Plasmid DNA-based immunization for hepatitis C virus structural proteins: immune responses in mice.

BACKGROUND & AIMS: Plasmid DNA-based immunization has been shown to be an effective means of vaccination in animal models. In this study, the immune responses to various hepatitis C virus structural protein antigens were evaluated using this technique. METHODS: Six recombinant plasmids were constructed. These include, individually, the coding regions for the core protein (pC); E1 (pE1) and E2 (pE2); as well as core, E1, and E2 together (pCE1E2); E1 and E2 together (pE1E2); and finally an E2 construct from which the N-terminal hypervariable region had been deleted (pE2 deltaHVR). These plasmids were transfected into mammalian cells to test their protein expression and were injected into the quadriceps muscles of BALB/c mice to measure specific antibodies and cytotoxic T-lymphocyte responses. RESULTS: All the recombinant plasmids were shown to express specific antigens transiently in cells and elicited specific antibody responses to core, E1, and E2 in mice. Specific cytotoxic T lymphocyte responses were detected only in mice injected with plasmid constructs encoding the core. CONCLUSIONS: Genetic immunization can aid the development of hepatitis C virus vaccines by allowing for the rapid construction and evaluation of different expression plasmids as potential immunogens.

Trends in the prevalence of congenital heart disease: comprehensive observations over a 24-year period in a defined region of Canada.

OBJECTIVE: To determine the prevalence of congenital heart disease (CHD) in the three Maritime provinces, and to study prevalence differences among provinces and defined regions within these provinces. DESIGN: Each province was divided by counties into regions. All cases of CHD who were born alive in the study area between 1966 and 1989 were entered in a registry. Prevalences were analyzed for each province and for selected regions per year, per 1000 live births, and by diagnosis made by one year of age and by the 16th birthday. Comparison was then made with prevalences of a group who had severe lesions. INTERVENTIONS: Excepting a small number of CHD cases who were diagnosed by autopsy only, diagnosis was made by pediatric cardiologists using appropriate procedures, including cardiac ultrasound and cardiac catheterization. SETTING: The only tertiary care centre for children's heart disease in the provinces of Nova Scotia, New Brunswick and Prince Edward Island, areas of relative geographic isolation (combined population of 1.75 million people). MAIN RESULTS: A statistically significant positive linear trend occurred in these provinces during the study. The recorded prevalence of CHD in New Brunswick was significantly lower. Pooled prevalences by the first and 16th birthdays (8.0 and 12.5 per 1000 live births, respectively) of two regions of highest prevalence for 1980-86 were significantly higher (P < 0.05) than the pooled prevalence rate of all the remaining regions. Prevalence rates of a group with severe lesions were stable for 1976-86 in all regions. CONCLUSIONS: Differences in prevalence of CHD among provinces and regions were related to ascertainment levels. Prevalence of CHD with diagnosis by the first and 16th birthdays were approximately 8.0 and 12.5 per 1000 live births, respectively. The prevalence rate of a severe lesion group was a stable measure.

Birth weight percentiles by gestational age in Canada.

OBJECTIVE: To develop current birth weight norms by gestational age for singleton and twin births in Canada. METHODS: Birth weight data were obtained from vital statistics and health department birth registrations for over one million live births in Canada from 1986-1988. Unlikely combinations of birth weight and gestational age were defined within each stratum of multiplicity, gender, and gestational age as records with birth weights more than two interquartile ranges above the 75th percentile or below the 25th percentile. Birth weight percentiles (from first to 99th) by gestational age and sex were calculated for singleton and twin live births. RESULTS: Of the total records, 0.4% were missing data on birth weight or gestational age, and an additional 0.4% were identified as extreme outliers and were excluded from the analysis. Charts of birth weight by gestational age show percentiles 1, 3, 5, 10, 25, 50, 75, 90, 95, 97, and 99 by sex for singleton and twin live births. CONCLUSIONS: The large data base assembled for this analysis provides current, stable birth weight-gestational age percentiles for classifying newborns from a developed country as small, appropriate, or large for gestational age. Compared with birth weight distributions from the 1970s, these current norms are heavier for full-term infants and the interdecile range for preterm infants is narrower. We recommend that birth weight norms be updated every 5-10 years.

A teratoma in a duck infected congenitally with duck hepatitis B virus.

