Growth of singletons born after frozen embryo transfer until early adulthood: a Finnish register study

STUDY QUESTION

Are there growth differences between singleton children born after frozen embryo transfer (FET), fresh embryo transfer (ET), and natural conception (NC)?

SUMMARY ANSWER

Adolescent boys born after FET have a higher mean proportion and increased odds of overweight compared to those born after fresh ET.

WHAT IS KNOWN ALREADY

Children born after FET have higher mean birthweights and an increased risk of large-for-gestational-age compared to those born after fresh ET and even NC. This raises questions about possible growth differences later in childhood. Previous studies on child growth after FET report partly conflicting results and lack long-term data until adolescence.

STUDY DESIGN, SIZE, DURATION

This was a cohort study based on national population-based registers, the Finnish Medical Birth Register and the Register of Primary Health Care visits, including singletons born after FET (n = 1825), fresh ET (n = 2933), and NC (n = 31 136) in Finland between the years 1995 and 2006.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The proportions of overweight (i.e. age- and sex-adjusted ISO-BMI for children ≥ 25) were compared between the groups. Odds ratios (ORs) and adjusted odds ratios (aORs) of overweight were calculated. Adjustments were made for birth year, preterm birth, maternal age, parity, and socioeconomic status. Mean heights, weights, and BMIs were compared between the groups each year between the ages of 7 and 18.

MAIN RESULTS AND THE ROLE OF CHANCE

FET boys had a higher mean proportion of overweight (28%) compared to fresh ET (22%, P < 0.001) and NC (26%, P = 0.014) boys. For all ages combined, the aOR of overweight was increased (1.14, 95% CI 1.02-1.27) for FET boys compared to fresh ET boys. For girls, the mean proportions of overweight were 18%, 19%, and 22% for those born after FET, fresh ET, and NC, respectively (P = 0.169 for FET vs fresh ET, P < 0.001 for FET vs NC). For all ages combined, FET girls had a decreased aOR of overweight (0.89, 95% CI 0.80-0.99) compared to NC girls. Growth measurements were available for 6.9% to 30.6% of FET boys and for 4.7% to 29.4% of FET girls at different ages.

LIMITATIONS, REASONS FOR CAUTION

Unfortunately, we were not able to adjust for parental anthropometric characteristics. The growth data were not available for the whole cohort, and the proportion of children with available measurements was limited at the start and end of the follow-up. During the study period, mainly cleavage stage embryos were transferred, and slow freezing was used for ART.

WIDER IMPLICATIONS OF THE FINDINGS

The risk of overweight among FET boys warrants further research. Future studies should aim to investigate the mechanisms that explain this sex-specific finding and combine growth data with long-term health data to explore the possible risks of overweight and cardiometabolic disease in adulthood.

STUDY FUNDING/COMPETING INTEREST(S)

Funding was obtained from the Päivikki and Sakari Sohlberg Foundation, the Alma and K.A. Snellman Foundation (personal grants to A.M.T.), and the Finnish Government Research Funding. The funding sources were not involved in the planning or execution of the study. The authors declare no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Health of singletons born after frozen embryo transfer until early adulthood: a Finnish register study

STUDY QUESTION

Is the health of singletons born after frozen embryo transfer (FET) comparable to that of singletons born after fresh embryo transfer (ET) until early adulthood?

SUMMARY ANSWER

The health of singletons born after FET does not differ from that of singletons born after fresh ET.

WHAT IS KNOWN ALREADY

The differences in perinatal outcomes of children born after FET and fresh ET are well known. FET is associated with an increased risk of large-for-gestational-age but diminished risks of preterm birth (PTB), small-for-gestational-age and decreased perinatal mortality compared to fresh ET. However, knowledge on the long-term health after FET is scarce.

STUDY DESIGN, SIZE, DURATION

This retrospective register-based cohort study compares singletons born after FET (n = 1825) between the years 1995 and 2006 to those born after fresh ET (n = 2933) and natural conception (NC, n = 31 136) with a mean follow-up time of 18-20 years.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Singletons born after FET were compared to those born after fresh ET and NC regarding the frequencies of diagnoses in the main ICD-10 chapters (International Statistical Classification of Diseases and Related Health Problems, 10th revision), the number of outpatient visits and hospital admissions, and mortality. Adjustments were made for PTB, maternal age, parity, socioeconomic status based on mother's occupation and offspring sex. The study combines data from the Finnish Medical Birth Register, the Finnish Care Register for Health Care (CRHC) and the Cause-of-Death Register at Statistics Finland. The Student's T-test was used for continuous variables, and the Chi-square test was used for categorical variables. Cox regression was used to estimate crude and adjusted hazard ratios (HRs and aHRs, respectively). A general linear model was used to compare the means of outpatient visits, hospital admissions and lengths of hospital stays per person.

MAIN RESULTS AND THE ROLE OF CHANCE

No significant differences between the FET and fresh ET groups were found in the frequency of diagnoses in any of the ICD-10 chapters or in the parameters describing the need for hospital care. However, compared to the NC group, higher proportions in the FET group had outpatient visits in the hospital (93.5% vs 92.2%, aHR 1.23, 95% CI 1.17, 1.30) or hospital admissions (48% vs 46.5%, aHR 1.28, 95% CI 1.19, 1.37). Compared to the NC group, the FET group had elevated adjusted risks of diagnoses of infectious and parasitic diseases (aHR 1.24; 95% CI 1.11, 1.38), neoplasms (aHR 1.68; 95% CI 1.48, 1.91), diseases of the eye and adnexa, the ear or mastoid process (aHR 1.11; 95% CI 1.01, 1.21), the respiratory system (aHR 1.15; 95% CI 1.06, 1.23), the digestive system (aHR 1.17; 95% CI 1.05, 1.32), the skin or subcutaneous tissue (aHR 1.28; 95% CI 1.14, 1.43) and the genitourinary system (aHR 1.27; 95% CI 1.11, 1.45), as well as congenital malformations or chromosomal abnormalities (aHR 1.31; 95% CI 1.14, 1.50) and symptoms, signs or abnormal clinical or laboratory findings (aHR 1.25, 95% CI 1.16, 1.34).

LIMITATIONS, REASONS FOR CAUTION

Only hospital-based inpatient and outpatient care is covered by the CRHC register, excluding milder cases diagnosed elsewhere. We were not able to study the effect of ART treatments and subfertility separately in our setting. In addition, although our cohort is reasonably sized, even larger cohorts would be needed to reliably study rare outcomes, such as cancer.

WIDER IMPLICATIONS OF THE FINDINGS

For many ICD-10 chapters, we present the first published data on the long-term outcome of singletons born after FET. The results on FET versus fresh ET are reassuring, whereas the results on FET versus NC warrant further investigation.

STUDY FUNDING/COMPETING INTEREST(S)

Finnish government research funding was obtained for this study. Funding was also obtained from the Finnish Medical Society Duodecim, the Päivikki and Sakari Sohlberg Foundation, Orion Research Foundation, Finnish Society of Obstetrics and Gynaecology (research grants to A.M.T.) and Finnish government research funding. The funding sources were not involved in the planning or execution of the study. The authors have no competing interests to declare.

TRIAL REGISTRATION NUMBER

N/A.

P–791 Comparison of the live birth rate after single embryo transfer in fresh versus frozen cycle: no evidence to support routine freeze-all strategy

Study question

Is the treatment outcome compromised after superovulation for fresh IVF/ICSI in comparison to frozen cycle with spontaneous ovulation and luteal support with progesterone?

Summary answer

Live birth rate (LBR) is dependent on embryo quality both in the fresh and frozen cycles with no sign of harmful effect of the superovulation.

What is known already

Freeze-all strategy has been advocated in recent years based on the assumption that luteal phase after superovulation is not optimal for embryo implantation. The effects of variable hormonal treatments, given in association with ART, on the endometrium, are still largely unknown. Therefore, more data is needed in order to optimize the treatment policies.

Study design, size, duration

This is an observational retrospective single-center cohort study. Data were collected from Oulu University Hospital’s ART-database including a total of 5647 single embryo transfer cycles from years 1995–2020. Patients stimulated with long agonist protocol for IVF/ICSI and day 2–3 transfer were included. Frozen embryo transfer was performed in a natural cycle with an ovulation test used for timing of transfer. Luteal support with progesterone was given for two weeks in all cycles.

