A longitudinal study of campylobacter infection of broiler flocks in Great Britain

One hundred flocks associated with five integrated poultry companies were monitored for one production cycle to investigate risk factors for campylobacter infection of poultry broiler flocks. Bacteriological samples were collected from one house of birds on each site at weekly intervals from 3 to 4 weeks of age until the birds were infected with campylobacter or the flock was depopulated (whichever was sooner). Environmental samples were obtained from 20 houses after cleansing and disinfection of the site before chick arrival. Conventional methods were used for the isolation of campylobacter. Questionnaires were used to collect information on potential risk factors for campylobacter infection. Discrete-time survival analysis was used to assess the influence of various exposures on the age at which the flock was infected with campylobacter.More than 40% of flocks were infected with campylobacter by the time the chicks were 4 weeks old and >90% by 7 weeks. Infection spread rapidly to most birds in a flock. Infection was not predictable by campylobacter status of the last flock reared on the site. (However, because most flocks were infected, the power to detect such an association was poor.) There was no evidence of environmental survival of campylobacters in broiler houses after adequate cleansing and disinfection. The most important predictors of protection from campylobacter were related to effective hygiene barriers (such as housing birds in buildings in a good state of repair, appropriate usage of disinfectant boot dips and a high standard of cleansing and disinfection of the drinking-water equipment). There was no evidence that rodents were a source of infection (but most sites operated effective vermin-control programmes).     

Seroprevalence of Histomonas meleagridis in pullets and laying hens determined by ELISA

Serum samples from 1120 layers from 56 flocks and 400 pullets from 20 flocks were tested by an indirect sandwich ELISA to investigate the prevalence of antibodies to Histomonas meleagridis in chickens kept in alternative husbandry systems. The overall prevalence of antibodies to H meleagridis in layers was 37.3 per cent, and positive birds were identified in 50 flocks. This was significantly higher than in pullets, where only 8.3 per cent of the birds tested positive. Optical density (OD) values obtained from pullet sera were much lower than the OD values from layers; however, positive birds were detected in half of the pullet flocks. In particular, all birds from an organic pullet flock were found to be positive, with high OD values. Overall, the highest prevalence of positive sera was obtained from birds kept in free-range flocks. Attempts to reisolate live histomonads from birds in 18 layer flocks were unsuccessful.     

A survey of Newcastle disease in Swiss laying-hen flocks using serological testing and simulation modelling

Newcastle disease (ND) is a highly contagious viral disease of birds particularly domestic poultry. Switzerland is currently declared free from ND; since vaccination is prohibited, the detection of antibodies against ND virus (NDV) results in the destruction of the respective flock (stamping-out policy). However, in 1995 and 1996, antibody-positive flocks were detected and sporadic ND outbreaks even occurred in Switzerland. Therefore, a serosurvey was done to look for evidence of NDV infections in Swiss laying-hen flocks. The survey was designed to provide 95% confidence of detecting at least one seropositive flock if the flock prevalence were 1%. Thirty blood samples from each of 260 commercial laying-hen flocks were collected during 1996 in a central poultry slaughterhouse. Sera were screened for NDV antibodies with a commercial blocking enzyme-linked immunosorbent assay (ELISA). Samples with a questionable or positive test result were retested with the same ELISA. A stochastic computer model was applied to define a cut-off number of test-positive samples to help to differentiate between true- and false-positive flocks and to estimate the true flock prevalence of infection. Four flocks were identified as NDV-seropositive and the NDV true seroprevalence among commercial laying-hen flocks in Switzerland was most likely between 1.35 and 1.55%. This indicates that Swiss laying-hen and parental flocks with more than 150 animals have been in contact with strains of NDV that cause subclinical infection in chicken, because no clinical symptoms have been observed. In this context, computer simulation was a useful technique to interpret survey results.     

