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A virulent strain of Mycoplasma gallisepticum (MG) was used to infect groups of 40 2-day-old poults kept in separate pens of 10 each. Of the six groups, three were treated with separate concentrations of tilmicosin, one was treated with tylosin, one remained untreated, and a final group was not infected and not treated. Mortality, clinical signs, and gross lesions were significantly less (P < 0.001) in the uninfected and infected medicated groups than in the infected unmedicated group. Also, the mean body weight gain of poults surviving to the end of the experiment was greater (P < 0.005) in the uninfected and infected medicated groups. MG was not recovered from the uninfected birds, and, among the infected poults, it was recovered from significantly fewer (P < 0.05) poults in the medicated groups. Serologic results were negative for the uninfected group, and there were fewer positive reactors for the infected medicated than the infected unmedicated group. In consideration of these results, tilmicosin should prove to be a useful addition to the antimicrobials in the treatment of MG infection in poults.

The minimum inhibitory concentrations (MICs) for valnemulin, tiamulin, enrofloxacin, tylosin, and lincomycin/spectinomycin were determined for a virulent strain of Mycoplasma gallispeticum (MG). At the initial reading, the lowest MICs were seen with valnemulin and tiamulin, followed by tylosin, enrofloxacin, and a relatively high MIC for lincomycin/spectinomycin. At the final reading, at 14 days, a similar pattern was obtained, with valnemulin giving the lowest MIC (< 0.008 mg/ml). The same strain of MG was used to infect groups of 20 2-day-old chicks in two separate experiments. In both, several concentrations of valnemulin and tiamulin and one each of tylosin and enrofloxacin were administered to separate groups in the drinking water. In the second experiment, one group of chicks was given lincomycin/spectinomycin. Each experiment had one infected unmedicated group and an uninfected unmedicated group. Mortality, clinical signs, and gross lesions, in both experiments, were significantly less (P < 0.001) in the uninfected and infected medicated groups (except for the two lowest dosages of valnemulin, lincomycin, and spectinomycin) than in the infected unmedicated groups. Also, the mean body weight gain was greater in the uninfected and infected medicated groups. Among the infected birds, MG was recovered from fewer chicks in the infected medicated groups except for the lowest two dosages of valnemulin. Serologic results were negative for the uninfected groups, and there were fewer positive reactors for the infected medicated groups except for the group treated with lincomycin/spectinomycin. Valnemulin should prove to be a useful addition to the antimicrobials in the control of MG infection in chickens.

The minimum inhibitory concentrations of tylosin tartrate and a new macrolid antimicrobial agent, tilmicosin, were assessed for six strains of Mycoplasma gallisepticum (MG) and three strains of Mycoplasma synoviae (MS) in vitro by the microbroth method. For four of the strains of MG, tilmicosin showed a slightly lower minimum inhibitory concentration (MIC) than did tylosin at both the initial reading (when pH 7.0 is first seen in the dilutions under test) and the final reading at 14 days of incubation. For one of the remaining strains, the MIC for tilmicosin was equal to or less than that for tylosin at the initial reading but greater at the final reading. For the other strain, the MIC for tilmicosin was greater than for tylosin, and for both of them the MICs were very much higher than for other strains. For the three strains of MS, there was little difference between the two drugs for one strain whereas the MIC for tilmicosin was slightly less for the other two groups. Groups of 30 chicks were infected with a virulent strain of MG and treated with either tylosin (0.5 g/liter) or tilmicosin (at concentrations of 0.125, 0.25 or 0.5 g/liter). One infected group was untreated and another group was uninfected and untreated. Clinical signs, mainly depression and nervous signs, were seen in two to five birds in the infected treated groups. In contrast, in the infected untreated group, 16 of 30 birds showed clinical signs. Mortality was significantly less in the infected treated groups compared with the infected untreated group (P < 0.001), and following infection there were significantly (P < 0.05) greater weight gains in the infected medicated groups. At necropsy the prevalence of gross lesions of the airsac walls was similar in all the infected medicated groups and was less than that for the infected unmedicated group. For the group on tylosin, MG was recovered from five chicks during life and from six dead chicks. The corresponding figures for the group receiving the lowest dose of tilmicosin were four for each; however, the organism was not recovered from the groups on the higher doses of tilmicosin either during life or from dead chicks. Serological results were negative for all groups except the infected untreated group, in which all three birds that were tested were positive.

