Reduction in Anti-Dengue Virus IgG Antibody Levels with the Use of a Larvicide for Vector Control in Rural Lao People's Democratic Republic.

The Lao People's Democratic Republic is an endemic area of dengue, with cases reported in urban and rural areas every year. In this study, we indirectly evaluated the efficacy of a larvicide (SumiLarvTM 2MR discs) that was used for vector control against Aedes mosquitoes. Villages in a rural area of Lao PDR were selected as study areas, non-intervention and intervention villages. At the intervention village, the larvicide was used to treat refillable water containers for 27 months (October 2017 to February 2020), while at the non-intervention villages were no treatment. The serum samples of villagers from both villages were randomized to collect in the pre-intervention and in post-intervention periods. An enzyme-linked immunosorbent assay (ELISA) was used to examine anti-dengue virus (DENV) IgG antibody levels in serum samples. Recombinant DENV serotype 2 non-structural protein1 was used as an antigen for the ELISA, the optical density (OD) values were analyzed for comparison. The results showed that the OD values decreased significantly (p < 0.01) between the pre-intervention and post-intervention periods at the intervention site. The treatment of water storage containers in rural areas with SumiLarvTM 2MR discs may help to protect residents from Aedes mosquito bites, and hence, reduce DENV infections.

Phenotypic and haplotypic profiles of insecticide resistance in populations of Aedes aegypti larvae (Diptera: Culicidae) from central Lao PDR.

BACKGROUND: Aedes aegypti, which is widely distributed in the Lao People's Democratic Republic (PDR), is the primary vector of arboviral diseases. Chemical insecticides have been intensively used to eliminate mosquito-borne diseases, resulting in the development of insecticide resistance. However, little is known about the insecticide resistance of mosquito populations in Lao PDR and the mechanisms responsible for it, which have important implications for vector management programs. Here, we examined the phenotypic and haplotypic profiles of insecticide resistance in populations of Ae. aegypti larvae from central Lao PDR. METHODS: Ae. aegypti larvae were collected from four sites in Lao PDR, and their susceptibility to temephos, deltamethrin, permethrin, and Bacillus thuringiensis israelensis (Bti) was tested using larval bioassays. Synergistic tests were also conducted to evaluate the activity of insecticide-metabolizing enzymes in the larvae. Deltamethrin-resistant and Deltamethrin-susceptible larvae were then genotyped for knockdown resistance (kdr) mutations to determine the associations between each genotype and resistance. RESULTS: Ae. aegypti larvae from central Lao PDR were considered to be "resistant" (<98% mortality) to organophosphates and pyrethroids. The bio-insecticide Bti remains effective against such larvae. The resistance mechanisms of Ae. aegypti larvae were found to vary among populations, especially for pyrethroid resistance. Kdr mutations were significantly associated with deltamethrin resistance in Ae. aegypti from the Xaythany population. In contrast, synergist assays with piperonyl butoxide suggested that cytochrome P450 monooxygenases played an important role in the resistance seen in the Khounkham and Thakhek populations. CONCLUSION: This study obtained information that will aid the design and implementation of insecticide-based vector management of Ae. aegypti in central Lao PDR. Ae. aegypti larvae from central Lao PDR were highly susceptible to Bti, while they were resistant to temephos at a diagnostic dose of 0.0286 mg/L. Given the limited number of insecticides that are approved for vector control, it is important to alternate between temephos and other larvicides, such as Bti and pyriproxyfen. The differences in pyrethroid resistance mechanisms seen among the Ae. aegypti populations highlight the need to tailor vector-control strategies to each region to increase the success of dengue control in Lao PDR.

Aedes mosquito surveillance and the use of a larvicide for vector control in a rural area of the Lao People's Democratic Republic.

