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A Novel Dimorphic Fungus as an Emerging Cause of Reproductive Losses in Mares and Other Livestock
Department of Veterinary Sciences
A newly isolated dimorphic fungus has been isolated from equine fetuses and neonates, and from other species including cattle, goats, sheep, pigs and chickens. In addition to fetal tissues, the fungus has been isolated from the semen. The fungus has been isolated from grains and forages of animals exposed to these feedstuffs. In addition to the diet the fungus may be transmitted in the semen, and in addition to fetal loss, may be responsible for non-conception and early embryonic loss.
2011 Project Description
The cause of pregnancy losses in livestock, primarily in herbivores, continues to be an emerging syndrome of unknown etiology. Pregnancy losses, especially in early gestation is of major concern in livestock of economic significance. In addition to the mare, dairy and beef cattle are also affected, where losses in some herds are reported to be between 20 to 50 percent. Also, some swine herds have similar losses.
Seemingly, the abortigenic agent is not specific to any species as several are affected without any known cause. It is suspected that the abortigenic agent may be present in grains and forages consumed by affected animals since several species are affected, and the diet appears to be a common factor.
Pathologic and microbiologic examinations of affected fetuses and fetal membranes have revealed a suspect agent that is commonly demonstrated where no other known cause of abortion can be found. Originally, it was suspected that the agent may be a dimorphic fungus because very minute structures were demonstrated with the aid of transmission electron microscopy in and around fungal hyphae. However, similar minute pleomorphic forms were found to be associated with some bacteria as well as fungi.
This finding suggests that these structures may be either a parasite or a commensal of bacteria and fungi. Also, the suspect abortigenic agent is very fastidious and requires other organisms, or nutrients from these organisms to grow when cultivated with cell free media. These structures are vacuolar and coccoid with a dense center. Other forms include very minute tubular irregular filaments attached to the minute vacuoles with dense centers. In some specimens the small vacuolar, coccoid bodies appear to be budding off and within a larger vacuolar body. The dense centers of the coccoid vacuoles appear to form smaller spore-like structures.
It is hypothesized that the suspect abortigenic agent is being carried by other microorganisms and is affecting young embryos and early developing fetuses. These minute forms are filterable and pathogenic for embryonic chicken eggs.
Fetuses that are not lost early in pregnancy may be aborted later in gestation. Affected fetuses not aborted may be born alive, but their placental membranes have typical lesions. The abortigenic agent has a predilection for small vessels of affected fetal membranes. The vascular changes include hyperplasia of vessels of the amnion and amnionic umbilical cord, and edema of the amnion.
The suspect abortigenic agent appears to be novel, unlike any agent currently seen in aborted fetuses that abort from any known cause. Genetic tests are being performed to further characterize the suspect agent. It may be necessary to determine the entire genome of the suspect agent so specific genetic tests can be used to study the ecology of the suspect abortigenic agent in the environment and to use the genetic data to develop tests for diagnostic specimens. Also, controlled tests in experimental animals are necessary to determine if the suspect abortigenic agent induces abortion in pregnant animals.
In a recent publication in Hoard's Dairyman, November, 2011, p771, Dr. Jenks Britt, an international reproductive specialist for the dairy industry suggests that the lost pregnancy issue needs to be investigated throughout North America. These losses are not only occurring in dairy cattle, but are emerging in all classes of livestock of economic significance.
The current project is addressing the concerns of Dr. Britt as fetal specimens have been received in 2011 from problem herds throughout North American and the only common factor found is the suspect abortigenic agent. No other known abortigenic agent can be demonstrated in affected fetuses.