole, albendazole, and pyrantel was evaluated against syphaciosis at the recommended dosages of 20, 10, and 12.5 mg/kg, respectively. Each drug was given orally, individually, twice with an interval of 7 days. The third experiment tested different schemes for treating syphaciosis with fenbendazole. One group of rats was given the drug orally individually using an esophageal tube at a dose of 20 mg/kg once a day for 7 consecutive days. Other groups were given fenbendazole daily with food for 7 days (150 mg fenbendazole per 1 kg of food). In all three experiments, all animals were divided into groups, and their cells underwent a complex of additional disinfection measures, and those kept in cages without disinfection.Results and discussion. Praziquantel showed 100% efficacy at a single dose of 10 mg/kg in R. nana therapy. In animals without additional disinfection procedures, cestode eggs were again recorded starting from day 14 after the drug administration. In the group of animals with disinfection measures, pathogens were not detected during the experiment. Double administration of fenbendazole, albendazole and pyrantel in the recommended dosages against syphaciosis did not result in eradicated nematodes in the animals. The disinfection did not affect the obtained results. Fenbendazole administered daily for 7 days ensured helminth eradication in animals. However, on day 7 after the therapy, Syphacia sp. eggs were again found in the groups that received the drug individually intragastrically through a tube, regardless of whether their cells were disinfected. The animals that received fenbendazole with food and were regularly disinfested remained free from nematodes throughout the experiment until the additional disinfection measures were cancelled. In the absence of disinfection, released helminth eggs were recorded on day 14 after therapy.

Fenbendazole treatment against Dentostomella translucida in Syrian golden hamsters

Dentostomella translucida is an oxyurid nematode that was first discovered in the Mongolian gerbil but has also been detected in other wild and housed rodents. In conventional laboratory animals, oxyurid nematode parasites are widespread infections. A proven treatment strategy for pinworm eradication is the oral application of benzimidazoles, such as fenbendazole. In general, this drug is regarded as safe with minimal side effects. Nevertheless, in Sprague Dawley rats, a significantly reduced litter size could be seen after longer treatment with fenbendazole. Even though Dentostomella translucida was already described in Syrian golden hamsters (Mesocricetus auratus), data on treatment with fenbendazole and its effects on reproduction is lacking. Therefore, the main purposes of the study were (1) the verification of the effectiveness of fenbendazole as medicated feed (150 ppm) against this parasite in naturally infected Syrian golden hamsters in conventional husbandry and (2) monitoring of possible effects on reproduction during the treatment. Results show that fenbendazole treatment was highly effective against Dentostomella translucida, as numbers of pinworm eggs in the faeces were significantly reduced already after the first week of treatment in all animals. After four weeks of treatment, eggs were eradicated entirely. Interestingly, the average weaning weight was significantly reduced during treatment, but the litters were in good health.

An Update on the Biologic Effects of Fenbendazole

Fenbendazole remains the drug of choice to treat pinworm infection in laboratory rodents. When fenbendazole was last reviewed (15 y ago), the literature supported the drug's lack of toxic effects at therapeutic levels, yet various demonstrated physiologic effects have the potential to alter research outcomes. Although more recent reports continue to reflect an overall discordancy of results, several studies support the premise that fenbendazole affects the bone marrow and the immune system. No effects on reproduction were reported in an extensive study that assessed common treatment protocols in mice, and food intake was unchanged in rats. Behavioral studies are sparse, with only a single report of a subtle change in a rotarod performance in mice. Notably, unexpected results in tumor models during facility treatment with fenbendazole have prompted preclinical and clinical studies of the potential roles of benzimidazoles in cancer.

Effects of Maternal Fenbendazole on Litter Size, Survival Rate, and Weaning Weight in C57BL/6J Mice

Fenbendazole is a broad-spectrum benzimidazole commonly used in laboratory animal medicine as an anthelmintic for elimination of pinworms. This drug is generally regarded as safe, with minimal side effects. Some data in rodent species indicate multiple physiologic effects of fenbendazole, including changes in immune parameters and behavior, but no studies to date have evaluated possible effects on reproduction in mice. The purpose of the current study was to determine the effects of several treatment regimens of fenbendazole on reproductive parameters in C57BL/6J mice. Uninfected mice were given fenbendazole-treated feed continuously or every other week until pups were born or weaned. This treatment also was combined with environmental decontamination. No significant differences in litter size, survival rate, or weaning weight were detected between groups. Under the conditions of this study, fenbendazole treatment does not affect reproduction in C57BL/6J mice.

Old enemies, still with us after all these years

Although some previously common infections, such as Sendai virus and Mycoplasma pulmonis, have become rare in laboratory rodents in North American research facilities, others continue to plague researchers and those responsible for providing biomedical scientists with animals free of adventitious disease. Long-recognized agents that remain in research facilities in the 21st century include parvoviruses of rats and mice, mouse rotavirus, Theilers murine encephalomyelitis virus (TMEV), mouse hepatitis virus (MHV), and pinworms. The reasons for their persistence vary with the agent. The resilience of parvoviruses, for example, is due to their resistance to inactivation, their prolonged shedding, and difficulties with detection, especially in C57BL/6 mice. Rotavirus also has marked environmental resistance, but periodic reintroduction into facilities, possibly on bags of feed, bedding, or other supplies or equipment, also seems likely. TMEV is characterized by resistance to inactivation, periodic reintroduction, and relatively long shedding periods. Although MHV remains active in the environment at most a few days, currently prevalent strains are shed in massive quantities and likely transmitted by fomites. Pinworm infestations continue because of prolonged infections, inefficient diagnosis, and the survivability of eggs of some species in the environment. For all of these agents, increases in both interinstitutional shipping and the use of immunodeficient or genetically modified rodents of unknown immune status may contribute to the problem, as might incursions by wild or feral rodents. Elimination of these old enemies will require improved detection, strict adherence to protocols designed to limit the spread of infections, and comprehensive eradication programs.