Prevalence and risk factors for Salmonella spp. and Campylobacter spp. caecal colonization in broiler chicken and turkey flocks slaughtered in Quebec, Canada

We conducted an observational study to estimate prevalence and risk factors for Salmonella spp. and Campylobacter spp. caecal colonization in poultry. Eighty-one broiler chicken and 59 turkey flocks selected among flocks slaughtered in the province of Quebec, Canada, were included in the study. Flock status was evaluated by culturing pooled caecal contents from about 30 birds per flock. Exposure to potential risk factors was evaluated with a questionnaire. Odds ratios were computed using multivariable logistic regression.

The prevalence of Salmonella-positive flocks was 50% (95% CI: 37, 64) for chickens and 54% (95% CI: 39, 70) for turkeys, respectively. Odds of Salmonella colonization were 2.6 times greater for chicken flocks which failed to lock the chicken house permanently. In turkeys, odds of Salmonella colonization were 4.8–7.7 times greater for flocks which failed to be raised by ≤2 producers with no other visitors allowed onto the premises, or origin from a hatchery.

The prevalence of Campylobacter-positive flocks was 35% (95% CI: 22, 49) for chickens and 46% (95% CI: 30, 62) for turkeys. Odds of colonization were 4.1 times higher for chicken flocks raised on farms with professional rodent control and 5.2 times higher for flocks with manure heap >200 m from the poultry house, and also increased with the number of birds raised per year on the farm and with the age at slaughter. For turkeys, odds of Campylobacter flock colonization were 3.2 times greater in flocks having a manure heap at ≤200 m from poultry house and 4.2 times greater in flocks drinking unchlorinated water.     

Serological investigations of infectious bursal disease virus and reticuloendotheliosis virus infections in New Zealand chickens

Extract

Sir:- Between 1975 and 1981, sera were collected from 89 New Zealand chicken farms representing a variety of laying and meat birds of different ages from both primary breeders and commercial flocks. In some instances samples were collected from one or more flocks on a farm. In most cases between ten and 20 birds were sampled in a flock and the sera pooled to give a composite sample for testing.     

Measurements of footpad dermatitis in broiler chickens at processing plants

A four-point photographic scale was developed to score the severity of lesions of footpad dermatitis (FPD) in broiler chickens. There was a linear relationship between the square root of the relative area of the lesions and their scores, and good agreement between different assessors using the scale. The scale was used to assess samples of 100 birds from each of 190 flocks slaughtered at two uk processing plants in 2002 and 2003; 12 of the flocks (6.3 per cent) had no lesions, but the others had lesions of different prevalences and severity. The maximum proportion of affected birds in a flock was 92 per cent. In the 178 affected flocks, 84.0 per cent of the birds had no lesions and 16.0 per cent had some evidence of FPD. The overall unweighted prevalence of birds with FPD in all 190 flocks sampled was 18.1 per cent; 10.2 per cent had only small lesions, on average equivalent in area to 2.1 per cent of the total area of the foot, 6.2 per cent had lesions on average equivalent to 6.6 per cent of the area of the foot, and 1.7 per cent had lesions on average equivalent to 21.5 per cent of the area of the foot. There were differences between the two plants in the overall prevalence and severity of FPD, but this may have been due to the fact that the plants were sampled at different times of the year.     

High seroprevalence of Histomonas meleagridis in Dutch layer chickens

Histomona meleagridis is a protozoan parasite that may cause outbreaks of histomonosis with high mortality, especially in turkey flocks. Chickens are less susceptible to the disease than are turkeys, but are considered to act as an important reservoir. To determine the seroprevalence of H. meleagridis in Dutch layer chicken flocks, a large scale seroepidemiologic study (3376 samples) was performed by sampling 12 organic flocks, 24 free-ranging flocks, 40 flocks with floor housing, and 40 flocks with cage housing. At the end of the laying period, approximately 30 blood samples per flock were collected for serology. The seroprevalence found was high. In every flock, at least one of the samples tested positive while in 87% of the flocks, at least one of the samples was strongly positive. There were no significant statistical differences in seropositivity between the housing types. To confirm the enzyme-linked immunosorbent assay (ELISA) results, a small-scale seroepidemiologic study (576 samples) was performed in 29 additional layer chicken flocks kept in different housing systems. Subsequently, a subset of five seropositive flocks was selected. Five birds were obtained from each of these flocks in order to detect the parasite using culture and PCR. In all five flocks, H. meleagridis was either isolated from (culture), detected in (PCR), or both, the birds sampled. Together with the previously performed validation studies, the latter results confirm that the positive ELISA serology found is genuine. We conclude that the seroprevalence of H. meleagridis in layers is, as anticipated, high.     