Participants/materials, setting, methods

There were 3053 IVF/ICSI fresh cycles (2237 top and 816 N-top) and 2594 frozen cycles (806 top and 1788 N-top). The main outcome measure was LBR compared between fresh and frozen cycles when either a top or a N-top embryo was transferred. As a secondary outcome, clinical pregnancy rate was investigated. Data on the age and body mass index (BMI) of the patients was available. Student’s T-test was used to compare continuous variables.

Main results and the role of chance

The groups did not differ regarding the age and BMI of the patients. After the transfer of a top quality embryo the clinical pregnancy rate (35.4 vs. 30.8%; p &lt; 0.05) and LBR (29.4 vs. 25.5%; p not significant) was slightly higher in the fresh cycle. After the transfer of a N-top quality embryo the clinical pregnancy rate (19.9 vs. 19.4%) and LBR (15.9 vs. 15.4%) were similar both in the fresh and frozen cycles.

Limitations, reasons for caution

This study only represents cleavage stage embryo transfers, and all FETs were performed in a natural cycle. In a retrospective study there may also be residual confounding that could not be excluded.

Wider implications of the findings: This study provides further evidence that treatment outcome regarding LBR is not affected by superovulation therapy. Hence, the use of freeze-all strategy is warranted only in cases with a risk of ovarian hyperstimulation syndrome.

Trial registration number

Not applicable

High birth weight and large-for-gestational-age in singletons born after frozen compared to fresh embryo transfer, by gestational week: a Nordic register study from the CoNARTaS group

STUDY QUESTION

When do the differences in birth weights become apparent between singletons born after frozen embryo transfer (FET) and fresh embryo transfer (fresh ET)?

SUMMARY ANSWER

Mean birth weights after FET become significantly higher starting from gestational week (GW) 33 among boys and from GW 34 among girls.

WHAT IS KNOWN ALREADY

In recent years, there has been a steep rise in recorded FET treatments, enabling widespread use of elective single embryo transfer, thus reducing the risks associated with multiple gestations. However, singletons born after FET are heavier and there is a higher risk of large-for-gestational-age (LGA) (birth weight > 90 percentiles) compared to fresh ET. In contrast, risk of small-for-gestational-age (SGA, birth weight < 10 percentiles) is lower in singletons born after FET compared to fresh ET. The reasons, timing and consequences of these differences remain largely unclear. There is limited evidence about whether this difference in growth develops before the last trimester of pregnancy.

STUDY DESIGN, SIZE, DURATION

This retrospective Nordic register-based cohort study compared singletons born after FET (n = 17 500) to singletons born after fresh ET (n = 69 510) and natural conception (NC, n = 3 311 588). All live born singletons born between the years 2000 and 2015 in Denmark, Norway and Sweden at gestational age ≥22 weeks were included from the population-based Committee of Nordic ART and Safety (CoNARTaS) study population.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Children born after FET were compared to those born after fresh ET and NC for mean birth weight and proportion of LGA and SGA for each GW at birth. Chi-square test and tests for relative proportions were used to compare categorical variables and Student's t-test was used to compare continuous variables. Adjusted odds ratios (aORs) for LGA and SGA were calculated using logistic regressions, adjusting for year of birth, maternal age, parity, BMI, chronic hypertension, diabetes, smoking and offspring sex.

MAIN RESULTS AND THE ROLE OF CHANCE

Mean birth weights were significantly higher after FET compared to fresh ET starting from GW 33 (range from 75 g to 228 g by week) for boys and starting from GW 34 (range from 90 g to 236 g by week) for girls. Boys born after FET had a significantly higher proportion of LGA (11.0-15.1%) at birth between GW 36 and 42, compared to those born after fresh ET (7.1-9.4%) (range from P < 0.001 to P = 0.048 by week). For girls born after FET, the difference was seen between GW 37 and 42 (10.6-13.4%) compared to those born after fresh ET (6.6-8.0%) (range from P < 0.001 to P = 0.009 by week).The proportion of SGA was significantly lower among boys born after FET (7.6-8.7%) compared to fresh ET (11.9-13.6%) between GW 36 and 42 (range from P < 0.001 to P = 0.016 by week). For girls born after FET, the difference was seen between GW 38 and 42 (7.0-9.3%) compared to those born after fresh ET (13.0-14.6%) (P < 0.001). The proportion of LGA (12.3-15.1%) was significantly higher for boys born after FET between GW 38 and 41 (P < 0.001) and for girls born after FET (12.6-13.4%) between GW 37 and 40 (range from P < 0.001 to P = 0.018 by week), compared to naturally conceived boys (9.7-9.9%) and girls (9.0-10.0%). All singletons born after FET had a higher risk of LGA compared to singletons born after fresh ET (aOR 1.87, 95% CI 1.76-1.98) and singletons born after NC (aOR 1.28, 95% CI 1.22-1.35).

LIMITATIONS, REASONS FOR CAUTION

There may be residual confounding factors that we were not able to control for, most importantly the causes of preterm birth, which may also influence foetal growth. A further limitation is that we have no knowledge on growth patterns between implantation and GW 22. Finally, the number of children born extremely preterm or post-term was limited even in this large study population.

WIDER IMPLICATIONS OF THE FINDINGS

This is, to date, the largest study on birth weights among preterm and term ART singletons with a population-based design and NC control group. The results suggest that the freeze-thaw process is associated with higher birthweights and greater risk of LGA at least in the last trimester of pregnancy. This is an important aspect of the safety profile of ART. More research is needed on the long-term outcome of these children.

STUDY FUNDING/COMPETING INTEREST(S)

The CoNARTaS collaboration has received the following funding: the Nordic Trial Alliance: a pilot project jointly funded by the Nordic Council of Ministers and NordForsk [71450], the Central Norway Regional Health Authorities [46045000], the Norwegian Cancer Society [182356-2016], the Nordic Federation of Obstetrics and Gynaecology [NF13041, NF15058, NF16026 and NF17043], the Interreg Öresund-Kattegat-Skagerrak European Regional Development Fund (ReproUnion project) and the Research Council of Norway's Centre of Excellence funding scheme [262700]. None of the authors have any competing interests to declare.

TRIAL REGISTRATION NUMBER

ISRCTN11780826.

110 Absence of transmission of Mycoplasma bovis via naturally contaminated semen during invitro fertilization

Mycoplasma bovis (Mbo) has been isolated from genital tracts of bulls, and it can survive in processed semen. Experimental studies have shown that Mbo inoculation into the uterus or insemination with Mbo-infected semen can cause bursitis, salpingitis, abortion, and infertility. The control of Mbo is very difficult because of latent carrier animals, increasing resistance to antibiotics, and unavailability of effective vaccines. The aim of this study was to follow the passage of Mbo infection from naturally contaminated semen to transferable embryos during bovine invitro embryo production (IVP). (Unless otherwise stated, all chemicals used were purchased from Sigma-Aldrich.) Two batches of slaughterhouse-derived oocytes were matured in tissue culture medium 199 (TCM-199) with glutamax-I (Gibco™; Invitrogen Corporation) supplemented with 0.25mM sodium pyruvate, 100IUmL−1 penicillin, 100µgmL−1 streptomycin, 2ngmL−1 FSH (Puregon, Organon), 1µgmL−1 β-oestradiol (E-2257), and 10% heat-inactivated fetal bovine serum (FBS; Gibco™) for 24h at 38.5°C in maximal humidity in 5% CO2 in air. Matured oocytes were fertilized for 20h in IVF-TL medium supplemented with 10µgmL−1 of heparin and 2mM of PHE at 38.5°C in maximal humidity in 5% CO2 in air, using spermatozoa per mL as a final concentration. The batches of oocytes were divided between uninfected IVP bull (N=205) and naturally Mbo-infected AI bull (N=690). Zygotes were cultured in G1/G2 media (Vitrolife) supplemented with bovine serum albumin, fatty acid free (4mgmL−1), at 38.5°C in maximal humidity in 5% O2, 5% CO2, and 90% N2. Blastocysts were collected for Mbo cultures on Days 7 and 8 (IVF=Day 0). Samples of washed semen, fertilization medium, cumulus cells, culture medium, all wash media, and transferable embryos (with and without zona pellucidae) were collected for Mbo cultures. Half of the embryos were treated with trypsin according to IETS standards after the collections. The Mbo cultures were performed in accordance with procedures previously described by Bölske (1988 Zentralbl. Bakteriol. Mikrobiol. Hyg. A 69, 331-340), followed by detection with real-time PCR. Infection with Mbo does not seem to have negative effects on fertilization (cleavage rates: 77.1% and 89.0% for IVP and Mbo AI bulls, respectively) or embryo development rates (blastocyst rate: 26.3% and 32.5% for IVP and Mbo AI bulls, respectively). Following Mbo cultures, only washed semen was found to be Mbo positive via real-time PCR. We conclude that M. bovis is not likely transmitted in bovine IVP when using naturally infected semen. We acknowledge Tiina Kortelainen for technical assistance and the Ministry of Agriculture and Forestry for funding.

