Detection of Neospora caninum DNA in a mummified bovine fetus
Andrés de la Concha-Bermejillo, DVM, MS, PhD, Pam Ferro, PhD, Megan Schroeder, PhD
The body of a midterm bovine fetus and the attached placenta were submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) for necropsy and gross examination. Upon examination, the entire fetus and placenta exhibited severe mummification. Tissues of this fetus were submitted to the molecular section for bovine herpesvirus (BHV)-1, BVDV, Leptospira spp. and Neospora caninum rtPCRs.
Neospora caninum DNA was detected in the brain of the fetus at a Ct of 33.60 indicating a moderate amount of N. caninum DNA. BHV-1, BVDV and Leptospira spp. nucleic acids were not detected.
Neospora caninum is an obligate intracellular apicomplexan protozoan parasite that was first recognized more than 35 years ago as the etiological agent of abortion in infected cattle. Neospora caninum is one of the most important causes of abortion in cows. Dogs are both intermediate and definitive hosts and cattle, sheep, goats and other animals are definitive hosts. Transplacental transmission is considered the major route of transmission of N. caninum in cattle.
Neospora caninum fetal infection in cattle can result in abortion (generally between 5 to 7 months of gestation), fetal mummification, birth of weak calves, or the birth of clinically normal infected neonates that preserve the infection in the herd. In herds where the infection is endemic, up to 35% of pregnant dairy cows can abort over a period of several months. In naïve herds, over 10% of susceptible cows can abort in 6 to 8 weeks.
Testing for antibodies against N. caninum in maternal serum by ELISA or IFA tests are used to determine the herd and individual animal infectious status, but alone, the presence of maternal antibodies does not prove neosporosis as the cause of the abortion.
In cattle, fetal mummification occurs after formation of the placenta and fetal ossification. Fetal mummiﬁcation needs to be differentiated from fetal maceration, in which the fetus putreﬁes resulting from the presence of bacteria and oxygen in the uterus when the cervix is open. Mummified fetuses die in utero and undergo subsequent autolysis (there is an absence of a bacterial infection and putrefaction does not occur). In mummification, the fetal fluids are resorbed via the maternal blood and lymphatics and the soft tissues become gradually dehydrated. Eventually, the entire fetus and placenta become brown or black and leather-like (there is no exudate or odor).
Several possible causes of fetal mummification in cattle have been proposed including Neospora caninum, bovine viral diarrhea virus (BVDV), leptospirosis, mechanical factors, such as torsion of the umbilical cord, uterine torsion; defective placentation; genetic and chromosomal defects and abnormal hormonal profiles. However, a definitive etiology is seldom determined. The mummification process usually renders worthless the analysis of bacteria, protozoa and viruses by standard methods. For the last two decades, real time PCR (rtPCR) has been the pillar in the diagnosis of infectious abortion in ruminants and it is of particular value in mummified fetuses where other ancillary tests are inadequate.
de la Concha-Bermejillo A, Romano JE: Pregnancy loss in cattle. Clinical Theriogenology; 2021, Submitted.
de la Concha-Bermejillo A, Romano JE: The use of laboratory in pregnancy loss. Clinical Theriogenology 2021; Submitted.