Experimental reproduction of Mycoplasma gallisepticum disease in chukar partridges (Alectoris graeca).

An outbreak of conjunctivitis and severe respiratory disease occurred in an integrated chukar partridge (Alectoris graeca) operation that involved about 8000 birds. The main clinical features were conjunctivitis and sinusitis and frequent mouth breathing, but almost no gasping or coughing. In 1000 breeders, egg production declined from 73% to 20%. Morbidity reached 100%, and losses from mortality and culling approached 60%. At necropsy, a conjunctivitis (often bilateral) and extensive caseated sinusitis were common. There was an occasional slight mucoid tracheitis, but no significant air sac lesions were noted. Mycoplasma gallisepticum, designated strain GM1125, was isolated and identified. Exposure of susceptible chukars to GM1125 reproduced the field disease. GM1125 was reisolated from the conjunctiva of all exposed birds 12 days postinfection, but infrequently from there or the respiratory system 36 days postexposure, even though clinical disease was still present. The experimental disease was confined to the conjunctiva and the upper respiratory tract. An occasional mucoid tracheitis was noted, but generally, the lungs and air sacs were not involved. Infection was followed by an appreciable serological response to M. gallisepticum.

Delineation of the lateral spread of Mycoplasma gallisepticum infection in chickens.

Lateral spread of S6 strain Mycoplasma gallisepticum (MG) was studied in small populations of chickens. One experimentally exposed bird served as the source of infection, and the presence of MG-agglutinating antibody was evidence of infection in individuals. The results were subjected to survival data analysis. In the seven experiments, four similar but not identical phases of lateral spread were observed: phase 1, a generally long latent phase (median 15, range 12-21 days) before antibody was first detected in the MG-inoculated bird; phase 2, a generally short period (median 1, range 1-21 days) in which infection gradually appeared in 5-10% of the population; phase 3, a fairly constant characteristic phase (median 24, range 7-32 days) in which 90-95% of the remaining population developed MG antibody; phase 4, a generally short terminal phase (median 4, range 3-19 days) in which the remainder of the population became positive. Increasing the population density increased the rate at which lateral spread occurred.

Prevalence of Mycoplasma gallisepticum and M. synoviae in commercial layers in southern and central California.

The prevalence of Mycoplasma gallisepticum (MG) and M. synoviae (MS) in commercial pullet and layer flocks in Southern and Central California was estimated by testing serum and egg-yolk samples from 360 sample flocks in Southern California and 41 sample flocks in Central California. Data relating to potential risk factors associated with MG and MS infections were collected. The estimated true prevalence rate of MG was 73% in Southern California and 3% in Central California. The estimated true prevalence rate of MS was 91% in Southern California and 32% in Central California. Compared with uninfected flocks, MG-infected flocks in Southern California were significantly older and were medicated less (P less than 0.05). More managements were under a multiple-age system, more flocks had molted, more were vaccinated with F-strain, and more had concurrent infection with MS (P less than 0.05). Only one sample flock in Central California was MG-infected; none were vaccinated with F-strain. In Southern California, MS-infected flocks were older than uninfected flocks, more had molted, more were medicated, and more had concurrent infection with MG (P less than 0.05). In Central California, MS-infected flocks did not differ significantly from uninfected flocks in any factor examined; the lack of statistical significance may be due to small sample size.

Observations on commercial layers vaccinated with Mycoplasma gallisepticum (MG) bacterin on a multiple-age site endemically infected with MG.

A commercially available inactivated Mycoplasma gallisepticum (MG) bacterin was administered to chickens on a multiple-age farm endemically infected with MG. A total of 3400 MG-free pullets were vaccinated with the MG bacterin at 19 weeks of age, and 4300 unvaccinated pullets served as controls. The vaccinated group became serologically positive by the rapid plate agglutination (RPA) test within 3 weeks, and the unvaccinated group became positive in 7 weeks. The hemagglutination-inhibition test responses were observed at approximately the same time as the RPA in both of the groups. Egg production and mortality through 50 weeks of age did not differ significantly between the two groups. MG was isolated from birds of the vaccinated and control groups near the termination of the study.

Histologic characterization of the involuting bursa of Fabricius in single-comb white Leghorn chickens.

