K. Frankena

Bayesian estimation of hepatitis E virus seroprevalence for populations with different exposure levels to swine in The Netherlands.

Hepatitis E virus (HEV) is ubiquitous in pigs worldwide and may be zoonotic. Previous HEV seroprevalence estimates for groups of people working with swine were higher than for control groups. However, discordance among results of anti-HEV assays means that true seroprevalence estimates, i.e. seroprevalence due to previous exposure to HEV, depends on choice of seroassay. We tested blood samples from three subpopulations (49 swine veterinarians, 153 non-swine veterinarians and 644 randomly selected individuals from the general population) with one IgM and two IgG ELISAs, and subsets with IgG and/or IgM Western blots. A Bayesian stochastical model was used to combine results of all assays. The model accounted for imperfection of each assay by estimating sensitivity and specificity, and accounted for dependence between serological assays. As expected, discordance among assay results occurred. Applying the model yielded seroprevalence estimates of approximately 11% for swine veterinarians,approximately 6% for non-swine veterinarians and approximately 2% for the general population. By combining the results of five serological assays in a Bayesian stochastical model we confirmed that exposure to swine or their environment was associated with elevated HEV seroprevalence.

The course of hepatitis E virus infection in pigs after contact-infection and intravenous inoculation.

BackgroundWorldwide, hepatitis E virus (HEV) genotype 3 is observed in pigs and transmission to humans is implied. To be able to estimate public health risks from e.g. contact with pigs or consumption of pork products, the transmission routes and dynamics of infection should be identified. Hence, the course of HEV-infection in naturally infected pigs should be studied.ResultsTo resemble natural transmission, 24 HEV-susceptible pigs were infected either by one-to-one exposure to intravenously inoculated pigs (C1-pigs; n = 10), by one-to-one exposure to contact-infected pigs (C2-pigs: n = 7; C3-pigs: n = 5) or due to an unknown non-intravenous infection route (one C2-pig and one C3-pig). The course of HEV-infection for contact-infected pigs was characterized by: faecal HEV RNA excretion that started at day 7 (95% confidence interval: 5–10) postexposure and lasted 23 (19–28) days; viremia that started after 13 (8–17) days of faecal HEV RNA excretion and lasted 11 (8–13) days; antibody development that was detected after 13 (10–16) days of faecal HEV RNA excretion. The time until onset of faecal HEV RNA excretion and onset of viremia was significantly shorter for iv-pigs compared to contact-infected pigs, whereas the duration of faecal HEV RNA excretion was significantly longer. At 28 days postinfection HEV RNA was detected less frequently in organs of contact-infected pigs compared to iv-pigs. For contact-infected pigs, HEV RNA was detected in 20 of 39 muscle samples that were proxies for pork at retail and in 4 of 7 urine samples.ConclusionThe course of infection differed between infection routes, suggesting that contact-infection could be a better model for natural transmission than iv inoculation. Urine and meat were identified as possible HEV-sources for pig-to-pig and pig-to-human HEV transmission.

Estimation of hepatitis E virus transmission among pigs due to contact-exposure.

Locally acquired hepatitis E in humans from industrialized countries has been repeatedly suggested to originate from pigs. Pigs may serve as a reservoir of hepatitis E virus (HEV) for humans when a typical infected pig causes on average more than one newly infected pig, a property that is expressed by the basic reproduction ratio R(0). In this study, R(0) for HEV transmission among pigs was estimated from chains of one-to-one transmission experiments in two blocks of five chains each. Per chain, susceptible first-generation contact pigs were contact-exposed to intravenously inoculated pigs, subsequently susceptible second-generation contact pigs were contact-exposed to infected first-generation contact pigs, and lastly, susceptible third-generation contact pigs were contact-exposed to infected second-generation contact pigs. Thus, in the second and third link of the chain, HEV-transmission due to contact with a contact-infected pig was observed. Transmission of HEV was monitored by reverse transcriptase polymerase chain reaction (RT-PCR) on individual faecal samples taken every two/three days. For susceptible pigs, the average period between exposure to an infectious pig and HEV excretion was six days (standard deviation: 4). The length of HEV-excretion (i.e. infectious period) was estimated at 49 days (95% confidence interval (CI): 17-141) for block 1 and 13 days (95% CI: 11-17) for block 2. The R0 for contact-exposure was estimated to be 8.8 (95% CI: 4-19), showing the potential of HEV to cause epidemics in populations of pigs.

Risk factors for clinical Salmonella enterica subsp. enterica serovar Typhimurium infection on Dutch dairy farms.