A comparison of pooled and individual bird sampling for detection of Salmonella in commercial egg laying flocks

The objective of this study was to determine the sensitivity of culturing pooled samples containing varying numbers of individual droppings for detection of Salmonella in commercial egg-laying flocks relative to the within-flock prevalence. A laboratory experiment was performed to directly measure the effect of diluting positive with negative faeces on the sensitivity of detection, and thus provide priors for a Bayesian model of pooled sampling. Pooled samples made up of different numbers of individual faecal droppings were collected from 20 flocks, and in addition bulked faeces and dust were also sampled using an in-house method that involved collecting 10 dust and 10 faeces samples into jars with buffered peptone water. The results from these flocks were analysed using Bayesian methods for diagnostic test evaluation in the absence of a gold standard, and the sensitivity of each pooled sample type was estimated relative to the within-flock prevalence. The sensitivity of pooled samples depended on the within-flock prevalence, and increased as the prevalence increased. The sensitivity of pooled sampling tended to increase with the number of droppings in the pool, and overall there was a higher proportion of positive samples from the pools of 20, 60 and the in-house faeces pooling method compared to the pools of 10, 5 and the individual droppings. Dust samples were more sensitive than the faeces samples, and so the inclusion of dust in sampling schemes is recommended.     

Necrotizing granulomatous hepatitis in slaughtered broilers

The present study describes a subclinical necrotizing granulomatous hepatitis in normal broilers routinely slaughtered in a medium-sized (72,000 birds per day) abattoir in the Netherlands. An exploratory investigation was scheduled on line during 20-min periods for 82 flocks (3000 birds examined per period). Liver and duodenum samples were collected for histopathology from 365 birds with liver pathology. Bacteriology was performed from 240 livers with lesions and 80 control livers. In addition to the hepatic pathology, other gross lesions of the carcasses, such as footpad dermatitis and broken legs/wings, were noted. The average prevalence for gross liver lesions was 0.16% (ranging from 0% to 0.63% per flock); 89.59% of the livers were enlarged, had a firm consistency, and revealed multifocal necrotic spots. Microscopically, 51.66% showed a granulomatous reaction in addition to the necrosis. There was no consistent anaerobic or aerobic bacterial growth in comparison to normal livers. A large proportion of the livers revealed growth of Escherichia coli, Bacteroides spp., Lactobacillus spp., Staphylococcus spp., and Streptococcus spp., and this was often with more than one type of bacterial colony. The duodenum mucosa grossly showed some redness with a mucous mass on its surface. Microscopically (n = 176) in 5.70% there were no changes in anatomy and cellular activities; 64.20% had a mildly increased number of lymphoid cells and heterophils in the lamina propria and between villus epithelial cells. The remaining 30.10% had moderate degenerative changes of villus epithelium with a mixed cellular infiltration in the lamina propria; 23.29% of the duodenum samples contained coccidia (infestation stage: mild to moderate). Signs of overgrowth with Clostridium spp. were not observed. There was a small, but significant correlation (rs = 0.30; P = 0.006) between prevalence of liver pathology and footpad dermatitis.     

Development of a monitoring program for antibiotic resistance in bacteria from Swiss food-producing animals

Resistant bacteria from food-producing animals may compromise the success of antibiotic treatment in animals and in humans. Therefore, the level of antibiotic resistance in bacteria from farm animals and its development over time needs to be monitored. In Switzerland, a monitoring program for antibiotic resistance is currently being developed. Pilot-monitoring programs were conducted in selected animal species in order to obtain current data on antibiotic resistance. The data on the prevalence of bacteria and antibiotic resistance in poultry were used to optimize the sampling plan. The influence of sampling more farms compared to sampling more animals per farm on the prevalence estimate for antibiotic resistance was analyzed by a Monte Carlo simulation model. Accounting for the costs for sample collection, transportation and laboratory analysis of the samples, the number of samples to be taken at the respective step in the production line was optimized. Optimization was defined as maximizing the precision of the prevalence estimate while minimizing the costs. The model will be expanded to other bacterial and animal species in the future.     

