It is difficult to firmly establish the cause of abortive processes. In general, it is estimated that only 30-40% of all abortions referred to the laboratory are successfully diagnosed. This is due to the following reasons:
- Fetal infection and/or death often occurs weeks or months before actual abortion, and the pathogen is sometimes no longer detectable when the clinical picture appears.
- The fetus is retained within the uterus after death, and the process of autolysis complicates the diagnosis.
- Genetic or toxic factors responsible for the abortive process are not detectable in the samples examined.
- Many causes of abortion are either not known, or the routine diagnostic procedures are unable to identify them.
- No paired serum samples are available to establish seroconversion.
In general, "abortion outbreaks" are diagnosed without difficulty, though insidious abortive processes are often attributable to non-infectious causes and cannot be diagnosed.
In diagnosing an abortive process, the first requirement is to determine whether the underlying cause is infectious or not. In this context, it has been estimated that only 50% of all abortions are infectious in origin, while the rest are due to intoxications, environmental stress, nutritional alterations and systemic diseases in the gestating female (any process that causes fever and stress).
A series of opportunistic germs have been defined that while not manifestly pathogenic at reproductive level can nevertheless cause uterine infection with abortion in any stage of pregnancy and in any animal species. Their pure isolation from fetal organs and vaginal swabs from the gestating female may orientate the diagnosis.
The diagnostic laboratory should therefore have a case history as complete as possible, including the number of affected animals (e.g., if only one female has aborted or whether the phenomenon affects 30% of the herd), the age of the affected animals, the gestational stage in which abortion occurred, vaccinations, a description of the fetal and placental lesions, recent diseases identified on the farm, and other symptoms of the female animal (vaginal discharge, respiratory or neurological symptoms, diarrheic processes, etc.).
The samples of choice for establishing a diagnosis comprise at least the following:
1.- Serum from the aborted animals (at least 10 animals or 10% of the herd in the case of abortive outbreaks). If a viral etiology is suspected, paired serology (first, a serum sample at the time of abortion, and second, a sample 10 or 15 days later) may help to establish the diagnosis if seroconversion has occurred (i.e., a significant increase in antibody titer). Considering the high seroprevalence of many pathogens on our farms (Chlamydia, porcine parvovirus, Aujesky, etc.), an individualized diagnosis cannot be established, because when abortion occurs the antibody peak may have already started to decline in some animals — though the procedure is useful from the perspective of the global farm.
2.- Genital swabs from the aborting females. The vaginal discharge expels the germ causing the abortion. Vaginal swabs sometimes provide a diagnosis when the placenta or fetuses are contaminated or are difficult to find (sheep).
3.- Stomach contents of the fetus and placental cotyledons. These are the most reliable samples for diagnosing Chlamydia and other germs that are isolated in pure fetal culture.
4.- A full case history. This is essential for orientating the diagnosis.
Other samples that can contribute to establish the diagnosis are:
- Whole fetuses (sheep, goats and pigs). The fetuses should be refrigerated, not frozen.
- Fetal serum. The presence of antibodies in fetal serum allows a definitive diagnosis, since the uterus should normally remain sterile during gestation.
ABORTIVE PROCESSES IN GOATS
Chlamydia psitacil appears to be the most often implicated pathogen. It accounts for up to 50% of all ovine and caprine abortions diagnosed in Spain. Chlamydia causes abortion in the last trimester of gestation, as well as pneumonia, lameness and keratoconjunctivitis. Placental retention and the appearance of mummification, placentitis or petechiae are relatively frequent. The fetuses are usually well preserved. The females show few symptoms (wasting or thinning). On the other hand, 90% of the females are serologically positive; consequently, serology is only valid when based on fetal serum, and the technique is consequently of little use in application to routine diagnosis.
Infection occurs as a result of the ingestion of Chlamydia expelled in the vaginal discharge of the aborting female, and can take place for up to three weeks after abortion. Chlamydia has also been found to be excreted in certain moments of the hormonal cycle.
