When called upon to investigate the occurrence of several abortions in a dairy herd our thoughts turn first to three infectious diseases. It is useful to remember that, characteristically, brucellar abortions are late (about 7 months), while those due to trichomoniasis are early (1 to 4 months); and vibriosis tends to be intermediate in this regard. Points which should never be overlooked, however, are that the embryo or foetus can be slipped at any stage of pregnancy from any of these causes; that two or more of the conditions may be present concurrently in a herd; and that abortion may be neither the most obvious nor the most important feature of such infections. Further, some degree of resistance or at least temporary immunity is likely to be acquired as a result of initial infections, and so particular attention to the behaviour of heifers is called for in many instances.
In the case of brucellosis our task is simplified considerably by the application of the blood serum agglutination test for diagnosis, as it offers reliable information about each individual animal; and by being able to confer a resistance by means of Strain 19 vaccination where indicated. We can aim to build up either a disease-free resistant herd or a disease-free susceptible one, according to circumstances and the requirements of the case.
With trichomoniasis both diagnosis and control measures must be on a herd basis. Having recovered the organism from one animal we must regard the herd to which it belongs as positive, and proceed accordingly—remembering that one mating with an infected cow is likely to render a bull infective for life (though he may show no signs of ill-health, and continue to serve normally and initiate pregnancies), while an infected cow tends to recover spontaneously within a few months, or even weeks, if given sexual rest.
It is seldom possible to be quite certain that any given bovine is not harbouring T. foetus. Nevertheless it often is reasonable and helpful to divide a herd into two or more groups, for breeding purposes, on the assumption that some are free. Virgin heifers may be put to a "known" clean bull, particular care being taken to ensure that the latter does not come in contact with positive or suspect cows. It may be decided to include also any cow which has carried her last calf to full term and then been rested for three months. Such decision should be made in consultation with the District Veterinary Officer or Inspector of Stock.
It is even more difficult to establish a definite diagnosis of vibriosis—another disease which might prove to be fairly widespread in this country. While the protozoon Trichomonas foetus is relatively large and readily recognisable under the microscope (in fresh wet smears of vaginal exudates, etc.), Vibrio foetus is very small and its identification calls for involved laboratory procedures. Generally it is necessary to submit a freshly aborted foetus or pipettes of its stomach contents for examination. Fortunately, the tendency towards self-cure seems to be even greater in this disease than in trichomoniasis, though bulls sometimes act similarly as carriers.
If suspicions of trichomoniasis are aroused, either through early abortions or because of an undue number of cows “returning,” including some which had been believed to be in calf, especially if such occurrences have commenced or increased after an outside service or an introduction into the herd, we set out to find the organism. In infected bulls the trichomonad population appears to remain fairly constant, mainly on the surface of the glans penis and prepuce, and they may be found in preputial washings (using N. saline) or in smegma samples obtained by means of a suitably shaped glass pipette fitted with a rubber bulb or a syringe; but negative findings are not entirely reliable, and it may be necessary to have a suspect bull serve a couple of virgin heifers and to obtain samples of vaginal exudate at certain specified times—notably between the 12th and 19th days post-coitus.
Material obtained from the breeding organs of a cow immediately after an abortion may be teeming with trichomonads, but none may be found 48 hours later. Sometimes they will show up in the vagina of a susceptible subject at about the time of the first and second heat periods after service by an infected bull; being present in the uterus but not the vagina in the meantime. It is fairly common for a cow to develop sufficient immunity as a result of one infection to become pregnant subsequently to an infected bull and have a normal calf at full term, though the immunity is rarely, if ever, permanent. This can be taken into account when planning control measures, and must be borne in mind in connection with diagnosis. Some cows develop pyometra, and may remain a menace for considerable periods. It is often advisable to dispose of these as they seldom will be an economically sound proposition thereafter.
Among the useful articles which may be consulted for more detailed information on this subject is an excellent one by Bartlett (1949).
Trichomonas foetus has one posterior and three anterior flagella, and is characterised by an undulating membrane. Though present in some other trichomonads and other mastigophora, the latter feature serves to differentiate it from cercomonads and other protozoa (which may be present as a result of faecal contamination) and from ciliated epithelial cells, etc., sometimes seen "swimming" in specimens submitted for diagnosis. The organism, being somewhat larger than the average polymorph, can be seen under the low power of the microscope, but the high power reveals more morphological details. As it tends to progress with a spiral movement the undulating membrane may appear first on one side and then on the other, not being so obvious when either above or beneath the cell proper. It is approximately 1/3rd the width of the latter, and may be seen fluttering rapidly or barely moving, depending upon the vitality of the organism and the nature and viscosity of the medium. In an unsuitable environment trichomonads tend to assume a roughly spherical shape with the flagella wrapped closely around them, becoming unrecognisable.
