Social contagion in a world with asymmetric influence.

Social media has blurred the distinction between news outlets and social networks by giving everyone access to mass communication. We simulate how influencers compete for attention on a social network by spreading information. The network structure occupies an ordered metastable state where one influencer maintains dominance for a sustained period or a fragmented state that divides attention between influencers. Numerical simulations are performed to map the domain of the ordered regime on various network topologies. Mutual coexistence between a few dominating influencers occurs on a scale-free social network. Our findings suggest the perception of fake news as a pervasive problem is endemic to a society where everyone can become a news outlet.

Distribution of Ixodes ricinus ticks and prevalence of tick-borne encephalitis virus among questing ticks in the Arctic Circle region of northern Norway.

This study investigated the geographical distribution of Ixodes ricinus and prevalence of the tick-borne encephalitis virus (TBEV) in northern Norway. Flagging for questing I. ricinus ticks was performed in areas ranging from Vikna in Nord-Trøndelag County, located 190km south of the Arctic Circle (66.3°N), to Steigen in Nordland County, located 155km north of the Arctic Circle. We found that ticks were abundant in both Vikna (64.5°N) and Brønnøy (65.1°N). Only a few ticks were found at locations ∼66°N, and no ticks were found at several locations up to 67.5°N. Real-time PCR (RT-PCR) analyses of the collected ticks (nymphs and adults) for the presence of TBEV revealed a low prevalence (0.1%) of TBEV among the nymphs collected in Vikna, while a prevalence of 0% to 3% was found among nymphs collected at five locations in Brønnøy. Adult ticks collected in Vikna and Brønnøy had higher rates of TBEV infection (8.6% and 0%-9.0%, respectively) than the nymphs. No evidence of TBEV was found in the few ticks collected further north of Brønnøy. This is the first report of TBEV being detected at locations up to 65.1°N. It remains to be verified whether viable populations of I. ricinus exist at locations north of 66°N. Future studies are warranted to increase our knowledge concerning tick distribution, tick abundance, and tick-borne pathogens in northern Norway.

Detection of MTRR 66A-->G polymorphism using the real-time polymerase chain reaction machine LightCycler for determination of composition of allele after restriction cleavage.

The MTRR gene codes for methionine synthase reductase, one of the enzymes involved in the conversion of homocysteine to methionine. This conversion influences the overall level of total plasma homocysteine (tHcy) and mutations, which reduces the enzyme activity and results in an increased concentration of tHcy. A high homocysteine level is a well-documented independent risk factor for cardiovascular disease. A polymorphism in the gene for methionine synthase reductase (MTRR 66 A>G) has been shown to be associated with the risk of giving birth to a child with Down's syndrome, and the risk of having a foetus with neural tube defects. We have established a method for analysing MTRR 66A>G on DNA from dried blood spots using melting temperature analysis. The DNA was extracted from dried blood spots using a fast procedure by boiling only.

Expected, prenatally discovered, and born cases of Down syndrome in Denmark during the period 1980-1998.

In order to elucidate the consistency between generally used age-dependent risk values for Down syndrome (DS) and estimates of the probability of miscarriage in Down pregnancies we have compared expected numbers with estimated numbers of births with DS in Denmark had no intervention at all been carried out. The expected numbers were calculated from the distribution of newborn children according to maternal age combined with the age-related risk of DS. The estimated numbers of children that actually would have been born without any intervention were estimated from observed numbers of cases of DS, i.e. the cases born plus - with corrections because of the high probability of miscarriage in DS pregnancies - a proportion of those cases discovered prenatally. The analysis was carried out separately for mothers aged 35 years or older and for younger mothers. We found a high degree of compatibility between expected and estimated numbers, probably with a minor underestimation of the expected values for the older mothers. The performance of DS screening in Denmark in the period under consideration (1980-1998) is discussed in relation to the figures presented. Despite the fact that 11.8% of all pregnancies were subjected to an invasive diagnostic procedure, only about 38% of all births with DS were prevented. This means that in the period 1990-1998, reluctance to accept serological screening has indirectly resulted in the birth of almost 300 cases of DS in Denmark and at the same time the miscarriage of an unreasonable high number of normal fetuses.

Risk factors for parvovirus B19 infection in pregnancy.

