Dairy cow abortion associated with Neospora caninum and other infectious agents

The protozoa Neospora caninum has been described in several countries as an important cause of abortion in dairy cattle, mainly from the third month of pregnancy. The infection can occur by ingestion of animal tissues infected with bradyzoites or tachyzoites, through water or food contaminated with infectious oocysts, besides by vertical transmission. Abortion may be the only sign observed in adult cows (Björkman et al., 1996; Dubey, 1999a). Vaccines are not available to prevent oocysts elimination by dogs, the definitive host of N. caninum (McAllister et al., 1998).

The protozoa Neospora caninum has been described in several countries as an important cause of abortion in dairy cattle, mainly from the third month of pregnancy.The infection can occur by ingestion of animal tissues infected with bradyzoites or tachyzoites, through water or food contaminated with infectious oocysts, besides by vertical transmission.Abortion may be the only sign observed in adult cows (Björkman et al., 1996;Dubey, 1999a).Vaccines are not available to prevent oocysts elimination by dogs, the definitive host of N. caninum (McAllister et al., 1998).
This study aimed to verify antibodies to N. caninum, T. gondii, B. abortus, Leptospira spp., Bovine Herpesvirus-1 (BHV-1) and Bovine Viral Diarrhea Virus (BVDV) in serum of dairy cattle herds that miscarried, one or more times, between the third and the seventh month of pregnancy, in Northern Paraná State, Brazil.
Thirty-five cow blood samples were collected on the day of abortion, and 20 and 65 days later.The separated sera were processed by indirect immunofluorescent assay (IFA) for the detection of anti-N.caninum (Conrad et al.,1993) and anti-T.gondii(Camargo, 1973) antibodies, using slides adsorbed with anti-N.caninum sera (VMRD-Pullman-EUA) and anti-T.gondii sera (DMVP-UEL), respectively.Reactions with titles ≥ 200 to N. caninum and ≥ 64 to T. gondii were considered positive.Microscopic serumagglutination test (SAM) was carried out for the detection of Leptospira sp.antibodies.Live cultures of 22 Leptospira spp.serovars were used.The sera were initially diluted at 1:100 and those that presented 2+ or higher agglutination at this dilution were considered positive.Acid buffered antigen test was used to detect antibodies to B. abortus and seroneutralization technique, using MDBK cells, was performed to detect BHV-1 and BVDV antibodies.Reactions with titles ≥ 8 were considered positive.The sera were serially diluted until the maximum positive dilution was determined.
The interpretation of seroposotivity, as indicative of infection or vaccinal response, was based on consecutive serology and epidemiologic survey of aborted cows.Overall 35 aborted cows, 21 (60%) were seropositive to some of the investigated agents.The serological titles observed in 12 (34.3%)aborted cows were in line with vaccinal response to Leptospira sp., BHV-1 and BVDV.Two (2/35) animals (5.7%) were seronegative to all the evaluated agents.
From 21 (21/35) seropositive cows, five (5/21) were seroreactive to N. caninum, two (2/21) to T. gondii, nine (9/21) to Leptospira sp., 12 (12/21) to BVDV and 15 (15/21) to BHV-1.Seven cows (7/21) were seropositive to a single agent (four to BHV-1 and three to BVDV).Nine different associations among two or more investigated agents were observed in 14 cows (Table 1).None of the tested sera showed reactivity to B. abortus.Aborted fetuses from five (5/21) N. caninum seropositive cows were analyzed and in all of them the presence of the protozoa were confirmed by immunohistochemistry, using anti-N.caninum sera (Santos, 2000).1).Alves et al. (1996) stated that out of 32 herds diagnosed with N. caninum, five were, simultaneously, infected by BVDV.Thurmond et al. (1997) studying 20 bovine herds, with fetal losses cases, observed that N. caninum contributed to the abortions in one of them, but not in the others, where BVDV and Leptospira sp. were also detected.Barr et al. (1991) reported that maternal viral infection (BHV-1/BVDV) increases the susceptibility to N. caninum infection.The serological titles observed for T. gondii in two cows were not considered an infection, because this parasite is not related to cattle abortion (Björkman et al., 1996).
Infection by N. caninum can not be the only cause of reproductive disorders in bovine (Alves et al., 1996;Otter and Wilson, 1997;Caldow, 1998).It is important to look at the synergism among N. caninum and other factors like virus infections, immunossupressive agents or hereditary factors (Björkman et al., 1996).Histological and immunohistochemical procedures from aborted fetuses must be performed to confirm the etiology of N. caninum in abortion.Serological tests have not been conclusive to discard abortions by neosporosis in N. caninum infections (Dubey, 1999b).
This study showed, for the first time, the presence of N. caninum antibodies in cows with a history of abortion in Paraná State, Brazil.Evidences of participation of other potentially abortive agents (Leptospira spp., BHV-1 and BVDV) associated with N. caninum in evaluated cows were also observed.Keywords: cattle, abortion, Neospora caninum, reproductive disorder

Table 1 .
Associations among Neospora caninum, Toxocara gondii, Leptospira sp., BHV-1 and BVDV observed in dairy cows with a history of abortion, with titles indicative of infection in herds from Northern Paraná State