Infectious Abortion

INFECTIOUS ABORTION (contagious) of cattle, abortus infectio-sus, abortus enzooticus (Bang), is most commonly observed in cows; it causes great losses, especially in breeding and dairy farms. After a contagious abortion has occurred, the following is noted: 1) death of calves, 2) decrease in milk production, 3) retention of the placenta, and 4) failure to conceive, despite repeated breeding of aborting cows. I.A. has been found in all parts of the globe; it occurs in cows without visible clinical signs. Abortion most often occurs in the 7th (50%) and 8th (16%) months of pregnancy. Natural infection in cows occurs mainly through the intestine as a result of consuming contaminated feed or water, or as a consequence of a cow being covered by an infected bull. Of those infected, first-calving cows typically abort, less frequently those calving for the second time, and abortion is rarely observed in those that have calved more than twice. The causative agent of I.A. of cattle is Bact. abortus Bang; its length varies from 1-2 μ, width 0.3-0.8 μ; this bacillus is immobile, polymorphic, and in its protoplasm the presence of 1-2 and rarely 3 granules is noted [see separate table (pp. 743-744), fig. 1]. The microbe is stained unevenly (often bipolarly) by ordinary stains, but better by Giemsa or Leishman; by Gram's method it does not stain. Cultures of Bact. abortus Bang develop either with reduced oxygen content (down to 4-5%) or in almost pure (90%) oxygen. On simple ordinary nutrient media, the I.A. microbe does not grow, but when serum or amniotic fluid is added to them, with a medium pH of 7.3-7.5, it develops well. After several transfers, Bact. abortus begins to grow even under aerobic conditions. Bact. abortus Bang can be found: in vaginal discharge, exudate of fetal membranes, in uterine exudate of cows, in the contents of the stomach and intestines of the fetus, as well as in the milk of cows. In the infected organism, Bact. abortus persists for a very long time (5-9 or more months); in cultures - up to 2 years; in moist manure - up to 75 days. Both heating to 65°C (5-10 min.) and ordinary disinfectant solutions cause rapid death of the abortion bacillus. Spontaneous I.A. has been observed, besides in cattle, in pigs and sheep. Artificially, cows, pigs, sheep, rabbits, guinea pigs, and sometimes white mice can be infected with cultures of Bact. abortus Bang. Diagnosis can be established serologically by means of agglutination and complement fixation. To stop and limit I.A. among animals, veterinary-sanitary measures (isolation, disinfection, etc.) are carried out, and preventive vaccinations are given to all adult cattle. The causative agent of I.A. of cows is not distinguishable either morphologically or biologically from the causative agent of Malta fever (see) - Micrococcus melitensis Bruce. In America, Germany, France, the Netherlands, Denmark, Switzerland and other countries in recent years, many cases of human infection with Bang's infection have been described when caring for sick cattle, when consuming raw milk from sick cows; in veterinarians, infection is observed when providing obstetric assistance to cows. A number of reports and papers on this topic have been made in recent years (1925-29) at the annual sessions of the Committee of the International Office of Public Health in Paris. Bact. abortus Bang is therefore not an innocent microbe for humans. Infection in humans may resemble tuberculosis, typhoid fever, and rheumatism; a remittent fever persists for a long time (months), sometimes reaching 41°C, with slight disturbance of consciousness (very characteristic); the fever may after 10-14 days give way to an afebrile pause; in the sick, swelling of the spleen, liver, orchitis, neuralgia, etc. is noted. The prognosis is generally favorable, as fatal cases are rare. Pure cultures of both Bact. abortus Bang obtained from sick humans and Micrococcus melitensis Bruce cause abortion in cows when injected; however, for guinea pigs, cultures from humans prove to be more virulent than cultures obtained from cows. I.A. (contagious) of mares (abortus infectiosus equorum) is most often observed in enzootic form in stud farms and causes enormous harm to breeding horse breeding. In certain years, I.A. occurs as an epizootic among peasant horses. This affliction of mares is clinically manifested only shortly before the onset of abortion: specifically, 1-2 days before, discharge from the vagina and swelling of the lips appear, and 8-10 hours before abortion, signs of restlessness (as if from colic) are sometimes observed. Abortion is most often confirmed between the 6th and 11th months of pregnancy. The causative agent of contagious abortion of mares is most often (77%) Bact. abortus equorum Poyakov, who was the first to thoroughly study the morphology, biology, and virulence of this microbe. Bact. abortus equorum belongs to the paratyphoid group of bacteria; it has the appearance of a short bacillus with rounded ends [see separate table (pp. 743-744), fig. 2], very motile, does not form spores, and does not stain by Gram's method; usually the microbe is polymorphic; it occurs either in the form of streptobacilli or cocco-bacilli. Growth on nutrient media does not differ from the growth of Bac. paratyphi B. Infection with cultures of Bact. abortus equorum, isolated from aborted fetuses or aborting mares, causes abortion in pregnant mares both by feeding cultures and by injection into the uterine cavity. In infected foals, joints swell, temperature rises to 40°C, then an exhausting diarrhea appears, and they die in several weeks. In mares after abortion, endometritis occurs, which is quickly eliminated with proper treatment. It has been experimentally proven that infection of horses most often occurs as a result of feeding infected hay. To stop infectious abortion of mares, the following are recommended: preventive vaccinations with vaccines, change of feed and transfer of animals to other, uninfected areas and stables.