Influence of physical and chemical factors on the embryonation, hatching and infectivity of Spirocerca lupi

Spirocerca lupi is a parasitic nematode which causes spirocercosis, a severe disease of dogs. Its life cycle involves dung beetles as intermediate hosts and canids as definitive hosts. The effect of different physical conditions and chemical factors on the embryonation and hatching of S. lupi eggs were investigated in this study in order to understand the triggers for progression in the early development of this parasite. Exposure to potassium dichromate significantly enhanced the embryonation of eggs compared to formaldehyde and controls (p < 0.0001), reaching the maximum embryonation level of 83% within 2 days of incubation. Hatching of eggs was significantly (p < 0.05) enhanced in the presence of 2.5% trypsin, pH 6.0 and 8.0, a temperature of 26 °C, 20% CO₂ and mechanical force by stirring with 3-mm beads. Dissection of Onthophagus sellatus beetles 8 h post-feeding with eggs showed that 13% of the ingested eggs hatched in the buccal cavity and the midgut. Finally, the pH range of the beetle's gut was 6.0-6.2 compared to 7.2 ± 0.4 in dog feces suggesting that this pH change may induce hatching in the beetle. These findings contribute to the understanding of the early steps in the life cycle of S. lupi and may be used in the future to block the development of S. lupi and prevent dog infection and disease.