Neospora caninum-associated abortion in cattle: the time of experimentally-induced parasitaemia during gestation determines foetal survival

Abstract

The parasite, Neospora caninum is an important cause of abortion in cattle. It is transmitted vertically or horizontally and infection may result in abortion or the birth of a live, healthy but infected calf at full-term. Only a proportion of infected cattle abort and the pathogenesis of abortion is not understood. Groups of cattle were infected with 10(7) N. caninum tachyzoites intravenously at different times relative to gestation. Intravenous inoculation was chosen to reproduce the putative haematogenous spread of N. caninum following either recrudescence of endogenous infection or de novo infection. In all cattle, infection was accompanied by high gamma-interferon and lymphoproliferative responses, and a biased IgG2 response indicating that N. caninum infection is accompanied by a profound Th1 helper T cell-like response. Infection at 10 weeks gestation resulted in foetopathy and resorption of foetal tissues 3 weeks after infection in 5 out of 6 cows. Infection at 30 weeks gestation resulted in the birth of asymptomatic, congenitally-infected calves at full term in all 6 cows, whereas the 6 cows infected before artificial insemination gave birth to live, uninfected calves. These results suggest that the reason some cows abort is related to the time during gestation when they become infected or an existing infection recrudesces.

Intrauterine Neospora caninum inoculation of heifers and cows using contaminated semen with different numbers of tachyzoites

“…This general pattern of IgG response was similar to those reported for heifers inoculated in utero by AI via semen contaminated with 10 7 tachyzoites [16], and for calves [9,21,22] and pregnant cows [10,23] challenged with tachyzoites or oocysts. However, we made two interesting observations apparently irrespective of the number of tachyzoites inoculated.…”

Experimental neosporosis in bulls: Parasite detection in semen and blood and specific antibody and interferon-gamma responses

“…The nested-PCR used to detect N. caninum DNA in semen samples is highly sensitive, amplifying DNA products corresponding to one tachyzoite in 250 ml of artificially-contaminated semen [2][3][4]. The non-uniform N. caninum distribution and the limited amount of parasite DNA present in fluids and tissues have been reported in naturally or experimentally infected adult cattle [11,12]. Moreover, infected seropositive cattle testing negative for specific DNA in the semen, as assessed by PCR, have been reported for other infectious agents such as Brucella melitensis [13] or bovine herpesvirus type 1 [14].…”

Natural postnatal Neospora caninum infection in cattle can persist and lead to endogenous transplacental infection

“…However, endogenous TPI could not be demonstrated in experimentally infected cattle. Cows experimentally infected before insemination gave birth to uninfected calves (Williams et al, 2000;Innes et al, 2001). Also, seven cows experimentally infected with oocysts during their first pregnancy gave birth to uninfected calves in a subsequent pregnancy (McCann et al, 2007).…”