Comparison of Finnish meat inspection records and average daily gain for cattle herds differing in Mycoplasma bovis test-status

Detecting Mycoplasma bovis on cattle farms represents a challenge in the absence of an outbreak or cases of M. bovis mastitis, yet identification of an infection is essential to control the spread of the disease successfully. The objectives of this study were: (1) to determine whether meat inspection records can aid identification of cattle farms supporting M. bovis infection, and (2) to compare the average daily weight gain estimated from carcass weight for cattle originating from farms differing in M. bovis test-status. Meat inspection records were collected from two abattoirs in 2015; 80 677 animals in total. All the dairy and mixed breed cows and bulls used for meat production were categorized according to known M. bovis infection status of the farms from which the cattle were derived; positive, contact or control farms. The associations between animals from different M. bovis categories and lung lesions of bulls and cows (pneumonia and pleuritis), identified during meat inspection, and estimated average daily gain (ADG) of bulls, were investigated. The odds ratios for lung lesions, especially pleuritis, were higher in M. bovis test-positive or contact farms compared with control farms. Additionally, odds ratios for pleuritis were higher among animals from M. bovis test-positive farms and animals from contact slaughtering farms originating from M. bovis-free rearing farms. Bulls originating from M. bovis test-positive farms had higher estimated average daily gain than cattle from control farms. Meat inspection records can be used alongside other methods to detect M. bovis-positive farms where M. bovis causes lung lesions.

Variation in the hyphal growth rate and the virulence of two genotypes of the crayfish plague organism Aphanomyces astaci

Crayfish plague, a devastating disease of freshwater crayfish, is caused by an oomycete organism, Aphanomyces astaci. Currently five genotypes of A. astaci are known, but variable features between the strains or genotypes have not been studied extensively. This study analysed 28 isolates of the As genotype and 25 isolates of the Ps1 genotype and reveals that the radial growth rate is significantly (P < 0.001) different between these two genotypes, although highly variable inside the genotype As. Two Ps1 genotype isolates and two As genotype isolates with different radial growth rates were tested in an infection trial. Clear differences were detected in the development of mortality in the test groups. The representatives of the Ps1 genotype caused total mortality within a short time span. The As genotype isolates were much less virulent. The slow-growing As isolate showed higher virulence than the As isolate with a high growth capacity. Although slow growth could be one survival strategy of the pathogen, several other mechanisms are involved in the pathogenicity and warrant further studies.

Physical health of singleton children born after frozen embryo transfer using slow freezing: a 3-year follow-up study

STUDY QUESTION

Are there differences in the physical health of singleton children born after frozen embryo transfer (FET) compared with children born after fresh embryo transfer (fresh ET)?

SUMMARY ANSWER

Register-based health indicators were similar among FET and fresh ET singletons during a 3-year follow-up.

WHAT IS KNOWN ALREADY

Large cohort studies have shown that perinatal outcomes are similar or even better in FET than fresh ET children. The early childhood morbidity among FET and fresh ET children has been shown to be quite similar, but so far these studies have been small. The short-term health outcomes of assisted reproductive technology (ART) children have been shown to be slightly worse compared with spontaneously conceived children.

STUDY DESIGN, SIZE, DURATION

This register-based study includes women who had undergone ART treatments leading to singleton live births (n = 4758 children) in 1995-2006. A 10% random sample of women with spontaneous pregnancies from the Finnish Medical Birth Register (FMBR) served as the reference group (n = 31 137 children). The children were identified through the FMBR by using the mother's personal identification (ID) number. Children's ID numbers were linked with two nationwide registries; the Finnish Hospital Discharge Register and the Cause-of-Death Register at Statistics Finland. Information on all visits was received until 2009 using ICD-10 codes.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The study includes 1825 children born after FET, 2933 children born after fresh ET and 31 137 children born after spontaneous pregnancies. The risk estimates for diseases were adjusted for the child's year of birth and maternal age, parity, socio-economic status and prematurity. The study focused on the differences between FET and fresh ET children.

MAIN RESULTS AND THE ROLE OF CHANCE

Most health indicators were similar among FET and fresh ET children during the 3-year follow-up. The most common discharge diagnoses, including gastroenteritis and colitis, otitis, upper and lower respiratory diseases, asthma and allergies were similar between the ART groups. A large proportion of FET children (70.1%) and fresh ET children (69.9%) had visited a hospital at least once (P = 0.877). The risk of hospital admission did not differ between the two groups after adjusting for premature births [adjusted odds ratio (aOR) 1.01; 0.88-1.17]. Comparing with children born after spontaneously conceived pregnancies, the risk of hospital admission was slightly increased in the ART group, even after adjusting for premature births (aOR 1.10; 1.02-1.19).

LIMITATIONS, REASONS FOR CAUTION

Due to the study design, we were not able to control for some parental background factors, such as the cause and length of infertility. Furthermore, the health registries do not include data on the growth of the children. Our findings are generalizable only to the slow-freezing method.

WIDER IMPLICATIONS OF THE FINDINGS

Our study provides further evidence of the safety of embryo cryopreservation. The early physical health of FET children is similar to that of children born after fresh ET.

STUDY FUNDING/COMPETING INTERESTS

This study was funded by the University Hospital of Oulu and Helsinki, Finland. The National Institute for Health and Welfare (THL) covered the data linkages and the work of Mika Gissler. There are no competing interests to be reported.

Hybrids of Shigatoxigenic and Enterotoxigenic Escherichia coli (STEC/ETEC) Among Human and Animal Isolates in Finland

Diarrhoeagenic Escherichia coli (DEC) cause serious foodborne infections in humans. Total of 450 Shigatoxigenic E. coli (STEC) strains isolated from humans, animals and environment in Finland were examined by multiplex PCR targeting the virulence genes of various DEC pathogroups simultaneously. One per cent (3/291) of the human STEC and 14% (22/159) of the animal and environmental STEC had genes typically present in enterotoxigenic E. coli (ETEC). The strains possessed genes encoding both Shiga toxin 1 and/or 2 (stx1 and/or stx2 ) and ETEC-specific heat-stable (ST) enterotoxin Ia (estIa). The identified stx subtypes were stx1a, stx1c, stx2a, stx2d and stx2g. The three human STEC/ETEC strains were isolated from the patients with haemolytic uraemic syndrome and diarrhoea and from an asymptomatic carrier. The animal STEC/ETEC strains were isolated from cattle and moose. The human and animal STEC/ETEC strains belonged to 11 serotypes, of which O2:H27, O15:H16, O101:H-, O128:H8 and O141:H8 have previously been described to be associated with human disease. Identification of multiple virulence genes offers further information for assessing the virulence potential of STEC and other DEC. The emergence of novel hybrid pathogens should be taken into account in the patient care and epidemiological surveillance.

