High rate of transplacental infection and transmission of Neospora caninum following experimental challenge of cattle at day 210 of gestation

Abstract

In order to investigate the pathogenesis of neosporosis following a primary infection in late pregnancy, cattle were subcutaneously challenged with 5 × 108Neospora caninum (NC1 isolate) tachyzoites at day 210 of gestation and serial necropsies were then carried out at 14, 28, 42 and 56 days post-infection (dpi). No abortions occurred and all the foetuses were viable at the time of euthanasia. There was a high rate of vertical transmission, as parasites were detected by immunohistochemical labelling and PCR in all the foetuses from 28 dpi. Focal necrotic lesions were observed in the placentomes of the placenta from 28 dpi and showed resolution during later time points, denoted by infiltration of inflammatory cells at 42 dpi and fibrosis at 56 dpi. Foetuses at 28 and 42 dpi showed scarce and isolated lesions which are unlikely to represent a threat to foetal viability. No lesions were observed in the foetuses at 14 or 56 dpi suggesting control of the infection and resolution of the lesions by maternal and foetal immune responses. Once infection was established, it could not be cleared from the host and vertical transmission of the parasite occurred in all infected hosts. Parasite was detected in the placenta at 28 dpi, while in previous experimental infections of cattle at day 70 and 140 of gestation using the same challenge model, it was already present at day 14 post infection. This suggests that a change in the maternal immune response plays a crucial role in limiting the initial infection during the last term of pregnancy.

Development of maternal and foetal immune responses in cattle following experimental challenge with Neospora caninum at day 210 of gestation

“…Similar finding were observed in mice by where TLR-2 was associated with APC maturation and pro-inflammatory cytokine production [28,29]. Cantón et al [40] observed large numbers of phagocytic cells (in particular macrophages) in resolving lesions in the placenta of infected animals from this experiment from 42 dpi onwards, While on 42 dpi Benavides et al [30] described lesions in foetal lung and liver characterised by the infiltration of macrophages, lymphocytes and plasma cells. The presence of these cells in the circulatory system may account for the increased levels of TLR-2 expression seen in the spleens of the infected compared to control animals.…”

Neospora caninum infection during early pregnancy in cattle: how the isolate influences infection dynamics, clinical outcome and peripheral and local immune responses

“…Sections from placentome and foetal viscera wax blocks were cut and treated for the immunohistochemical identification of N. caninum antigens using an in-house anti- N. caninum polyclonal serum according to previously described [24]. …”

Abortos por Neosporacaninum em bovinos do sul de Minas Gerais

“…As lesões mais frequentemente descritas em fetos bovinos com neosporose são a necrose focal circundada por infiltrado inflamatório mononuclear discreto, encontradas principalmente no sistema nervoso central (Sager et al 2001, Maley et al 2003, Benavides et al 2012. No presente estudo, apesar destas lesões estarem presentes, o achado mais comum foi o infiltrado inflamatório mononuclear, na musculatura cardíaca e esquelética.…”

“…A necrose hepática e hepatite ocorerram menos frequentemente neste estudo. Estes achados são semelhantes aos descritos por Maley et al (2003) e Benavides et al (2012). Dos 14 abortos comprovadamente positivos, quatro (28,57%) foram confirmados em ambos os testes, cinco (35,71%) apenas pela PCR e cinco apenas (35,71%) pela imuno-histoquímica.…”