Effects of disinfectants on Toxocara canis embryogenesis and larval establishment in mice tissues

The objectives of this study were (i) to evaluate the effects of several different disinfectant solutions on embryonic development of Toxocara canis eggs and (ii) to investigate the potential infectivity of exposed eggs by assessing larval establishment in various tissues in a murine model. All the disinfectants tested were products routinely used in veterinary clinics, kennels, animal shelters and laboratories. Ova were obtained from gravid female T. canis uteri. Thirty samples containing 10,000 eggs were divided into five groups of six identical sample tubes per group. The treatments for the groups were as follows: Group H benzalconium chloride, Group A 70% ethanol, Group B 2-2.5% sodium hypochlorite solution, Group L 7.99% formaldehyde-based disinfectant and Group C tap water (controls). Samples were incubated at 27 ± 1°C and 80 ± 10% relative humidity. Embryonic development was evaluated on days +6, +9, +12, +15, +18, +21, +25, +28 and +36 of exposure by visual observation under light microscopy. Seventy percent ethanol degenerated all eggs within a few days and thus inhibited larval development. Sodium hypochlorite removed the external layer of the ova, but eggs harboured infective larvae for up to 2 weeks. Benzalconium chloride and formaldehyde-based disinfectants had no effect on T. canis embryogenesis according to comparison with control eggs (P > 0.05). Embryonated eggs from each of the six samples from Groups C, H and L were administered to mice as only these ova were considered viable based on in vitro trial. On day 30pi, those were euthanized and had their tissues were submitted to organ compression (brains) or acid-isolation technique (kidneys, lungs, livers and carcasses) for larval counting. The mean number of recovered larvae for Groups C, H and L were: 512.8, 393.7 and 477 respectively (P > 0.05). Larvae derived from Groups H and L eggs maintained their ability to migrate. However, larval establishment pattern differed from control. While certain disinfectants do negatively affect embryogenesis (70% ethanol) and reduce the integrity and durability (sodium hypochlorite) of infective T. canis eggs, others have no effect upon embryogenesis. Those eggs can still be a threat to human and animal health even after over a month of disinfectant exposure.