Risk factors for outbreaks in 1999 of clinical Salmonella enterica subsp. enterica serovar Typhimurium infection on dairy farms were studied in a matched case-control study with 47 case farms and 47 control farms. All 47 case farms experienced a clinical outbreak of salmonellosis which was confirmed with a positive bacteriologic culture for serovar Typhimurium in one or more samples. Serovar Typhimurium phage type 401 and 506 (definitive type 104, DT104) were the most frequently isolated phage types (13 isolates). On most farms (66%), clinical signs were seen only among adult cows. The most frequently reported clinical signs were diarrhoea (in 92% of the farms) and depression (in 79% of the farms). Control farms were matched on region and had no history of salmonellosis. A questionnaire was used to collect data on case and control farms. The relationship between serovar Typhimurium status of the farm and possible risk factors was tested using conditional logistic regression. Significant factors in the final model were presence of cats on the farm (OR=0.06), purchase of manure (OR=21.5), feeding colostrum only from own dam (OR=0.08), a non-seasonal calving pattern (OR=25), unrestricted grazing of lactating cows (OR=0.07), and a high mean mowing percentage of pasture (OR=1.02).

A randomised controlled trial into the effects of food on ADHD.

The aim of this study is to assess the efficacy of a restricted elimination diet in reducing symptoms in an unselected group of children with Attention deficit/hyperactivity disorder (ADHD). Dietary studies have already shown evidence of efficacy in selected subgroups. Twenty-seven children (mean age 6.2) who all met the DSM-IV criteria for ADHD, were assigned randomly to either an intervention group (15/27) or a waiting-list control group (12/27). Primary endpoint was the clinical response, i.e. a decrease in the symptom scores by 50% or more, at week 9 based on parent and teacher ratings on the abbreviated ten-item Conners Scale and the ADHD-DSM-IV Rating Scale. The intention-to-treat analysis showed that the number of clinical responders in the intervention group was significantly larger than that in the control group [parent ratings 11/15 (73%) versus 0/12 (0%); teacher ratings, 7/10 (70%) versus 0/7 (0%)]. The Number of ADHD criteria on the ADHD Rating Scale showed an effect size of 2.1 (cohen’s d) and a scale reduction of 69.4%. Comorbid symptoms of oppositional defiant disorder also showed a significantly greater decrease in the intervention group than it did in the control group (cohens’s d 1.1, scale reduction 45.3%). A strictly supervised elimination diet may be a valuable instrument in testing young children with ADHD on whether dietary factors may contribute to the manifestation of the disorder and may have a beneficial effect on the children’s behaviour.

An inactivated gE-negative marker vaccine and an experimental gD-subunit vaccine reduce the incidence of bovine herpesvirus 1 infections in the field.

An inactivated glycoprotein E-negative vaccine and an experimental glycoprotein D-subunit vaccine against bovine herpesvirus 1 (V1) were examined for their effectiveness in a randomized, double-bline, placebo-controlled field trial comprising 130 dairy farms. The use of these marker vaccines enabled us to monitor the incidence of infections in vaccinated populations. The aims of this trial were to evaluate whether these vaccines: (1) reduce the proportion of outbreaks in dairy herds; and (2) reduced virus transmission within dairy herds and to what extent. Vaccination with either of the two vaccines significantly reduced the proportion of herds wherein an outbreak occurred as well as the virus transmission within herds, as compared to placebo-treated herds. The estimated number of secondary cases caused by one infectious animal, expressed as the reproduction ratio R, was for both vaccines significantly > 1. This indicates that when BHV1 is introduced into vaccinated herds, major outbreaks may still occur.

A cross-sectional study into prevalence and risk indicators of digital haemorrhages in female dairy calves

Abstract Hind claws of 1141 female dairy calves, between 2.5 and 12 months old, were examined for signs of sole haemorrhages. The prevalence of sole haemorrhages was 37.9%. The presence of these haemorrhages was related positively to age. Apparently, the presence of sole haemorrhages had become a common condition during the early rearing period of these calves. The aetiology of sole haemorrhages might include internal (metabolic, other diseases) as well as external (trauma) factors. The aetiological relevance of these factors for sole haemorrhages (breed, age, nutrition, health status, housing, hygiene measures and management) was determined using a questionnaire and claw trimming for diagnosis. Housing on straw was a preventive factor for sole haemorrhages compared with housing on slatted floors. The presence of dermatitis interdigitalis was related positively to sole haemorrhages as well. Also, internal factors were important, because feeding of hay and supplying concentrates were related negatively to red discoloration.