Bursas from specific-pathogen-free white leghorn chickens of both sexes were examined at several intervals from hatching to 28 weeks of age. No histologic alterations other than scattered atrophic or cystic follicles were observed through 20 weeks. Obvious involution, first noted at 24 weeks, was in early stages in females and quite advanced in males. Involution was essentially complete by 26 weeks, and only cicatrized vestiges of bursas were present at 28 weeks of age. Gross manifestations included bursal atrophy, variable yellowish discoloration of the mucosa, and matting or total loss of identity of the mucosal plicae. Histologic characteristics of involution are summarized by the following approximate sequence: atrophy and exfoliation of plica epithelium; subepithelial stromal fibrosis; fusion and ultimate collapse of plicae; liquefactive necrosis of first medullary then cortical elements of follicles, which seemed to progress from basal to apical portions of the plicae; progressive proliferation of stromal connective tissue and infiltration of macrophages into areas occupied by necrotic follicles; and, finally, complete fibrous organization of luminal debris, leaving a firm nodule formed by a contracted muscularis surrounding the cicatrized remains of the mucosa.

Comparative susceptibility of embryonated hen eggs and pig lung alveolar macrophages to chlamydial infection.

Pig lung alveolar macrophages provided a suitable cell culture system for primary isolation of ovine chlamydia and sustained their growth through several passages. In centrifuged preparations, titres of established strains compared favourably with those obtained in fertile eggs, and in parallel titrations on primary isolation, evidence of chlamydial infection was detectable in macrophages several days earlier than in eggs.

Growth of chlamydia in pig lung alveolar macrophages; preparation of macrophages and demonstration of growth.

The harvesting, storing and utilisation in tissue culture of lung alveolar macrophages from 2-3 weeks old piglets were investigated. An average yield of 4 X 10(8) cells was obtained, which in culture usually remained healthy for at least 8 days. In liquid nitrogen at -173 degrees C about 50% of the cells were still viable after 3 months. Pig cells sustained the growth of ovine Chlamydia psittaci and a rising titre was demonstrated over 4 passages.

Experimental chlamydial pneumonia in pigs.

Naturally occurring disease in pigs associated with chlamydial infections has not been reported in Britain, though evidence of chlamydial challenge has been demonstrated in two separate serological surveys. An isolate of Chlamydia psittaci (28/68) from an ovine pneumonia produced pneumonia in pigs following intratracheal inoculation. Transient pyrexia at 24 hr was followed by increased respiratory rates and inappetance which lasted for a further 48 hr in challenged pigs. Histologically acute exudative reactions were present in the lungs by 24 hr with proliferative changes predominating after 10 days. While variations in the concentrations of inocula were reflected by corresponding increases and/or decreases in gross lung damage, clinical signs and histological reactions were unaltered. Chlamydial organisms were recovered only from lung tissues.

Immunity following inoculation of the H120 and H52 vaccine strains of infectious bronchitis virus into the crop of the domestic fowl.

The serological responses and protection associated with inoculation of the HI20 and H52 vaccine strains of infectious bronchitis virus (IBV) into the trachea and directly into the crop of chickens were compared. Intratracheal inoculation at 3 weeks of age with HI20 resulted in the moderate log2 haemagglutination inhibition (HI) titres of 6, previously found to be characteristic of this highly attenuated vaccine strain of IBV. More than 80% of these birds gave a positive reaction to the agar gel precipitin (AGP) test. These precipitin responses had waned in most birds by the time they were re-vaccinated with H52 at 11 weeks of age, when moderate but somewhat higher HI titres of 7 and 8 were obtained and 70% of the birds were AGP-positive. At 15 weeks of age, the inoculates and susceptible controls were challenged intravenously with H52. The intratracheally inoculated birds were fully protected against this challenge which severely damaged the kidneys of 80% of the controls. Crop inoculation of HI20 and H52 failed to produce circulating antibody as measured by the HI and AGP tests. Intravenous challenge, however, showed that the kidneys of 50% of the crop inoculates resisted the challenge which severely damaged the kidneys of 80% of the controls, demonstrating a degree of protection in the absence of circulating antibody.

Field observations on serological responses to vaccine strains of infectious bronchitis virus administered by coarse spray and via the drinking water.

