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.     

The efficacy of three commercial Mycoplasma gallisepticum vaccines in laying hens

The efficacy of three commercial Mycoplasma gallisepticum (MG) immunizing agents-a bacterin, a recombinant fowlpox-MG vaccine, and a live F-strain vaccine-was compared in specific-pathogen-free hens in egg production. Three groups of 25 chickens were vaccinated with one of the vaccines at 10 wk of age and 25 birds were not vaccinated. At 25 wk of age (and approximately 50% egg production), 20 birds from each of the three vaccinated groups and 15 nonvaccinated controls were challenged with virulent R-strain via aerosol; the birds were necropsied and evaluated at 10 days post-challenge. The MG bacterin and live F-strain vaccinations were both protective and resulted in significant differences in air sac lesions, tracheal lesions, and ovarian regression compared to the nonvaccinated controls and the recombinant fowlpox-MG vaccine (P < or = 0.05). The evaluation of ovarian regression is a useful method of testing the efficacy of MG vaccines in laying hens.     

The comparison of an aqueous preparation of tilmicosin with tylosin in the treatment of Mycoplasma gallisepticum infection of turkey poults.

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.     

Evaluation of factors associated with infection of commercial layers with Mycoplasma gallisepticum and M. synoviae

Information on factors possibly associated with the risk of infection with Mycoplasma gallisepticum (MG) or M. synoviae (MS) were collected from nearly 400 layer flocks in California. Factors associated with the probability of flock infection with either MG or MS were identified, and their magnitude was quantified by statistical analysis. More frequent administration of several vaccines was associated with decreased probability of both MG and MS infection of flocks. Also identified were housing or hygiene factors and system of management (i.e., multiple-age status) that could reduce the probability of infection of flocks with mycoplasma. The change in probability of MG infection resulting from modifying certain management factors was examined.     

The effect of killed Salmonella enteritidis vaccine prior to induced molting on the shedding of s. enteritidis in laying hens

Effects of administering killed Salmonella enterica serovar enteritidis (SE) vaccines to laying hens prior to induced molting on egg production and on shedding of SE were investigated. Forty hens were vaccinated with one of two SE vaccines available commercially in the United States and Japan. Twenty-five days after vaccination, feed was withdrawn for 2 wk from 20 vaccinated plus 10 unvaccinated hens to induce molt. Four days after molt induction, all hens were challenged with a dose of 2.4 X 10(9) of SE. For the 25 days following administration of the SE bacterins, egg production in vaccinated hens showed approximately a 15% decrease. After molt induction, egg production in molted hens ceased and then returned to normal levels 8 or 9 wk postvaccination. Through the 3-mo experimental period, the decreases in numbers of eggs laid in the unvaccinated/molted group and two vaccinated/molted groups were 225 (26.2%), 245 (28.4%), and 274 (31.9%), respectively, compared with 860 in the unvaccinated/unmolted group. There was no significant difference in egg lay at the P < 0.05 level among the former three groups. Hens in the vaccinated/molted groups shed about two logs less SE than hens in the unvaccinated/molted group 3 14 days postchallenge (P < 0.05 or 0.01). These results indicate that vaccination prior to induced molting might be effective in preventing the exacerbation of SE problems within flocks in which the potential for SE contamination may exist.     

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.     

The spread of Corynebacterium pseudotuberculosis infection to unvaccinated and vaccinated sheep

SUMMARY The decrease in the prevalence of Corynebacterium pseudotuberculosis after two generations of vaccination against the disease it causes, was used to estimate the rate of control of caseous lymphadenitis (CLA). Three groups of 150 sheep, of which 50 in each group were artificially infected with C pseudotuberculosis and 100 in each group were uninfected sheep, were run separately for 40 months and shorn 5 times to promote the spread of CLA. One lot of 50 infected sheep and 2 lots of 100 uninfected sheep were vaccinated against CLA. The rate of spread of CLA was recorded. Sheep vaccinated against CLA and naturally exposed to infection had a 74% lower infection rate than unvaccinated sheep. Sheep vaccinated against CLA and exposed to only vaccinated infected sheep had a 97% lower infection rate. Unvaccinated sheep had a 76% infection rate, with 77% of the transmission occurring at the 4th and 5th shearings, without any discharging CLA abscesses being observed. This study supports the view that in Australian wool producing flocks, CLA spreads mainly from sheep with discharging lung abscesses to sheep with shearing cuts. Vaccinated sheep infected with CLA have 96% fewer lung abscesses compared with unvaccinated infected sheep and are therefore less likely to spread this disease to other sheep .     