Bayesian estimation of flock-level sensitivity of detection of Salmonella spp., Enteritidis and Typhimurium according to the sampling procedure in French laying-hen houses

A study was carried out to estimate the prevalence of flocks infected by Salmonella spp., S. Enteritidis and S. Typhimurium in 521 French laying-hen farms from October 1st 2004 to September 30th 2005 as part of a European Union-wide baseline study to define targets for Salmonella reduction in member states. The sampling scheme prescribed and financed by the European Commission to detect Salmonella in laying-hen flocks was based on 2 dust-samples and 5 faeces-samples per farm. A latent-class Bayesian approach for correlated tests was used to estimate the sensitivity of detection of reduced sampling schemes corresponding to the 16 combinations of 2 dust- and 5 faeces-samples. For each model the full sampling scheme (7 samples) and the reduced protocol were considered as two correlated tests, the biological principle being identical and the reduced protocol being a subset of the full sampling scheme. As the observed apparent prevalence in cage flocks was higher than in other systems (barns, outdoor, or organic) these two sub-populations were considered separately. Bayesian estimation of posterior medians with 95% probability intervals for true prevalence in cage flocks were 0.34 (0.29; 0.39) and 0.13 (0.10; 0.18) for Salmonella spp. and Salmonella Enteritidis+Typhimurium respectively. In alternative flocks posterior medians with 95% probability intervals for true prevalence were 0.09 (0.06; 0.13) and 0.05 (0.03; 0.08) for Salmonella spp. and Salmonella Enteritidis+Typhimurium, respectively. In cage flocks Bayesian estimation of posterior distributions for sensitivity indicated that at least 5 samples, including 2 dust samples were necessary to attain comparable sensitivity levels to the full sampling scheme. In alternative flocks and for Salmonella spp. 6 samples were required to ensure a comparable sensitivity level to the full sampling scheme. Detection sensitivity was improved by increasing the number of dust samples in cage farms and by increasing the total number of samples whatever their type in alternative farms.     

A national survey to estimate the prevalence of Salmonella species among Canadian registered commercial turkey flocks.

In 1990-1991, a national survey was conducted to estimate the prevalence of Salmonella species among Canadian commercial turkey flocks. Two hundred and seventy flocks were randomly selected across Canada. The proportion sampled from each province was selected according to each province's share of the national turkey market. Samples, consisting of 12 pooled litter and four pooled dust samples, were used to determine the Salmonella status of the environment of each flock. Additionally, a one kilogram sample of feed was taken from each flock premise. Salmonella was recovered from environmental samples in 234/270 (86.7%) of flocks and from feed samples in 26/266 (9.8%) of flocks. Forty-eight different Salmonella serovars were isolated from flock environmental samples. The most prevalent serovars were S. anatum, S. hadar, S. agona, S. heidelberg and S. saintpaul which were isolated from 53/270 (19.6%), 49/270 (18.1%), 49/270 (18.1%), 42/270 (15.6%) and 34/270 (12.6%) flocks, respectively.     

Faecal Sampling Underestimates the Actual Prevalence of Salmonella in Laying Hen Flocks

Summary In all European Union member states, Salmonella monitoring in poultry flocks is obligatory. In these monitoring programmes, a limited number of pooled faeces and/or dust samples are collected to determine whether Salmonella is present in the flocks or not. Whether these limited sampling protocols are sufficiently sensitive to detect expected low within‐flock prevalences of an intermittently shed pathogen is not yet clear. In this study, a comparison is made between different sampling procedures for the assessment of the between‐ and within‐flock prevalence of Salmonella in laying hens. In total, 19 farms were sampled. Using a comparable sampling methodology as in the official surveillance programmes, Salmonella could not be detected in any of the flocks. After transportation of the hens to the laboratory and subsequent analysis of cloacal swabs and caecal contents, Salmonella Enteritidis was detected in laying hens from five of 19 farms. The observed within‐flock prevalence ranged from 1% to 14%. Based on the results of this study, it can be expected that, depending on the sampling procedure, different estimates of the prevalence of Salmonella can be obtained and the proportion of Salmonella infected flocks is underestimated based on the results of the official monitoring programme.     