Distribution and epidemiology of genotypes of the crayfish plague agent Aphanomyces astaci from noble crayfish Astacus astacus in Finland

The crayfish plague agent Aphanomyces astaci was isolated from 69 noble crayfish Astacus astacus samples in Finland between 1996 and 2006. All isolates were genotyped using randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR). Altogether, 43 isolates belonged to the genotype group of Astacus strains (As), which is assumed to represent the genotype originally introduced into Europe around 1860 and into Finland in 1893. There were 26 crayfish plague isolates belonging to the group of Pacifastacus strain I (Ps1), which appeared in Europe after the stocking of the North American species signal crayfish Pacifastacus leniusculus. The geographical distribution of the 2 genotypes in Finland corresponded with the stocking strategies of signal crayfish. The majority of Ps1-strains (83%) were associated with a classical crayfish plague episode involving acute mortality, compared with only 33% of the As-strains. As-strains were found more often by searching for reasons for population declines or permanently weak populations, or through cage experiments in connection with reintroduction programmes. In some water bodies, isolations of the As-strains were made in successive years. This study shows that persistent crayfish plague infection is not uncommon in noble crayfish populations. The described epidemiological features suggest a difference in virulence between these 2 genotypes.

Eradication of endemicBrachyspira pilosicoliinfection from a farrowing herd: a case report

Brachyspira pilosicoliandB. innocenswere isolated repeatedly from a herd of 60 sows which mostly produced feeder pigs but also raised some fattening pigs. Postweaning diarrhea had been a severe problem in this herd for years. TheB. pilosicolieradication plan was based on the general guidelines for elimination ofB. hyodysenteriae, with some modifica-tions. The eradication measures were run in August 1997. In-feed medication with 200p.p.m. tiamulin lasted for 18–30 days, depending on the age group. The piggery unit was emptied, cleaned, disinfected and dried, and all worn surfaces were repaired. The animals were removed to temporary sheds situated 0–100m from the piggery unit. Only the sows and the boar returned to the piggery unit. All other pigs were sold from the sheds within 3 months after the eradication. Immediately after the eradication, the clinical postweaning diarrhea disappeared. The success of the program was monitored four times bacteriologically, and the last control sampling was in December 1999, 7 months after the total withdrawal of antimicrobial feed additives. The primary cultures from the last three samplings were also analysed withB. pilosicoli-specific PCR. All the samples were negative forB. pilosicoli. However,B. innocenscould be isolated from each batch of samples. The analysis ofB. inno-censisolates by pulsed-field gel electrophoresis indicated that at least one genotype persisted in the herd. The clinical and laboratory findings suggest that the eradication ofB. pilosicolihad succeeded in this herd

Etiology of respiratory disease in non-vaccinated, non-medicated calves in rearing herds

The aim of this study was to examine the occurrence of bacterial, mycoplasmal and viral pathogens in the lower respiratory tract of calves in all-in all-out calf-rearing units. According to clinical status, non-medicated calves with and without respiratory disease signs were selected of the 40 herds investigated to analyse the micro-organisms present in healthy and diseased calves. Tracheobronchial lavage (TBL) and paired serum samples were analysed for bacteria, mycoplasmas, respiratory syncytial virus (RSV), parainfluenza virus 3 (PIV3), bovine corona virus (BCV) and bovine adenovirus (BAV). Pasteurella multocida was the most common bacterial pathogen. It was isolated from 34% of the TBL samples in 28 herds and was associated with clinical respiratory disease (p < 0.05) when other pathogenic bacteria or mycoplasma were present in the sample. Mannheimia spp. and Histophilus somni were rarely found. Mycoplasma bovis was not detected at all. Ureaplasma diversum was associated with clinical respiratory disease (p < 0.05). TBL samples from healthy or suspect calves were more often negative in bacterial culture than samples from diseased calves (p < 0.05). No viral infections were detected in six herds, while 16-21 herds had RSV, BCV, BAV or PIV3. In the herds that had calves seroconverted to BCV, respiratory shedding of BCV was more frequently observed than faecal shedding. This study showed that the microbial combinations behind BRD were diverse between herds. M. bovis, an emerging pathogen in many countries, was not detected.

Neither hippurate-negative Brachyspira pilosicoli nor Brachyspira pilosicoli type strain caused diarrhoea in early-weaned pigs by experimental infection

A hippurate-negative biovariant of Brachyspira pilosicoli (B. pilosicoli^hipp-) is occasionally isolated in diarrhoeic pigs in Finland, often concomitantly with hippurate-positive B. pilosicoli or Lawsonia intracellularis. We studied pathogenicity of B. pilosicoli^hipp- with special attention paid to avoiding co-infection with other enteric pathogens. Pigs were weaned and moved to barrier facilities at the age of 11 days. At 46 days, 8 pigs were inoculated with B. pilosicoli^hipp- strain Br1622, 8 pigs were inoculated with B. pilosicoli type strain P43/6/78 and 7 pigs were sham-inoculated. No signs of spirochaetal diarrhoea were detected; only one pig, inoculated with P43/6/78, had soft faeces from day 9 to 10 post inoculation. The pigs were necropsied between days 7 and 23 after inoculation. Live pigs were culture-negative for Brachyspira spp., but B. pilosicoli^hipp- was reisolated from necropsy samples of two pigs. The lesions on large colons were minor and did not significantly differ between the three trial groups. In silver-stained sections, invasive spirochaetes were detected in colonic mucosae of several pigs in all groups. Fluorescent in situ hybridisation for genus Brachyspira, B. pilosicoli and strain Br1622 was negative. However, in situ detection for members of the genus Leptospira was positive for spirochaete-like bacteria in the colonic epithelium of several pigs in both infected groups as well as in the control group. L. intracellularis, Salmonella spp., Yersinia spp. and intestinal parasites were not detected. The failure of B. pilosicoli strains to cause diarrhoea is discussed with respect to infectivity of the challenge strains, absence of certain intestinal pathogens and feed and management factors.

A quantitative risk assessment of the public health impact of the Finnish Salmonella control program for broilers

In order to study the public health effects of the Finnish Salmonella control program (FSCP), a quantitative risk assessment model of Salmonella from slaughtered broiler flocks to consumers was developed. Based on the model, approximately 0.21% of domestically produced broiler meat mass was contaminated with Salmonella (95% probability interval 0.05-0.48%). This model was combined to the model on primary production of broilers. By this way, the effect of eliminating breeder flocks from production which have tested positive for Salmonella and heat-treating the meat of detected positive broiler flocks on public health could be simulated. Based on the whole model, if detected positive breeder flocks were not removed this would result in 1.0-2.5 more reported human cases compared to the expected number of cases under current FSCP (95% predictive interval). Without heat treatment of meat the increase would be 2.9-5.4-fold and without both interventions 3.8-9.0-fold. In scenarios with one grandparent or five parent flocks infected, the combined effect of these two interventions was 9.3-25.8-fold and 4.9-11.7-fold compared to the baseline level under each scenario, respectively. The scenario analyses suggest that with a higher infection level, inclusion of both interventions will be more effective than either of the interventions alone. Replacement of half of the current retail broiler meat by meat with 20-40% contamination could result in 33-93 times more human cases compared to the expected value under current situations. On the basis of the model, the interventions applied in FSCP clearly protect the public health.

Molecular characterization of Salmonella enterica subsp. enterica serovar Typhimurium DT1 isolates

Salmonella Typhimurium DT1 is endemic to Finland and has caused human outbreaks since the 1960s. Domestic DT1 isolates (n=235) from 1972 to 1999 from human cases, animals and other sources, as well as foreign DT1 isolates from human cases (n=20) were analysed by molecular methods. Pulsed-field gel electrophoresis (PFGE) yielded 38 XbaI profiles. Of these, XbaI profile 10 was seen in 49% (125/255) of the isolates. Twelve IS200 profiles were obtained; the most common IS200 profile D was seen in 64% (33/52) of the isolates. Two clusters were formed by compilation of the XhaI-, BlnI- and SpeI-PFGE and IS200 profiles and possession of the serovar-specific virulence plasmid. The major cluster contained eight IS200 profiles, including IS200 profile D and XhaI profile 10, and had no virulence plasmid, and can be regarded as typical of the endemic Typhimurium DT1 infection.