Comparison of culture, PCR, and different serologic tests for detection of Mycoplasma gallisepticum and Mycoplasma synoviae infections

In this study, the technical performance of culture, two commercially available polymerase chain reaction (PCR) tests, rapid plate agglutination (RPA) test, hemagglutination inhibition (HI) test, and eight commercially available enzyme-linked immunosorbent assays (ELISAs) were compared for the detection of avian mycoplasma infections from 3 days postinfection (d.p.i.) through 35 d.p.i. The tests were carried out on samples from specified pathogen-free layers that were infected at 66 wk of age with recent Mycoplasma synoviae (MS) and Mycoplasma gallisepticum (MG) field strains, MS and MG ATCC strains, and Mycoplasma imitans (MIM), respectively. Results showed a high percentage of positive samples in the homologous infected groups and a high percentage of negative samples (100%) in the uninfected and heterologous infected groups during 35 d.p.i. of both culture and PCR tests. For the group infected with the MG 15302 ATCC strain, serology was more sensitive than bacteriology. All MG and MS tests, with the exception of MG ELISA kit D showed a lower percentage of positive samples during 35 d.p.i. for the detection of the MG and MS ATCC strain infection compared with that of the field strains. Also, the number of cross-reactions (false positives) in the serologic tests was lower after infection with an ATCC strain than after an infection with the MG or MS field strain. Contradictory to other studies, the ELISAs and the RPA test using undiluted serum showed a relatively high number of false-positive results. The MG ELISAs (except ELISA kit D) showed more false-positive results (up to 37%) in the MIM-infected group than in the MS-infected groups. This was not unexpected, as MIM and MG have a close antigenic relationship. The results of the serologic tests in this study showed that a certain level of false-positive results can be expected in about any serologic test. Although the level of false-positive results varied between several serologic tests, this study showed that it is not advisable to rely completely on one test (system) only.     

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.     

Survey of Toxoplasma antibodies among sheep in western United States

A survey was conducted to determine the prevalence of toxoplasma antibodies among breeding ewes and among lambs slaughtered for food in western United States. Each serum was tested by the indirect hemaglutination method, using microtiter technique. Agglutination (greater than or equal to 2 +) at the 1:64 dilution was considered to be a positive reaction. Of 2,164 ewes from 18 flocks tested in California, 523 (24%) were seropositive for Toxoplasma gondii, with prevalence rates among flocks ranging from 4 to 51%. In 9 of those flocks, 1,495 ewes were stratified by whether ewes had lambed or were barren. On an overall basis, the antibody prevalence was similar (about 25%) in both groups, but there was a significant difference (P less than 0.05) in 1 flock in which 30% of the nursing ewes were seropositive, compared with 21% of the barren ewes. Of 1,056 market lambs from 19 lots tested, 85 (8%) were seropositive. The antibody prevalence in lambs tested at slaughter in California, by state of origin, were: Oregon, 11/51 (22%); Nevada, 32/159 (20%); Idaho, 12/147 (5%), and California, 30/699 (4%).     

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.     

Serological survey of infectious bursal disease virus serotypes 1 and 2 in California turkeys

The prevalence of two infectious bursal disease (IBD) viruses--serotype 1, of chicken origin, and serotype 2, of turkey origin--was studied in California turkeys. Serum samples were collected from 15 turkey flocks representing nine counties. The virus-neutralization test was used. Overall, only 15% of 342 samples were positive for serotype 1, whereas 89% were positive for serotype 2. However, 12 out of 15 flocks had a least one sample positive for serotype 1, and 14 out of 15 flocks had at least one sample positive for serotype 2. Flocks with antibodies to serotype 1 had low geometric mean titers (GMTs) (1.5 to 8.8) and low-to-medium prevalence rates (5 to 53.3%). Flocks with antibodies to serotype 2 had high GMTs (36.8 to 2048) and high prevalence rates (60 to 100%). Results of this study lead us to question the efficacy of IBD vaccination in turkeys.     

Pathogenicity of two strains of Mycoplasma gallisepticum in broilers

Strains F and R of Mycoplasma gallisepticum (MG) were compared in two laboratory trials for their relative pathogenicity in terms of inducing airsacculitis and antibody production to MG. Chickens exposed to the R strain had significantly higher incidence of air-sac lesions (P less than 0.05) and greater severity of airsacculitis than did chicks exposed to the F strain. In both trials, chickens vaccinated simultaneously with Newcastle disease-infectious bronchitis vaccine and exposed to MG had more severe lesions than did chickens exposed to mycoplasma alone. chickens exposed to the F strain had significantly lower geometric mean hemagglutination-inhibition antibody titers to MG than did chicks exposed to the R strain. Chickens vaccinated simultaneously with Newcastle disease-infectious bronchitis vaccine and exposed to R strain had significantly lower body weights than did chickens in the other group.     

Epidemiology and financial impact of fowl cholera in turkeys: a retrospective analysis

A retrospective study of the epidemiology and financial impact of fowl cholera (FC) in California meat turkeys during 1984 was performed. Data were collected from 64 flocks--23 FC-outbreak flocks and 41 controls (non-outbreak)--raised in the Central Valley of the state. Mean flock age at the time of the FC outbreak was 11.3 weeks. Flocks that reported a colibacillosis outbreak had increased odds (P = 0.11) of also having an FC outbreak. (This association may or may not indicate a cause-effect relationship.) There was no significant difference between FC-outbreak and control flocks in number of diseases reported, age at onset, or duration of diseases or syndromes except age at onset of roundheart disease. The relative mortality rates were 52% higher in FC-outbreak toms and 26% higher in FC-outbreak hens than in their controls. Medication costs were nearly tripled, and the relative condemnation rate was 60% higher in FC-outbreak flocks than in control flocks. The average costs of FC were nearly $0.40 per bird, or $18,750 per flock, in an outbreak flock of 50,000 birds, and $0.12 per bird, or $6000 per flock, in non-outbreak flocks vaccinated against FC.     