BACKGROUND: Refillable water containers are commonly used in rural areas of Lao PDR, and they act as Aedes mosquito breeding sites. Aedes aegypti and Ae. albopictus mosquitos are transmission vectors for the dengue virus, which causes dengue fever. METHODS: Two isolated rural villages in the central part of Lao PDR were selected as study sites. In the intervention village, domestic water containers were continuously treated with a long-lasting matrix release formulation, containing pyriproxyfen, named SumiLarv®2MR. In the control village, entomological activity was monitored, but no intervention was performed. Baseline data were collected in both villages during the late rainy season (October 2017) then distributed SumiLarv®2MR disks in intervention village. This data was compared with data collected during the intervention periods in the dry season (February 2018), rainy season (July 2018 and 2019), and late rainy season (September 2018) in the region. RESULTS: Compared with the baseline data (20.24%), the percentage of water containers infested with Ae. aegypti larvae was significantly decreased in the treated village, especially in the rainy seasons in July 2018 (4.11%; P < 0.001) and July 2019 (2.46%; P < 0.001), while the percentage of water containers infested with Ae. albopictus larvae did not decrease significantly in prevalence. No reduction in the frequency of Aedes species was seen in the control village. The Ae. albopictus liked to breed in small habitats (the median water volume of its habitats was 5 L and 10 L in the control and treated village, respectively, while the equivalent values for Ae. aegypti were 30 L and 50 L, respectively). CONCLUSION: The treatment of refillable water storage containers in a rural village with SumiLarv®2MR disks led to significant reductions in the Ae. aegypti population. However, the Ae. albopictus population did not decrease in either the control or treated village. This discrepancy was due to differences in habitat-seeking behaviors and preferred breeding sites such as types of water, water container, and water volume, then led to the differences in results of mosquito prevalence after SumiLarv®2MR disk treatments. The SumiLarv®2MR disk treatment was proven to be effective against the primary dengue-virus vector mosquitoes, Ae. aegypti.

Correction to: Multiple arboviral infections during a DENV-2 outbreak in Solomon Islands.

[This corrects the article DOI: 10.1186/s41182-020-00217-8.].

Multiple arboviral infections during a DENV-2 outbreak in Solomon Islands.

BACKGROUND: Solomon Islands, a country made up of tropical islands, has suffered cyclic dengue fever (DF) outbreaks in the past three decades. An outbreak of dengue-like illness (DLI) that occurred in April 2016 prompted this study, which aimed to determine the population's immunity status and identify the arboviruses circulating in the country. METHODS: A household survey, involving 188 participants in two urban areas (Honiara and Gizo), and a parallel hospital-based clinical survey were conducted in April 2016. The latter was repeated in December after a surge in DLI cases. Arbovirus IgG ELISA were performed on the household blood samples to determine the prevalence of arboviruses in the community, while qPCR testing of the clinical samples was used to identify the circulating arboviruses. Dengue virus (DENV)-positive samples were further characterized by amplifying and sequencing the envelope gene. RESULTS: The overall prevalence rates of DENV, Zika virus, and chikungunya virus were 83.4%, 7.6%, and 0.9%, respectively. The qPCR positivity rates of the clinical samples collected in April 2016 were as follows: DENV 39.6%, Zika virus 16.7%, and chikungunya virus 6.3%, which increased to 74%, 48%, and 20% respectively in December 2016. The displacement of the circulating serotype-3, genotype-1, with DENV serotype 2, genotype cosmopolitan was responsible for the outbreak in 2016. CONCLUSIONS: A DENV outbreak in Solomon Islands was caused by the introduction of a single serotype. The high prevalence of DENV provided transient cross-protection, which prevented the introduction of a new serotype from the hyperendemic region for at least 3 years. The severe outcomes seen in the recent outbreak probably resulted from changes in the causative viruses and the effects of population immunity and changes in the outbreak pattern. Solomon Islands needs to step up surveillance to include molecular tools, increase regional communication, and perform timely interventions.

Hematobium schistosomiasis control for health management of labor force generation at Nkhotakota and Lilongwe in the Republic of Malawi-assumed to be related to occupational risk.

BACKGROUND: In Malawi, hematobium schistosomiasis is highly endemic. According to previous studies, countermeasures have been conducted mainly in school-aged children. In this study, we focused on the age groups, which are assumed to be major labor force generation. Hematobium schistosomiasis is supposed to be related to occupational activities in schistosome-endemic countries because of its infectious route. We chronologically followed the transition of schistosome egg-positive prevalence before and after mass drug administration of praziquantel (MDA) by using a urine filtering examination. We also analyzed the effectiveness of urine reagent strips from the cost perspective. RESULTS: The egg-positive prevalence was 34.3% (95% CI 28.5-40.5) just before MDA in June 2010 and the highest prevalence was in the age of twenties. The egg-positive prevalence reduced to 12.7% (95% CI 9.2-17.3, p < 0.01) 8 weeks after the first MDA and the prevalence reduced to 6.9% (95% CI 4.6-10.0, p < 0.01) after the second MDA in August 2011. The egg-positive prevalence after MDA in 2013 was reduced from 3.8% (95% CI 2.1-6.9) to 0.9% (95% CI 0.3-3.4) and p value was 0.050. Using urine reagent strips after MDA, the positive predictive value decreased, but the negative predictive value remained high. The cost of one urine reagent strip and one tablet of praziquantel were US$0.06 and US$0.125 in 2013 in Malawi. If the egg-positive prevalence is 40%, screening subjects for MDA using urine reagent strips, the cost reduction can be estimated to be about 24%, showing an overall cost reduction. CONCLUSIONS: MDA of praziquantel can assuredly reduce schistosome egg-positive prevalence. The combination of MDA and urine reagent strips could be both a practical and cost-effective countermeasure for hematobium schistosomiasis. It is key to recognize that hematobium schistosomiasis could be considered a disease that is assumed to have some concern with occupational risk at Nkhotakota and Lilongwe in Malawi. From this point of view, it is very important to manage workers' health; the sound labor force generation is vital for economic growth and development in these areas and countries.

