Touchdown-touchup nested PCR for low-copy gene detection of benzimidazole-susceptible Wuchereria bancrofti with a Wolbachia endosymbiont imported by migrant carriers

Investigation of Armigeres subalbatus, a vector of zoonotic Brugia pahangi filariasis in plantation areas in Suratthani, Southern Thailand

In recent years, children in Thailand have been infected with zoonotic Brugia pahangi. However, the local environment of rubber or oil palm plantations, which would increase their exposure to risk factors of the infection due to mosquito transmission, is unclear. The present study first sought to determine the extent to which variations in the local landscape, such as the elevated versus low-lying ecotope of rubber or oil palm plantations, in a 2-km radius of the geographically defined landscape in a rural area of Suratthani, Southern Thailand could influence the abundance of Armigeres subalbatus and its susceptibility to zoonotic filarial parasite infections compared to Mansonia, Aedes, and Culex, and Coquillettidia. Thereafter, the filarial larvae found in the infected mosquitoes were molecularly investigated. Ar. subalbatus plantation ecotype was not only found to outnumber the local mosquitoes, but was identified as the predominant species that adapted well to the elevated ecotopes of the rubber or oil palm plantations, which existed at altitudes of 60–80 m. The overall rate of zoonotic filarial parasite infections (L₁, L₂, or L₃ larvae) of Ar. subalbatus was 2.5% (95% CI, −0.2 to 4.1), with an average L₃ load of 2.3 larvae per infected Ar. subalbatus (95% CI, −0.6 to 13.0); this is because the infections were found to be concentrated in the elevated ecotopes alone. Based on filarial orthologous β-tubulin gene-specific touchup-nested PCR and sequence analysis using 30 L₃ larva clones as representatives of 9 Ar. subalbatus infectious pools, Ar. subalbatus either carried B. pahangi or Dirofilaria immitis, or both species. Such findings suggest that Ar. subalbatus might have played an imperative role in the transmission of B. pahangi in the plantation areas infested with Ar. subalbatus.

•

Ar. subalbatus is the natural vector for zoonotic Brugia pahangi.

•

Ar. subalbatus plantation ecotype adapted to rubber or oil palm plantations.

•

Local landscape variation influencing its abundance and susceptibility to zoonotic filarial infection.

•

Touchup-nested PCRs specific for amplifying filarial beta-tubulin genes of L₃ larvae present in Ar. subalbatus.

•

Implying that Ar. subalbatus carried either B. pahangi or D. immitis, or both.

GoFish: A versatile nested PCR strategy for environmental DNA assays for marine vertebrates

Here we describe GoFish, a strategy for single-species environmental DNA (eDNA) presence/absence assays using nested PCR. The assays amplify a mitochondrial 12S rDNA segment with vertebrate metabarcoding primers, followed by nested PCR with M13-tailed, species-specific primers. Sanger sequencing confirms positives detected by gel electrophoresis. We first obtained 12S sequences from 77 fish specimens for 36 northwestern Atlantic taxa not well documented in GenBank. Using these and existing 12S records, we designed GoFish assays for 11 bony fish species common in the lower Hudson River estuary and tested seasonal abundance and habitat preference at two sites. Additional assays detected nine cartilaginous fish species and a marine mammal, bottlenose dolphin, in southern New York Bight. GoFish sensitivity was equivalent to Illumina MiSeq metabarcoding. Unlike quantitative PCR (qPCR), GoFish does not require tissues of target and related species for assay development and a basic thermal cycler is sufficient. Unlike Illumina metabarcoding, indexing and batching samples are unnecessary and advanced bioinformatics expertise is not needed. From water collection to Sanger sequencing results, the assay can be carried out in three days. The main limitations to this approach, which employs metabarcoding primers, are the same as for metabarcoding, namely, inability to distinguish species with shared target sequences and inconsistent amplification of rarer eDNA. In addition, the performance of the 20 assays reported here as compared to other single-species eDNA assays is not known. This approach will be a useful addition to current eDNA methods when analyzing presence/absence of known species, when turnaround time is important, and in educational settings.

