A prospective study of the effect of Neospora caninum and BVDV infections on bovine abortions in a dairy herd in Arequipa, Peru
Introduction
Neospora caninum is a major cause of bovine abortions, and both chronically and acutely infected cattle run an increased risk of aborting (for review see: Anderson et al., 2000, Dubey, 2003). Abortions associated with the infection occur from month 3 of gestation to term with a peak in incidence during months 4–6. Whether N. caninum infection also causes foetal loss in the earlier stages of gestation is less clear. The main transmission route in cattle is vertical, i.e. transplacental infection from cow to calf during gestation, and infected calves remain persistently infected and can pass the infection to their offspring (Björkman et al., 1996). Postnatal transmission also occurs (Thurmond et al., 1997, McAllister et al., 2000, Dijkstra et al., 2002b), apparently through ingestion of oocytes excreted by a definitive host (De Marez et al., 1999, Dijkstra et al., 2002a).
Bovine viral-diarrhoea virus (BVDV), endemic in most cattle-raising countries, also causes reproductive failure. Infections during pregnancy can result in embryonic death, abortions, birth of stillborn or weak calves, or can lead to birth of persistently infected (PI) calves that will shed virus throughout their lifetime (for review see Grooms, 2004). BVDV is immunosuppressive, which might increase susceptibility to other infectious agents (Elvander et al., 1998).
Abortion due to N. caninum is the result of transplacental transmission of the infection to the foetus after a maternal parasitemia. The mechanism for reactivation of latent N. caninum infections and what decides the outcome of pregnancy in an infected cow is still unknown (Innes et al., 2002). Immunosuppressive events during pregnancy have been suggested and the role of immunosuppression by concurrent infection has been addressed (Dubey, 2003). Björkman et al. (2000) reported an association between N. caninum and BVDV seropositivity and abortions, but results from other studies are contradictory (Bartels et al., 1999, Davison et al., 1999b; Mainar-Jaime et al., 2001). These previous studies have used case–control approaches to relate abortions with N. caninum and BVDV seropositivity in individual animals. Thus, they have not been able to discriminate between animals with active BVDV infection, vaccinated animals or previously exposed animals. So far, to our knowledge, no one has reported a study of the effect of an active BVDV infection on N. caninum-associated abortions.
We used a prospective seroepidemiological approach to investigate endemic abortion in a dairy herd in Arequipa, Peru, and its association with N. caninum infections in a herd with active BVDV infection.
Section snippets
Study design
We did this study between January 2002 and April 2004 in a dairy herd in Arequipa (the main dairy region in southern Peru) to assess the association between endemic abortions and concurrent N. caninum and BVDV infections. The serological status to N. caninum and BVDV was assessed using results from a single screening in March 2002. Cows, heifers and calves (>6 months) present at the farm the day of the screening were included in the study. Abortions and calvings were recorded prospectively.
Results
Between January 2002 and March 2004, 1094 pregnancies were confirmed in 538 cows. Of these, 137 pregnancies (13%) in 121 cows ended in abortion (Table 1) and 207 (19%) cows were lost from follow-up before abortion or 260 days gestation because of death, culling or censoring at the end of the study period. Forty-three abortions (31%) were registered between day 42 and day 100 in gestation. The median foetal age at abortion was estimated at 140 days (range 43–259).
Discussion
In this study, we found an overall significant association between N. caninum infection and abortions detected after day 100 in gestation, but the effect of the infection decreased with parity. Very similar results were reported in a study where Thurmond and Hietala (1997) followed 468 heifers on a Californian dry-lot dairy farm during 3 years. In that study, risk of abortion was 7.4-fold higher in congenitally infected cows during the initial pregnancy and 1.7-fold higher during the first
Acknowledgements
We thank Professor Stefan Alenius for comments on the manuscript. We also thank Maj Hjort and Katarina Näslund for technical assistance, Mister Daniel Lozada and the employees at the dairy farm for their participation and assistance, and finally, Miguel Cauti for his assistance during the sampling in March 2002. This work was supported by the Swedish International Development Cooperation Agency, Sida/SAREC.
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