Sandwich dot-immunogold filtration assay (DIGFA) for specific immunodiagnosis of active neuroangiostrongyliasis

Serological tests may yield false-negative results for specific antibodies detection before or at the early seroconversion phase. Tests that detect circulating antigens of Angiostrongylus cantonensis would therefore be of value in diagnosis to distinguish current or past infection. Here, a quick, easy to perform, portable and inexpensive diagnostic device for detection of 31-kDa A. cantonensis specific antigens had been developed. This sandwich dot-immunogold filtration assay (AcDIGFAAg), for detecting active angiostrongyliasis was produced using anti-A. cantonensis polyclonal antibody dotted on the nitrocellulose membrane as a capture agent and colloidal gold-labelled anti-31 kDa A. cantonensis antibody as a detection agent. A well-defined pink dot, indicating positivity, was seen readily by naked eye within 10-15 min. The AcDIGFAAg detected A. cantonensis-specific antigens in cerebrospinal fluid samples from 4 out of 10 serologically confirmed angiostrongyliasis cases and 2 out of 5 suspected cases with negative anti-A. cantonensis antibodies. Among the 19 patient sera with A. cantonensis infection, 2 showed positive reaction by AcDIGFAAg. No positive AcDIGFAAg reaction was observed in all the serum samples with other parasitic diseases, and the healthy controls. The present 'AcDIGFAAg' enables rapid qualitative detection of the specific 31-kDa antigens of A. cantonensis in clinical samples with potential for application even under resource-limited settings.

Geometric morphometrics of the scutum for differentiation of trombiculid mites within the genus Walchia (Acariformes: Prostigmata: Trombiculidae), a probable vector of scrub typhus

The vectors of scrub typhus are the larval stage of trombiculid mites, termed "chiggers". These vectors are very small - the larvae are approximately 0.2 mm in size - and therefore their morphological identification is difficult. Trombiculid mites are widely distributed across Asia and they can be identified at the genus level by the shape, size and setae/sensilla distribution of their dorsal chitin plate (scutum = shield), while morphological identification at the species level requires more mite characteristics. We recently developed a methodology to ascertain paired matched genotype and morphotype of individual chiggers, based on autofluorescence and brightfield microscopy with subsequent molecular identification using the COI gene (approximately 640bp length). However, based on 20 chigger specimens characterised by paired genotypic and morphological data consisting of the four species [Walchia ewingi with 2 subspecies]: Walchia ewingi lupella (n = 9), W. ewingi ewingi (n = 2), W. alpestris (n = 2), W. kritochaeta (n = 5) and W. minuscuta (n = 2) we found evidence of genetic polymorphism and morphological plasticity within the genus Walchia. The phylogenetic inference of the intra-genus relationships within the Walchia spp., based on COI gene (Blankaartia spp. served as outgroup), delineated the five included species by an average interspecific divergence of mean distance 0.218 (0.126 - 0.323). We therefore applied landmark-based and outline-based geometric morphometric (GM) approaches to differentiate Walchia species using scutum measurements. A total of 261 scutum images of Walchia spp. were examined by landmark-based GM (140 chigger specimens) and outline-based GM (121 specimens) techniques. All Walchia spp. showed significant differences in scutum size and shape. W. minuscuta showed the smallest mean scutum size in both techniques. The largest scutum was found in W. ewingi lupella and W. ewingi ewingi by landmark-based and outline-based GM analysis, respectively. The scutum shapes of W. alpestris and W. minuscuta were clearly distinguished from the other species. Cross-validated classification scores were different depending on species and digitizing techniques and landmark-based GM showed better scores than outline-based GM. We conclude that the morphologically closely-related trombiculid mite species can be further differentiated by their scutum features alone, using GM approaches. This technique is a promising tool for the much-needed characterization studies of chiggers and needs evaluation using matched morphometric and genotyping data for other genera of trombiculids.

Molecular phylogeography and genetic diversity of Angiostrongylus cantonensis and A. malaysiensis (Nematoda: Angiostrongylidae) based on 66-kDa protein gene

Angiostrongylus cantonensis is the main causative agent of human angiostrongyliasis. A sibling species, A. malaysiensis has not been unequivocally incriminated to be involved in human infections. To date, there is only a single report on the application of the partial 66-kDa protein gene sequence for molecular differentiation and phylogeny of Angiostrongylus species. Nucleotide sequences of the 66-kDa protein gene of A. cantonensis and A. malaysiensis from Thailand, as well as those of the laboratory strains of A. cantonensis from Thailand and Hawaii, A. cantonensis from Japan and China, A. malaysiensis from Malaysia, and A. costaricensis from Costa Rica, were used for the reconstruction of phylogenetic tree by the maximum likelihood (ML) method and the haplotypes by the median joining (MJ) network. The ML phylogenetic tree contained two major clades with a full support bootstrap value - (1) A. cantonensis and A. malaysiensis, and (2) A. costaricensis. A. costaricensis was basal to A. cantonensis and A. malaysiensis. The genetic distance between A. cantonensis and A. malaysiensis ranged from p = .82% to p = 3.27%, that between A. cantonensis and A. costaricensis from p = 4.90% to p = 5.31%, and that between A. malaysiensis and A. costaricensis was p = 4.49% to p = 5.71%. Both A. cantonensis and A. malaysiensis possess high 66-kDa haplotype diversity. There was no clear separation of the conspecific taxa of A. cantonensis and A. malaysiensis from different geographical regions. A more intensive and extensive sampling with larger sample size may reveal greater haplotype diversity and a better resolved phylogeographical structure of A. cantonensis and A. malaysiensis.