Serological profiles of commercial broiler breeders and their progeny. 2. Newcastle disease virus

Newcastle disease virus (NDV) hemagglutination-inhibition (HI) titers were determined for serum samples from eight commercial broiler breeder flocks and their progeny. The chickens sampled had been vaccinated and reared by different producers in different regions of the United States. Breeder flocks had the highest number of NDV-positive HI titers (greater than or equal to 1:10). Eighty percent or more of the samples from six of eight breeder flocks were positive; the geometric mean titers (GMTs) for those six breeder flocks ranged from 19 to 92. Only 3 of 8 broiler flocks had an increased frequency of positive titers and higher GMTs after vaccination. The frequency of positive titers was greater than 80% in only 2 of 8 of the oldest broiler flocks. The number of NDV-negative titers (less than 1:10) increased with age in most broiler flocks, even though all had been vaccinated once or more with live NDV vaccines.     

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).     

Characterization of a ts-1-like Mycoplasma galisepticum isolate from commercial broiler chickens

Several commercial broiler flocks in northeastern Georgia that were the progeny of the same parent flock (Flock 40) were diagnosed as Mycoplasma gallisepticum (MG) positive by serology, culture, and PCR. Flock 40 had been vaccinated with ts-11 live MG vaccine. Several isolates were obtained from the MG-positive broiler flocks, and these isolates were indistinguishable from the ts-11 vaccine strain by the molecular strain differentiation methods used. A pathogenicity study was performed to compare the virulence of one of the isolates, K6216D, to the ts-11 vaccine strain. K6216D elicited a significantly stronger antibody response and significantly increased colonization of the tracheas and air sacs. K6216D also elicited significantly greater air sac and tracheal lesions than the ts-11 vaccine strain at 10 and 21 days postinoculation (P < or = 0.05). This is the first report of a field case of the apparent reversion to virulence and vertical transmission of the ts-11 vaccine.     

Economic effects of subclinical chicken anemia agent infection in broiler chickens

To evaluate the economic effects of subclinical chicken anemia agent (CAA) infection on broiler performance, clinically normal broiler flocks were grouped into two categories: A) flocks in which none of 10 birds sampled at slaughter had antibody to CAA, and B) flocks in which six or more of 10 similarly sampled birds had CAA antibody. Production and performance parameters of 25 flocks in each category were compared. No statistically significant differences were found between category A and category B flocks in major production parameters such as sex, feed manufacturer, type of litter, stocking density, and age at slaughter. However, category A flocks achieved 13% (P less than 0.05) greater net income per 1000 birds, 2.0% better feed-conversion ratio (P less than 0.05), and 2.5% (P less than 0.05) greater average weight per bird than category B flocks. No significant differences in hockburn bonus per 1000 birds (a bonus payable to growers whose broilers have the lowest prevalence of contact dermatitis lesions on the hocks) and mortality were found between category A and category B flocks. These results show that subclinical CAA infection has a substantial, statistically significant effect on commercial broiler performance and profitability.     

The effect of oil-emulsion vaccines on the occurrence of nonspecific plate agglutination reactions for Mycoplasma gallisepticum and M. synoviae

Six groups of ten 18-week-old mycoplasma-free white leghorn pullets were vaccinated with one of the following: Mycoplasma gallisepticum (MG) bacterin. Haemophilus gallinarum bacterin, Pasteurella multocida bacterin, combined infectious bursal disease (IBD)-Newcastle (NDV) chicken-embryo-origin (CEO) vaccine. IBD-NDV tissue-culture-origin (TC) vaccine, or saline emulsified in oil; one group received no vaccine. Plate agglutination tests for M. synoviae (MS) and MG were done for 10 weeks after vaccination using three different test antigens. Pullets vaccinated with H. gallinarum bacterin and IBD-NDV TC vaccine showed the greatest incidence of nonspecific plate agglutination reactions. The incidence of positive plate agglutination reactions varied with test antigens. Five groups of fifty 18-week-old mycoplasma-free heavy-breed pullets were vaccinated with one of the following: saline emulsified in oil, chicken embryo fibroblasts emulsified in oil, allantoic fluid emulsified in oil, chicken embryos emulsified in oil, or MS-contaminated chicken embryos emulsified in oil. Plate agglutination tests for MS and MG were done for 8 weeks after vaccination. Chickens vaccinated with chicken embryo fibroblasts emulsified in oil had the greatest incidence of nonspecific plate agglutination reactions. Pullets vaccinated with MS-contaminated chicken embryo vaccine had only a small increase in MS-positive plate agglutination reactions compared with pullets vaccinated with uncontaminated chicken embryo vaccine.     

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.