Seroprevalence of Brucella ovis infection in commercial ram flocks in the Tamworth area

Commercial ram flocks in the Tamworth area of northern New South Wales were surveyed to estimate the proportion of flocks, and rams, infected with Brucella ovis. The flock prevalence (percentage of flocks containing seropositive rams) of 9.1% for Merino flocks was significantly lower than that for British-breed flocks (43.8%, p=0.006) and mixed-breed flocks (46.7%, p=0.017). The mean flock prevalence over all flock types was 32.9%. These estimates were supported by data obtained from diagnostic testing for brucellosis carried out during the previous 6 years. The seroprevalence in rams was 10.8% overall, 2.5% for Merinos, 19% for Border Leicester and 26% for Dorset rams. Within infected flocks, the estimated prevalences were 21%, 65% and 67% for Merinos, Border Leicester and Dorset rams respectively. The seroprevalence in Merino rams was significantly lower than that for both other breeds (p<0.001) for all flocks and in infected flocks. There was no apparent association between age and serological status, or age and the prevalence of epididymitis.     

Epidemiological studies of clinical and subclinical ovine mastitis in Awassi sheep in northern Jordan

Forty-six Awassi sheep flocks selected by stratified random sampling were subjected to a cross-sectional study to determine the prevalence of intramammary infections, to assess the influence of flock size and parity on the prevalence of somatic cell count (SCC) and to identify major udder pathogens. Of the 3472 udder halves examined, 29.8% had over 10⁶ SCC/ml and 0.03% had dry teats due to chronic mastitis. Flocks with 30–49 milking ewes (small flock size) were much younger (P < 0.001) than flocks with 50–99 ewes (medium) and flocks with ≥ 100 ewes (large). Pairwise analysis of the InSCC of both halves of the udders revealed significant mean differences for small and large flock size (P < 0.05), and for medium and large flock size (P < 0.001). Mean InSCC was lower (P < 0.05) in samples obtained from the left half compared with samples of the right half of the udder. Multiparous ewes had higher (P < 0.001) mean InSCC than primiparous ewes. Also, ewes with twin lambs had higher (P < 0.001) mean InSCC in the right half of the udder compared with single-lamb ewes. Samples collected in January (winter) had lower (P < 0.05) mean InSCC compared with samples collected in June. The most common organisms isolated from subclinical mastitis cases were coagulase-negative Staphylococci (17.8%), E. coli (13.6%), Streptococcus agalactiae (6.8%) and Staphylococcus aureus (6.8%). Of the 46 flocks, 20 were monitored monthly for 9 consecutive months to determine the incidence of clinical mastitis diagnosed by shepherds or/and sheep farmers with major pathogens. The incidence of clinical mastitis (expressed as the number of clinical cases per 100 ewe-months) were 2.1 ± 1.9 (SD), 1.9 ± 1.1, and 1.2 + 2.1 for small, medium and large flocks size strata, respectively. The overall population estimate was 1.7 ± 0.02 cases per 100 ewe-months. The most-common clinical isolates were S. aureus (22% of all clinical isolates) and E. coli (14.2%).     

Sensitivity of two-stage sampling to detect sheep biting lice (Bovicola ovis) in infested flocks.

The sampling distribution of Bovicola ovis (Schrank) on sheep was examined in two flocks, one with a light and one with a heavy infestation of lice. The derived distributions were used to calculate the sensitivity of detecting lice on individual sheep and in flocks by fleece parting regimes that varied in number of parts per animal and number of sheep per flock, different scenarios of flock sizes, proportion infested and louse density were examined. Lice were aggregated among fleece partings in the heavily infested flock and described by a negative binomial distribution with k values between 0.3 and 1.92. The distribution was indistinguishable from Poisson in the lightly infested flock. The assumed distribution had little effect on sensitivity, except when only one fleece part per animal was examined. On individual sheep where louse density was 0.5 per 10 cm part or greater, there were only marginal gains from inspecting more than 10 parts per animal. Increasing the number of sheep inspected always increased sensitivity more than increasing number of parts per sheep by an equivalent amount. This advantage was greatest in situations where a low proportion of sheep in the flock were infested with a high density of lice, and less where a low proportion of sheep were infested with a low density of lice, or a high proportion of sheep were infested with a high density of lice.     

