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

HECKER Y; BURUCÚA M; FIORANI, FRANCO; MALDONADO RIVERA, J.E.; CIRONE, K.M.; DORSCH, M.A.; CHEUQUEPÁN VALENZUELA F; CAMPERO, LUCÍA M.; CANTÓN G; MARIN M; ORTEGA-MORA, LUIS M.; MOORE D

Berna

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

APICOWPLEXA

Neospora caninum is recognized for causing cattle abortion, provoking severe economic lossesin the livestock industry worldwide. Field observations suggested that naturally exposed cattledevelop protective immune mechanisms against abortions in a subsequent Neospora-relatedoutbreak. Furthermore, endogenous transplacental transmission is more likely to occur in cattlethan postnatal infection. It has been reported that N. caninum vertical transmission could beprevented when cows are experimentally inoculated with live tachyzoites before mating andthen challenged during their gestation. Recently, our group showed that inoculation with livetachyzoites of the NC-Argentina LP1 local isolate in 6-month-old female calves elicited a specificcellular immune response with antibody levels that decreased at day 120 post-infection.Nevertheless, whether these infected animals could reactivate the infection and transmit theparasite during their reproductive life on the farm was not studied. In addition, it would beinteresting to know if the memory immune response generated at a young age in these animalscould protect against a heterologous challenge. The aim of the present study was to evaluatethe reactivation and foetal infection in pregnant heifers inoculated with live N. caninumtachyzoites before puberty. Fifteen 30-month-old pregnant heifers were allocated into fourgroups: animals inoculated 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); animalsmock inoculated before puberty and challenged with NC-1 strain at 210 DG (Group B), animalsinoculated before puberty but not subsequently challenged (Group C); and noninfected andnonchallenged animals (Group D). The results of the present study clearly show that animalsinoculated before puberty had parasitic reactivation, as Neospora-DNA was detected in theirPBMCs, and an increase in the specific antibody titres from the 7th month of gestation onwardswas observed. In addition, in 3 and 2 calves from Groups A and C, respectively, congenitalinfection was confirmed. The results of the present study show for the first time that theinoculation of live tachyzoites of N. caninum in prepubertal female calves is not effective inpreventing the reactivation of the parasite during pregnancy, showing that the infected animalswere unable to eliminate the parasite at their young age. In addition, although prepubertalinfection elicited a specific immune response against N. caninum, this response was notsufficient to prevent congenital infection after heterologous challenge. Therefore, we provideevidence that the use of live N. caninum tachyzoites in young animals as a strategy to induceprotection is neither safe nor effective.