Bovis ISSN 2398-2993
Contributor(s): Wendela Wapenaar
, Andrew Forbes
- Phylum: Apicomplexa.
- Family: Sarcocystidae.
- Genus: Neospora.
- Neospora caninum is a coccidian parasite that was identified as a species in 1988.
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- Cattle get infected by ingesting sporulated oocysts or by vertical transmission via the placenta.
- Although conflicting results are presented in studies, semen and milk appear to be unlikely sources of infection.
- Oocysts are only found in fecal material from definitive hosts. Thus far only the dingo, coyote and domestic dog have been confirmed to be definitive hosts.
- Cows that have aborted once due to N. caninum are more likely to have either subsequent abortions or infected fetuses in future pregnancies.
- In the cow the parasite appears to localize to neuromuscular tissue in its slow growing stage (bradyzoite), but in its initial fast growing stage (tachyzoite) it can pass the placenta and infect the fetus.
- N. caninum does not always cross the placenta. Uninfected calves can therefore be born, but the majority of fetuses in seropositive dams will be infected via the placenta.
- The majority of these infected fetuses will develop without any clinical signs but are persistently infected.
Other Host Effects
- In some studies seropositive heifers and multiparous cows have been found to have lower milk production compared to seronegative animals.
- A UK study demonstrated that seropositive heifers were more likely to suffer gestational loss (late embryonic, early fetal loss and abortion) than seronegative heifers during their first and second pregnancy.
- Offspring of seropositive heifers were also four times more likely to experience perinatal mortality (calf born dead or dying within 24 hours of parturition) at first and second calving. However, current studies fail to show a significant association between seropositivity and fertility parameters (age at first breeding and calving, days from calving to first service and conception, services per conception and calving interval) or conception failure; this lack of association may have been due to an insufficient sample size.
Control via chemotherapies
- None available, except for supportive therapy where required after abortion.
Control via environment
Prevent vertical transmission
- In low prevalence herds: consider culling of all seropositive animals.
- In high prevalence dairy herds: breed seropositive animals to beef, do not keep offspring.
- Only seronegative females should be introduced into the herd. However, a seropositive cow is unlikely to be a risk on the farm until she calves/aborts.
- Embryo transfer Embryo transfer: overview: harvest embryos from a seropositive dam, implant embryos in seronegative recipients.
- Avoid any condition that may lower the immunity of pregnant animals; for example, implement control measures for other diseases such as BVDv Bovine viral diarrhea virus and leptospirosis Leptospirosis.
- Dairy herds: lower abortion rates have been reported when using beef bull semen for AI, possibly due to the improved placental function in cross bred pregnancies.
Prevent horizontal transmission
- Prevent access of dogs, especially puppies, to silage pits, hay sheds, feeding areas and concentrate food stores.
- Soiling of pasture by canine faeces should be avoided.
- Access of birds, rodents and other wildlife to on farm food should be prevented.
- Dogs should not have access to calving areas or recently calved animals.
- Dead fetuses, dead animals, uterine discharges and placentae should be disposed of so that dogs and wildlife cannot get access to them.
- The safest practice would be not to feed any form of raw meat to dogs.
- It is advisable to calve known neospora-positive animals in isolation from seronegative animals, even though horizontal transmission between cattle has not (yet) been shown to occur.
- There is no reason to remove the farm dog; once infected the dog will remain infected but is unlikely to shed oocysts again. There is even an argument of keeping the dog, as it may have a protective effect by keeping rodents and other possible intermediate hosts of the property.
- No effective vaccine available (vertical transmission has often occurred before vaccination can take place).
- See control measures above.
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- Recent references from PubMed and VetMedResource.
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Other sources of information
- School of Veterinary Medicine and Science, University of Nottingham, UK.