A teratoma was diagnosed in an 8-month-old pekin duck based on the presence of tissue derived from embryonic ectoderm, mesoderm, and endoderm in the neoplasm. The neoplasm was examined for the presence of duck hepatitis B virus, because the duck was congenitally infected with the virus, a member of the hepadnavirus family that is associated with hepatic neoplasms in hepadnavirus-infected mammals. Persistent infection occurred in the liver, but no evidence of viral infection was found in the neoplasm.

Birth outcomes and infant mortality by income in urban Canada, 1986.

For 1986, 219,470 live births were reported for residents of Canada's 25 Census Metropolitan Areas (CMAs). For each of these births, street address information as shown on the birth registration was used to code the census tract where the mother lived. Data by census tract were obtained for 1,650 infant deaths in 1986, and from the 1986 census for the population of 4,727,770 women aged 10-49 in 1986. Births, infant deaths and census population data (adjusted for undercount) were then used to calculate rates of infant mortality, low birth weight (LBW), very low birth weight (VLBW), prematurity, small for gestational age (SGA), and total fertility. The results are presented by neighborhood income quintile group (based on percentage of low income), and by the mother's age, parity (number of live births), marital status and country of birth, as well as by CMA.

Hepatic neoplasms in aflatoxin B1-treated, congenital duck hepatitis B virus-infected, and virus-free pekin ducks.

To assess the effects of the combination of persistent hepadnavirus infection and chemical carcinogen exposure, aflatoxin B1 (AFB) was administered p.o. for 60 days to congenitally duck hepatitis B virus (DHBV)-infected and virus-free Pekin ducks, starting at 3 days of age, during a 28-month study. Hepatic neoplasia occurred only in AFB-dosed ducks. Hepatocellular carcinomas or biliary carcinomas occurred in 4 of 8 DHBV-infected and 3 of 4 DHBV-free ducks, and hepatocellular adenomas developed in 2 DHBV-infected AFB-dosed ducks that survived 20 months or longer. Altered foci of hepatocytes similar to those observed in chemical carcinogen-dosed rodents, characterized by enlarged eosinophilic hepatocytes or vacuolated cytoplasm, occurred in AFB-dosed ducks. Cells in foci or hepatic neoplasms did not contain histochemically detectable gamma-glutamyltranspeptidase but were distinguished from uninvolved parenchyma by altered glycogen content. Immunohistochemical staining indicated that DHBV core antigen persisted in liver, spleen, pancreas, and, to a lesser extent, kidney of most congenitally infected ducks up to 28 months of age. Hepatic neoplasms contained only patches of hepatocytes were detectable viral antigen. Southern blot analysis of restriction endonuclease-digested neoplastic and normal liver DNA revealed high molecular weight forms of DHBV DNA consistent with integration of viral DNA into the genome of hepatic neoplasms from 3 of 4 DHBV-infected ducks but not nontumorous liver. These findings indicate that AFB is a potent hepatic carcinogen in ducks and that persistent congenital DHBV infection did not contribute significantly to the emergence of hepatic neoplasia in ducks under these conditions.

Mortality from breast cancer after irradiation during fluoroscopic examinations in patients being treated for tuberculosis.

The increasing use of mammography to screen asymptomatic women makes it important to know the risk of breast cancer associated with exposure to low levels of ionizing radiation. We examined the mortality from breast cancer in a cohort of 31,710 women who had been treated for tuberculosis at Canadian sanatoriums between 1930 and 1952. A substantial proportion (26.4 percent) had received radiation doses to the breast of 10 cGy or more from repeated fluoroscopic examinations during therapeutic pneumothoraxes. Women exposed to greater than or equal to 10 cGy of radiation had a relative risk of death from breast cancer of 1.36, as compared with those exposed to less than 10 cGy (95 percent confidence interval, 1.11 to 1.67; P = 0.001). The data were most consistent with a linear dose-response relation. The risk was greatest among women who had been exposed to radiation when they were between 10 and 14 years of age; they had a relative risk of 4.5 per gray, and an additive risk of 6.1 per 10(4) person-years per gray. With increasing age at first exposure, there was substantially less excess risk, and the radiation effect appeared to peak approximately 25 to 34 years after the first exposure. Our additive model for lifetime risk predicts that exposure to 1 cGy at the age of 40 increases the number of deaths from breast cancer by 42 per million women. We conclude that the risk of breast cancer associated with radiation decreases sharply with increasing age at exposure and that even a small benefit to women of screening mammography would outweigh any possible risk of radiation-induced breast cancer.