The diagnosis should be based on immunolabeling techniques applied to placental cotyledons, and is confirmed by latex agglutination from vaginal brushing or swabs in aborting females, since isolation of the germ is extremely difficult. Commercial vaccines are available.
This is caused by Brucella melitensis, B. ovis or B. abortus in animals in contact with bovine cattle. Brucella causes late abortion, infertility, orchitis, fever, metritis, mastitis and the surviving neonates are weakened at birth. Placental retention is frequent, and the placenta may appear necrotic. Transmission is via the oral route from the ingestion of Brucella in milk and in vaginal discharge — though there are also sterile periods without discharge. In order to establish the diagnosis, serology is only valid if vaccination has not been carried out. Isolation of the germ can be achieved from the stomach and other fetal organs and — provided contamination is not excessive — from vaginal swabs and even milk.
Various Salmonella species can be implicated — the main pathogen being Salmonella abortus ovis. This agent causes middle- to late-phase abortions that are usually sporadic and secondary to a diarrheic episode. In addition to the abortive process, the female typically presents diarrhea, fever, metritis and purulent vaginal discharge. The fetus is in turn degenerated, autolytic and edematous, with lesions characteristic of septicemia. The diagnosis is established from isolation of the germ in stomach and other fetal organs, or in vaginal swabs and lymph nodes. Serology is not usually performed since isolation of the culprit microorganism is relatively simple.
Toxoplasma gondii is the main agent implicated in abortive processes in the United States and in England. Abortion occurs in the first half of pregnancy, though reabsorptions are also possible. The female is asymptomatic. The most characteristic lesions are necrotic foci and calcifications in cotyledons and placenta, which can be better visualized by immersing the placenta in an isotonic saline solution. The same lesions can be identified in brain tissue and fetal organs. The diagnosis can be established via paired serology, the identification of IgM - though immunofluorescence from placental imprints is the most commonly used procedure. Figure (Toxoplasma in a macrophage).
Produced by Campylobacter fetus, intestinalis, or jejuni, this disease can cause abortion in up to 70% of all the females on the farm- though it does not affect fertility in sheep. The transmission is oral, from the aborting ewes or carriers. Abortion takes place in the last 6 weeks of pregnancy. The lesions are nonspecific, though hemorrhage and necrotic or degenerated zones in the placenta and fetus predominate. The diagnosis is established by Campylobacter culture from the stomach of the fetus or vaginal discharge of the female. Campylobacter can be visualized by immunolabeling of the fetus or female fluids.
This agent causes abortion generally in the last trimester. Contagion results from the ingestion of contaminated silo fodder or soil, since Listeria is a telluric organism habitually found in soil. Listeria causes placentitis, septicemia and fetal death. The fetus usually presents autolysis, and necrotic foci are often visible in the liver or spleen. The diagnosis is made by culture and isolation of the germ, or via immunolabeling from placenta, liver or stomach of the fetus.
Caused by Coxiella burnetti. This process causes abortion in up to 50% of the herd. Abortion occurs at term, and some animals are born weak. The ewes are usually asymptomatic. The fetus is habitually well preserved and no significant lesions are observed — though the placenta shows necrotic areas that can be coated with a grayish exudate. The diagnosis is usually established by immunolabeling from placental cotyledons, vaginal discharge or the stomach contents of the fetus. Isolation of the germ is difficult. Since asymptomatic sheep without abortive processes can be observed, the diagnosis cannot be based on the serology findings.
This infection is caused by a pestivirus related to bovine viral diarrhea (BVD). Infection in the gestating female causes placentitis and abortion in any phase of pregnancy. The fetus is often mummified. Those animals that are born appear weakened and with alterations in their wool, muscle tremor and dark pigmentation. The diagnosis is established by immunolabeling of cervical swabs or of fetal stomach and lung tissue. Serology in animals that have not received colostrum, or of fetal fluids, is also important.