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Vet Focus
SPRING 2021 ❁ BC HOLSTEIN NEWS 37
 Neospora Abortions Remain Concerning
 Dr. Christina Lyn, Greenbelt Veterinary Services
Dr. Stephen Raverty, Animal Health Centre
All abortions are alarming and can result in significant reproductive and financial losses. A low incidence of sporadic abortions, less than 5% per year, is anticipated as part of the ongoing costs of production for dairy farms. When outbreaks of abortion occur, there may be significant losses for farmers. Currently, the cause of an abortion can be classified as either non-infectious (genetic, nutritional) or infectious (bacterial, viral, parasitic).
A study conducted in British Columbia from 2007 to 2014 categorized the cause of abortions in Fraser Valley herds. From their findings, the leading cause of infectious abortions was Neospora caninum (N. caninum), a protozoan parasite. Cumulatively, 61.9% of abortions presented with evidence of an infectious processes, but a disease agent was identified in only 39.4% of the cases. In those fetuses with an identified infectious agent leading to abortion, 46.2% were caused by N. caninum representing just under 20% of dairy abortion cases submitted for diagnostic evaluation.
Neospora has a complex lifecycle. Canines (i.e. dogs and coyotes) are considered definitive hosts; whereby this parasite can infect, replicate and the infective stages are shed into the environment. In contrast, cattle are incidental or intermediate hosts infected with immature stages of the parasite. In the dairy cow, N. caninum cannot replicate and there is no shedding of infective stages, instead the immature stages encyst in tissues, making them intermediate hosts. In cattle, the parasite can be transmitted across the placenta and infect the fetus, which may abort, succumb shortly after birth, or may survive and maintain the infection in the herd by transgenerational transmission.
Dogs become infected after consuming tissue cysts of infected intermediate hosts. These tissues typically include muscle, placenta or aborted fetuses. The life cycle of the parasite in the definitive host has not yet been fully determined, but once ingested, the parasite
invades through the intestinal wall of the canine, localizes to the liver, replicates in the intestine and ultimately infective stages are shed in the feces. The eggs (oocysts) are quite robust and capable of surviving for extended periods of time in the environment. Each egg contains several intermediate stages of the parasite which are released once consumed by cattle and encyst in muscle and neuronal tissue. Infected cattle generally do not show clinical signs of disease, but remain persistently infected for life. When an infected cow becomes pregnant the encysted parasite can become reactivated and relocate to the placenta and fetus via the blood stream. The parasite can be transmitted to the fetus during multiple subsequent pregnancies, either consecutively or intermittently.
In cattle, the most significant route of infection is through vertical transmission from dam to offspring. Horizontal transmission (cattle consuming oocysts in canine feces) is less commonly observed. Occasionally we see Neospora abortion storms which we assume are caused by new cattle infections.
Infected cows can give birth to:
• A clinically normal but persistently infected calf. These calves maintain neosporosis in the herd and can pass it on to their fetus or cause abortion when bred.
• An alive or weak calf, possibly with neurologic signs.
• Abortion, usually in the 4th-6th month of gestation.
• A very small portion of calves born to an infected cow will be uninfected
Prevention:
• Prevent dogs from defecating in feed.
• Prevent dogs and coyotes from having access to any/all aborted fetuses, placenta, and dead stock.
• Test and cull.
Unfortunately, abortions prove to be a diagnostic challenge, since the cause of fetal loss is undetermined
in 50% of cases. However, with the majority of abortions caused by infectious pathogens, it is valuable to work up abortion cases in order to rule out an infectious agent and to implement appropriate preventative strategies.
The Animal Health Centre in Abbotsford provides a post mortem on bovine abortions for $80. Abortion submissions can provide valuable information on diseases that may not be on your radar. We have identified Salmonella Dublin on herds through abortion submissions and there have been sporadic cases of bovine viral diarrhea virus (BVDV) and bovine herpesvirus (IBR).
Recommended Samples for Abortion Submission:
• Fresh/frozen fetus
• Fresh/frozen placenta
• Blood sample in a red top tube
Dr. Stephen Raverty is a veterinary pathologist at the Animal Health Centre, Abbotsford, BC and continues to research causes of abortion in the Fraser Valley, BC with particular emphasis on protozoa. Please contact Dr. Raverty at 1-800-661-9903 or stephen.raverty@gov.bc.ca if you have increased fetal losses or an abortion storm.
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