Frequency of horizontal and vertical transmission for Sarcocystis cruzi and Neospora caninum in dairy cattle

Abstract

Sarcocystis cruzi and Neospora caninum infections in cattle are common throughout the world, and cause important economical losses. N. caninum can be transmitted horizontally by ingestion of oocysts or vertically from the infected dam to the fetus via the placenta. Vertical transmission for S. cruzi is infrequent and horizontal transmission is considered the most important route of infection. The objectives of this study were to evaluate the frequency of horizontal and vertical transmission for S. cruzi and N. caninum in a dairy cattle herd and to analyze IFAT titers as predictors of vertical transmission. Serum samples (n = 173) were collected from dairy calves at birth prior to colostrum ingestion and from their dams. In addition, 12 calves were also sampled after ingestion of colostrum, 25 female calves were sampled at 7 months, and 81 of the dams were also sampled at breeding. Sera were evaluated for S. cruzi and N. caninum antibodies by IFAT starting at 1:25 dilution. For S. cruzi, vertical transmission frequency was 1.7%, and all female calves evaluated at 7 months and cows were seropositive. Seroprevalence for N. caninum was 80.9% in cows and 30% in precolostrum calves. Vertical transmission frequency was 37.1%. Cows with high antibody titers (≥400) showed higher vertical transmission frequency (94.8%) than cows with low antibody titers (between 25 and 200) (14.8%). Negative precolostrum calves (7/12) had postcolostrum N. caninum titers 2–8 times higher than their dams. Estimated horizontal transmission frequency was 51 and 47%, based on differences of seroprevalences in calves and dams, and on the seroconversion of 9/19 negative precolostrum female calves when retested at 7 months, respectively. Average N. caninum titers of cows at breeding and calving were 120.6 and 320.9, respectively. Cows with a high titer at breeding had a high titer at calving. Therefore, N. caninum IFAT titers at breeding and calving could potentially be used as predictors of vertical transmission.

Introduction

Sarcocystis cruzi and Neospora caninum infections in cattle are common throughout the world, and cause important economical losses (Dubey, 2003, Dubey et al., 1989). In Argentina prevalence of S. cruzi infection was around 100% (Moré et al., 2008) and N. caninum seroprevalence, evaluated by indirect fluorescent antibody test (IFAT), was 73% for slaughter animals (Moré et al., 2008) and 82% for 576 dairy cows from several herds (Venturini, L. unpublished data).

In cattle, S. cruzi and N. caninum can be transmitted horizontally by ingestion of sporocysts or oocysts excreted in the feces of dogs and other canids (Basso et al., 2001, Dubey et al., 1989) or vertically, from the infected dam to the fetus via the placenta. Vertical transmission of S. cruzi has been documented in experimental studies (Lopes et al., 2005, Savini et al., 1996) and sporadically in natural infections (Dubey and Bergeron, 1982, Hong et al., 1982). Although generally considered an infrequent event, to our knowledge the frequency of S. cruzi vertical transmission is unknown. On the other hand, vertical transmission was considered the most important route of N. caninum infection (Anderson et al., 1997, Davison et al., 1999, Paré et al., 1996). Different methods have been used to evaluate transmission by both routes (Dubey and Schares, 2006). Evaluation of antibody titers in calves prior to ingestion of colostrum (precolostrum calves) provides evidence of vertical transmission, since maternal antibodies do not cross the placenta in cattle; therefore it can be assumed that antibodies present in precolostrum calves are generated in utero due to infection. Detection of N. caninum antibodies by IFAT at a 1:25 dilution in fetal fluids confirms infection (Wouda et al., 1997).

Frequency of vertical transmission can be estimated by the number of seropositive precolostrum calves born to seropositive dams. Horizontal transmission can be estimated by the difference between seroprevalence in precolostrum calves and seroprevalence in adult cows and/or by reevaluating seronegative precolostrum calves after maternal antibodies disappear (Bartels et al., 2007, Dubey and Schares, 2006, Hietala and Thurmond, 1999). In order to determine preventive and control measures towards these infections it is necessary to determine which route of infection is predominant (Dubey et al., 2007).

The objectives of this study were to evaluate frequency of horizontal and vertical transmission for S. cruzi and N. caninum in dairy cattle and to analyze IFAT titers as predictors of vertical transmission.