Neospora caninum in persistently infected, pregnant cows: spontaneous transplacental infection is associated with an acute increase in maternal antibody

Nine cows which were naturally and persistently infected with Neospora cani num were housed and observed intensively throughout pregnancy. No recrudesc ence of a latent infection was detected by PCR tests on maternal blood but fetal infection, implying a recrudescence of maternal parasitosis, was asso ciated with a marked increase in maternal antibody. The increase occurred i n the second half of pregnancy in five cows which infected their calves, an d before mid-pregnancy in one cow which aborted. There was no change in the avidity of the antibody, which remained high and characteristic of long-te rm infection. in three infected cows that gave birth to uninfected calves t here was no marked increase in maternal antibody. Antigen-specific interfer on gamma responses of peripheral blood mononuclear cells were observed in a ll the infected cattle but they did not vary significantly either during pr egnancy, or whether the cows did or did not infect their calves, although t he responses were consistently higher in the latter. There was no change in the plasma concentrations of cortisol or acute phase proteins associated w ith the recrudescence of the parasite. Three uninfected cows housed with th e infected cows remained uninfected throughout the experiment. No immunosup pressive event was detected which might have provoked parasite recrudescenc e but the acute antibody rise associated with transplacental infection prov ides a valuable, non-invasive marker for further studies to investigate the cause and consequences of parasite recrudescence in N caninum infection in cattle.