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.     

Clinical, cultural, and serologic observations of avian mycoplasmosis in two chicken breeder flocks.

Two chicken breeding flocks from different breeding lines were studied serologically and culturally for Mycoplasma gallisepticum (MG) throughout their growing and laying period. Infection was proven by successful isolation of MG from both breeders and progeny originating from these two flocks. Observations of these flocks which were serologically and culturally negative for Mycoplasma synoviae (MS) further disclosed that: 1) negative plate tests of large numbers of day-old progeny may sometimes be found in flocks known to be infected with MG; 2) it may be very difficult to isolate MG consistently from some infected flocks; 3) overgrowth of M. gallinarum may interfere with successful cultivation of MG; 4) a persistent breeder flock reactor rate of greater than 10-20% but less than 80-100% for a 4-to-12-week period is a strong indication of MG infection despite weak or negative MG hemagglutination-inhibition (HI) test results; and 5) antibodies for all strains of MG may not react equally to the standard USDA MG-HI antigen.     

Control of avian mycoplasma infections in commercial poultry

Control of pathogenic avian mycoplasmas can consist of one of three general approaches: Maintaining flocks free of infection, medication, or vaccination. Maintaining flocks free of pathogenic mycoplasmas consists of maintaining replacements from mycoplasma-free sources in a single-age, all-in all-out management system. Good biosecurity and an effective monitoring system are necessary aspects of this program. Medication can be very useful in preventing clinical signs and lesions, as well as economic losses, but cannot be used to eliminate infection from a flock and is therefore not a satisfactory long-term solution. Vaccination against Mycoplasma gallisepticum (MG) or M. synoviae (MS) can be a useful long-term solution in situations where maintaining flocks free of infection is not feasible, especially on multi-age commercial egg production sites.     

Breeder turkey hens seropositive and culture-negative for Mycoplasma synoviae.

Four flocks of clinically normal turkey breeder hens were shown to have suspect and positive Mycoplasma synoviae (MS) hemagglutination-inhibition (HI), enzyme-linked immunosorbent assay, and, in some cases, serum plate agglutination serology in the absence of MS isolation. In all cases, HI serology for Mycoplasma gallisepticum (MG) and M. meleagridis was negative. Acholeplasma laidlawii was isolated from some hens in each of these MS-seropositive culture-negative flocks. Immunoblotting was used to help determine if this positive MS serology was a result of cross-reactive antibodies to A. laidlawii or to some other Mycoplasma species. When sera from two of the flocks were reacted with MS antigen in immunoblotting, a strong and characteristic MS immunoblot profile was seen. Immunoblotting gave no evidence of a strong antibody response to A. laidlawii, M. iowae, or MG. This suggests the presence (or earlier presence) of MS in these flocks that is difficult to isolate by routine methods. Furthermore, this work shows that immunoblotting can be an important tool in the diagnosis of poultry diseases.     

Maintenance of a captive flock of house finches free of infection by Mycoplasma gallisepticum

Since the beginning of an epidemic of conjunctivitis in wild house finches caused by Mycoplasma gallisepticum (MG), all captive colonies established by capturing free-ranging house finches from the eastern population have also either been infected at the time of capture or developed infection shortly after capture. In an attempt to avoid this infection in captive flocks being maintained for studies of the finches' behavior and ecology, we compared two different flock management strategies and were able to prevent the development of mycoplasmal conjunctivitis with one of the strategies. Single-sex flocks were built by introducing only seronegative wild-caught birds showing no clinical signs of conjunctivitis and covering their outdoor flight cages with netting to prevent interaction with other wild birds although only the female flocks were initially treated with a 6-wk course of tylosin tartrate (0.3 mg/ml). The female flocks never developed conjunctivitis although the disease did develop in the male flocks. Furthermore, serologic assessments of the healthy flock by serum plate agglutination assays for MG indicated that the females remained free of MG infection in the final 7 wk of the study, during which they were unmedicated. We conclude that any low-level MG infection not diagnosed by the initial test for seroconversion was cleared by the prolonged drug treatment.     