O Serogroup-Specific Touchdown-Multiplex Polymerase Chain Reaction for Detection and Identification of Vibrio cholerae O1, O139, and Non-O1/Non-O139

A novel, sensitive locus-specific touchdown-multiplex polymerase chain reaction (TMPCR), which is based on two-stage amplification pertaining to multiplex PCR and conditional touchdown strategy, was used in detecting and differentiating Vibrio cholerae serogroups. A panel of molecular marker-based TMPCR method generates reproducible profiles of V. cholerae-specific (588 bp) amplicons derived from ompW gene encoding the outer membrane protein and serogroup-specific amplicons, 364 bp for the O1 and 256 bp for the O139, authentically copied from rfb genes responsible for the lipopolysaccharide biosynthesis. The TMPCR amplification efficiency yields either equally or unequally detectable duplex DNA bands of the O1 (588 and 364 bp) and O139 (588 and 256 bp) or a DNA fragment of non-O1/non-O139 (588 bp) while providing no false positive identifications using the genomic DNA templates of the other vibrios and Enterobacteriaceae. The reciprocal analysis of two-template combinations demonstrated that, using V. cholerae O1, O139, or equally mixed O1 and O139, the TMPCR had a detection limit of as low as 100 pg of the O1, O139, or non-O1/non-O139 in reactions containing unequally or equally mixed gDNAs. In addition, the O serogroup-specific TMPCR method had 100% agreement with the serotyping method when examined for the serotyped V. cholerae reference strains and those recovered from clinical samples. The potential benefit of using this TMPCR tool would augment the serotyping method used in epidemiological surveillance and monitoring of V. cholerae serogroups, O1, O139, and non-O1/non-O139 present in clinical and environmental samples.

Current Bancroftian Filariasis Elimination on Thailand-Myanmar Border: Public Health Challenges toward Postgenomic MDA Evaluation

From regional and global perspectives, Thailand has progressed toward lymphatic filariasis transmission-free zone in almost entire endemic provinces, being verified by WHO by the end of 2012 after the 5-year implementation of mass drug administration (MDA) with diethylcarbamazine and albendazole as part of the National Program to Eliminate Lymphatic Filariasis (PELF) (2002–2006) and a 4-year expansion of post-MDA surveillance (2007–2010). However, Thai PELF has been challenging sensitive situations of not only border crossings of local people on Thailand-Myanmar border where focal distribution of forest- and forest fringe-related border bancroftian filariasis (BBF) is caused by nocturnally subperiodic Wuchereria bancrofti in local people living in pockets of endemic villages, but also intense cross-border migrations of Mon and Tanintharyi workers from Myanmar to Thailand who harbor nocturnally periodic W. bancrofti microfilaremic infection causing the emergence of imported bancroftian filariasis (IBF). Thus, this paper discusses the apparent issues and problems pertaining to epidemiological surveillance and postgenomic MDA evaluation for 2010–2020 convalescent BBF and IBF. In particular, the population migration linked to fitness of benzimidazole-resistant W. bancrofti population is a topic of interest in this region whether the resistance is associated with pressure of the MDA 2 drugs and the vulnerabilities epidemiologically observed in complex BBF or IBF settings.

Development of loop-mediated isothermal amplification method for detecting Wuchereria bancrofti DNA in human blood and vector mosquitoes

We have developed loop-mediated isothermal amplification (LAMP) method to detect Wuchereria bancrofti DNA. The sensitivity and specificity of LAMP method were equivalent to those of PCR method which detects SspI repeat sequence in W. bancrofti genomic DNA: both methods detected one thousandth of W. bancrofti DNA from one microfilaria (Mf), and did not cross-react with DNAs of Brugia malayi, B. pahangi, Dirofilaria immitis, human and Culex quinquefasciatus. We also examined the sensitivity of LAMP using the mimic samples of patient's blood or blood-fed mosquitoes containing one W. bancrofti Mf per sample. The LAMP method was able to detect W. bancrofti DNA in 1000 μl of blood or in a pool of 60 mosquitoes, indicating its usefulness in detecting/monitoring W. bancrofti infection in humans and vector mosquitoes in endemic areas.