Pathogen group specific risk factors at herd, heifer and quarter levels for intramammary infections in early lactating dairy heifers

Risk factors for intramammary infections caused by coagulase-negative staphylococci, contagious major pathogens and environmental major pathogens in early lactating heifers were evaluated at the herd, heifer and quarter levels. In total, 764 quarters of 191 dairy heifers in 20 randomly selected farms in Flanders (Belgium) were sampled. Quarter milk samples were collected between 1 and 4 days in milk and between 5 and 8 days in milk for bacteriological culture. Data were analyzed using multivariable, multilevel logistic regression analysis. Higher average herd milk somatic cell count (>200,000 cells/mL), not having an effective fly control strategy, contact with lactating cows prior to calving and moderate to severe udder edema prior to calving increased the odds of intramammary infections caused by contagious major pathogens. Poor heifer hygiene and lack of mineral/vitamin supplementation prior to calving were risk factors for intramammary infection caused by environmental major pathogens. Teat apex colonization with coagulase-negative staphylococci prior to calving seemed to protect quarters against intramammary infections caused by major pathogens. Poor heifer hygiene before calving, a non-clipped udder and not practicing of teat dipping prior to calving increased the odds of intramammary infection with coagulase-negative staphylococci. Although management is important in the prevention and control of intramammary infections in early lactating heifers, most variation in the prevalence of intramammary infections resided at the heifer and quarter levels, indicating that the susceptibility for intramammary infections around calving is mainly determined by heifer and quarter characteristics.

A quantitative microbial risk assessment for meatborne Toxoplasma gondii infection in The Netherlands.

Toxoplasma gondii is an important foodborne pathogen, and the cause of a high disease burden due to congenital toxoplasmosis in The Netherlands. The aim of this study was to quantify the relative contribution of sheep, beef and pork products to human T. gondii infections by Quantitative Microbial Risk Assessment (QMRA). Bradyzoite concentration and portion size data were used to estimate the bradyzoite number in infected unprocessed portions for human consumption. The reduction factors for salting, freezing and heating as estimated based on published experiments in mice, were subsequently used to estimate the bradyzoite number in processed portions. A dose-response relation for T. gondii infection in mice was used to estimate the human probability of infection due to consumption of these originally infected processed portions. By multiplying these probabilities with the prevalence of T. gondii per livestock species and the number of portions consumed per year, the number of infections per year was calculated for the susceptible Dutch population and the subpopulation of susceptible pregnant women. QMRA results predict high numbers of infections per year with beef as the most important source. Although many uncertainties were present in the data and the number of congenital infections predicted by the model was almost twenty times higher than the number estimated based on the incidence in newborns, the usefulness of the advice to thoroughly heat meat is confirmed by our results. Forty percent of all predicted infections is due to the consumption of unheated meat products, and sensitivity analysis indicates that heating temperature has the strongest influence on the predicted number of infections. The results also demonstrate that, even with a low prevalence of infection in cattle, consumption of beef remains an important source of infection. Developing this QMRA model has helped identify important gaps of knowledge and resulted in the following recommendations for future research: collect processing-effect data in line with consumer style processing and acquire product specific heating temperatures, investigate the presence and concentration of viable bradyzoites in cattle, determine the effect of mincing meat on bradyzoite concentrations using actual batch sizes, and obtain an estimate of the fraction of meat that has been frozen prior to purchase. With more accurate data this QMRA model will aid science-based decision-making on intervention strategies to reduce the disease burden from meatborne T. gondii infections in The Netherlands.

The effect of digital lesions and floor type on locomotion score in Dutch dairy cows

This study describes the effects of floor system, digital dermatitis (DD) and interdigital dermatitis and heel-horn erosion (IDHE) on locomotion performance in 225 dairy cows of 12 commercial dairy herds. Nine herds were kept in cubicle houses with concrete passageways (either solid, slatted, or grooved concrete) and three herds were kept in straw yards. Animals were at most five times examined at monthly intervals for lesion severity of DD and IDHE and for locomotion score. Locomotion score was rated on a scale ranging from 1 to 5 (from normal to severe) and disturbed locomotion (lameness) was defined as a score > or =3. A logistic regression model was used to analyze the 943 observations using lameness (yes/no) as outcome variable. The proportion of observations scored as lame (locomotion score > or =3) increased from 18% 1 month after trimming to 29% at 4 months after trimming. Severe lesions of DD and IDHE were associated with a significantly higher proportion of lame cows. The proportion of animals with disturbed locomotion increased from 16% to 40% as the severity of DD increased and from 17% to 30% with increasing severity of IDHE lesions. Locomotion performance highly differed between the cubicle house and straw yard group. Only 1% of all gaits in straw yard cows were scored as lame, while in cubicle housed cows these percentages varied from 24% to 46% with grooved floors showing the highest average locomotion score. Due to the extreme low incidence of lameness in straw yards, the statistical analysis had to be restricted to observations on concrete floors (n=744). The logistic regression model with lameness (yes/no) as dependent variable and random effects of cow and herd resulted in Odds Ratios for severe DD and IDHE of, respectively, 3.2 and 3.2, both significantly larger than unity. Cows housed at grooved concrete floors showed the highest OR of 6.5 compared to solid concrete floors. Recovery of lameness was poor as disturbance in gait lasted several months.