Autofluorescence microscopy for paired-matched morphological and molecular identification of individual chigger mites (Acari: Trombiculidae), the vectors of scrub typhus

BACKGROUND

Conventional gold standard characterization of chigger mites involves chemical preparation procedures (i.e. specimen clearing) for visualization of morphological features, which however contributes to destruction of the arthropod host DNA and any endosymbiont or pathogen DNA harbored within the specimen.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, a novel work flow based on autofluorescence microscopy was developed to enable identification of trombiculid mites to the species level on the basis of morphological traits without any special preparation, while preserving the mite DNA for subsequent genotyping. A panel of 16 specifically selected fluorescence microscopy images of mite features from available identification keys served for complete chigger morphological identification to the species level, and was paired with corresponding genotype data. We evaluated and validated this method for paired chigger morphological and genotypic ID using the mitochondrial cytochrome c oxidase subunit I gene (coi) in 113 chigger specimens representing 12 species and 7 genera (Leptotrombidium, Ascoschoengastia, Gahrliepia, Walchia, Blankaartia, Schoengastia and Schoutedenichia) from the Lao People's Democratic Republic (Lao PDR) to the species level (complete characterization), and 153 chiggers from 5 genera (Leptotrombidium, Ascoschoengastia, Helenicula, Schoengastiella and Walchia) from Thailand, Cambodia and Lao PDR to the genus level. A phylogenetic tree constructed from 77 coi gene sequences (approximately 640 bp length, n = 52 new coi sequences and n = 25 downloaded from GenBank), demonstrated clear grouping of assigned morphotypes at the genus levels, although evidence of both genetic polymorphism and morphological plasticity was found.

CONCLUSIONS/SIGNIFICANCE

With this new methodology, we provided the largest collection of characterized coi gene sequences for trombiculid mites to date, and almost doubled the number of available characterized coi gene sequences with a single study. The ability to provide paired phenotypic-genotypic data is of central importance for future characterization of mites and dissecting the molecular epidemiology of mites transmitting diseases like scrub typhus.

Geographical distribution and incidence of Angiostrongylus lungworms (Nematoda: Angiostrongylidae) and their rodent hosts in Thailand

The rat lungworm Angiostrongylus cantonensis, a zoonotic parasite, is known to be responsible for eosinophilic meningitis and meningoencephalitis in humans in many countries worldwide. Another congener A. malaysiensis is a potential pathogen. Rodents as natural definitive host of the parasites are abundant and globally widespread. In this study, the prevalence of Angiostrongylus infection in wild rats was investigated in twenty-four provinces of Thailand during the period December 2011 to June 2014. Of the 669 wild rats sampled, 46 (6.88%) were infected with Angiostrongylus lungworms. The rodents harbouring A. cantonensis worms included Bandicota indica, Bandicota savilei, Rattus exulans, Rattus norvegicus, Rattus rattus complex and Rattus tiomanicus, and those harbouring A. malaysiensis were B. savilei, Rattus losea, R. norvegicus and R. rattus complex. No parasite was recovered from Maxomys surifer (n=11), Mus musculus (n=1), Niviventer fulvescens (n=2), Rattus argentiventer (n=4), Rattus nitidus (n=3) and Sundamys muelleri (n=3). In positive rats, the incidence of infection with Angiostrongylus lungworms was variable among host species and provinces. There were also considerable variation in the proportion of male and female worms among rodent hosts and localities. Two hundred and thirty-five of the collected worms were male and 282 were female. The mean worm burden in the positive rats was 11.24 and ranged from 1 to 61. 81.82% (423/517) of the adult worms were morphologically identified as A. cantonensis, and 18.18% (94/517) were A malaysiensis. One R. rattus from Prachuap Khiri Khan had mixed infection of A. cantonensis and A. malaysiensis (10 worms of each species). The overall number of male (202) and female (221) A. cantonensis worms was not significantly different (χ² = 0.86, 0.50 > P > 0.30). However, the overall number of male (33) and female (61) A. malaysiensis worms was significantly different (χ² = 8.34, P < 0.01). The present study added one new definitive host (R. tiomanicus) for A. cantonensis and two new definitive hosts (B. savilei and R. losea) for A. malaysiensis in Thailand. Our data update and contribute significantly to existing knowledge of the geographical distribution of A. cantonensis in wild rats in Thailand and confirm the occurrence of A. malaysiensis throughout the country.