Experimental infection of chickens and turkeys with Mycoplasma gallisepticum reference strain S6 and North Carolina field isolate RAPD type B

During an epidemic of mycoplasmosis in chicken and turkey flocks in North Carolina between 1999 and 2001, isolates of Mycoplasma gallisepticum (MG) from affected flocks were characterized by random amplification of polymorphic DNA (RAPD), and eight distinct RAPD types were identified. MG RAPD type B accounted for more than 90% of the isolates and was associated with moderate-to-severe clinical signs and mortality. The virulence of MG RAPD type B for chickens and turkeys was compared with sham-inoculated negative controls and MG S6 (a virulent strain)-inoculated positive controls. Clinical signs occurred in chickens and turkeys inoculated with either MG RAPD type B or MG S6. However, they were not as frequent or severe as those seen in naturally affected flocks, and there was no mortality in the experimental groups. Based on gross and microscopic findings, MG RAPD type B was equal to or more virulent than MG S6. All MG-inoculated birds were culture and PCR positive at 7 and 14 days postinoculation (PI). Among serological tests, the serum plate agglutination test was positive for the majority of chickens and turkeys (58%-100%) infected with either strain of MG at both 7 and 14 days PI. The hemagglutination inhibition test was negative for all birds at 7 days PI and positive for a few chickens (8%-17%) and several turkey sera (40%-60%) at 14 days PI. Only a single serum was positive by enzyme-linked immunosorbent assay (an MG S6-infected turkey) at 14 days PI.     

Economic impact of Mycoplasma gallisepticum and M. synoviae in commercial layer flocks

An egg-production function was constructed, using data collected from 366 commercial layer flocks in California, to predict the impact of Mycoplasma gallisepticum (MG) and M. synoviae (MS) on egg production while controlling for confounding factors. In the first and second cycles, respectively, an MG-infected flock produced 12 and 5 fewer eggs per hen than an uninfected flock. Flocks that became infected with MG after F-strain vaccination produced 6 eggs/hen more than unvaccinated infected flocks in the first cycle, but no significant difference was observed between such groups in the second cycle. No association was found between MS-infection and egg production. Commercial layer producers in Southern California lost an estimated 127 million eggs because of MG in 1984. This lost egg production and associated MG-control-program costs amounted to an estimated financial loss of approximately $7 million. This represented a loss of approximately $6 million in consumer surplus.     

Risk Factors Associated with Salmonella Status of Broiler Flocks Delivered to Grow‐Out Farms

In a prospective field observational study in the southeastern USA, we sampled gastrointestinal (GI) tracts from chicks of 65 broiler flocks delivered to conventional grow‐out farms for rearing. The flocks were hatched at seven broiler hatcheries. The mean within‐flock prevalence of Salmonella‐positive samples was 6.5% and ranged from 0% to 86.7%. Of the 65 flocks studied, 25 (38.5%) had at least one Salmonella‐positive sample. Accounting for confounding variability among the hatcheries and broiler companies, we tested whether the probability of detecting Salmonella in GI tracts of the chicks delivered was associated with certain characteristics of parent breeder flocks; hatchery production volume; hatchery ventilation system; hatchery egg‐room conditions; egg incubation, candling, hatching, eggshell and bird separation, and bird‐processing procedures; management of hatchery‐to‐farm transportation; day of week of hatch; weather conditions during transportation; or season of the hatch. Two risk factor models were adopted. The first model indicated that a greater number of parent flocks, manual separation of eggshell and bird, and a greater amount of fluff and feces on tray liners used during hatchery‐to‐farm transportation at delivery were associated with increased probability of detecting Salmonella in chick GI tracts, whereas a greater number of birds in the delivery vehicle was associated with decreased probability. The second model indicated that broiler flocks hatched on Tuesdays versus either Mondays or Thursdays (with no hatches on Wednesdays, Fridays or week‐ends), increased average hatchability of the eggs from the parent flocks, and greater amounts of fluff and feces on the transport tray liners at delivery were all associated with increased probability of detecting Salmonella in chick GI tracts. The results of this study suggest potential management decisions to lessen Salmonella contamination of broilers supplied by commercial hatcheries and areas for further research.     

Indirect micro-enzyme-linked immunosorbent assay for the detection of antibodies to Mycoplasma synoviae and M. gallisepticum

The sensitivity and specificity of the indirect micro-enzyme-linked immunosorbent assay (ELISA) was compared with that of the rapid serum-plate test (RSPT) and the hemagglutination-inhibition test (HIT) in detecting antibodies to Mycoplasma gallisepticum (MG) and M. synoviae (MS). Membrane antigens of MG strain S6 and MS strain NEL 61800 were used. ELISA was performed with single MS and single MG antigens and a combined MS/MG antigen. The MS-ELISA was as sensitive as the MS-RSPT and more sensitive than and as specific as the MS-HIT in detecting antibodies to MS. The MG-ELISA was less sensitive than the MG-RSPT and slightly less sensitive than the MG-HIT in detecting antibodies to MG in chickens experimentally infected with MG R strain but more sensitive in detecting antibodies in chickens infected with MG F strain. MG-ELISA resulted in fewer cross-reactions than the MG-RSPT but more than the MG-HIT. The combined MG/MS-ELISA was as sensitive as the ELISA with its individual antigen components. No nonspecific reactions were observed with sera from MG/MS-free flocks. The combined MG/MS-ELISA was found to be a practical screening test for antibodies to both MS and MG. Further improvement of the sensitivity and the specificity of the MG antigen is desirable.     

