Heifers inoculated with Neospora caninum live tachyzoites at prepubertal age reactivate their infection during gestation

HECKER Y.P.; BURUCÚA M.; FIORANI, F.; MALDONADO RIVERA, J.E.; CIRONE, K.M.; DORSCH, M.A.; CHEUQUEPÁN, FELIPE; CAMPERO L.M.; CANTON G.J.; MARIN, M.S.; ORTEGA-MORA L.M.; MOORE D.P.

Berna

Congreso; 6th International Meeting on Apicomplexan Parasites in Farm Animals; 2022

ApicoWplexa network

Neospora caninum is recognized for causing cattle abortion, provoking severe economic losses in the livestock industry worldwide. Field observations suggested that naturally exposed cattle develop protective immune mechanisms against abortions in a subsequent Neospora-related outbreak. Furthermore, endogenous transplacental transmission is more likely to occur in cattle than postnatal infection. It has been reported that N. caninum vertical transmission could be prevented when cows are experimentally inoculated with live tachyzoites before mating and then challenged during their gestation. Recently, our group showed that inoculation with live tachyzoites of the NC-Argentina LP1 local isolate in 6-month-old female calves elicited a specific cellular immune response with antibody levels that decreased at day 120 post-infection. Nevertheless, whether these infected animals could reactivate the infection and transmit the parasite during their reproductive life on the farm was not studied. In addition, it would be interesting to know if the memory immune response generated at a young age in these animals could protect against a heterologous challenge. The aim of the present study was to evaluate the reactivation and foetal infection in pregnant heifers inoculated with live N. caninum tachyzoites before puberty. Fifteen 30-month-old pregnant heifers were allocated into four groups: animals inoculated with live tachyzoites of NC-Argentina LP1 isolate before puberty and challenged with live tachyzoites of NC-1 strain at 210 days of gestation (DG) (Group A); animals mock inoculated before puberty and challenged with NC-1 strain at 210 DG (Group B), animals inoculated before puberty but not subsequently challenged (Group C); and noninfected and nonchallenged animals (Group D). The results of the present study clearly show that animals inoculated before puberty had parasitic reactivation, as Neospora-DNA was detected in their PBMCs, and an increase in the specific antibody titres from the 7th month of gestation onwards was observed. In addition, in 3 and 2 calves from Groups A and C, respectively, congenital infection was confirmed. The results of the present study show for the first time that the inoculation of live tachyzoites of N. caninum in prepubertal female calves is not effective in preventing the reactivation of the parasite during pregnancy, showing that the infected animals were unable to eliminate the parasite at their young age. In addition, although prepubertal infection elicited a specific immune response against N. caninum, this response was not sufficient to prevent congenital infection after heterologous challenge. Therefore, we provide evidence that the use of live N. caninum tachyzoites in young animals as a strategy to induce protection is neither safe nor effective.