Experimental infection with a low virulence isolate ofNeospora caninumat 70 days gestation in cattle did not result in foetopathy

Abstract

The Nc-Spain 1H isolate of Neospora caninum, which was newly obtained from the brain of a congenitally asymptomatic infected calf, demonstrated a reduced in vitro tachyzoite yield and viability rate, as well as low virulence in mouse models. The objective of the present study was to determine the ability of this isolate to induce foetal death in a pregnant bovine model. For this purpose, 13 naïve pregnant heifers were divided into three groups and were experimentally challenged with either 107 tachyzoites of Nc-1 (group 1, n = 5), Nc-Spain 1H (group 2, n = 5) isolates or phosphate-buffered saline (group 3, n = 3) intravenously at 70 days of gestation. After inoculation, pregnancy was monitored and dams were sacrificed when foetal death was detected. The remaining animals were slaughtered at 45 days post-infection. Maternal and foetal samples were collected for examination by histology and parasite DNA detection. Parasitaemia, specific anti-N. caninum IgG and interferon γ responses were also studied. At 3–4 weeks after infection, foetal death was detected in 3 out of 5 Nc-1-infected dams. However, no evidence of foetal death was observed in either Nc-Spain 1H-infected or control groups during the period studied. The most severe histopathological lesions were observed in the placenta and foetal organs from Nc-1-infected cattle that exhibited foetal death. It was in these animals that N. caninum DNA was more frequently detected. Parasitaemia was observed in all Nc-1-infected dams and in only 3 out of 5 Nc-Spain 1H-infected animals. The magnitude of the immune response was significantly higher in the Nc-1-inoculated group than in the group inoculated with the Nc-Spain 1H isolate. These data reveal the reduced virulence of the Nc-Spain 1H isolate in cattle.

Effect of vaccination of cattle with the low virulence Nc-Spain 1H isolate of Neospora caninum against a heterologous challenge in early and mid-gestation

“…Subsequently, their antibody levels decreased to levels similar to those observed in the non-immunised heifers, and they fluctuated around the cut-off value until the end of the experiment, suggesting that there was no recrudescence of the Nc-Spain 1H infection during gestation that might have led to foetal infection. A similar situation was previously described when an experimental infection of cattle with live tachyzoites of this isolate resulted in antibody levels that declined to undetectable levels from the third week after infection [7]. However, immunisation induced high levels of IFNγ production that persisted throughout the experiment.…”

Neosporosis in animals—The last five years

“…As of yet, neither intact N. caninum nor parasite DNA were demonstrable in asymptomatic adult cows Wapenaar et al, 2007a;Moré et al, 2008a;Santos et al, 2010). However, N. caninum could be isolated from the brains of asymptomatic naturally infected calves (Fish et al, 2007;Goździk and Cabaj, 2007;Regidor-Cerrillo et al, 2008;García-Melo et al, 2009;Rojo-Montejo et al, 2009b).…”

“…(2008) Abortion or fetal infections have been induced in cattle using a variety of isolates in different laboratories but a meaningful comparison in pregnant cattle will be economically prohibitive to do . In a recent study, cows inoculated with a Spanish bovine isolate did not damage the fetus even though cows were inoculated at an early (70 days) stage of gestation age (Rojo-Montejo et al, 2009a). On the other hand, in beef cattle experimentally infected at 110 days of gestation with a beef strain, fetal death occurred in one fetus .…”

Avaliação da infecção experimental por Neospora caninum em fêmeas bubalinas e bovinas, no terço inicial da gestação

“…Houveram também alterações detectáveis em fígado, coração, pulmão, musculatura esquelética e rins fetais, com lesões mais graves nos animais inoculados com o isolado mais patogênico. Buxton, McAllister e Dubey (2002) relataram as mesmas lesões em fetos naturalmente infectados, assim como foram descritas lesões semelhantes em diversos outros estudos (DUBEY et al, 1992;MALEY et al, 2003;MACALDOWIE et al, 2004;INNES et al, 2005;MALEY et al, 2006;ROJO-MONTEJO et al, 2009;. Com base nos resultados da infecção experimental de vacas e búfalas prenhes, com 5 x 10 8 taquizoítos de diferentes isolados de N. caninum, no período inicial da gestação, pôde-se concluir:…”

“…• 2 minutos xileno. (MACALDOWIE et al, 2004;ROJO-MONTEJO et al, 2009;KONRAD et al, 2012). Estas lesões na parte materna da placenta podem diminuir a oxigenação fetal e a passagem de nutrientes, sendo as prováveis causadoras do abortamento (DUBEY et al, 1992).…”