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).     

Epidemiological and clinical investigations into big liver and spleen disease of broiler breeder hens

SUMMARY The epidemiological and clinical features of big liver and spleen disease (BLS) in flocks on two broiler breeder farms were investigated by serology and gross pathology. The most common necropsy findings on farm 1 were splenomegaly and hepatomegaly, with kidney enlargement in some birds. In one flock (farm 1), a decline in egg production began at 40 weeks of age and lasted for 9 weeks. Seroconversion to BLS antigen was first detected at 45 weeks (3.1% of birds) and increased to 72% at 50 weeks, which coincided with clinical recovery in the flock. Antigen was detected before antibody at 44 weeks and persisted at low incidence (<15%). Farm egg production statistics and serology indicated that the disease affected all flocks on the farm. In three of eight flocks, seroconversion was detected in birds before peak production. The birds in the remaining sheds did not seroconvert or become sick until after peak production. On the second farm, sampling began within a flock already experiencing BLS. Clinical signs and pathology were similar to those seen in flocks on farm 1. However, the lesions that were seen in the pancreas in 15% of birds have not been reported previously. BLS antibody was detected in 78%, and circulating antigen in 14%, of sick birds.     

Nutritional factors associated with vaginal prolapse in ewes

Serum calcium, magnesium and phosphate values of ewes recently affected by vaginal prolapse were compared with unaffected ewes in four flocks. Subclinical hypocalcaemia was demonstrated in some affected and unaffected ewes in three flocks. Magnesium and phosphate values were normal. In two flocks the body condition of ewes recently affected by vaginal prolapse was variable and reflected the variation in condition found in the flock. In a third flock affected ewes had significantly lower body condition scores than unaffected ewes (P less than 0.001). Analysis of the fourth flock was not possible. Oestrogenic mycotoxins were not detected in any of the feed samples taken from these flocks. The following year the management, nutrition and energy, and the protein and calcium status of ewes in 12 flocks of greyface/mule ewes with a history of a regular high (greater than 3 per cent) or low (less than 1 per cent) prevalence of vaginal prolapse were compared. A high prevalence was not associated with any particular feedstuff. A high or intermediate (1 to 3 per cent) prevalence of vaginal prolapse was found in three of the four flocks managed as a single group and these three flocks were fed on an unrestricted basis. Body condition scoring and beta-hydroxybutyrate estimation confirmed that ewes in these flocks were overfed. The prevalence of vaginal prolapse in the flocks was not related to the serum albumin, calcium or urea of the ewes. Therefore subclinical hypocalcaemia was probably a consequence of vaginal prolapse rather than a cause.     

Disease Condition of Turkey Poults Characterized by Enlarged and Rounded Hearts

The occurrence of a disease condition in two flocks of young turkey poults characterized by enlarged hearts and marked distension of the right ventricle is described.

Only males were observed to exhibit the condition in the first flock and approximately five per cent of this sex died with the characteristic enlargement. Abnormal hearts were found in progeny from 2-5 sires in each of four strains.

In a second flock at a second location, a small number of females also exhibited the condition. Approximately one per cent of this sex died with enlarged hearts. The incidence in males was similar in both flocks. The second flock was composed of poults from a commercial strain and poults which were a cross of the four laboratory-raised strains with this unrelated commercial strain. The condition was found in both pure and cross strain poults from this flock.

A second type of anomaly which grossly resembled “round-heart disease” of chickens was observed in birds from both flocks over six weeks of age. It was not associated with the death of the birds and was found during examination of injured or sacrificed males and females.

Histological findings have not been consistent, but are being continued. Transmission trials are being conducted.