Molecular epidemiological study of Brachyspira pilosicoli in Finnish sow herds

Brachyspira (B.) pilosicoli, the causative agent of intestinal spirochaetosis in pigs, is a quite common laboratory finding from faecal samples of weaned and growing pigs in Finland. A better understanding of the epidemiology of B. pilosicoli in and between Finnish pig farms is needed. Altogether 131 B. pilosicoli isolates from 49 Finnish sow herds were studied by pulsed-field gel electrophoresis. MluI was used as a restriction enzyme for all the isolates, and SmaI for 70 isolates. The isolates were divided into 54 different macrorestriction profiles (MRP) by MluI. Most farms had distinct B. pilosicoli genotypes, and common genotypes among herds were rare. B. pilosicoli was re-isolated after 3 years in three herds; the same MRP persisted in each of these herds. A genetic clustering of B. pilosicoli isolates between two major pork production areas was not detected.

Putative virulence factors of atypical Aeromonas salmonicida isolated from Arctic charr, Salvelinus alpinus (L.), and European grayling, Thymallus thymallus (L.)

Atypical Aeromonas salmonicida (AAS) causes generalized lethal infections in farmed Arctic charr, Salvelinus alpinus (L.), and European grayling, Thymallus thymallus (L.), and is thus a serious threat for culture of these fish species. Virulence factors were studied among isolates of AAS from Arctic charr (n = 20), European grayling (n = 19) and other fish species (n = 20), of which 48 were of Finnish and 11 of Swedish origin. All isolates produced an A-layer. Extracellular products (ECP) of the AAS isolates did not produce detectable gelatinase and caseinase activity in test assays. Analysis of the same ECP preparations with substrate sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed weak proteolytic activity, indicating the different sensitivity of the detection methods used. The ECP from AAS isolates showed low cytotoxic activity against cultured cells. However, the ECP did not induce mortality in challenged Arctic charr. The results suggest that toxic components, like ECP, secreted by the bacterium may not be the major virulence factor in AAS-infection in Arctic charr and European grayling, and hence the pathogenesis also differs from the pathogenesis of AAS-infection in Atlantic salmon, Salmo salar L.

Mapping the binding domain of the F18 fimbrial adhesin

F18 fimbrial Esherichia coli strains are associated with porcine postweaning diarrhea and pig edema disease. Recently, the FedF subunit was identified as the adhesin of the F18 fimbriae. In this study, adhesion domains of FedF were further studied by constructing deletions within the fedF gene and expressing FedF proteins with deletions either together with the other F18 fimbrial subunits or as fusion proteins tagged with maltose binding protein. The region essential for adhesion to porcine intestinal epithelial cells was mapped between amino acid residues 60 and 109 of FedF. To map the binding domain even more closely, all eight charged amino acid residues within this region were independently replaced by alanine. Three of these single point mutants expressing F18 fimbriae exhibited significantly diminished capabilities to adhere to porcine epithelial cells in vitro. In addition, a triple point mutation and a double point mutation completely abolished receptor adhesiveness. The result further confirmed that the region between amino acid residues 60 and 109 is essential for the binding of F18 fimbriae to their receptor. In addition, the adhesion capability of the binding domain was eliminated after treatment with iodoacetamide, suggesting the formation of a disulfide bridge between Cys-63 and Cys-83, whereas Cys-111 and Cys-116 could be deleted without affecting the binding ability of FedF.

Mapping the binding domain of the F18 fimbrial adhesin

F18 fimbrial Esherichia coli strains are associated with porcine postweaning diarrhea and pig edema disease. Recently, the FedF subunit was identified as the adhesin of the F18 fimbriae. In this study, adhesion domains of FedF were further studied by constructing deletions within the fedF gene and expressing FedF proteins with deletions either together with the other F18 fimbrial subunits or as fusion proteins tagged with maltose binding protein. The region essential for adhesion to porcine intestinal epithelial cells was mapped between amino acid residues 60 and 109 of FedF. To map the binding domain even more closely, all eight charged amino acid residues within this region were independently replaced by alanine. Three of these single point mutants expressing F18 fimbriae exhibited significantly diminished capabilities to adhere to porcine epithelial cells in vitro. In addition, a triple point mutation and a double point mutation completely abolished receptor adhesiveness. The result further confirmed that the region between amino acid residues 60 and 109 is essential for the binding of F18 fimbriae to their receptor. In addition, the adhesion capability of the binding domain was eliminated after treatment with iodoacetamide, suggesting the formation of a disulfide bridge between Cys-63 and Cys-83, whereas Cys-111 and Cys-116 could be deleted without affecting the binding ability of FedF.

Temperature effect on the immune defense functions of Arctic charr Salvelinus alpinus

The Arctic charr Salvelinus alpinus is an endangered fish species in Finland, and thus farming is carried out mainly for stocking purposes. Farmed charr are susceptible to infection with atypical Aeromonas salmonicida (aAS). Losses of valuable brood stock will severely reduce the genetic diversity of stocked charr. No commercial vaccines are available to prevent aAS infection, and vaccines against furunculosis (caused by typical A. salmonicida, tAS) do not protect the charr against aAS infection. The effects of a metabolizable oil-adjuvanted, bivalent vaccine (containing killed aAS and A. salmonicida salmonicida bacteria) on the immune system of 1 yr old hatchery-reared charr originating from Lake Inari in Northern Finland were examined. Fish vaccination in Finland generally takes place either from October to November or from February to April, when the water temperature is low (1 to 3degrees C). The water temperature starts to increase in mid-May. Therefore, we also investigated whether post-vaccination (p.v.) temperature had an influence on the immune system of this cold-water fish species. The fish were immunized intraperitoneally at 2.9 degrees C at the end of April. After 52 d, during which the water temperature increased from 2.9 to 10.0 degrees C, the charr were exposed to 1 of 3 test temperatures: 10.3, 14.1 or 18.1 degrees C. Prior to vaccination, and 49, 75 and 103 d p.v., several immune parameters were measured in both unvaccinated and vaccinated charr. Vaccination induced a significant anti-aAS-specific antibody response, and increased plasma lysozyme activity at all p.v. temperatures. The haemolytic activity of the complement system was unaffected either by vaccination or p.v. temperatures. There was a slight positive correlation between p.v. temperature and lysozyme activity of the charr. The significant increase in lysozyme activity took place in vaccinated charr in the first 49 d p.v. as water temperatures increased from 2.9 to 10 degrees C. Furthermore, the highest activity of lysozyme in the plasma was observed 49 d p.v. Our results indicate that a rise in water temperature above 10 degrees C does not significantly enhance the vaccination response of charr. This could be one reason why farmed Arctic charr, which are well adapted to a cold climate, are highly susceptible to aAS infection in the summer.

Virulence factors of Escherichia coli isolated from bovine clinical mastitis

Escherichia coli isolates from bovine mastitis were examined for a selection of virulence factors. The strains originated from Finland and Israel, which have differences in the proportion of mastitis caused by E. coli, clinical pictures of coliform mastitis, environmental conditions and herd management. The genes of nine virulence factors were detected by polymerase chain reaction. Presence of K1 and K5 capsules was assessed by use of specific bacteriophages. Serum resistance was tested by a turbidimetric assay. Out of 160 Finnish isolates, 37% had traT, 14% cnf2, 8% cnf1, 11% aer, 9% f17, 8% sfa, 7% pap, 1% afa8D and 1% afa8E. Out of 113 Israeli isolates, 41% had traT, 4% aer, 3% cnf2, 1% cnf1, 1% sfa and 1% f17. Some of the genes were distributed among two major pathotype groups, with either f17 family or sfa, pap and cnf1 as major determinants. Genes for F17a, CS31A, Afa7D and Afa7E were not detected. Altogether 49% of Finnish and 42% of Israeli isolates had at least one virulence gene, but genes other than traT were present in only 24% of Finnish and 5% of Israeli isolates. Serum resistance was more common among Finnish (94/160) than Israeli isolates (19/113). K1 and K5 capsules were not detected.

Characterization of the adhesin of Escherichia coli F18 fimbriae

Previous research has suggested that the adhesin encoded by the F18 fimbrial operon in Escherichia coli is either the FedE or FedF protein. In this work, we show that anti-FedF antibodies, unlike anti-FedE serum, were able to inhibit E. coli adhesion to porcine enterocytes. Moreover, specific adhesion to enterocytes was shown with purified FedF-maltose binding protein.