Meningoencephalitis in commercial meat turkeys associated with Mycoplasma gallisepticum.

Mycoplasma gallisepticum (MG) infection was diagnosed in three different flocks of 12-to-16-week-old commercial meat turkeys displaying torticollis and/or opisthotonos. MG was isolated from the brain, air sacs, trachea, and sinus of one bird with neurological signs. Histological examination of brains in all three cases revealed moderate-to-severe encephalitis with lymphoplasmacytic cuffing of vessels, fibrinoid vasculitis, focal parenchymal necrosis, and meningitis. Birds with neurological signs were seropositive for MG by the serum-plate agglutination and hemagglutination-inhibition tests. The encephalitic form of MG has been described previously but is rarely mentioned in the current literature.     

Laboratory infection of house sparrows (Passer domesticus) with Mycoplasma gallisepticum and Mycoplasma synoviae

House sparrows were infected by aerosol with Mycoplasma gallisepticum (MG) or M. synoviae (MS). MG was reisolated from 5 to 11 sparrows 10 days postinfection, but infection appeared to be temporary. Mycoplasma-free chickens reared in the experimental house became infected with MG during the trial. MS was recovered from only one sparrow. Serological tests were unsatisfactory for diagnosing infected birds. The results suggest that house sparrows may be temporary biological carriers of MG.     

Salmonella Brandenburg: case-control survey in sheep in New Zealand

AIM: To identify environmental, management and animal risk factors associated with the occurrence and severity of disease attributed to Salmonella Brandenburg infection in sheep. METHODS: A retrospective case-control study was undertaken, and details of disease prevalence and farm management methods were collected from two affected regions in southern New Zealand. Associations between possible risk factors and disease attributed to S. Brandenburg were evaluated using odds ratios. A case-control approach was used to assess risk factors associated with outbreaks of disease at the farm level, using unaffected farms as controls. A separate analysis was then performed within affected farms only, to assess risk factors associated with increasing severity of disease. RESULTS: Data were collected from 405 farms containing a total of 1,170,737 ewes. Of the 177 case farms, 172 (97%) had diseased mixed-age ewes, 78 (45%) had diseased two-tooth ewes and eight (5%) had diseased hoggets. Increased odds of farms being affected with S. Brandenburg were reported for farms that strip-grazed sheep, and as total numbers of sheep increased. Reduced odds of being affected were associated with feeding crops, and hilly terrain on those farms not feeding crops. Within affected farms, increased severity of disease was associated with strip-grazing and feeding hay in TT flocks, and later removal of rams in MA flocks. Reduced severity of disease was associated with shearing or crutching after July, and vaccination of sheep against Salmonella spp. CONCLUSIONS: Salmonella Brandenburg occurred in flocks that reported using intensive farming methods and that maintained high numbers of sheep. CLINICAL RELEVANCE: Risk factors associated with the occurrence and severity of the disease due to S. Brandenburg have been identified. This information is necessary to identify preventative and control measures that may be effective in reducing the risk of disease.     

Infection of turkeys with Ornithobacterium rhinotracheale and Mycoplasma synoviae

Within 1 mo, two separate outbreaks of respiratory disease occurred in two flocks on the multiage market turkey farm in Slovenia. More severe dinical signs and higher mortality were observed in male birds. Ornithobacterium rhinotracheale (ORT) was isolated in pure culture from tracheas of the affected birds in both outbreaks. Commercial enzyme-linked immunosorbent assay test showed the presence of antibodies to ORT in sera of birds from both clinically affected flocks and also in two flocks of younger birds without clinical sings. Immunoblotting with ORT culture isolated during the outbreak as an antigen confirmed the presence of antibodies to ORT in sera of turkeys of all four flocks examined. In addition, three different serologic assays also detected antibodies to Mycoplasma synoviae (MS) in three out of four flocks. The concomitant infection with MS did not show an obvious effect on mortality rates nor on the antibody response against ORT. Younger birds appeared to be less susceptible to ORT pathogenicity because in those flocks the infection was subclinical.     