In a preliminary experiment, a field infection with Mycoplasma iowae was simulated by inoculating turkey eggs with various doses of two strains of M. iowae immediately before incubation. The strain and dose chosen for further study were those that best multiplied and resulted in infection of embryos from which the organism could be isolated after 25 days of incubation. Ten turkey hens free from infection with mycoplasmae were housed in isolation. The hens were given enrofloxacin in the drinking water at a concentration of 50 ppm on 3 successive days, on two occasions at intervals of 14 days. Within 48 hours of lay, their eggs were each inoculated with 0.1 ml of the selected strain and dose (10(5) colony-forming units/ml) of M. iowae. M. iowae was recovered from almost all eggs laid by hens before the initial medication but not from any of the eggs laid for several days after each period of medication. Thereafter, the organism could be recovered from a high proportion of inoculated eggs. The treatment of infected turkey laying flocks with enrofloxacin at strategic periods might be helpful in the control of this Mycoplasma by limiting both vertical and horizontal transmission.

Groups of chicks were infected with a virulent strain of Mycoplasma gallisepticum (MG) and treated with either danofloxacin or tylosin while one infected group was left untreated and a further group was uninfected and untreated. Control of clinical signs and mortality was better with danofloxacin than tylosin and there was significantly (P < 0.05) greater weight gain with danofloxacin at 21 days after infection. However at necropsy the prevalence of lesions of the airsac walls was similar in both groups. MG was recovered from fewer live chicks for the first week following treatment with danofloxacin, but at 2 weeks and at necropsy, at the termination of the experiment, it was recovered from a similar proportion of birds in both treated groups. This was reflected also in the serological results at the end of the trial.

Mycoplasmaa-induced arthritis of poultry under field conditions is almost entirely caused by Mycoplasm synoviae (Ms) infection. Experimentally, Mycoplasma synoviae, Mycoplasma gallisepticum, Mycoplasma meleagridis and Mycoplasma iowae have all been shown to cause arthritis, tenosynovitis and lesions of periarticular tissue. However, greatest attention has been given to Ms in this respect. The leg joints are most consistently involved, and of these particularly the tibiotarsal-tarsometatarsal and tarsometatarso-phalangeal joints. Acute amd chronic arthritis have been described, and in the later the arthritic lesions may be progressive. The histopathological changes include invasion with heterophils (polymorphs) and later monocytes. Villus formation is shown by the synovium, and lymphofollicular aggregates appear. In severe cases, there is progressive erosion of articular cartilage and there are degenerative changes in underlying bone. Systemic changes include anemia, reticulitis, arteritis, and atrophy of the thymus and bursa of Fabricius. The mechanism of disease production may involve a direct inflammatory response as well as immunoinflammatory complexes.

A group of six racing pigeons naturally infected with Mycoplasma columborale and M columbinum were housed in isolation and treated with tiamulin hydrogen fumarate in the drinking water for 35 days. Swabs from the oropharynx, the oesophagus and the trachea were negative for mycoplasmas at the end of this period. Mycoplasmas were recovered from two of the birds after a further nine days, and 13 weeks after the cessation of treatment mycoplasmas were recovered from all six birds.

Tissues of mycoplasma infected chicks and turkey poults were cultured and subcultured on mycoplasma agar. Usually, colonies which grew on the agar initially inoculated could be subcultured, but sometimes they could not. At other times, colonies were not seen on the agar initially inoculated but appeared on the subcultured plate.

Two groups of day-old ducklings were infected with Mycoplasma gallisepticum and M anatis respectively by air sac inoculation. Clinical disease was not produced but air sacculitis was produced by both infections. M gallisepticum could be recovered readily from respiratory tissue 10 and 30 days after infections but RSA tests were negative. M anatis was not reisolated from these tissues or from the cloaca but a positive RSA test was observed on the serum of a few ducklings.

