Resistance of Parascaris equorum eggs to formalin

Ascariosis due to Parascaris equorum is an important disease of horses all over the world. The eggs of the parasite are resistant to disinfectants and also adverse environmental conditions. The faeces of a naturally infected horse was incubated at room temperature in 10% formalin to check the resistance of the parasite eggs against this fixative. Twenty one days after incubation, motile larvae were observed inside the eggs. The larvae remained alive till 126 days of incubation, confirming the high degree of impermeability of the parasite egg shell and high resistance of the eggs against 10% formalin.