Mutant bacteriophage with non-catalytic endosialidase binds to both bacterial and eukaryotic polysialic acid and can be used as probe for its detection

There is a molecular mimicry between the polysialic acid polysaccharide of bacterial pathogens causing sepsis and meningitis, and the carbohydrate units of the neural cell adhesion molecule NCAM. We investigated whether bacteriophage mutants with catalytically disabled endosialidase, which bind but do not cleave polysialic acid, could recognise and bind to bacterial and eukaryotic polysialic acid. In nitrocellulose dot blot assay the mutant bacteriophages, but not the wild-type phages, remained specifically bound to polysialic acid-containing bacteria including Escherichia coli K1 and K92, group B meningococci, Mannheimia (Pasteurella) haemolytica A2, and Moraxella nonliquefaciens. A minimum binding requirement was determined to be 10 sialyl residues in the polysialic acid chain. In Western blots the mutant phages specifically bound to the embryonic polysialylated form of NCAM, but not to the adult less sialylated form of the molecule. The mutant phages together with secondary anti-phage antibodies were subsequently successfully used in fluorescence microscopy of cultured cells and light microscopy of paraffin-embedded tissue sections as a probe for the eukaryotic polysialic acid. Thus, mutant bacteriophages of meningitis causing bacteria bind to and detect the molecularly mimicked polysialic acid of the neural cell adhesion molecule in host tissues.

Eradication of endemic Brachyspira pilosicoli infection from a farrowing herd: a case report

Brachyspira pilosicoli and B. innocens were isolated repeatedly from a herd of 60 sows which mostly produced feeder pigs but also raised some fattening pigs. Postweaning diarrhea had been a severe problem in this herd for years. The B. pilosicoli eradication plan was based on the general guidelines for elimination of B. hyodysenteriae, with some modifications. The eradication measures were run in August 1997. In-feed medication with 200 p.p.m. tiamulin lasted for 18-30 days, depending on the age group. The piggery unit was emptied, cleaned, disinfected and dried, and all worn surfaces were repaired. The animals were removed to temporary sheds situated 0-100 m from the piggery unit. Only the sows and the boar returned to the piggery unit. All other pigs were sold from the sheds within 3 months after the eradication. Immediately after the eradication, the clinical postweaning diarrhea disappeared. The success of the program was monitored four times bacteriologically, and the last control sampling was in December 1999, 7 months after the total withdrawal of antimicrobial feed additives. The primary cultures from the last three samplings were also analysed with B. pilosicoli-specific PCR. All the samples were negative for B. pilosicoli. However, B. innocens could be isolated from each batch of samples. The analysis of B. innocens isolates by pulsed-field gel electrophoresis indicated that at least one genotype persisted in the herd. The clinical and laboratory findings suggest that the eradication of B. pilosicoli had succeeded in this herd.

Deletion of the DQ52 element within the Ig heavy chain locus leads to a selective reduction in VDJ recombination and altered D gene usage

The process of V(D)J recombination that leads to the assembly of Ig gene segments is tightly controlled during B cell differentiation. Two germline transcripts, one of which (mu(0)) originates from the promoter region of DQ52, may control the accessibility of the heavy chain locus. Here, we present the analysis of a mouse line in which the DQ52 gene together with its regulatory sequences is deleted by a Cre/loxP-based strategy. In F(1) (DQ52(+/-)) mice, the use of the JH3 and JH4 elements in DJ or VDJ junctions of the DQ52(-) allele was strongly reduced in both the bone marrow pre-B and spleen cells, while the JH1 and JH2 elements were used with normal frequencies. In addition, IgM(+) B cells of bone marrow and spleen used the DQ52(-) allele less frequently. On DJ joints of the DQ52(-) allele, there was 2 times less processing of JH3 ends, which resulted in clearly increased addition of P nucleotides. Although the use of D elements in DJ joints was quite similar, an altered D repertoire was found in VDJ joints of the DQ52(-) allele. In splenic B cells of the DQ52(-/-) mouse the amino acid distribution of the CDR3 was skewed, probably to compensate for the altered processing of JH3 ends. Thus, we have shown an interesting selective effect of the DQ52 region on controlling accessibility to 3' JH elements on the Ig locus, which also seems to influence the processing of DJ joints. We propose a model in which the DQ52 promoter region enhances the induction of secondary DJ rearrangements.

Prevalence and characteristics of shiga toxin-producing Escherichia coli from healthy cattle in Japan

The prevalence of Shiga toxin-producing Escherichia coli (STEC) in Japan was examined by using stool samples from 87 calves, 88 heifers, and 183 cows on 78 farms. As determined by screening with stx-PCR, the prevalence was 46% in calves, 66% in heifers, and 69% in cows; as determined by nested stx-PCR, the prevalence was 100% in all animal groups. Of the 962 isolates picked by colony stx hybridization, 92 isolates from 54 farms were characterized to determine their O serogroups, virulence factor genes, and antimicrobial resistance. Of these 92 isolates, 74 (80%) could be classified into O serogroups; 50% of these 74 isolates belonged to O serogroups O8, O26, O84, O113, and O116 and 1 isolate belonged to O serogroup O157. Locus of enterocyte effacement genes were detected in 24% of the isolates, and enterohemorrhagic E. coli (EHEC) hlyA genes were detected in 72% of the isolates. Neither the bundle-forming pilus gene nor the enteropathogenic E. coli adherence factor plasmid was found. STEC strains with characteristics typical of isolates from human EHEC infections, which were regarded as potential EHEC strains, were present on 11.5% of the farms.

Vaccination influences growth of Arctic charr

There is limited knowledge about the effects of oil-based vaccines on the growth of Arctic charr Salvelinus alpinus, in particular at different rearing temperatures. One-year-old Arctic charr were immunized intraperitoneally at 2.9 degrees C with a metabolizable oil-adjuvanted, bivalent vaccine containing killed typical and atypical Aeromonas salmonicida bacteria. After vaccination the non-vaccinated (controls) and vaccinated individually marked fish were held for 20 d at 10.0 degrees C and then for 7 wk at 10.3, 14.1 or 18.1 degrees C. During the first 20 d at 10.0 degrees C the growth rate (G) was higher for non-vaccinated than vaccinated fish. Thereafter vaccinated charr had higher G than control fish at 10.3 and 14.1 degrees C. In contrast, at 18.1 degrees C there was no difference in G and therefore no compensation of earlier growth suppression in vaccinated fish was observed at that temperature. The study indicates that vaccination has no ultimate negative effects on the growth of Arctic charr at temperatures ranging from 10.3 to 14.1 degrees C.

Early activation of TCR alpha gene rearrangement in fetal thymocytes

We have previously demonstrated that the onset of TCR alpha gene rearrangement is mainly restricted to the J alpha50 gene in fetal day 1delta thymocyte hybridomas. Now, J alpha50 rearrangements from fetal thymocyte hybridomas and from day 15.5 fetal thymus have been isolated and sequenced. We demonstrate that J alpha50 is rearranged to the rearranged Vdelta1 Ddelta2 gene segment. This indicates that the TCR alpha rearrangement process is initiated in fetal thymocytes far earlier than previously thought. These thymocytes have their delta genes still accessible for rearrangement and therefore, are controlled by the TCR delta enhancer (Edelta) (and/or another TCR delta specific cis-acting element). Our results further suggest that both Edelta and the TCR alpha enhancer (Ealpha) are active at the onset of alpha rearrangements or alternatively, the initial activation of the J alpha locus is controlled by Edelta. In addition, Vdelta1 Ddelta2 J alpha50 gene segments are replaced by secondary alpha rearrangements, indicating that thymocytes with the early alpha rearrangement are committed to the alphabeta lineage.

Discrimination between endemic and feedborne Salmonella Infantis infection in cattle by molecular typing

Salmonella enterica serovar Infantis is endemic in Finnish cattle. Feed contaminated with S. Infantis was distributed to cattle farms in May 1995. Following increased sampling, S. Infantis was detected on 242 farms in 1995. Molecular typing was used to differentiate the farms that were infected by the feed-related Infantis from those infected by other endemic strains. Twenty-three isolates from feed in 1995 and 413 from cattle (72 from 19924, 324 from 1995, 17 from 1996-7) were analysed. The feed-related Infantis was clonally related to the endemic infection by the ribotype, IS200-type and XbaI-profile. The feed isolates had a distinctive plasmid that appeared in pulsed-field gel electrophoresis as a 60 kb band when cleaved with XbaI or linearized by S1-nuclease. This plasmid appeared in cattle only since the outbreak and seemed stable on the follow-up farms. In addition to contact farms, the feedborne strain was found on 19% of the farms infected with S. Infantis in 1995 but not having bought suspected feedstuffs, possibly as secondary infections.