The mycoplasma infecting and sometimes causing disease of the respiratory system in both species are M. gallisepticum and M. synoviae, while M. meleagridis affects the turkey only. M. gallisepticum has received the greatest attention and natural infection is reported to result in protection varying greatly in degree and duration. Vaccination with living organisms either by the respiratory or intravenous routes results in a high degree of protection against air sac challenge for at least a few weeks. Killed organisms administered intravenously result in a lesser degree of protection to this challenge but when given intranasally provide no protection. M. gallisepticum survives in the respiratory tract and perhaps in other organs and tissues for long periods after infection, perhaps in latent form. However, intercurrent infection and other avian respiratory pathogens may precipitate multiplication of the organism and disease in birds apparently resistant to challenge with mycoplasma alone. The mechanism of protection has not been extensively studied and production and significance of local antibody or a cell-mediated response have not been determined. However, bursectomized chickens vaccinated against M. gallisepticum show much less resistance compared with controls but the exact part played by humoral antibody is still in doubt. Similar observations have been made with M. synoviae.

Mycoplasma gallisepticum, Mycoplasma synoviae and Mycoplasma meleagridis are the most widespread pathogenic poultry mycoplasmas. The epidemiology of the infections, and clinical signs, lesions, pathogenesis, diagnosis and control of disease are described. In epidemiology, the constant antigenic composition, variation in virulence, tropism, survival of the mycoplasma outside and within the host and susceptibility to drugs are outlined. The significance of species, age and immune status of the host and the importance of intercurrent infection and debilitating factors in the production of disease are given. The transmission of infection, clinical signs of disease, and gross and histopathological appearances of lesions are described. The interpretation of the pathogenesis of disease is based on the appearance of lesions in untreated birds and in bursectomized or thymectomized chickens. The means of recognizing infection, and the methods used in ameliorating the worst effects of disease or eradicating infection follow.

The virulence of three strains of Mycoplasma gallisepticum (S6 of low broth passage, S6 of high broth passage and A514) and of one strain of M gallinarum was investigated in specific pathogen free chicks, turkey poults, chick embryo tracheal organ cultures and embryonated fowl eggs. One strain of M gallisepticum, S6, of low passage, caused high mortality in newly hatched chicks, and turkey poults, high embryo mortality, and rapid suppression of ciliary activity in tracheal organ cultures. The other strains of M gallisepticum and M gallinarum had relatively less effect. In view of its greater sensitivity, chick embryo mortality is preferable to tracheal organ culture for assessing the virulence of experimental strains of M gallisepticum.

Man in managing poultry for human benefit has found that his methods may precipitate or exacerbate certain diseases: among which are the mycoplasmosis of fowls and turkeys. Control measures for these conditions have therefore been sought and to make them effective it has been necessary to study the epidemiology, diagnosis and pathogenesis of these conditions. Much is now known about their epidemiology although certain aspects still require investigation. More sensitive and specific methods of diagnosis are also required and although it is possible to control these conditions by eradication the mycoplasmosis are still an economic problem. Under existing management systems, therefore, development and use of effective vaccines and additional drugs are essential. It is noteworthy that the pathogenesis of at least one of the avian mycoplasmosis is similar to human immune-complex disease. In further elucidation of this complex the fowl may be a useful experimental animal. Thus the association of people, poultry and pathogenic mycoplasmas not only involves attempts to control the pathogens in order to attain maximum production by poultry but also could include the utilisation of poultry and the pathogen in an attempt to elucidate some of the diseases of people.

A survey of mycoplasma infections of chickens, turkeys and ducks was made on tissues from a variety of sources and birds of various ages, and from pipped and dead-in-shell turkey embryos. The tissues examined consisted mainly of respiratory tissue and the cloaca and contents and also a small number of joint lesions and other tissues. From chickens, mycoplasmas were isolated from a total of 138 tissues with Mycoplasma gallisepticum in preponderance. This was followed by M gallinarum, untyped organisms, M synoviae and a number of other mycoplasmas and Acholeplasma laidlawii. From turkeys, poults and embryos, mycoplasmas were recovered from 164 tissues with M meleagridis in preponderance. This was followed by M gallisepticum, serovar I, M synoviae and a number of other species including untyped isolates. From ducks, M gallisepticum and M anatis were recovered in equal numbers. Mycoplasma infections with more than one species occurred in the same tissue in all species of stock but especially in turkeys.