Hydroxyapatite-binding Silver/Titanium Dioxide as a Potential Control Compound Against Mosquito Vectors, Aedes aegypti (Diptera: Culicidae) and Anopheles dirus (Diptera: Culicidae).

Controlling mosquitoes is vital for counteracting the rising number of mosquito-borne illnesses. Vector control requires the implementation of various measures; however, current methods lack complete effectiveness, and new control agents or substances are urgently needed. Therefore, this study developed a nonwoven fabric sheet coated with hydroxyapatite-binding silver/titanium dioxide compound (hydroxyapatite-binding silver/titanium dioxide sheet [HATS])and evaluated its effectiveness on all stages of laboratory Aedes aegypti (Linnaeus); Diptera: Culicidae and Anopheles dirus (Peyton & Harrison); Diptera: Culicidae. We reared larvae with HATS and control sheets and assessed their mortality, emergence, and hatching rates. The submersion rates of engorged female mosquitoes in submerged HATS and control sheets were also compared. The HATS strongly affected mosquito development, resulting in high mortality rates (mean ± SE) of 99.66 ± 0.58% (L1-L2) and 91.11 ± 9.20% (L3-L4) for Ae. aegypti and 100% of both stages for An. dirus. In contrast, mosquitoes raised in the control sheet showed relatively high survival rates of 92.33 ± 3.21% (L1-L2) and 95.67 ± 0.58% (L3-L4) for Ae. aegypti and 86.07 ± 3.53% (L1-L2) and 92.01 ± 8.67% (L3-L4) for An. dirus. Submersion of engorged females was found in the HATS oviposition cup, leading to a decreased number of eggs and a low hatching rate compared to that of the control. Overall, HATS may be a useful new control method for Ae. aegypti and An. dirus.

Effectiveness of Herbal Essential Oils as Single and Combined Repellents against Aedes aegypti, Anopheles dirus and Culex quinquefasciatus (Diptera: Culicidae).

Mosquito repellents reduce human-vector contact of vector-borne diseases. We compared the repellent activity of 10 undiluted essential oils (anise, basil, bergamot, coriander, patchouli, peppermint, petitgrain, rosemary, sage and vetiver) against A. aegypti, A. dirus and C. quinquefasciatus using the arm-in-cage method. Petitgrain oil was the most effective against A. aegypti (270 min). Peppermint oil was the most effective against A. dirus (180 min). Interestingly, all single oils had attributes of repellency against C. quinquefasciatus (ranged, 120−360 min). Moreover, we integrated their binary combinations of highly effective essential oils against A. aegypti and A. dirus to potentially increase the protection time. A 1:1 combination of petitgrain/basil, petitgrain/coriander, basil/coriander and basil/sage reduced the median complete-protection time of 150 min for A. aegypti; a combination of sage and patchouli oils prolonged the median complete-protection time of 270 min for A. dirus. Combining essential oils effect protection time from these two mosquito species.

Global research alliance in infectious disease: a collaborative effort to combat infectious diseases through dissemination of portable sequencing.

OBJECTIVE: To disseminate the portable sequencer MinION in developing countries for the main purpose of battling infectious diseases, we found a consortium called Global Research Alliance in Infectious Diseases (GRAID). By holding and inviting researchers both from developed and developing countries, we aim to train the participants with MinION's operations and foster a collaboration in infectious diseases researches. As a real-life example in which resources are limited, we describe here a result from a training course, a metagenomics analysis from two blood samples collected from a routine cattle surveillance in Kulan Progo District, Yogyakarta Province, Indonesia in 2019. RESULTS: One of the samples was successfully sequenced with enough sequencing yield for further analysis. After depleting the reads mapped to host DNA, the remaining reads were shown to map to Theileria orientalis using BLAST and OneCodex. Although the reads were also mapped to Clostridium botulinum, those were found to be artifacts derived from the cow genome. An effort to construct a consensus sequence was successful using a reference-based approach with Pomoxis. Hence, we concluded that the asymptomatic cow might be infected with T. orientalis and showed the usefulness of sequencing technology, specifically the MinION platform, in a developing country.

Susceptibility of Aedes flavopictus miyarai and Aedes galloisi mosquito species in Japan to dengue type 2 virus

