Reactivation and Foetal Infection in Pregnant Heifers Infected with Neospora caninum Live Tachyzoites at Prepubertal Age

HECKER, YANINA; BURUCÚA, MERCEDES; FIORANI, FRANCO; MALDONADO RIVERA, JAIME E.; CIRONE, KARINA M.; DORSCH, MATÍAS A.; CHEUQUEPÁN, FELIPE A.; CAMPERO, LUCÍA M.; CANTÓN, GERMÁN; MARIN, MAIA; ORTEGA-MORA, LUIS M.; MOORE, DADÍN P.

Berna

Congreso; ApicoWplexa 2022: 6th International Conference on Apicomplexan Parasites in Farm Animals; 2022

Neospora caninum is recognized for causing cattle abortion, provoking severe economiclosses in the livestock industry worldwide. Field observations suggested that naturallyexposed cattle develop protective immune mechanisms against abortions in a subsequentNeospora-related outbreak. Furthermore, endogenous transplacental transmission is morelikely to occur in cattle than postnatal infection. It has been reported that N. caninumvertical transmission could be prevented when cows are experimentally inoculated withlive tachyzoites before mating andt hen challenged during their gestation. Recently, ourgroup showed that inoculation with live tachyzoites of the NC-Argentina LP1 local isolatein 6-month-old female calves elicited a specific cellular immune response with antibodylevels that decreased at day 120 post-infection. Nevertheless, whether these infectedanimals could reactivate the infection and transmit the parasite during their reproductivelife on the farm was not studied. In addition, it would be interesting to know if the memoryimmune response generated at a young age in these animals could protect against aheterologous challenge. The aim of the present study was to evaluate the reactivation andfoetal infection in pregnant heifers inoculated with live N. caninum tachyzoites beforepuberty. Fifteen 30-month-old pregnant heifers were allocated into four groups: animalsinoculated with live tachyzoites of NC-Argentina LP1 isolate before puberty andchallenged 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 (GroupC); and noninfected and non-challenged animals (Group D). The results of the presentstudy clearly show that animals inoculated before puberty had parasitic reactivation, asNeospora-DNA was detected in their PBMCs, and an increase in the specific antibodytitres from the 7th month of gestation onwards was observed. In addition, in 3 and 2 calvesfrom Groups A and C, respectively, congenital infection was confirmed. The results ofthe 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 theparasite during pregnancy, showing that the infected animals were unable to eliminate theparasite at their young age. In addition, although prepubertal infection elicited a specificimmune response against N. caninum, this response was not sufficient to preventcongenital infection after heterologous challenge. Therefore, we provide evidence thatthe use of live N. caninum tachyzoites in young animals as a strategy to induce protectionis neither safe nor effective.