Comparison of egg yolk and serum for the detection of Mycoplasma gallisepticum and M. synoviae antibodies by enzyme-linked immunosorbent assay

Egg yolk was evaluated in the enzyme-linked immunosorbent assay (ELISA) as an alternative source of antibodies for detection of Mycoplasma gallisepticum (MG) and M. synoviae (MS) infections in chickens. There was no statistically significant difference (P greater than 0.05) between the ELISA geometric mean titers (GMTs) of saline-diluted egg yolk and chloroform-extracted egg yolk, and both preparations had a high correlation coefficient (0.87 for MG; 0.97 for MS). The saline-diluted and chloroform-extracted yolk had a relative sensitivity of 90% and specificity of 98% in the MG ELISA; in MS ELISA they were 100% and 96%, respectively. Hemagglutination-inhibition (HI) results with chloroform-extracted samples were satisfactory, but those with saline-diluted samples were not. Neither preparation was satisfactory for use in the rapid plate agglutination (RPA) test. A 1-ml sample of yolk was compared with the whole-yolk method. The chloroform-extracted whole yolk yielded a significantly higher (P less than 0.05) GMT in the MG ELISA; however, there was no statistically significant difference (P greater than 0.05) between GMTs yielded by the two procedures in the MS ELISA. The correlation coefficients for the two sampling methods were 0.73 for MG ELISA and 0.63 for MS ELISA. ELISA detected no statistically significant difference (P greater than 0.05) between GMTs of serum and chloroform-extracted yolk from individual birds. Results with the HI test were comparable to those with ELISA on the same samples. The RPA test yielded comparable results on the serum samples. No statistically significant differences (P greater than 0.05) were observed in HI or ELISA antibody levels between egg-yolk samples and sera on random samples collected from nine flocks that were MG- and MS-free or were infected with MG, MS, or both; however, egg-yolk samples tended to have slightly higher titers than sera in both tests. The optimum screening dilution of chloroform-extracted yolk for detecting MG and MS antibodies by ELISA was 1:800.     

A case-control study on scrapie in Norwegian sheep flocks

Scrapie first was detected in indigenous sheep in Norway in 1981, and from 1995 to 1997 an increase in the number of flocks with scrapie cases was recorded. These flocks were mainly in one geographical region. A study to identify risk factors for scrapie was conducted. The study had three frequency-matched controls selected for every case within the same Veterinary District. A questionnaire was submitted to 176 sheep flocks (42 had been scrapie flocks). The data obtained by the questionnaire were linked to data collected from governmental and industry registers. After imputing missing data using single random imputation, the statistical analysis was performed using multivariable conditional logistic regression.

Purchase of female sheep from scrapie flocks, sharing of rams, or sharing of pastures between different flocks were the risk factors associated with the occurrence of scrapie. Of factors potentially sustaining and promoting the infection in the flock, number of winter-fed sheep, number of buildings for housing sheep, rams and ewes shared room during mating period and increase in the flock size were associated with scrapie. We interpret these findings to show that factors involving transfer of sheep between flocks or direct contact between sheep of different flocks are important for the spread of scrapie. Management factors are important for the development of scrapie. However, it was not possible to discriminate between the different management factors in this study at the flock level. Also, factors indicating awareness and interest of the farmer (as well as willingness to contact a veterinarian for diseased sheep) were related to the detection of scrapie in the flock.     

Poor serologic response to upper respiratory infection with Mycoplasma synoviae in turkeys

Mycoplasma synoviae (MS) was isolated from a flock of commercial tom turkeys in which a small percentage of the birds exhibited clinical signs and lesions typical of MS synovitis. However, serologic testing of such flocks revealed poor to inconsistent reactivity by agglutination, enzyme-linked immunosorbent assay (ELISA) or hemagglutination inhibition; isolation of MS from such flocks proved to be very difficult. Turkeys were challenged with one of the isolates (K4463B) either by aerosol or systemically by a combination of intravenous, foot pad, and eyedrop routes. Turkeys challenged by the systemic route responded normally to all serologic tests, whereas those challenged by aerosol either responded very poorly on all serologic tests or were seronegative up to 6 wk postchallenge even though they were positive for MS by tracheal culture. These results suggest that turkeys may harbor an upper respiratory infection with MS while remaining serologically negative.     

An outbreak of Mycoplasma synoviae infection in North Carolina turkeys: comparison of isolates by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and restriction endonuclease analysis.

