Effects of indoor residual spraying and outdoor larval control on Anopheles coluzzii from São Tomé and Príncipe, two islands with pre-eliminated malaria.

BACKGROUND: Vector control is a key component of malaria prevention. Two major vector control strategies have been implemented in São Tomé and Príncipe (STP), indoor residual spraying (IRS) and outdoor larval control using Bacillus thuringiensis israelensis (Bti). This study evaluated post-intervention effects of control strategies on vector population density, composition, and knockdown resistance mutation, and their implications for malaria epidemiology in STP. METHODS: Mosquitoes were collected by indoor and outdoor human landing catches and mosquito light traps in seven districts. Mosquito density was calculated by numbers of captured adult mosquitoes/house/working hour. Mitochondrial cytochrome c oxidase subunit I (COI) was PCR amplified and sequenced to understand the spatial-temporal population composition of malaria vector in STP. Knockdown resistance L1014F mutation was detected using allele-specific PCR. To estimate the malaria transmission risks in STP, a negative binomial regression model was constructed. The response variable was monthly incidence, and the explanatory variables were area, rainfall, entomological inoculation rate (EIR), and kdr mutation frequency. RESULTS: Malaria vector in STP is exophilic Anopheles coluzzii with significant population differentiation between Príncipe and São Tomé (mean FST = 0.16, p < 0.001). Both vector genetic diversity and knockdown resistance mutation were relatively low in Príncipe (mean of kdr frequency = 15.82%) compared to São Tomé (mean of kdr frequency = 44.77%). Annual malaria incidence rate in STP had been rapidly controlled from 37 to 2.1% by three rounds of country-wide IRS from 2004 to 2007. Long-term application of Bti since 2007 kept the mosquito density under 10 mosquitoes/house/hr/month, and malaria incidence rate under 5% after 2008, except for a rising that occurred in 2012 (incidence rate = 6.9%). Risk factors of area (São Tomé compared to Príncipe), rainfall, outdoor EIR, and kdr mutation frequency could significantly increase malaria incidence by 9.33-11.50, 1.25, 1.07, and 1.06 fold, respectively. CONCLUSIONS: Indoor residual spraying could rapidly decrease Anopheles density and malaria incidence in STP. Outdoor larval control using Bti is a sustainable approach for controlling local vector with exophilic feature and insecticide resistance problem. Vector control interventions should be intensified especially at the north-eastern part of São Tomé to minimize impacts of outbreaks.

Rapid control of malaria by means of indoor residual spraying of alphacypermethrin in the Democratic Republic of São Tomé and Príncipe.

A nationwide yearly cycle of indoor residual spraying (IRS) with a pyrethroid, alphacypermethrin, at a dosage of 50 mg/m(2) was instituted in 2004 in the Democratic Republic of São Tomé and Príncipe. Rates of IRS acceptance were high, varying from 82% to 95% for dwellings and outhouses. Epidemiologic surveys of the children < 9 years of age before and after the first IRS cycle revealed a rapid reduction in malaria. Overall prevalence of malaria parasitemia for all districts was lowered from 20.1% to 2.8% at 12 months after the first IRS and reached 0.7% at 8 months after the second IRS. Longer insecticidal persistence was found on wood than on cement with alphacypermethrin.

Seroprevalence of antibodies against dengue virus among pregnant women in the Democratic Republic of Sao Tome and Principe.

Dengue fever has become a worldwide public health concern, threatening an estimated 40% of the world's population. However, most resources and attention are still focused on malaria, while dengue statuses are poorly recognized in many African countries. In this serological survey, dengue virus (DENV) transmission was demonstrated by using serum samples collected from 78 pregnant women in the Democratic Republic of Sao Tome and Principe (DRSTP) during 2003 to 2004. Immunofluorescence assay was performed and 31 samples (39.74%) were found positive for DENV antibodies. Indirect enzyme-linked immunosorbent assay (ELISA) showed that 53 samples (67.95%) were positive for dengue E IgG, and 38 samples (48.72%) were positive for NS1 IgG. A prevalence of 35.90% was therefore determined for dengue IgG by considering samples that yielded positive results by all three tests. Cross-reactions with other flaviviruses were examined by indirect ELISA against Japanese encephalitis virus, West Nile virus, and yellow fever virus. Only one sample exhibited stronger absorbance against Japanese encephalitis virus and West Nile virus. Moreover, one sample was positive for dengue IgM. These results agreed with the previous researches in neighboring countries and suggested DENV exposure. The study contributes to raising public awareness of dengue and supporting future control strategies.