Trichomonads usually will remain active and identifiable in specimens of vaginal exudate, etc., for a couple of days, and may continue so for as many as five. In a refrigerator they may "keep" more satisfactorily, due partly to the effect on bacteria, etc., but freezing destroys them. Their shape and activity vary with their vitality and the fluidity of the medium.
Trichomonads occur in great number and variety in nature. They are common in both the alimentary and urogenital tracts of many animals, and in insects and birds. It is sometimes held that there are more names than are justified. Dobell, for instance, considers that T. vaginalis and T. hominis are synonyms for an organism of which various strains showing minor differences occur. Apparently he bases this conclusion partly on the fact that a rich culture of Trichomonas from his own stools, when inoculated into the vagina of a monkey, continued to grow there for more than 3 years (without apparent harm to the new host (hostess?). Some investigators would include T. elongata also. Stabler and co-workers (1941-42) obtained negative results on inoculating volunteer human subjects intra-vaginally with cultures of T. hominis and T. elongata. These three organisms occur as commensals in the human vagina, colon and ileum, and mouth (tartar and gums) respectively, in the order named. Each has four anterior flagella, and one posterior flagellum, the latter being an extension of the margin of an undulating membrane. The few who suggest that all trichomonads are variants of the same organism are surely going too far: but we do know that T. foetus may become established in the reproductive organs of certain other species, and sometimes cause abortion (see Morgan’s Monograph).
This raises the question of hygiene. The fact that bovine genital trichomoniasis is a truly venereal disease does not mean that it could not be spread by any means other than coitus. It could be passed easily from infected to clean animals by the careless use of instruments, or the hands, when carrying out a series of examinations for vaginitis, or when inseminating. Some farmers’ vaginitis control procedures could have the same result.
The writer infected a cow experimentally in such a manner at Glenfield recently. A little vaginal exudate containing a very small number of sluggishly motile trichomonads was smeared on the hand, which was then introduced in to the vagina of a 2½ months-pregnant cow. After three days exudate rich in T. foetus was present in the latter. (Following natural infection the organism is rarely recoverable in much less than about 10 days). In this particular case the organisms disappeared within a few days—apparently without penetrating the cervical plug, as pregnancy was not interrupted. This subject had developed an immunity as a result of a previous (natural) infection. Trichomonads had appeared in her vagina at intervals for a time following her first service by an infected bull. None were recovered after a second service some months later, and the normal pregnancy had followed a third service by the same bull—which had infected another experimental heifer in the meantime. (Material from the latter was used for the abortive attempt to induce abortion in the former).
The oral trichomonas of man was observed in 1773 by G. F. Miller, who named it Cercaria tenax. In 1854 Davaine found trichomonads in the stools of human cholera patients. Early this century it was realised that trichomoniasis could be responsible for lowered herd fertility and abortion in bovines, but this discovery appears to have been overshadowed by brucellosis and for some years little progress was made with the former. It was recorded in Italy in 1900, Germany m 1927, U.S.A. in 1932 and U.K. in 1937.
Coming closer to home, bovine venereal trichomoniasis was found to be present on King Island (Bass Strait) in 1945/46. Farmers on the island recalled similar occurrences in 1914/15, so possibly it was present then. The first confirmed diagnosis on the Australian mainland was on the near south coast of N.S.W. in October, 1948. Since then it has been found in one herd in Queensland, several in Victoria and many in New South Wales. Whether it had spread up recently from the south, gained entry elsewhere or been present here for many years we do not know. Mr. W.L. Hindmarsh, and probably others also, suspected its presence years before the first definite diagnosis. The first bull incriminated in this State had come up from Victoria some months previously. On the other hand, imported heifers have aborted from this cause at the Abottsford (Sydney) Animal Quarantine Station on two occasions since October, 1948—suggesting that the disease could have been introduced into any State independently at any time through importations from overseas.
Much remains to be learned concerning trichomoniasis, but we have sufficient knowledge to wage a fairly effective war against it. As usual, field officers are important front-line troops. An alliance with country practitioners is called for, and already there have been numerous instances of fruitful co-operation.