The agar gel precipitin (AGP) and haemagglutination inhibition (HI) responses to vaccination with infectious bronchitis virus (IBV) were investigated in three flocks. The vaccines were administered by coarse spray in one large flock of commercial layers and via the drinking water in two smaller flocks of broiler breeders. In two flocks, one vaccinated by coarse spray and one vaccinated via the drinking water, the chicks had high levels of maternal antibody and failed to respond serologically to the primary vaccination at 2 to 3 weeks of age. However, a vigorous antibody response, probably due to cycling vaccine virus, was demonstrated at 6 to 7 weeks of age after the maternal antibodies had waned. By contrast the chicks in the third flock, with low levels of maternal antibody at 2 weeks, responded promptly and vigorously to the primary vaccination. Passive immunity, mediated by maternal antibodies, was thought to have inhibited the initial AGP and HI responses to vaccine in the first two flocks. Between 10 and 20 weeks, in spite of repeated vaccination, the IBV geometric mean HI titres did not increase and the number of AGP-positive sera remained low. In the densely populated group receiving the coarse spray, the AGP response was virtually absent and in those smaller groups of birds receiving water-borne vaccine only 33% became AGP-positive. As in the young chicks with passive immunity, active immunity in the older birds, associated either with deliberate vaccination or inadvertent cycling vaccine virus, was thought to have inhibited the serological responses to the second and third exposures to vaccine. There was a marked rise in the number of AGP-positive birds (84% and 68% respectively) at 25 weeks of age in two flocks. HI test results indicated that this was due to exposure to a field strain of IBV in one flock and to a cycling vaccine strain in the other. The AGP results at this time were similar in both of these flocks and this test could not be used to differentiate the responses to the different types of IBV. Only 25% of the sera were AGP-positive at 25 and 30 weeks in the third flock and therefore in such a flock any sudden rise to above 50% in the number of AGP-positive birds might be attributed to recent exposure to field or vaccine strains of IBV.

Immunity following vaccination with the H120 strain of infectious bronchitis virus via the drinking water.

Administration of the H120 vaccine strain of infectious bronchitis virus (IBV) via the drinking water caused mild respiratory symptoms in six out of 57 susceptible 3-week-old chickens and 45 became positive to the agar gel precipitin (AGP) test for IB. This was associated with complete protection against subsequent intratracheal challenge with the H52 strain of IBV at 11 weeks of age. The vigorous AGP response to H120 recorded here in susceptible birds contrasts with previous reports of failure of precipitins to appear following administration of water-borne IB vaccines to 1-day-old and 2-week-old chicks carrying maternally derived antibodies. We have previously shown that artificial passive immunity suppresses the AGP response to intravenous challenge with the H52 strain of IBV. Natural passive immunity, mediated by maternal antibodies, may similarly have been responsible for the failure of precipitins to appear following vaccination under field conditions.

Active and passive immunisation against nephritis induced by an avian infectious bronchitis virus.

Intranasal vaccination with the H120 strain of infectious bronchitis virus (IBV) produced serum neutralisation indices of three or more in nine out of 12 birds. This afforded complete protection against intravenous challenge with the nephritogenic H52 strain of IBV and prevented the multiplication of virus in the kidney. Passive immunisation with homologous convalescent serum protected the kidney but not the respiratory tract against similar challenge. The frequency of virus isolations from the kidney was reduced, the agar gel precipitin response lowered and the haemagglutination inhibition response abolished.

An inverse age resistance of chicken kidneys to infectious bronchitis virus.

Ten-fold serial dilutions of the H52 vaccine strain of infectious bronchitis virus were inoculated intravenously into 3-week-old and 10-week-old chickens. The severity of the histological lesions in the kidney was graded and described. The younger birds were much more resistant to the nephritogenic effects of the virus. Although very small doses of virus caused nephritis, no marked dose-related response was demonstrated in either age group.

Experimental pneumonia in red deer (Cervus elaphus L) produced by an ovine chlamydia.

An isolate of Chlamydia psittaci from ovine pneumonia produced extensive pneumonia in red deer after endobronchial inoculation. Associated clinical signs lasting for several days included pyrexia, inappetance, increased pulse and respiration rate, and physical distress after handling, but no coughing or upper respiratory symptoms. Histologically, an acute exudative reaction was present after two days, and an early proliferative response after seven days. Both the clinical and pathological responses were more marked than those usually associated with chlamydial pneumonia in other large animals after endobronchial infection. A small survey for chlamydial antibody in wild red deer was negative.

An outbreak of malignant catarrhal fever in red deer (Cervus elephus).

Nine of 15 housed red deer developed an acute disease. Six died and three were killed when severely affected. The clinical and post mortem changes suggested a diagnosis of malignant catarrhal fever (MCF) which was consistent with the pantropic lymphoproliferative histopathological lesions observed. Attempts to isolate an agent or transmit the condition to cattle failed. The relation of the vasculitis to the pathogenesis of the disease and the susceptibility of red deer are discussed.