Monitoring of Japanese encephalitis virus infection in mosquitoes (Diptera: Culicidae) at Guandu Nature Park, Taipei, 2002-2004.

Japanese encephalitis virus (JEV) infection in mosquitoes was monitored at Guandu Nature Park in Taipei City from September 2002 to December 2004. In total, 30,386 female mosquitoes consisting of six genera and 14 species were processed for virus in 1,229 pools by using Flavivirus NS5 gene sequences detected by reverse transcription-polymerase chain reaction (PCR) and nested PCR assay. Overall, 101 pools were positive, including 95, 1, 4, and 1 for Culex tritaeniorhynchus Giles, Culex sitiens Wiedemann, Culex rubithoracis (Leicester), and Aedes vexans noctunmus (Theobald), respectively.

Molecular (sub) grouping of endosymbiont Wolbachia infection among mosquitoes of Taiwan.

Wolbachia are maternally inherited bacteria that infect a wide range of arthropods as well as filarial worms. The infection usually results in reproductive distortions of the host, primarily cytoplasmic incompatibility, parthenogenesis, and feminization. This study showed that Wolbachia infection (15/29; 51.72%) was prevalent among field-caught mosquitoes in Taiwan. Three mosquito species were identified as having Wolbachia A infection, eight species as having Wolbachia B, and four other species were dually infected by both groups. Each Wolbachia isolate from different mosquitoes was further divided into a specific subgroup. However, there were still some isolates that did not belong to any known subgroup, suggesting that more subgroups remain to be identified. Investigation of tissue tropism in either Aedes albopictus (Skuse) or Armigeres subalbatus (Coquillett) revealed that Wolbachia were extensively distributed within the host, although the ovary was most susceptible to infection. This report provides preliminary features of molecular relationships among Wolbachia groups of mosquitoes from Taiwan.

Molecular detection and characterization of spotted fever group rickettsiae in Taiwan.

Rickettsioses are emerging infectious diseases caused by rickettsiae in association with arthropods. We report the detection of spotted fever group rickettsiae (SFGR) in Taiwan using molecular methods. Phylogenetic analyses of the 17-kd protein and citrate synthase (gltA) genes showed that SFGR TwKM01 detected in Rhipicephalus haemaphysaloides ticks was most similar to Rickettsia rhipicephali. Three TwKM01 isolates were obtained from three individual R. haemaphysaloides ticks. Small, intracellular, coccobacillary bacteria were found in infected L929 cells using immunofluorescence antibody testing and transmission electron microscopy. Two other SFGRs, TwKM02 and TwKM03, identified in Leptotrombidium chigger mites, were closely related to R. australis and R. felis URRWXCal(2), respectively. The TwKM03 strain was also detected in Ixodes granulatus ticks and widely distributed in Hualien, Kinmen, and Lienchiang counties in Taiwan. The endonucleases MaeII and HhaI selected for restriction fragment length polymorphism analysis of the gltA and 17-kd polymerase chain reaction products, respectively, were useful for genotyping Rickettsia species TwKM01, TwKM02, TwKM03, and other SFGRs. Although their infectivity and pathogenicity for vertebrates are unknown, the finding of SFGRs raises the possibility that bacteria other than Orientia tsutsugamushi, Coxiella burnetii, and R. typhi may be involved in rickettsial diseases in Taiwan.

Characterization of two mosquito STATs, AaSTAT and CtSTAT. Differential regulation of tyrosine phosphorylation and DNA binding activity by lipopolysaccharide treatment and by Japanese encephalitis virus infection.

Two mosquito STATs, AaSTAT and CtSTAT, have been cloned from Aedes albopictus and Culex tritaeniorhynchus mosquitoes, respectively. These two STATs are more similar to those of Drosophila, Anopheles, and mammalian STAT5 in the DNA binding and Src homology 2 domains. The mRNA transcripts are expressed at all developmental stages, and the proteins are present predominantly at the pupal and adult stages in both mosquitoes. Stimulation with lipopolysaccharide resulted in an increase of tyrosine phosphorylation and DNA binding activity of AaSTAT and CtSTAT as well as an increase of luciferase activity of a reporter gene containing Drosophila STAT binding motif in mosquito C6/36 cells. After being infected with Japanese encephalitis virus, nuclear extracts of C6/36 cells revealed a decrease of tyrosine phosphorylation and DNA binding activity of AaSTAT which could be restored by sodium orthovanadate treatment. Taking all of the data together, this is the first report to clone and characterize two mosquito STATs with 81% identity and to demonstrate a different response of tyrosine phosphorylation and DNA binding of these two STATs by lipopolysaccharide treatment and by Japanese encephalitis virus infection.