Survey of entomopathogenic nematodes and associate bacteria in Thailand and their potential to control Aedes aegypti

Aedes aegypti is an insect vector that transmits several viruses affecting humans worldwide. Entomopathogenic nematodes (EPNs) and their symbiotic bacteria are organisms with the potential to control many insects. In this study, we did a survey aimed to identify EPNs and their symbiotic bacteria and evaluate the larvicidal activity of bacteria against Ae. aegypti. We collected 540 soil samples from 108 sites in Phitsanulok Province, lower northern Thailand. Baiting techniques and White traps were used to isolate EPNs from soil samples. By sequencing of 28S rDNA and internal transcribed spacer regions, 51 EPN isolates were identified as Steinernema surkhetense (35 isolates), Heterorhabditis indica (14 isolates) and Heterorhabditis sp. SGmg3 (two isolates). Based on sequencing of a partial region of the recA gene, 35 isolates of Xenorhabdus were identified as Xenorhabdus stockiae, and 20 Photorhabdus isolates were identified as Photorhabdus luminescens subsp. akhurstii (10 isolates), P. luminescens subsp. hainanensis (seven isolates) and P. asymbiotica subsp. australis (three isolates). Screening for larvicidal activity of bacteria against Ae. aegypti was performed in the laboratory. Xenorhabdus WB5.4 and Xenorhabdus WB12.5, which were closely related to X. stockiae, resulted in high mortality of Ae. aegypti (99.99% and 70%, respectively) at 96 hr after exposure. Comparing with control groups, mortality of Ae. aegypti larvae was low (1.11%–6.67%) after exposure for 24–96 hr. Our findings showed the potential of X. stockiae for controlling Ae. aegypti. Further studies are needed to elucidate the mechanisms through which these bacteria kill Ae. aegypti larvae.     

Infant male sex as a risk factor for shoulder dystocia but not for cephalopelvic disproportion: An independent or confounded effect?

Background: Shoulder dystocia (ShD) and cephalopelvic disproportion (CPD) share some common risk factors. Whether infant male sex is an independent risk factor for ShD, or if the risk is confounded by other known factors, is uncertain.Objective: The aim of this study was to explore the unconfounded effect of infant male sex on the risk for ShD and its interaction with other risk factors compared with CPD.Methods: A retrospective data analysis was conducted of deliveries in Lamphun Hospital, Lamphun, Thailand. All vaginal deliveries complicated by ShD were collected as ShD cases. All labors terminated by cesarean delivery (CD) due to CPD were collected as CD/CPD cases. Vaginal deliveries that took place immediately before or after the index ShD cases were collected as controls. Multivariable adjusted odds ratios (AORs) for infant male sex and its 95% CI in cases of ShD and CD/CPD were computed by multichotomous logistic regression controlling for other obstetric risks. The effects of maternal height, gestational age, and birth weight on the risk for ShD or CD/CPD among male or female infants was also explored. Stability of the effect of the risk between male and female infants was tested with Chow tests.Results: Thirty-five ShD cases and 199 CD/CPD cases were collected, as were 586 controls. Infant male sex was a significant independent risk factor for ShD (AOR = 5.00; 95% CI, 1.83-13.61; P = 0.002), but not for CD/CPD (AOR = 1.09; 95% CI, 0.75-1.59; P = NS). For CD/CPD, the effects of maternal height, gestational age, and birth weight were similar for male and female infants, but the corresponding effect on ShD was more pronounced in male than in female infants (P < 0.001 for all comparisons).Conclusions: Infant male sex is a risk factor for ShD independent of other known risks. Male sex also amplified the existing effects of short maternal height, extended gestational age, and greater birth weight. If infant sex is known to be male before delivery, the obstetrician may consider avoiding vaginal delivery in mothers who have other strong risks for ShD.