Detection of Chlamydia and Chlamydia-like organisms in bovine placental tissue.

This study aimed to investigate the presence of Chlamydia spp. and Parachlamydia acanthamoebae in bovine placental tissue originating from abortion and non-abortion cases in Belgium. Placentas of 164 late term bovine abortions (last trimester of gestation) and 41 non-abortion (collected after calving) cases were analysed by PCR for Chlamydia spp., Chlamydia abortus, C. psittaci and P. acanthamoebae. Additionally, a subset of 101 (75 abortion and 26 non-abortion cases) of these placenta samples were also analysed by histopathology to detect possible Chlamydia-induced lesions. In 5.4% (11/205) of the cases, Chlamydia spp. were detected, and three of those cases were positive for C. psittaci. Parachlamydia acanthamoebae was detected in 36% (75/205) of the cases, being 44% (n = 72) in abortions and 7.3% (n = 3) in non-abortions cases (p < .001). None of the cases was positive for C. abortus. Purulent and/or necrotizing placentitis with or without vasculitis was observed in 18.8% (19/101) of the histopathologically analysed placenta samples. In 5.9% (6/101) of the cases, placentitis was observed along with vasculitis. In the abortion cases, 24% (18/75) of the samples showed purulent and/or necrotizing placentitis, while purulent and/or necrotizing placentitis was visible in 3.9% (1/26) of the non-abortion cases. Placental lesions of inflammation and/or necrosis were present in 44% (15/34) of the cases where P. acanthamoebae was detected, while inflammation and/or necrosis was present in 20.9% (14/67) of the negative cases (p < .05). The detection of Chlamydia spp. and especially P. acanthamoebae, in combination with correlated histological lesions such as purulent and/or necrotizing placentitis and/or vasculitis in placental tissue following abortion, suggests a potential role of this pathogen in cases of bovine abortion in Belgium. Further in-depth studies are necessary to unravel the role of these species as abortifacient agents in cattle and to include them in bovine abortion monitoring programmes.

Detection of Anaplasma phagocytophilum in fetal and placental tissue of bovine abortions and perinatal mortalities.

BACKGROUND: Anaplasma phagocytophilum is a tick-borne zoonotic bacterium that is the aetiologic pathogen of tick-borne fever (TBF) in ruminants. In clinical bovine cases of TBF, abortion and stillbirth may be observed. However, in this regard, the pathophysiology of TBF has not yet been completely elucidated, and no clear guidelines to diagnose A. phagocytophilum-related abortions and perinatal mortalities (APM) are available. METHODS: This exploratory study aimed to investigate the presence of A. phagocytophilum in bovine cases of APM and determine whether placental or fetal spleen tissue has the greatest sensitivity for A. phagocytophilum identification. The placenta and fetal spleen of 150 late-term bovine APM cases were analysed using real-time PCR to detect A. phagocytophilum. RESULTS: A total of 2.7% of sampled placentas were positive for A. phagocytophilum, while none of the fetal spleen samples was. LIMITATIONS: No histopathology to detect associated lesions was performed. Consequently, no evidence of causality between the detection of A. phagocytophilum and APM events could be achieved. CONCLUSION: The detection of A. phagocytophilum suggests a potential role of this pathogen in bovine APM, and placental tissue seems to be the most suitable tissue for its identification.

Comparison of Salmonella enteritidis phage types isolated from layers and humans in Belgium in 2005.

OBJECTIVES: The aim of this study was to investigate the available results for Belgium of the European Union coordinated monitoring program (2004/665 EC) on Salmonella in layers in 2005, as well as the results of the monthly outbreak reports of Salmonella Enteritidis in humans in 2005 to identify a possible statistical significant trend in both populations. MATERIALS AND METHODS: Separate descriptive statistics and univariate analysis were carried out and the parametric and/or non-parametric hypothesis tests were conducted. A time cluster analysis was performed for all Salmonella Enteritidis phage types (PTs) isolated. The proportions of each Salmonella Enteritidis PT in layers and in humans were compared and the monthly distribution of the most common PT, isolated in both populations, was evaluated. RESULTS: The time cluster analysis revealed significant clusters during the months May and June for layers and May, July, August, and September for humans. PT21, the most frequently isolated PT in both populations in 2005, seemed to be responsible of these significant clusters. PT4 was the second most frequently isolated PT. No significant difference was found for the monthly trend evolution of both PT in both populations based on parametric and non-parametric methods. DISCUSSION AND CONCLUSION: A similar monthly trend of PT distribution in humans and layers during the year 2005 was observed. The time cluster analysis and the statistical significance testing confirmed these results. Moreover, the time cluster analysis showed significant clusters during the summer time and slightly delayed in time (humans after layers). These results suggest a common link between the prevalence of Salmonella Enteritidis in layers and the occurrence of the pathogen in humans. Phage typing was confirmed to be a useful tool for identifying temporal trends.