Objective: To evaluate the potential of local mosquitoes to act as vectors for dengue transmission in Japan. Methods: Serotype 2 ThNH28/93 was used to test the dengue susceptibility profiles of Aedes flavopictus miyarai (Ae. f. miyarai), Aedes galloisi (Ae. galloisi) and Aedes albopictus (Ae. albopictus), which were collected in Japan. We used Aedes aegypti from Thailand as a positive control. The mosquitoes were infected with the virus intrathoracically or orally. At 10 or 14 days post infection, the mosquitoes were dissected and total RNA was extracted from their abdomens, thoraxes, heads and legs. Mosquito susceptibility to dengue virus was evaluated using RT-PCR with dengue virus-specific primers. Differences in the infection and mortality rates of the different mosquito species were tested using Fisher's exact probability test. Results: The infection rates for dengue virus administered intrathoracically to Ae. f. miyarai, Ae. galloisi and Aedes aegypti mosquitoes were identical by RT-PCR on Day 10 post infection. All of the body parts we tested were RT-PCR-positive for dengue virus. For the orally admin-istered virus, the infection rates in the different body parts of the Ae. f. miyarai mosquitoes were slightly higher than those of Ae. albopictus mosquitoes, but were similar to the control mosquitoes (P>0.05). The mortality rates for Ae. f. miyarai and Ae. albopictus mosquitoes were similar (P=0.19). Our data indicated that dengue virus was able to replicate and disseminate to secondary infection sites in all of the four mosquito species (Japanese and Thai). Conclusions: Ae. albopictus is a well-known candidate for dengue transmission in Japan. However, our data suggest that Ae. f. miyarai from Ishigaki Island (near Okinawa Island) and Ae. galloisi from Hokkaido (Northern Japan) should also be regarded as potential vectors for dengue transmission in these regions. Further studies on these mosquitoes should be conducted.

Dengue-2 virus carrying capacity of Thai Aedes aegypti strains with different susceptibility to deltamethrin.

Deltamethrin-resistant Aedes aegypti currently threatens the effectiveness of dengue hemorrhagic fever control operations in Thailand. Although a previous study has suggested that insecticide resistance may increase Ae. aegypti susceptibility to dengue-2 virus infection, our experimental data showed no significant association between laboratory-induced deltamethrin-resistance in a Thai Ae. aegypti isolate and its susceptibility to dengue -2 infection.

Field-collected permethrin-resistant Aedes aegypti from central Thailand contain point mutations in the domain IIS6 of the sodium channel gene (KDR).

One of the mechanisms responsible for pyrethroid resistance in mosquitoes is mutations in domain IIS6 of voltage-gated sodium channel gene (kdr). Aedes aegypti larvae were collected from the central provinces of Thailand (Bangkok, Prachin Buri and Ratchaburi) and colonized until they became adults. Partial fragment of kdr of permethrin-resistant mosquitoes were amplified by RT-PCR and sequenced. Among the four nucleotide mutations detected, two mutations resulted in two amino acid substitutions, S(TCC) 989 P(CCC) and V(GTA)1016 G(GGA). Among 94 permethrin-resistant mosquitoes, the SS genotype (SS/VV) was found to predominate (n = 74), followed by SR (SP/VG) (n = 15) and RR (PP/ GG) genotypes (n = 5), with the resistant allele frequency ranging from 0.03 to 0.17. As pyrethroid insecticides are currently being advocated for use in Thailand, investigations of pyrethroid resistance in other regions of the country are needed to prevent potential cross-resistance among different types of insecticides.

Insecticide susceptibility of the dengue vector, Aedes aegypti (L.) in Metropolitan Bangkok.

Mosquito larvae were collected from the houses of dengue infected patients in Bangkok, Thailand from 55 sites (36 out of the 50 districts of Metropolitan Bangkok). Aedes aegypti larvae were tested against temephos using WHO bioassay techniques. Adult mosquitoes were tested for susceptibility to permethrin, deltamethrin, cyfluthrin, malathion and DDT using WHO diagnostic doses. Most of the larvae tested were susceptible to temephos. Only few specimens were resistant to temephos. Most adult mosquitoes were highly susceptible to malathion. Deltamethrin resistance was seen in 6 districts of Bangkok. Variable levels of susceptibility were seen with cyfluthrin. Most of the specimens showed resistance to permethrin and all specimens were resistant to DDT.

Residual effects of Mossmann 100 (permethrin 10% EC) impregnated bed nets and its impact on malaria vectors and incidence of malaria.

The objective of this field trial was to assess the residual effectiveness of permethrin 10% treated mosquito nets on malaria control compared with untreated nets. The study was carried out between July and December 2007 in the Pong Nam Ron District of Chantaburi Province, Thailand. Mosquito population densities were assessed using the landing catch method. Mosquitoes were collected between 6:00 PM and 12:00 PM. Residual effectiveness of the treated nets was assessed using standard WHO bioassay tests carried out monthly using Anopheles dirus mosquitoes reared in the insectary of the Department of Medical Entomology, Faculty of Tropical Medicine, Mahidol University, Thailand. The results showed the population densities of Anopheles spp, including the malaria vector Anopheles minimus, were unaffected in the study area where mosquito nets treated with Mossmann 100 (permethrin 10% EC) at 300 mg/m2 were used. WHO bioassay tests showed the nets treated with Mossmann 100 remained biologically effective against An. dirus for up to six months. Indigenous cases of malaria were reduced by 27.7% at the site where the nets treated with Mossman 100 (permethrin 10%EC) were used but no changes in malaria cases at the control site were seen.

