Attempt to control ticks (Acari: Ixodidae) on deer on an isolated island using ivermectin-treated corn.

We report an attempt by an offshore island community to control the vector tick of Lyme disease by providing ivermectin-treated corn to an isolated herd of free-ranging white-tailed deer, Odocoileus virginianus Zimmerman. Medicated corn was supplied in troughs within the island village and from automatic feeders at remote sites during 5 consecutive fall and spring adult tick questing seasons. Acaricide consumption was monitored by assaying its presence in fresh deer pellets and its concentration in deer sera. Its effectiveness was evaluated by recording the number of adult ticks collected from the hides of deer, the number of females becoming sufficiently engorged to oviposit, and the success of subsequent oviposition and eclosion. Entomologic risk was monitored by collecting immature ticks from hosts and adult ticks from vegetation. Estimates based on a subsequent deer reduction program indicated that up to twice as many deer had been present during the project as originally presumed. For this and other reasons related to deer behavior, target levels of serum ivermectin were achieved in a minority of deer. Nevertheless, > 90% control of female tick infestation, subsequent oviposition, and larval eclosion was obtained in those 8 of 16 sampled deer with serum ivermectin levels of > or = 15 ng/ml. In addition, the ratio of females to males, the numbers of females engorging > 10 mg body weight, and the numbers of those eventually hatching, were all significantly less among ticks from island deer in comparison with ticks from untreated deer. No consistent changes in the numbers of ticks found on immature-stage hosts or removed from vegetation were noted within 3 yr of the cessation of treatment.

Young maternal age and smoking during pregnancy as risk factors for gastroschisis.

Three maternal risk factors (maternal age, cigarette smoking, and infant's month of birth) have been reported to be associated with fetal gastroschisis. In order to study these risk factors further, a prospective population-based study was designed, using 62,103 consecutive second-trimester singleton pregnancies enrolling in a maternal serum alpha-fetoprotein screening program between January 1, 1980 and April 30, 1989. Gastroschisis occurred in 21 of those pregnancies. Pregnancies in women younger than 20 years of age were at 7.3 times greater odds for being affected with gastroschisis than pregnancies in women aged 25 or older (95% confidence interval 2.4 to 22). For pregnant women aged 20 to 24 years, the odds were 1.9 times greater (95% confidence interval 0.7 to 5.0). Pregnant women who smoked cigarettes were at 2.1 times greater odds than non-smokers (95% confidence interval 0.9 to 4.8). When these smoking data were combined with smoking data from two other published studies, the consensus odds ratio was 1.6 (95% confidence interval 1.2 to 2.2). Infant's month of birth was not associated with gastroschisis. Evidence from the present study and other published studies clearly establishes a greater risk for fetal gastroschisis in pregnant women younger than age 20, even after adjustment for smoking status. Cigarette smoking also appears to be a risk factor, when data from this and two previously published studies are combined.

Can gestational dates routinely derived from very early ultrasound be used to interpret maternal serum alpha-fetoprotein measurements?

This study assesses the reliability of estimating gestational age via crown-rump or gestational sac measurements obtained at 8 weeks' gestation or earlier as part of routine physician office practice. To accomplish this, we studied 88 pregnancies managed at 45 different sites in which both an early first-trimester ultrasonically-derived gestational age estimate and a second-trimester biparietal diameter (BPD) estimate were available. The first- and second-trimester determinations were highly correlated, but the first-trimester determinations were, on average, 0.43 weeks earlier than the second. The first-trimester estimates were satisfactory for use in interpreting maternal serum alpha-fetoprotein (MSAFP) screening measurements, but second-trimester BPD measurements obtained prior to MSAFP screening should be the method of choice for interpreting MSAFP values, due to the increased sensitivity for detecting open spina bifida.

Maternal serum alpha-fetoprotein screening for fetal Down syndrome in the United States: results of a survey.

To determine the status of maternal serum alpha-fetoprotein screening for fetal Down syndrome in the United States, we surveyed member laboratories in the External Quality Assessment Scheme for Pregnancy alpha-Fetoprotein in the spring of 1988. Of the 123 member laboratories that provide screening services, 109 responded. The 109 laboratories screened 586,000 pregnancies annually, and 96 provided interpretations for risk of fetal Down syndrome, accounting for 534,000 pregnancies. Numbers of women screened annually per laboratory ranged from less than 200 to greater than 27,000 (median 3000). A total of 85 of the 96 laboratories used a combination of the maternal serum alpha-fetoprotein cut-off. Ultrasonographic gestational dating was used for the initial interpretation in 25% of the screened pregnancies. The median initial positive rate (the number of women initially classified as being at increased risk) was 3.7% overall, and smaller laboratories were more likely either to have outlying initial positive rates or to be unable to provide such rates. Median initial positive rates were lower for enzyme immunoassay kits than for radioimmunoassay kits (3.0% versus 4.8%). These results indicate that, whereas most laboratories appear to perform satisfactorily in screening for fetal Down syndrome, some laboratories appear to perform satisfactorily in screening for fetal Down syndrome, some laboratories need to refine their methods of assigning risk and others need to develop mechanisms to document initial positive rates and, when appropriate, to analyze the cause of outlying initial positive rates. This survey, combined with information from nonsurveyed laboratories known to screen for fetal Down syndrome, allows an estimation that 1 million pregnancies annually were provided with fetal Down syndrome interpretations in the United States in mid-1988.

Improved 125I radioimmunoassay for cotinine by selective removal of bridge antibodies.

We describe an 125I-based RIA for cotinine, the major metabolite of nicotine. The slope of the dose-response curve was quite shallow (6-8% change in binding per doubling dose), resulting in between-assay CVs of 15 to 20%. This effect occurred because the radioligand formed by linking a cotinine derivative to tyramine manifested greater affinity for the anti-cotinine antibodies than did cotinine itself. We absorbed the serum with a derivative of nicotine coupled to the carrier protein via a chemical bridge similar to that used to form the cotinine/carrier protein immunogen. An RIA in which we used such absorbed serum showed a significantly increased slope of the dose-response curve (11-13% change in binding per doubling dose), and between-assay CVS were only 6 to 8%. We suggest that this improvement results because absorption removes anti-bridge antibodies directed against the chemical-bond common to the cotinine/carrier-protein immunogen and to the cotinine/tyramine radioligand.

Acetylcholinesterase and fetal malformations: modified qualitative technique for diagnosis of neural tube defects.

A single-blind study involving amniotic-fluid samples from 214 pregnancies of known outcome confirms that an electrophoretically distinct isoenzyme of acetylcholinesterase is associated with fetal open neural tube defects. Furthermore, only one of 13 amniotic-fluid samples with false-positive results for alpha-fetoprotein showed the characteristic isoenzyme, indicating that qualitative acetylcholinesterase assessment can decrease the proportion of false positives from the alpha-fetoprotein assay. We have also identified this characteristic isoenzyme in amniotic fluids from pregnancies in which other serious fetal defects occurred. A detailed electrophoresis protocol for identifying this characteristic isoenzyme is described.