Redesigning the serological surveillance program for notifiable avian influenza in Belgian professional poultry holdings.

This study was aimed at redesigning the Belgian active surveillance program for domestic birds in professional poultry holdings based on a risk analysis approach. A stochastic quantitative analysis, combining all data sources, was run to obtain sensitivity estimates for the detection of an infected bird in the different risk groups identified. An optimal number of holdings for each risk group was then estimated on the basis of the different sensitivities obtained. This study proved to be a useful tool for decision makers, providing insight on how to reallocate the total amount of samples to be taken in the coming year(s) in Belgium, thus optimizing the field resources and improving efficiency of disease surveillance such as required by the international standards.

Bluetongue surveillance system in Belgium: a stochastic evaluation of its risk-based approach effectiveness.

BACKGROUND: The aim of this study was to assess the sensitivity of the four major bluetongue surveillance components implemented in Belgium in 2007 for farmed animals and prescribed by the European Union regulation; winter serological screening, sentinel system, passive clinical surveillance, export testing. Scenario tree methodology was used to evaluate the relative sensitivity of detection and targeted approach of each component in terms of early detection and freedom of infection substantiation. Field data collected from the previous year's outbreaks in Belgium were used to determine the risk groups to be considered. RESULTS: The best sensitivities at herd level, taking into account the diagnostic test sensitivity, design prevalence and the number of animals tested within a herd were obtained with the winter screening and sentinel component. The sensitivities at risk group level, taking into account the obtained herd sensitivity, effective probabilities of infection and number of herds tested were high in all components, except for the export component. Component sensitivities ranged between 0.77 and 1 for all components except for the export component with a mean value of 0.22 (0.17-0.26). In terms of early detection, the probability of detection was best using the passive clinical component or the sentinel component. Sensitivity analysis showed that the passive clinical component sensitivity was mostly affected by the diagnostic process and the number of herds sampled. The sentinel and export components sensitivity were mainly affected by the relative risk estimates whereas the winter screening component was mainly affected by the assumptions about the design prevalence. CONCLUSIONS: This study revealed interesting features regarding the sensitivity of detection and early detection of infection in the different surveillance components and their risk based approach as requested by the international standards.

Serological and virological BVDV prevalence and risk factor analysis for herds to be BVDV seropositive in Belgian cattle herds.

Bovine viral diarrhoea virus (BVDV) is a worldwide spread virus that most commonly infects cattle and can cause considerable economic losses. To determine the prevalence of BVDV in Belgium, a cross-sectional study was performed between November 2009 and March 2010. Young stock aged between 6 and 12 months from 773 randomly selected Belgian cattle herds were tested for BVDV-specific antibodies and antigen. With a target and maximum of 10 animals per sampled herd, a total of 5246 animals were selected. Additionally a questionnaire including different herd management topics and questions about participation in animal health programmes, including BVDV, was sent to 1100 Belgian cattle herds, including the 773 herds for BVDV testing. This paper focuses on results regarding these 773 herds. The true prevalence of BVDV-specific antibodies and antigen at herd level was respectively 47.4% and 4.4%, while at animal level this was respectively 32.9% and 0.3%. In 44.4% of the herds where BVDV-specific antibodies were detected at least 60% of the sampled young stock was BVDV seropositive. Interestingly, 83.4% of these farmers stated not to have suffered from problems related to BVDV. Moreover, only 8.4% of all farmers who completed the questionnaire (n=895) reported problems possibly related to BVDV the past 3 years. This demonstrates that farmers are often unaware of the presence of BVDV in their herd. Risk factors for a herd to be BVDV seropositive were identified by means of a multivariable logistic regression model. Large herds were significantly more likely to be BVDV seropositive (OR=1.004, p<0.01). The interaction between "Antigen positive animal detected in this study" and "BVDV vaccination in 2009" was significant (p<0.01). In non-vaccinating herds, the detection of antigen positive animals was significantly associated with BVDV seropositive herds (OR=13.8, p<0.01). In herds with no antigen positive animals detected, vaccination resulted in a significant risk factor to be BVDV seropositive compared to non-vaccinating herds (OR=3.4, p<0.01). Herds reporting BVDV-related problems the past 3 years were more likely to be BVDV seropositive (OR=1.9, p<0.05). This relation became non-significant (OR=1.8, p=0.08) when only a subset of herds with no vaccination of animals <12 months was taken into account. The results of the current study suggest an active circulation of BVDV in a considerable number of Belgian cattle herds.