CONTEXT: Parvovirus B19 infection during pregnancy has been associated with fetal death. However, the incidence of and risk factors for infection in pregnant women have not been well studied. OBJECTIVES: To estimate a pregnant woman's risk of infection with parvovirus B19 in epidemic and endemic situations and to study risk factors for infection. DESIGN: Population-based cohort study conducted between November 1992 and June 1994. SETTING: Three regions in Denmark. PARTICIPANTS: A total of 30946 pregnant women from a consecutive and population-based screening. MAIN OUTCOME MEASURES: Specific IgG antibodies in serum samples obtained in the first trimester of pregnancy and from the newborn infant to assess past infection and seroconversion. Information on family structure, educational background, socioeconomic status, and pregnancy outcome was obtained from national registers. RESULTS: Based on 30 946 serum samples, 65.0% of pregnant women had evidence of past infection. Annual seroconversion rates among susceptible women during endemic and epidemic periods were 1.5% (95% confidence interval [CI], 0.2%-1.9%) and 13.0% (95% CI, 8.7%-23.1 %), respectively. Baseline seropositivity was significantly correlated with increasing number of siblings, having a sibling of the same age, number of own children, and occupational exposure to children. Risk of acute infection increased with the number of children in the household as follows: 0 children odds ratio (OR), 1 (reference); 1 child OR, 3.17 (95% CI, 2.24-4.49); 2 children OR, 5.47 (95% CI, 3.55-8.45); 3 or more children OR, 7.54 (95% CI, 3.80-14.94). Having children aged 6 to 7 years resulted in the highest rate of seroconversion among mothers (6.8%; OR, 4.07; 95% CI, 1.89-8.73). Compared with other pregnant women, nursery school teachers had a 3-fold increased risk of acute infection (OR, 3.09; 95% CI, 1.62-5.89). Population-attributable risk of seroconversion was 55.4% for number of own children and 6.0% for occupational exposure. CONCLUSIONS: The risk of infection is high for susceptible pregnant women during epidemics and associated with the level of contact with children. Nursery school teachers have the highest occupational risk, but most infections seem to be the result of exposure to the woman's own children.

[Screening of school children for familial hypercholesterolemia]. / Screening af skolebørn for familiaer hyperkolesterolaemi.

A total of 3025 families with school children aged six to eight years were offered pilot screening for familial hypercholesterolaemia by measurement of the concentration of apolipoproteins A-1 and B in the children's capillary blood and by analysis of their family histories of early ischaemic heart disease. The concentrations of the apolipoproteins were determined by double rocket immunoelectrophoresis of an eluate of blood spotted on filter paper. Results were available from 2085 children. Because their B:A-1 ratio was above the 97.5 centile and their concentration of B was above the 99th centile, 54 children (2.6%) were selected to have their apolipoprotein concentrations reassessed. The 17 children (0.8%) whose values were persistently above the chosen cut-off points, and all of their available first and second degree relatives, had fasting determinations of serum lipid concentrations carried out. Raised serum concentrations of low density lipoprotein cholesterol and an autosomal dominant pattern of hypercholesterolaemia were found in respectively 12 children and 10 families, suggesting a higher incidence of familial hypercholesterolaemia than the reported 1:500. Further investigations among family members disclosed hypercholesterolaemia in 29 relatives. A family history of early ischaemic heart disease was elicited by questionnaire, and was positive in only five of the 12 school children with hypercholesterolaemia. We conclude that analysis of apolipoproteins from capillary blood spotted on filter paper is suitable for screening for familial hypercholesterolaemia, and that this method is more efficient than screening based on family history.

Screening for familial hypercholesterolaemia by measurement of apolipoproteins in capillary blood.

A total of 3025 families with schoolchildren aged 6-8 years were offered pilot screening for familial hypercholesterolaemia by measurement of the concentrations of apolipoproteins A-1 and B in the children's capillary blood and by analysis of their family histories of early ischaemic heart disease. The concentrations of the apolipoproteins were determined by double rocket immunoelectrophoresis of an eluate of blood spotted on filter paper. Results were available from 2085 children. Because their B:A-1 ratio was above the 97.5 centile and their concentration of B was above the 99th centile, 54 children (2.6%) were selected to have their apolipoprotein concentrations reassessed. The 17 children (0.8%) whose values were persistently above the chosen cut off points, and all of their available first and second degree relatives, had fasting determinations of serum lipid concentrations carried out. Raised serum concentrations of low density lipoprotein cholesterol and an autosomal dominant pattern of hypercholesterolaemia were found in 12 children and 10 families, respectively, suggesting a higher incidence of familial hypercholesterolaemia than the reported 1:500. Further investigations among family members disclosed hypercholesterolaemia in 29 relatives. A family history of early ischaemic heart disease was elicited by questionnaire, and was positive in only five of the 12 schoolchildren with hypercholesterolaemia. We conclude that analysis of apolipoproteins from capillary blood spotted on filter paper is suitable for screening for familial hypercholesterolaemia, and that this method is more efficient than screening based on family history.

Methylprednisolone pulse therapy induced fall in natural killer cell activity in rheumatoid arthritis.

Natural killer (NK) cell activity was studied in 8 patients with classic or definite rheumatoid arthritis (RA) by investigating the killing of K 562 cells by peripheral blood lymphocytes before, during, and after intravenous methylprednisolone pulse therapy (MPPT). MPPT produced a considerable fall in NK activity and after 3 months NK activity was less than half that before MPPT.

Azathioprine as single drug in the treatment of rheumatoid arthritis induces complete suppression of natural killer cell activity.

Natural killer (NK) activity against K 562 target cells was studied in 60 patients with definite or classic rheumatoid arthritis (RA), grouped by medication into 1) Controls not in remission-inducing therapy, 2) Patients treated with penicillamine, and 3) Patients treated with azathioprine. NK activity was found to be completely suppressed in the azathioprine group as compared with the controls (3.2 +/- 4.2% versus 35.9 +/- 14.8% specific lysis; p less than 0.01) except for one patient who received incomplete azathioprine treatment. The NK activity was not suppressed in the penicillamine group.