Suicide among military conscripts in Finland: a psychological autopsy study

This study describes suicides during compulsory military service and compares them with other young male suicides as part of a nationwide psychological autopsy study of all suicides in Finland during a single year. The victims' relatives and attending health care personnel were interviewed, and data from records were collected. Five of the seven conscript suicides had a depressive syndrome, often of short duration. Two victims previously had suicidal thoughts or attempted suicide. The most common suicide method was with firearms. Compared with other young male suicides, physical illness in conjunction with a psychiatric diagnosis was less common in the conscript victims. Civilian male suicides tended to have more substance abuse and more severe psychological impairment. They also committed suicide under the influence of alcohol more often than conscripts. Interpersonal separation was more often the precipitating event of the suicide among the conscripts than among the other suicides. Conscripts should be encouraged to utilize health and social services when they have psychosocial problems or even minor psychiatric symptoms.

Immunoblot analysis of bacterial polysaccharides: application to the type-specific polysaccharides of Streptococcus suis and Streptococcus agalactiae

A method for the immunoblot analysis of the type-specific capsular polysaccharides of streptococci was developed. The capsular polysaccharides were extracted by sonication and subjected to polyacrylamide gel electrophoresis in the absence of sodium dodecyl sulphate (SDS). After electrophoresis the polysaccharides were transferred to charged PVDF-N membranes and probed with the type specific antibodies. A characteristic ladder-like pattern of polysaccharide bands specific for the serotype (1, 2, 4, 7) was observed for capsular extracts of Streptococcus suis. Human immune sera against type-specific group B streptococcal polysaccharides reacted most strongly with the immunizing polysaccharide type (Ia, II, III). The previously observed crossreactions between the group B streptococcal type-specific capsular preparations were shown to be due to binding to the isomeric polysaccharide molecules. Thus, gel electrophoresis combined with immunoblot analysis seems to provide a novel method for the molecular and immunochemical characterization of bacterial polysaccharides and for the study of the specificity and properties of antibodies to capsular polysaccharides.

Characterization of Vibrio anguillarum strains isolated from diseased fish in Finland

Characterization of V. anguillarum strains (n = 109) isolated from diseased salmonids was performed. Eight O serovars were found among the strains. Serovar O1 was predominant (90%), while serovars O2, O3, O5, O8, O9, and a new serovar Va NT2, were represented by 1 or 2 strains. Two strains remained non-typeable. One of these was cross-reactive with several antisera, but had a LPS profile identical to that of serovar O8. All serovars showed specific LPS profiles. All but 1 of the O1 strains had a plasmid comparable in size to the pJM1 virulence plasmid, while plasmids of different sizes were found in O2, Va NT2 and the non-typeable strains. Apart from a single strain resistant to tetracycline, all the strains were sensitive to oxolinic acid, tetracycline, and trimethoprim-sulfonamides. By their biochemical and antigenic properties strains causing vibriosis among salmonids in Finland closely resemble Scandinavian strains. Predominance of the serovars O1 and O2 suggests that commercial vaccines containing these serovars should afford sufficient protection against vibriosis in Finland.

Differentiation of Salmonella serovar infantis isolates from human and animal sources by fingerprinting IS200 and 16S rrn loci

We genotyped Salmonella serovar infantis (referred to as S. infantis), which is the most widespread serovar among animals and the third most common cause of human salmonellosis in Finland. Molecular fingerprinting of the 16S rrn locus and the Salmonella-specific insertion sequence IS200 was used to type the 131 isolates originating from the main sources of S. infantis infection. The number of IS200 elements in S. infantis varied from zero to seven; three or more copies were present in 97% of the isolates, and 71% had four copies. There were four conserved chromosomal positions of IS200, which allowed us to group the isolates into three major clonal groups. We defined 11 unique IS200 profiles and five different ribotypes which, in combination, generated 15 genotypes highly restricted to the infection sources: 8 genotypes were typical of isolates from broiler chickens and cattle and seven genotypes were typical of isolates from humans. The eight genotypes of isolates from chickens represented two clonal groups which were differentially associated with chicken-producing companies. The typing scheme allows efficient discrimination between isolates from various infection sources and within sources and, therefore, provides a unique molecular tool for use in the study of the epidemiology of S. infantis infection.

Characterization of Vibrio anguillarum strains isolated from diseased fish in Finland

Characterization of V. anguillarum strains (n = 109) isolated from diseased salmonids was performed. Eight O serovars were found among the strains. Serovar O1 was predominant (90%), while serovars O2, O3, O5, O8, O9, and a new serovar Va NT2, were represented by 1 or 2 strains. Two strains remained non-typeable. One of these was cross-reactive with several antisera, but had a LPS profile identical to that of serovar O8. All serovars showed specific LPS profiles. All but 1 of the O1 strains had a plasmid comparable in size to the pJM1 virulence plasmid, while plasmids of different sizes were found in O2, Va NT2 and the non-typeable strains. Apart from a single strain resistant to tetracycline, all the strains were sensitive to oxolinic acid, tetracycline, and trimethoprim-sulfonamides. By their biochemical and antigenic properties strains causing vibriosis among salmonids in Finland closely resemble Scandinavian strains. Predominance of the serovars O1 and O2 suggests that commercial vaccines containing these serovars should afford sufficient protection against vibriosis in Finland.

Differential activities of bacteriophage depolymerase on bacterial polysaccharide: binding is essential but degradation is inhibitory in phage infection of K1-defective Escherichia coli

Host range mutants were derived from bacteriophages PK1A and PK1E specific for the K1 polysialic acid capsule of Escherichia coli. The mutants were selected for their ability to infect E. coli bacteria with a low level of the K1 capsule. A specific loss of the cleaving activity of the phage endosialidase was observed in all the mutants, while the ability to bind specifically to the polysialic acid capsule was retained. The results indicate that the polysaccharide-binding activity of the bacteriophage enzyme is essential for the infection process. The cleaving activity, in contrast, is required for the penetration of the dense polysaccharide of wild-type bacteria but is inhibitory in the infection of bacteria with a sparse capsular polysaccharide.

Use of hybridoma immunoglobulin switch variants in the analysis of the protective properties of anti-lipopolysaccharide antibodies in Escherichia coli K1 infection

Functional properties of rat immunoglobulins obtained from hybridoma isotype switch variants were studied in vivo in a rat model for neonatal bacterial sepsis. Escherichia coli 018:K1, a common cause of human neonatal sepsis and meningitis, was injected intravenously into 6-day-old rats after incubation with 018-specific antibodies IgM, IgG1, IgG2a, IgG2b, IgG2c, IgE and IgA. The clearance of bacteria treated with saline or IgE was low, whereas monoclonal antibodies of other isotypes triggered hepatic sequestration and killing of the K1 E. coli cells. All four IgG subclasses were more efficient than IgM and IgA. Comparable results were obtained upon injecting antibodies into rats with an established fulminating bacteraemia. IgM was inactive in animals depleted of complement with cobra-venom factor (CVF), whereas IgG2b was able to trigger hepatic clearance independently of complement.

Common cleavage pattern of polysialic acid by bacteriophage endosialidases of different properties and origins

The cleavage specificities of seven bacteriophage endosialidases degrading the alpha 2-8-linked polysialic acid common to bacterial polysaccharides and to the cell adhesion molecule N-CAM were investigated. The bacteriophages studied represented five different phenotypic groups by protein and DNA fragment analysis and two different morphology groups by electron microscopy. Characterization of the fragments arising from the native or chemically modified substrates of different sizes showed that cleavage specificity was influenced by enzyme concentration. At the initial phase of degradation, at concentrations ranging from 20- to 100-fold, the minimum substrate size was an oligomer of eight (in one case, nine) sialic acid units that was preferably cleaved at the same position. Under exhaustive conditions, the oligomers were degraded further, and each enzyme type had its own specificity. The similar initial cleavage of polysialic acid by endosialidases associated with phages of different properties and morphology suggests a conserved mechanism of enzyme-substrate interaction. This mechanism may be conformationally determined and related to the specific properties of polysialic acid in other molecular interactions.