Comparison of the risk factors for pre-term delivery and intrauterine growth retardation.

In a follow-up study of the pregnant women interviewed in the Nutrition Canada survey, we investigated predictors of intrauterine growth retardation (less than or equal to 10th percentile of the birthweight-gestational age distribution for the 1972 Canadian population), and pre-term delivery (less than 37 completed weeks of gestation), by classifying these two endpoints as either small-for-gestational age and not pre-term (SGA-NPT), or not small-for-gestational age but pre-term (NSGA-PT). Education, age, household income level, number of previous livebirths, number of cigarettes smoked per day while pregnant, alcohol consumption (spirits only), serum Vitamin C and haemoglobin levels, pre-pregnancy weight, height, and sex of the infant were related to NSGA-PT deliveries in univariate analyses; serum Vitamin A, smoking history, calorie intake, height and pre-pregnancy weight were similarly associated with the risk of SGA-NPT outcomes. When considered jointly in multivariate logistic regression analysis, however, the significant predictors were reduced to: height and pre-pregnancy weight for SGA-NPT and mother's education, sex of the infant, and household income level for NSGA-PT.

An analysis of birth weight by gestational age in Canada.

Birth-weight-gestational-age standards help to identify infants in need of special care and to determine causes and means for preventing retardation of intrauterine growth. Previously published standards either were based on small samples, data several decades old or characteristics of subpopulations in the United States or they were not specific for type of birth and sex. We compared the data for live births in 1972 with those in 1986 to develop current Canadian standards for type of birth (singleton or twin) and sex. We found that the 10th, 50th and 90th percentile figures for weight were slightly higher in 1986 than in 1972 for term deliveries (at 37 weeks' gestation or later), but the figures were virtually unchanged for preterm deliveries. The availability of reliable population-based standards should enhance the clinician's ability to identify true cases of retardation or acceleration of intrauterine growth.

Water nitrates and CNS birth defects: a population-based case-control study.

The relation between maternal exposure to nitrates in drinking water and risk of delivering an infant with a central nervous system (CNS) malformation was examined by means of a case-control study in New Brunswick, Canada. All cases of CNS defects for a "high" and a "low" prevalence area of New Brunswick, for the years 1973-1983, were included in the study. Controls were selected randomly from the livebirth files for the province, matched on county of maternal residence and date of birth. One hundred and thirty (130) cases were identified and individually matched with two controls each. Individual water samples were collected from the case and control mother's address given on the birth or stillbirth records. The study revealed that the effect of nitrate exposure in water was modified by whether the source of the drinking water was a private well or a public municipal distribution system. Compared to a baseline nitrate level of 0.1 ppm, exposure to nitrate levels of 26 ppm from private well water sources was associated with a moderate, but not statistically significant, increase in risk (risk odds ratio = 2.30; 95% confidence interval = 0.73-7.29). If the source of drinking water was a municipal distribution system or a private spring, an increase in nitrate exposure was associated with a decrease in risk of delivering a CNS-malformed infant; however, these effect estimates were not statistically significant. The positive increase in risk with nitrate exposure from well water sources requires further study using a larger case series and a larger proportion of exposures to nitrate levels exceeding 5 ppm.

Risk factors for postneonatal mortality: results from a record linkage study.

A population-based computer record linkage of infant births and deaths was conducted for 1978 and 1979 covering Canadian provinces. Birthweight was inversely related to risk of postneonatal death for all causes examined, including accidental deaths. Length of gestation was inversely associated with risk, but the strength of the relationship was much weaker than that noted for birthweight. A logistic regression model was used to assess the effects of variables, as reported on birth certificates, on postneonatal mortality. Maternal age less than 25 years, unmarried marital status and one or more previous births were all statistically significantly related to increased risk.

Risk factors for perinatal mortality in Canada.

A population-based computer record-linkage study of infant births and deaths in 1978 and 1979 in eight Canadian provinces (Quebec and Newfoundland were excluded) was undertaken to permit analysis of perinatal mortality in relation to maternal and infant characteristics. Perinatal mortality rates were significantly higher in nonurban than in urban areas (p less than 0.05). A logistic regression model was used to assess the effects on perinatal mortality of variables reported on birth and stillbirth records. This model included length of gestation, infant's birth weight and sex, number of previous births and number of previous stillbirths as well as an interaction term for length of gestation and birth weight. For early-neonatal mortality, odds ratios over 8 were observed for birth weight less than 2500 g or gestation less than 35 weeks. About 75% of early-neonatal mortality was attributable to low birth weight or fetal immaturity. Greater emphasis should be placed on the prevention of low birth weight.