Shared expression of mucin12 in Ascaris lumbricoides and the human small intestine.

This study focuses on the host-parasite relationship of human Ascaris lumbricoides, which is a parasite of the small intestine and is also one of the commonest parasites worldwide. As part of this investigation, we examined the host-parasite relationship assuming that there is a common antigenicity, shared protein between A. lumbricoides and human small intestinal mucosa, using molecular techniques. We obtained three DNA clones from human colon cDNA library by screening for anti-A. lumbricoides polyclonal antibodies. The transmembrane mucin12 gene was identified after sequencing analysis of these clones. Specific signals of immunostaining with polyclonal anti-mucin12 antibodies were observed in the mucous secretory organs, epidermis, and intestinal canal of A. lumbricoides. These signals disappeared when immunohistochemistry was performed using pre-absorbed polyclonal antibodies with a specific peptide. These results suggest that mucin12 is localized in the mucous secretory organs in the epidermis of A. lumbricoides. Furthermore, we examined the site of mucin12 localization in the host; specific mucin12 signals were observed on the mucosal epithelia present around intestinal crypts and villi of the small intestine. Therefore, we suggest that mucin12 is a protein that shows common antigenicity in both A. lumbricoides and its host. It is presumed that adult A. lumbricoides live in their preferred environment, which is the small intestine, by secreting mucin12 to avoid being attacked by the host immune system.

Development of a PCR Assay for Diagnosing Trematode (Opisthorchis and Haplorchis) Infections in Human Stools.

We developed a combined conventional polymerase chain reaction (PCR) and real-time PCR (qPCR)-based assay for detecting and discriminating between Opisthorchis viverrini and Haplorchis taichui parasite infections. The first PCR amplifies the mitochondrial cytochrome c oxidase subunit I (COI) genes of parasites, and differential diagnosis is achieved by performing qPCR with specific primers and SYBR Green I. The detection limit of the assay was found to be 2.0 × 102 plasmid copies in a test in which a stool sample was spiked with a single egg, which is equivalent to 5 eggs per gram (EPG). The testing of 34 clinical stool samples that had been demonstrated to contain "Opisthorchis-like" eggs by microscopy showed that the novel assay exhibited a sensitivity of 100% for "Opisthorchis-like" parasitic infections, and 71% and 91% of these samples were found to be infected with O. viverrini and H. taichui, respectively. A further four parasitic infections were diagnosed in the 16 negative samples, and the microscopic findings of these samples were confirmed to be false negatives by sequencing analysis. The assay also displayed high specificity during the testing of 10 samples containing other common parasites. The fact that our qPCR SYBR Green I-based assay detected submicroscopic traces of parasitic DNA and was able to differentiate between parasites that produce eggs with similar morphologies indicates that it has a good potential for development of diagnostic application to use in areas where multiple parasites coexist.

Co-circulation of the dengue with chikungunya virus during the 2013 outbreak in the southern part of Lao PDR.