Mycoplasma synoviae (MS) isolates made in 1988-89 from turkey flocks in North Carolina, Missouri, and Ontario, Canada, were compared with each other and MS reference strains (WVU-1853, F10-2AS, Neb-3S, and K1968) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of cell proteins and restriction endonuclease analysis (REA) of DNA. SDS-PAGE and REA indicated considerable homology among MS reference strains and recent field isolates. However, sufficient differences were resolved to identify the MS reference strains as different from each other and the field isolates, and to classify seven of nine recent field isolates as a cluster of nearly identical strains. The results suggest that flocks infected with members of the cluster were epizootiologically associated, possibly by a common or point source of infection.     

Risk Factors Associated with Detection of Salmonella in Broiler Litter at the Time of New Flock Placement

In this study, we investigated risk factors associated with the probability to detect Salmonella in samples of litter collected within 2 h prior to new flock placement in 76 grow‐out houses on 38 conventional broiler farms located in the US states of Mississippi, Alabama and Texas. We evaluated characteristics of location and layout of the farm; area adjacent to and surrounding the house; house construction; condition and type of equipment in the house; litter management and other production, sanitation, visitation and biosecurity practices; non‐broiler animal species on the farm; and weather conditions on the 3 days leading up to flock placement. Logistic regression was used to model the relationships between probability to detect Salmonella in litter and potential risk factors. In the screening process, each risk factor was evaluated as a single fixed effects factor in a multilevel model that accounted for variability among the sampled farms and their production complexes and companies. Of almost 370 risk factors screened, 24 were associated with the probability to detect Salmonella in litter. These were characteristics of the surroundings of the house, house construction and conditions, litter management, length of downtimes between flocks in the house, biosecurity and farm location. After investigation of collinearity between these variables and building of models for important risk factor categories, the list of candidate variables for the final model was refined to eight factors. The final model demonstrated that a higher probability of detecting Salmonella in litter was strongly associated with the use of wood to construct the base of the walls or to cover the inside of the broiler house foundation, and with the use of fresh wood shavings to top‐dress or completely replace the litter between flocks.     

Effects of housing on the incidence of visna/maedi virus infection in sheep flocks

The incidence of seroconversion to visna/maedi virus (VMV) infection and its relationship with management and sheep building structure was investigated in 15 dairy sheep flocks in Spain during 3–7 years. Incidence rates were 0.09 per sheep-year at risk in semi-intensive Latxa flocks and 0.44 per sheep-year at risk in intensive Assaf flocks and was greatest for the one year old Assaf replacement flock. Separate multivariable models developed for replacement and adult flocks indicated that in both cases seroconversion was strongly associated to direct contact exposure to infected sheep and to being born to a seropositive dam. The latter effect was independent of the mode of rearing preweaning and the risk of seroconversion was similar for sheep fed colostrum and milk from a seropositive or a seronegative dam. These results are further evidence of the efficiency of horizontal VMV transmission by close contact between sheep and also suggest a inheritable component of susceptibility and resistance to infection. In contrast, indirect aerogenous contact with seropositive sheep was not associated with seroconversion as evidenced in replacement sheep housed in separate pens in the same building as adult infected sheep for one year. Consequently, VMV may not be efficiently airborne over short distances and this is important for control of infection. Moreover, there was no relationship between seroconversion and shed open areas. The latter could be related to having examined few flocks in which high infection prevalence dominated the transmission process while ventilation, may depend on a variety of unrecorded factors whose relationship to infection needs to be further investigated.     

Detection of Oestrus ovis and associated risk factors in sheep from the central region of Yucatan, Mexico

A cross-sectional epidemiologic study was conducted in order to detect the presence of and to estimate the seroprevalence of Oestrus ovis L. infection in flocks of sheep from the central region of the state of Yucatan, Mexico. The risk factors associated with disease were also identified. A sample size of 10 animals per farm was used to detect seropositive animals, considering a 30% prevalence and 95% confidence level. Blood samples of 689 sheep from 88 flocks were collected and a questionnaire with questions about the flock and the host was applied. The thin layer immune assay test was used. The risk factors were screened using logistic regression procedures. 77% of the flocks had at least one-positive animal with antibodies against O. ovis. The overall seroprevalence and standard error was 30.6 +/- 3.5%. Only flock size and sheep nose color showed association (P < 0.05) with the disease. The odds ratios for flocks with less than 11 and with 11 to 25 sheep, as related to herds with 25 or more sheep, were 0.74 and 1.73, respectively. Sheep with dark noses had a higher risk (OR = 1.46) compared with sheep having light noses (P < 0.05).