Evaluation of the Salmonella surveillance program in Belgian pig farms.

Since July 2007, Belgium has implemented a national surveillance and control program for Salmonella in pigs. Pig farms are designated as Salmonella high risk farms based on serological profiles and are obliged to subsequently take part in a Salmonella specific action plan (SSAP). The SSAP was evaluated and potential risk factors for the persistence of Salmonella on the farm were investigated. First, the Kaplan-Meier method was used in order to study the period during which a farm maintains a Salmonella high risk status. Farms recovered more slowly from their high risk status before the SSAP was implemented compared to after the program was implemented (p<0.001). However, results showed that 29% of the farms were withdrawn from the program possibly only because of sampling error. The program should thus be adapted to accommodate for this. Secondly, the influence of several risk factors (type of farm, season of entrance into the SSAP, size of farm and farm density of the municipality) on the time to withdrawal from the high risk status was evaluated using univariable methods and a Cox multiple regression model for survival data. A statistically significant association was identified between the type of farm and the time to withdrawal from the high risk status. At any point in time after the onset of the SSAP, withdrawals from the high risk status occurred at a 39% and 28% higher rate in mixed (p=0.01) and fattening farms (p=0.05), respectively, compared to closed farms. The risk attributed to closed pig farms is related to the presence of sows in this particular type of structure, which underlines the importance of implementing control measures in this category of animals.

Identification of risk factors for the prevalence and persistence of Salmonella in Belgian broiler chicken flocks.

According to the European Food Safety Authority, salmonellosis is still one of the main causes of infectious foodborne gastroenteritis in humans. Broilers are an important source of salmonellosis after eggs and pork. Between 1987 and 1999 the trend of human salmonellosis incidence in Belgium increased constantly. However, from 2000 until 2005 a decrease in human cases was observed, probably following the sanitary measures implemented in the poultry breeder and laying sector. In order to decrease human infections it is essential to tackle the problem at the farm level to minimize cross-contamination from farm to fork. This paper seeks to answer two questions: (i) given the Salmonella status of the farm at a certain occasion (equal to the sampling time of the flock), what are the risk factors that the farm will be Salmonella positive at a following occasion? And (ii) what are the risk factors for a farm to be persistently positive for two consecutive flocks? We used surveillance data on 6824 broiler flocks studied for Salmonella infectivity from 2005 to 2006 in Belgium. The farms were tested regularly (3 weeks before slaughter of each broiler flock) for the presence of Salmonella based on multiple faecal samples per flock on a farm yielding clustered data. Generalized estimating equations, alternating logistic regression models, and random-intercept logistic regression models were employed to analyse these correlated binary data. Our results indicated that there are many factors that influence Salmonella risk in broiler flocks, and that they interact. Accounting for interactions between risk factors leads to an improved determination of those risk factors that increase infection with Salmonella. For the conditional analysis, the risk factors found to increase the risk of Salmonella infection on a farm at a current occasion given the previous Salmonella status included: Salmonella infection of day-old chicks (of the current flock); a previously infected flock even though the farm was equipped with a hygiene place to change clothes prior to entering the broiler house; having temporary workmen when there was a separation between birds of different species; and separating birds of different species in the Walloon region relative to the Flanders region. Sanitary measures such as a cleaning and disinfecting procedure conducted by an external cleaning firm, applying the all-in all-out procedure, and hand washing decreased the risk despite their interaction with other factors. From the joint analysis, the most important factors identified for increased risk for persistent Salmonella on a farm involved the interaction between having temporary workmen when there were poultry or farmers in contact with foreign poultry or persons, and the interaction between having temporary workmen when there were poultry or farmers in contact with external poultry or persons.