Molecular phylogeography of Angiostrongylus cantonensis (Nematoda: Angiostrongylidae) and genetic relationships with congeners using cytochrome b gene marker

Angiostrongylus cantonensis is an important emerging zoonotic parasite causing human eosinophilic meningitis (or meningoencephalitis) in many parts of the world. To-date there is only a single study using mitochondrial cytochrome b (CYTB) gene to determine its genetic structure in eight geographical localities in Thailand. The present study examined the molecular phylogeography of this rat lungworm and its phylogenetic relationship with congeners using CYTB gene marker. A total of 15 CYTB haplotypes was found in 37 sequences from 14 geographical localities (covering north, west, east, central and south regions) in Thailand. These CYTB haplotypes were distinct from those of A. cantonensis for China and Hawaii. In Thailand, some CYTB haplotypes appeared to be confined to specific geographical localities. The partial CYTB DNA nucleotide sequences separated unequivocally the A. cantonensis isolates of Thailand, China and Hawaii as well as the congeners Angiostrongylus malaysiensis, A. costaricensis and Angiostrongylus vasorum, with A. malaysiensis grouped with A. cantonensis and A. costaricensis grouped with A. vasorum. Likewise the congeners of Metastrongylus and Onchocerca genera could also be clearly differentiated. The present study added two new definitive hosts (Bandicota savilei and Rattus losea) and three new localities (Mae Hong Son in the north, Tak in the west, and Phang Nga in the south) for A. malaysiensis in Thailand, indicating its wide occurrence in the country. Three CYTB haplotypes were found in the Thailand samples of A. malaysiensis. In addition to differentiation of congeners, CYTB gene marker could be used for determining the genetic diversity of a given population/taxon.

Evaluation of dot immunogold filtration assay (DIGFA) for rapid serodiagnosis of eosinophilic meningitis due to Angio-strongylus cantonensis (Nematoda: Metastrongyloidea)

Angiostrongylus cantonensis is the most frequent cause of eosinophilic meningitis in humans in Thailand and worldwide. Because of difficulty of recovering the Angiostrongylus larvae from infected patients, detection of parasite-specific antibodies is used to support clinical diagnosis. This study tested serum samples from eosinophilic meningitis patients and individuals at risk of infection with A. cantonensis to evaluate a recently developed simple and rapid dot-immunogold filtration assay (DIGFA) for detection of specific antibodies against A. cantonensis. Purified 31-kDa glycoprotein of A. cantonensis and protein A colloidal gold conjugate were employed to detect the 31-kDa anti-A. cantonensis antibody in patients sera from the parasite endemic areas of northeast Thailand. The results were compared with those obtained by dot-blot enzyme-linked immunosorbent assay (ELISA) with 31-kDa A. cantonensis antigen. The overall positivity rate of DIGFA and dot-blot ELISA for A. cantonensis infection in 98 clinically diagnosed cases from three highly endemic districts in Khon Kaen province were 39.79% and 37.75%, respectively. Among 86 sera of subjects at risk of infection with A. cantonensis, 24.41% were positive by DIGFA and 23.25% by dot-blot ELISA. There were good correlation between the visual grading of DIGFA and dot-blot ELISA in both groups of defined sera. DIGFA is as sensitive and specific as dot-blot ELISA for confirming eosinophilic meningitis due to A. cantonensis infection, with advantages of simplicity, rapidity and without the use of specific and expensive equipment, and can be used in field settings.

Efficacy of plant essential oils for the repellents against chiggers (Leptotrombidium imphalum) vector of scrub typhus

Scrub typhus caused by the Orientia tsutsugamushi. Rodents, particularly rats, serve as principal reservoir hosts. Infection in man is transmitted by the, chigger bite. Repellents provide an effective agent of protecting individuals from chigger. In the present study 6 plant essential oils were tested for evaluation of their repellent activity against the chigger, Leptotrombidium imphalum. The results showed that Clove oil was significantly more effective than others with ED50 and EC50 of 0.420 mg and 2.3%, followed by Zingiber oil (8.458 mg and 42.3%), Vetiver oil (19.582 mg and 97.9%), Turmeric oil (24.343 mg and 121.7%), Orange oil (27.310 mg and 136.6%) and Boesenbergia oil (30.486 mg and 152.4%). These results suggested that Clove oil was the most efficient repellent against chigger which is the vector for scrub typhus.

Isolation and characterization of Orientia tsutsugamushi from rodents captured following a scrub typhus outbreak at a military training base, Bothong district, Chonburi province, central Thailand

Orientia tsutsugamushi, an obligate intracellular Gram-negative bacterium, is the causative agent of scrub typhus, a vector-borne disease transmitted by infected chiggers (trombiculid mite larvae). In 2002, an outbreak of scrub typhus occurred among Royal Thai Army troops during the annual field training at a military base in Bothong district, Chonburi province, central Thailand. This report describes the outbreak investigation including its transmission cycle. Results showed that 33.9% of 174 trained troops had scrub typhus-like signs and symptoms and 9.8% of those were positive for O. tsutsugamushi-specific antibodies by indirect fluorescence antibody assay. One hundred thirty-five rodents were captured from this training area, 43% of them had antibodies against O. tsutsugamushi. Six new O. tsutsugamushi isolates were obtained from captured rodent tissues and successfully established in cell culture. Phylogenetic studies showed that these six isolates were either unique or related to a native genotype of previously described isolates from Thailand.