Abortion

Bacterial and Fungal causes of Abortion

INTRODUCTION

Abortion in cattle is known as a loss of the fetus between the age of 42 days and 260 days. Pregnancies lost before 42 days are referred to as early embryonic deaths. A low rate of abortions is usually observed on farms.

However, the loss of any pregnancy can represent a significant loss of income to the producer and appropriate action should be taken to prevent abortions and to investigate the cause of abortions that may occur.

Abortion is caused by many factors as mechanical, chemical, nutritional, bacterial and mycotic causes.

Bacterial abortion is caused by Brucella spp, Campylobacter fetus, Listeria monocytogens, Salmonella spp, Escherichia coli, Leptospira, Staph. aureus, Streptococci, Corynebacterium pyogens and Chlamydia spp.

Mycotic abortion is caused by Aspergillus spp, Candida spp, Rhodotorula spp, Absidia spp, Alternaria spp, and Mucor spp.

Abortion in animals may be caused by non-infectious causes as genetic and non-genetic disorder. Risk factors associated with abortion in animals are genetic, environmental, management, geographical factors and infectious factors.

Diagnosis of animal abortion includes the collection of a complete history of the case and relevant epidemiological data and collected sample for analysis. However, determining the cause of animal abortion is difficult as abortions are caused by numerous infectious and noninfectious factors.

Bacteria which can cause abortion:

  • Brucella abortus (Brucellosis, Bang’s disease)

Brucella can cause very significant reproductive problems on dairy farms; brucellosis is now a disease that is primarily of historical significance. Effective Brucella abortus vaccines are available, although wide-scale use of the vaccine is decreasing in many parts of the country.

Brucellosis is a threat in most countries where cattle are raised.

In the USA, active control programs, including test, slaughter, and heifer vaccination, have greatly decreased its incidence.

Brucellosis causes abortions in the second half of gestation (usually ~7 month), and ~80% of unvaccinated cows in later gestation will abort if exposed to Brucella abortus.

  • Leptospira spp. L. hardjo and L. pomona

They are the two serovars of Leptospira that are the most important in North America. L. Pomona is usually associated with abortion outbreaks in the last trimester of gestation.

These occur sporadically since the cow is not its main host, and it is introduced to the herd from infected wildlife or swine – usually by means of water that becomes contaminated with the urine of these animals. Cattle, however, are the main host for L. hardjo (hardjo-bovis) and the organisms can establish as a chronic infection in the kidneys or reproductive tract of cows. Subsequently they can be shed intermittently during the life of the animal. These chronic infections can cause early embryonic death, abortions, stillbirths, or the birth of premature, weak calves. Vaccines are available against many different serovars; however, it appears that the protection offered is not very long-lasting and twice yearly boosters are usually recommended in high risk herds.

  • Listeria monocytogenes

Can cause abortions in addition to some of the common diseases seen due to infection with this bacteria (e.g. ‘Circling disease’).

Listeria can be found in many places in the environment on dairy farms. Abortions occur approximately one week after exposure, and occur most commonly during the last trimester of pregnancy, although they may occur as early as the 4th month of gestation.

The aborted fetus is often autolyzed. The cows may show clinical signs of disease as well, although once returned to health appear to resist reinfection. This organism may be the most common bacterial cause of multiple abortions in herds.

  • Ureaplasm diversum and Mycoplasma bovigenitalium

They are uncommon causes of abortions, although Ureaplasm can cause an outbreak of abortions if it is introduced into a ‘clean’ herd. These organisms have also been implicated as infectious causes of infertility. However, it is often difficult to determine if one of these agents is the cause of an abortion or infertility problem since they can also be found in the reproductive tract of ‘normal’ healthy cows.

  • Campylobacteriosis

Campylobacter fetus venerealis causes venereal disease that usually results in infertility or early embryonic death but occasionally causes abortion between 4 and 8 months of gestation.

  1. fetus and C. jejuni are transmitted by ingestion and subsequent hematogenous spread to the placenta. Both cause sporadic abortions, usually in the last half of gestation.
    • Chlamydiosis

    Chlamydia abortus, the cause of enzootic abortion of ewes, causes sporadic abortion in cattle. Most abortions occur near the end of the last trimester, but they can occur earlier.

    Placental lesions consist of thickening and yellow-brown exudate adhered to the cotyledons and intercotyledonary areas.

    1. abortus can be identified by examination of stained smears of the placenta or by ELISA, fluorescent antibody staining, PCR, or isolation in embryonated chicken eggs or cell culture.

    There are no vaccines for cattle, although they are produced for sheep.

    Fungal Causes of Abortion

    Fungi can also cause abortions in dairy cattle, most often in the last 2 months of gestation, although they have been observed to occur as early as 60 days. These usually occur during the winter and spring months.

    The mold spores are thought to reach the placenta and fetus through the blood supply of the cow, although the way that they gain access to the circulatory system is not well understood. Fungal abortions tend to occur sporadically although on some occasions a significant percentage (10-20 %) of the pregnant animals in a herd may be affected.

    Fungal placentitis due to Aspergillus sp, or to Mucor sp,  Absidia, Rhizopus sp, and a few other nonseptated fungi, is an important cause of bovine sporadic abortion.

    Abortions occur from 4 month to term and are most common in winter. It is believed the fungi gain entry through the oral or respiratory tracts and travel hematogenously to the placenta.

    Placentitis is severe and necrotizing. The diagnosis is based on the presence of fungal hyphae associated with necrotizing placentitis, dermatitis, or pneumonia. Fungi can also be isolated from the stomach contents, placenta, and skin lesions. Isolation must be correlated with microscopic and gross lesions to exclude contamination after abortion.

    For control, moldy feed should be avoided.

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