Correlations between cancer incidence rates from the Canadian National Cancer Incidence Reporting System, 1969-78.

Incidence rates for 19 cancers in females and 16 cancers in males have been computed from data reported by 8 Canadian provinces to the National Cancer Incidence Reporting System between 1969 and 1978. The rates, very similar in absolute and relative magnitude to those reported by the U.S. Third National Cancer Survey, have been used to examine patterns of correlation between various cancers within the 8 provinces. There is strong evidence of positive associations between a number of cancers, including a number of associations that have been reported in other similar correlational studies. Correlations that may be of particular interest in suggesting etiologic factors in common include clusters of smoking-related cancers (buccal cavity with pharynx, larynx, lung, and bladder), female sexual cancers (breast, corpus uteri, and ovary), and a group of cancers that have shown correlation in other studies (i.e., cancers of the pancreas and kidney, leukemias, lymphomas, and cancer of the prostate gland). Organs in the gastrointestinal tract (esophagus, stomach, colon, and rectum) anatomically close to each other show a high positive correlation in both females and males, but the further apart the organs are the lower is the correlation; these observations are consistent with other evidence of varying dietary etiologies. Two individual correlations of particular interest are those between female brain tumors and female bladder cancer (two cancers for which little is known of the etiology for a large percentage of them) and those between female breast cancer and female lung cancer. This study, the largest correlational study of incidence data reported to date, demonstrates the utility of such simple correlational analyses.

Epidemiological assessment of risk to humans from exposure to nitrosamines.

In order for epidemiologists to evaluate the 'nitrosamine hypothesis' it is necessary to develop measures of human exposure to N-nitrosamines - both exogenous and when formed internally through consumption precursors. Dissatisfied with indefinite findings using indirect indices of N-nitrosamine exposure, we have attempted to derive an index based on the known kinetics of N-nitrosamine formation. This has been applied in a case-control study of cerebral tumours and resulted in a suggestive finding of increased risk for exogenous but not total N-nitrosamine exposure. A potential difficulty with our index is doubt as to whether vegetable sources of nitrates and consequent endogenous formation of nitrites indeed result in N-nitrosamine exposure, in view of the possible presence of blocking agents or of vitamin C consumed at the same time as vegetables. Further work is necessary, but we hope to apply the index in a case-control study of gastric cancer currently under analysis.

Optimising the age, number of tests, and test interval for cervical screening in Canada.

Different approaches to screening for cancer of the cervix by cervical cytology have been evaluated using a computer simulation model developed by Knox and data on the natural history of carcinoma-in-situ (or worse) from a cohort study of women screened in British Columbia, 1949-69. The natural history input parameters and the output parameters without screening were modified to reflect the earlier onset of carcinoma-in-situ in younger cohorts now being experienced in British Columbia, resulting in simulated mortality from carcinoma of the cervix approximately 50% greater than that experienced in Canada in 1955. The simulations showed that the sensitivity of the test and the proportion of women in the population who accept invitations to attend for screening materially influence the extent to which programmes reduce mortality. Missed screens also have an important impact. With a 75% test sensitivity, and an 80% population acceptance, a programme designed to reduce mortality by 90% would commence at age 25, involve triennial screens to age 52, or triennial screens to age 40 and quinquennial screens to age 60, a total of 10 tests in a lifetime. A repeat test at age 26 contributes nothing to the mortality benefit. Nevertheless, additional modifications of the natural history specifications to accommodate high-risk younger women would require a more frequent schedule of examinations under the age of 35, though at a substantial 'cost' in terms of the total number of examinations required in a population.

Breast cancer mortality following fluoroscopic irradiation in a cohort of tuberculosis patients.

A study has been conducted to determine the mortality experience from 1950-1977 of a cohort of women treated for tuberculosis in Canadian sanatoria between 1930 and 1952. Approximately 50 percent of these women received substantial breast tissue doses of fluoroscopic irradiation in conjunction with their treatment by artificial pneumothorax. A preliminary analysis of 23572 women known alive at the beginning of 1950 has shown a highly significant breast cancer mortality risk for those women exposed to such radiation. There is evidence of decreasing effect with increasing age at first exposure, and no increase in risk is observed until ten years after first exposure.