BACKGROUND: During the 2013 outbreak, 4638 infection cases and 32 deaths have been recorded in the southern part of Laos. In recent years, the chikungunya virus (CHIKV) emerged in the part of the country bordering Cambodia. Dengue virus (DENV) and CHIKV are transmitted by common mosquito vectors. Both diseases have similar clinical presentations; therefore, CHIKV infections might go undiagnosed in DENV-endemic areas. Thus, rapid detection and accurate diagnosis are crucial for differentiating between the two viruses (DENV and CHIKV). In this study, we demonstrated that CHIKV and two serotypes of DENV are circulating in Laos. In addition, we encountered patients that had been concurrently infected with multiple DENV serotypes or DENV and CHIKV. METHODS: Plasma samples were collected from 40 patients with suspected DENV infections during an outbreak between July and August 2013. The reverse transcription polymerase chain reaction was performed to detect the four DENV serotypes and CHIKV using specific primers. Specifically, the complete envelope gene sequences of the viruses were sequenced and subjected to phylogenetic analysis. RESULTS: Forty acute-phase plasma samples from patients with suspected dengue infections were tested for the presence of DENV viral RNA using molecular methods. Among the 40 samples, 14 samples were positive for DENV, 2 samples were positive for both viruses (DENV-2 and DENV-3), whereas DENV-1 and DENV-4 were not detected during the study period. We also encountered 10 samples that were positive for CHIKV. Of the 10 CHIKV-positive samples, 3 samples were co-infected by DENV-2, and 2 samples were co-infected by DENV-3. Phylogenetic analysis revealed that the 2013 dengue outbreak in Laos involved DENV-2 genotype Asian I and DENV-3 genotype II. Moreover, the Laotian CHIKV strains grouped together with those isolated during outbreaks on the Indian Ocean Islands within the East Central South African genotype. CONCLUSIONS: These findings revealed that two serotypes (DENV-2 and DENV-3) and CHIKV were detected. Furthermore, infection of multiple DENV serotypes and CHIKV was also observed in the 2013 dengue outbreak. This is the first documented evidence of co-infection with CHIKV and one of two DENV serotypes.

Molecular epidemiology of rabies viruses circulating in two rabies endemic provinces of Laos, 2011-2012: regional diversity in Southeast Asia.

BACKGROUND: Although rabies is endemic in Laos, genetic characterization of the viruses in this country is limited. There are growing concerns that development in the region may have increased transport of dog through Laos for regional dog meat consumption, and that this may cause spillover of the viruses from dogs brought here from other countries. This study was therefore undertaken to evaluate the current rabies situation and the genetic characteristics of rabies viruses currently circulating in Laos. METHODS: We determined the rate of rabies-positive samples by analyzing data from animal samples submitted to the Lao Ministry of Agriculture and Forestry's National Animal Health Centre rabies laboratory from 2004 through 2011. Twenty-three rabies-positive samples were used for viral genetic characterization. Full genome sequencing was performed on two rabies viruses. RESULTS: Rabies-positive samples increased substantially from 40.5% in 2004 to 60.2% in 2009 and continued at this level during the study period. More than 99% of the samples were from dogs, followed by cats and monkeys. Phylogenetic analyses showed that three rabies virus lineages belonging to the Southeast Asian cluster are currently circulating in Laos; these are closely related to viruses from Thailand, Cambodia and Vietnam. Lineages of the circulating Laos rabies viruses diverged from common ancestors as recently as 44.2 years and as much as 55.3 years ago, indicating periodic virus invasions. CONCLUSION: There is an increasing trend of rabies in Laotian animals. Similar to other rabies-endemic countries, dogs are the main viral reservoir. Three viral lineages closely related to viruses from neighboring countries are currently circulating in Laos. Data provide evidence of periodic historic exchanges of the viruses with neighboring countries, but no recent invasion.

The first case in Japan of severe human leptospirosis imported from Vietnam.

Leptospirosis is a worldwide zoonosis and common in tropical and subtropical areas with high rainfall. It should be noted as an imported infectious disease although it is sporadic in Japan. Some imported cases already have been reported in Japan and these cases occurred mainly in Southeast Asia. The case discussed in this article is the first reported Japanese case infected in Vietnam. Four days after returning back to Japan after a two-week stay in the mountain area near Hue, in the middle part of Vietnam, the patient suddenly experienced chills, a high fever, sore throat, gastrocnemius pain, and headache. Conjunctival jaundice, renal function disorder, and proteinuria were observed on the third day of onset. Significant increase in antibody titers against serovar Australis and Autumnalis strains was observed in paired serum samples by microscopic agglutination test (MAT). Consequently we recognized this case as a diagnosis of severe leptospirosis (Weil's disease). Finally, renal function disorder did not deteriorate further, and then the patient recovered after the tenth day of onset with the administration of antibiotics and supportive care without sequelae. We experienced the first imported Japanese case of severe human leptospirosis infection from Vietnam that was successfully treated with ceftriaxone and minocycline.