Novel virus discovery in field-collected mosquito larvae using an improved system for rapid determination of viral RNA sequences (RDV ver4.0).

In this study, we improved a method for rapid determination of viral RNA sequences (RDV) to overcome the limitations of previous versions. The RDV ver4.0 method can detect RNA sequences with at least 1,000 copies as starting material. A novel virus, which was isolated from field-collected Aedes aegypti larvae in the Phasi Charoen district of Thailand using C6/36 cells, was identified using the RDV ver4.0 protocol. The virus was named Phasi Charoen virus (PhaV). We used a high-throughput pyrosequencing approach to obtain more information about the genome sequence of PhaV. Analysis of a phylogenic tree based on amino acid sequences strongly suggested that PhaV belongs to the family Bunyaviridae.

Residual effect of 10% bifenthrin wp on mosquitoes, and community acceptance, in eastern Thailand.

This study was conducted from May to October 2008 in two villages in Chanthaburi Province: village No. 2 Tup Sai Canton (control) and village No.12 Pong Nam Ron (treatment area). Indoor residual spraying, using 10% bifenthrin WP (Bitecthrin WP) was conducted at a concentration of 25 mg/m2 with 87.3% spray coverage of the houses in the treated area. Monthly entomological studies showed that in the control area, Anopheles minimus density was significantly higher than the treatment area. A WHO cone bioassay test showed the residual effect against laboratory-bred, An. dirus persisted for up to 6 months. Community acceptability was good and most preferred insecticide spraying. 10% bifenthrin WP applied six-monthly can be used as an indoor residual spray for malaria control.

Rapid determination of viral RNA sequences in mosquitoes collected in the field.

A method for rapid determination of viral RNA sequences (RDV) was applied to homogenates of Aedes aegypti collected in Thailand in an area in which dengue fever (dengue hemorrhagic fever) is endemic, using the mosquito cell line C6/36. Nucleic acid sequences of dengue virus type 4 and cell fusing agent virus were detected. This RDV method has the potential to become a standard method for detection of both known and newly emerging, unknown mosquito-borne viruses.

Biochemical detection of pyrethroid resistance mechanism in Aedes aegypti in Ratchaburi province, Thailand.

The emergence of insecticide resistance in mosquito vectors was an important issue to be considered as one of factors influencing the success of vector control. The early detection of resistance could help the health personnel to plan and select appropriate alternative control measures or insecticide for effective control. Therefore biochemical assay of enzymes in mosquito was conducted to detect the emergence of insecticide resistance and to define the machanisms involved in pyrethroid resistance. Adults of Aedes aegypti from two localtities in Ratchaburi province were subjected to permethrin and deltamethrin selection in laboratory. After three generations of selection, permethrin-selected and deltamethrin-selected strains were established. Their LT 50 increased to 7.46 and 1.18 folds in the F3 strains that were selected with permethrin and deltamethrin respectively. The enzymes of these mosquitoes were assayed biochemically to study the mechanisms of resistance. The results revealed significant increase of esterase activity and monooxygenase levels in both strains when compared with labolatory susceptible strain. Glutathione-S-transferase activity was found to increase in permethrin-selected strain but not in deltamethrin-selected strain. This suggested that not only esterase and monooxygenase but also glutathione-S-transferase were associated with permethrin resistance in Ae. aegypti. The exposing of permethrin-selected and deltamethrin-selected mosquitoes to diagnostic concentration of permethrin (0.75%) and deltamethrin (0.05%) indicated no cross resistance for permethrin to deltamethrin while slight cross resistance from deltamethrin to permethrin was evident. It seemed that glutathione S-tranferase was not associated with cross resistance since its activity in deltamethrin-selected strain remained unchanged as compared with that of laboratory susceptible strain.

Surveillance of commensal rat and shrew populations in the Bangkok area with references to flea index as the risk indicator of plague.

Commensal rats and shrews were trapped from 47 fresh food markets in Bangkok during the two study periods in the same markets: 21st June to 28th December 1999 and 1st March to 31st May 2000. Trapping was performed using wire live traps on three consecutive nights in each period. The trapped animals were identified for taxonomic species and flea infestation. Fleas were collected, identified and counted. Four species of rodents: Rattus norvegicus, Rattus rattus, Rattus exulans and Mus musculus, and one species of shrew: Suncus murinus were trapped in comparable numbers during the two study periods. Among the 1177 animals trapped, 84.3 per cent were R. norvegicus. Regarding sex prevalence, a higher number of female animals were trapped compared to males. Almost all the fleas collected were Xenopsylla cheopis, and there were very few Ctenocephalidesfelis-felis. Flea index based on the number of X. cheopis was 0.65 for all over Bangkok. Based on the geographical area of Bangkok, the inner area had the highest rodent population and the highest flea index of 0.86. Therefore, the inner region should be the priority for sanitation improvement.