Recombinant interleukin-1 stimulates clearance of Escherichia coli K1 bacteraemia

Enhancement of non-specific resistance to neonatal Escherichia coli K1 infection by interleukin-1 (IL-1) was analysed. Recombinant human IL-1 administered prophylactically to newborn LPS-non-responsive C3H/HeJ mice induced rapid clearance of E. coli 018:K1 bacteraemia. The effect was dose-dependent and was observed with mice treated immediately to 1 day before bacterial challenge, whereas treatment 2 days before challenge was ineffective. was ineffective. Clearance of intravenously injected radiolabelled 018:K1 E. coli suggested that IL-1 triggered defence mechanisms that contribute to bacterial sequestration and killing in the spleen and liver. Comparable increase in bacterial clearance occurred in naturally resistant LPS-responsive mice that had been subjected to transient E. coli K1 bacteraemia and showed increased resistance to reinfection. In the course of E. coli K1 bacteraemia a strong synthesis of acute phase reactants was observed in both susceptible and resistant mouse strains, which indicated that these proteins alone cannot confer natural resistance to E. coli K1. IL-1 induced a very rapid synthesis of acute phase proteins. The clearance of K1 E. coli when still viable in IL-1-treated animals suggested that acute phase proteins are not likely to be major mediators of the IL-1-enhanced non-specific resistance.

Structural similarity of the type-specific group B streptococcal polysaccharides and the carbohydrate units of tissue glycoproteins: evaluation of possible cross-reactivity

Type-specific capsular polysaccharides of group B streptococci show striking structural similarity with the terminal sugar sequences of tissue glycoconjugates. The polysaccharides have been put forward as vaccines against neonatal meningitis. A potential source of hazard in immunization of pregnant mothers may be the presence of the cross-reactive components in adult or fetal tissues. A radioactive ligand binding assay was used to test human immune sera to type Ia, II and III group B streptococcal polysaccharides for binding to tissue-derived glycopeptides showing structural similarities with the streptococcal polysaccharides. Of the 13 glycopeptides of human and rat tissues studied, representing a wide selection of structures known to occur in glycoproteins, only two showed some reactivity with the antisera. The reactivity with human small intestinal glycopeptides could be explained by the presence of natural blood group A antibodies, and was not related to the streptococcal group B antibodies. The basis of the reactivity of a high-molecular-weight glycopeptide from rat kidney with some of the sera was unknown, but was unrelated to the vaccination and clearly could not be inhibited with the streptococcal polysaccharides. Thus, no immunological cross-reactions of the tissue glycopeptides studied could be demonstrated with the group B streptococcal antisera.

Roles of spleen and liver in the clearance of Escherichia coli K1 bacteraemia in infant rats

The age-dependent increase in resistance of infant rats to K1 E. coli infection was studied by analysing the clearance of intravenously injected radiolabelled O18:K1 E. coli bacteria. In susceptible 7-day-old rats, the rate of reticuloendothelial clearance could not compete with bacterial multiplication, while the resistance of 18-day-old rats was attributed to the increased sequestration of bacteria in the spleen. After passive immunization with rat monoclonal anti-O18 IgG2b, the O18:K1 E. coli were rapidly cleared by the liver in both age groups. O1:K1, O18:K5 and O18:K- E. coli, which activate complement in an antibody-independent manner and are apathogenic for 7-day-old rats, were also rapidly sequestered in the liver. 7-day-old rats developed a fulminant bacteraemia after receiving 100 O18:K1 E. coli intravenously. After several hours a transient decrease in the level of bacteraemia was observed. However, the clearance remained incomplete, resulting in persistent bacteraemia and death. Endotoxin-responsive infant mice are able to clear the bacteraemia completely after a similar initial phase of bacterial multiplication while no clearance is observed in endotoxin-hypo-responsive mice. The marked host specificity of K1 E. coli infection thus appears to be related to differences in a clearance mechanism which may be sustained by an endotoxin-induced inflammatory response.

Polyacrylamide gel electrophoresis of the capsular polysaccharides of Escherichia coli K1 and other bacteria

Methods were developed for the polyacrylamide gel electrophoretic analysis of capsular polysaccharides of bacteria with Escherichia coli K1 as a model. Conditions were determined for the rapid and gentle extraction of the K1 polysaccharide by incubation of the bacteria in a volatile buffer and for the subsequent removal of the putative phospholipid moiety attached to the reducing end of the polysaccharide. Detection of the polysaccharides after gel electrophoresis was carried out by fluorography of samples labeled by sodium borotritiide reduction or by combined alcian blue and silver staining. The smallest components could be detected only by fluorography, owing to diffusion during staining. Components of the E. coli K1 polysialic acid capsule ranging from monomers to 80 sialic-acid-unit-containing polymers could be separated as distinct bands in a ladderlike pattern. A maximum chain length of 160 to 230 sialyl residues was estimated for the bulk of the K1 polysaccharide from the nearly linear reciprocal relationship between the logarithm of the molecular size and the distance of migration. Gel electrophoresis of capsular polysaccharides of other bacterial species revealed different electrophoretic mobilities for each polysaccharide, with a ladderlike pattern displayed by the fastest-moving components. There are many potential applications of this facile method for the determination of the sizes of molecules present in a polydisperse polysaccharide sample. When combined with the simple method for the isolation of the capsule, as in the case of the K1 capsule, it provides an efficient tool for the characterization and comparison of the capsular polysaccharides of bacteria.

Host factors in the resistance of newborn mice to K1 Escherichia coli infection

It is not clear which factors are responsible for the deficient resistance of human neonates to K1 E. coli sepsis and meningitis. To evaluate the relative importance of different defense mechanisms against bacterial invasion, we have analyzed the sensitivity of newborn mice with known immune deficiencies to infection after oral challenge with virulent K1 E. coli. T and B lymphocyte and complement (C5) defects had no significant effect on natural resistance. In contrast, both endotoxin-hyporesponsive mouse strains tested were highly sensitive. This susceptibility to infection was strongly age dependent. Infant endotoxin-hyporesponsive mice were killed by i.p. injection of less than ten virulent K1 E. coli cells. In contrast, endotoxin-responsive animals and F1 hybrids derived from crosses between endotoxin-responsive and hyporesponsive mice survived an injection with up to 10(4) bacteria. Mutants of a virulent 018:K1 E. coli strain defective in the synthesis of the capsular polysaccharide or the O-antigen of lipopolysaccharide were avirulent as were 01:K1 bacteria, which are under-represented among E. coli isolates from neonatal meningitis. Endotoxin-hyporesponsive mice were protected from lethal bacterial challenge by monoclonal IgG specific for the O-antigen of the challenge strain or by human recombinant interleukin 1. A fulminant bacterial multiplication in the bloodstream of endotoxin-hyporesponsive mice was observed after i.v. injection of 100 virulent K1 E. coli cells. Persistent bacteremia with 10(5) to 10(6) bacteria per ml of blood resulted in death of the animals one to two days after challenge. In the bloodstream of endotoxin-responsive mice the bacteria proliferated to a comparable extent within the first 6 h after challenge. Thereafter they were rapidly cleared from the circulation and the animals recovered from the infection.

Isolation of a herpesvirus serologically related to bovine herpesvirus 1 from a reindeer (Rangifer tarandus)

Serological evidence of exposure of reindeer (Rangifer tarandus) to a virus related to bovine herpesvirus 1 (BHV1) (Synonym: Infectious bovine rhinotracheitis (IBR) virus) has been reported in Canada (El Azhary 1979) and the USA (Dieterich 1981). A serological survey conducted in Finnish Lapland also detected neutralising antibodies to BHV1 in reindeer sera; 23 % of 300 reindeer had detectable antibodies, whereas none of 300 cattle sera from the same region contained antibodies to BHV1 (Ek-Kommonen et al. 1982). There is currently no evidence of BHV1 infection of cattle in Finland, so the isolation and characterisation of the reindeer herpesvirus was of considerable interest. This short communication describes the isolation and preliminary characterisation of a herpesvirus from a reindeer following the administration of dexamethasone.