Ecological niche model of Phlebotomus alexandri and P. papatasi (Diptera: Psychodidae) in the Middle East

<p>Abstract</p> <p>Background</p> <p>The purpose of this study is to create distribution models of two sand fly species, <it>Phlebotomus papatasi </it>(Scopoli) and <it>P. alexandri </it>(Sinton), across the Middle East. <it>Phlebotomus alexandri </it>is a vector of visceral leishmaniasis, while <it>P. papatasi </it>is a vector of cutaneous leishmaniasis and sand fly fever. Collection records were obtained from literature reports from 1950 through 2007 and unpublished field collection records. Environmental layers considered in the model were elevation, precipitation, land cover, and WorldClim bioclimatic variables. Models were evaluated using the threshold-independent area under the curve (AUC) receiver operating characteristic analysis and the threshold-dependent minimum training presence.</p> <p>Results</p> <p>For both species, land cover was the most influential environmental layer in model development. The bioclimatic and elevation variables all contributed to model development; however, none influenced the model as strongly as land cover.</p> <p>Conclusion</p> <p>While not perfect representations of the absolute distribution of <it>P. papatasi </it>and <it>P. alexandri</it>, these models indicate areas with a higher probability of presence of these species. This information could be used to help guide future research efforts into the ecology of these species and epidemiology of the pathogens that they transmit.</p

The relationship between mosquito abundance and rice field density in the Republic of Korea

<p>Abstract</p> <p>Background</p> <p>Japanese encephalitis virus (JEV), the causative agent of Japanese encephalitis (JE), is endemic to the Republic of Korea (ROK) where unvaccinated United States (U.S.) military Service members, civilians and family members are stationed. The primary vector of the JEV in the ROK is <it>Culex tritaeniorhynchus</it>. The ecological relationship between <it>Culex </it>spp. and rice fields has been studied extensively; rice fields have been shown to increase the prevalence of <it>Cx. tritaeniorhynchus</it>. This research was conducted to determine if the quantification of rice field land cover surrounding U.S. military installations in the ROK should be used as a parameter in a larger risk model that predicts the abundance of <it>Cx. tritaeniorhynchus </it>populations.</p> <p>Mosquito data from the U.S. Forces Korea (USFK) mosquito surveillance program were used in this project. The average number of female <it>Cx. tritaeniorhynchus </it>collected per trap night for the months of August and September, 2002-2008, was calculated. Rice fields were manually digitized inside 1.5 km buffer zones surrounding U.S. military installations on high-resolution satellite images, and the proportion of rice fields was calculated for each buffer zone.</p> <p>Results</p> <p>Mosquito data collected from seventeen sample sites were analyzed for an association with the proportion of rice field land cover. Results demonstrated that the linear relationship between the proportion of rice fields and mosquito abundance was statistically significant (R²= 0.62, r = .79, F = 22.72, p < 0.001).</p> <p>Conclusions</p> <p>The analysis presented shows a statistically significant linear relationship between the two parameters, proportion of rice field land cover and log₁₀of the average number of <it>Cx. tritaeniorhynchus </it>collected per trap night. The findings confirm that agricultural land cover should be included in future studies to develop JE risk prediction models for non-indigenous personnel living at military installations in the ROK.</p

Emergence of Japanese encephalitis virus genotype V in the Republic of Korea

<p>Abstract</p> <p>Background</p> <p>Japanese encephalitis virus (JEV) genotype V reemerged in Asia (China) in 2009 after a 57-year hiatus from the continent, thereby emphasizing a need to increase regional surveillance efforts. Genotypic characterization was performed on 19 JEV-positive mosquito pools (18 pools of <it>Culex tritaeniorhynchus </it>and 1 pool of <it>Cx. bitaeniorhynchus</it>) from a total of 64 positive pools collected from geographically different locations throughout the Republic of Korea (ROK) during 2008 and 2010.</p> <p>Findings</p> <p>Two regions of the JEV genome were sequenced from 19 pools; the envelope gene and the nonstructural protein 5 (NS5)/3'-untranslated region (UTR). Eighteen pools of <it>Culex tritaeniorhynchus </it>and one pool of <it>Cx. bitaeniorhynchus </it>were positive for genotype I and genotype V, respectively. Sequence alignment of the complete E gene from <it>Cx. bitaeniorhynchus </it>showed high amino acid similarity (98.8%) to the Muar strain, characterized as the first report of genotype V, isolated from an encephalitis patient in Malaysia in 1952.</p> <p>Conclusion</p> <p>This study represents the first report of JEV genotype V in the ROK. The reemergence of genotype V in Asia (China and ROK) after more than a half-century and its discovery in <it>Cx. bitaeniorhynchus</it>, a mosquito species previously unknown to carry JEV in the ROK, emphasizes the need for enhanced JE surveillance to monitor the dynamics of JEV strains within the region. Future findings may have implications with regard to JEV vaccination/prevention strategies.</p

Scientific achievements and reflections after 20 years of vector biology and control research at the Pu Teuy mosquito field research station, Thailand

Additional vector control tools are needed to supplement current strategies to achieve malaria elimination and control of Aedes-borne diseases in many settings in Thailand and the Greater Mekong Sub-region. Within the next decade, the vector control community, Kasetsart University (KU), and the Ministry of Higher Education, Science, Research and Innovation must take full advantage of these tools that combine different active ingredients with different modes of action. Pu Teuy Mosquito Field Research Station (MFRS), Department of Entomology, Faculty of Agriculture, Kasetsart University (KU), Thailand was established in 2001 and has grown into a leading facility for performing high-quality vector biology and control studies and evaluation of public health insecticides that are operationally relevant. Several onsite mosquito research platforms have been established including experimental huts, a 40-m long semi-field screening enclosure, mosquito insectary, field-laboratory, and living quarters for students and researchers. Field research and assessments ranged from ‘basic’ investigations on mosquito biology, taxonomy and genetics to more ‘applied’ studies on responses of mosquitoes to insecticides including repellency, behavioural avoidance and toxicity. In the course of two decades, 51 peer-reviewed articles have been published, and 7 masters and 16 doctoral degrees in Entomology have been awarded to national and international students. Continued support of key national stakeholders will sustain MFRS as a Greater Mekong Subregion centre of excellence and a resource for both insecticide trials and entomological research

Fipronil and Ivermectin Treatment of Cattle Reduced the Survival and Ovarian Development of Field-Collection Anopheles Albimanus in a Pilot Trial Conducted in Northern Belize

Background: Most malaria vector control programmes rely on indoor residual spraying of insecticides and insecticide-treated bed nets. This is efective against vector species that feed indoors at night and rest inside the house afterwards. In Central America, malaria vectors have diferent behaviours and are typically exophagic (i.e., bite outdoors), exophilic (i.e., remain outdoors after feeding), and zoophagic (i.e., as likely to feed on non-humans as humans). Thus, malaria elimination in Central America may require additional tactics. This pilot study investigated whether commercially-available products used to treat livestock for ticks could also be used to kill and/or sterilize zoophagic malaria vectors that feed on treated cattle in Belize. Methods: Cattle were treated with either a pour-on formulation of 1% fpronil (3 heifers) or injection of 1% ivemectin (1 heifer). Control heifers (n=2) were left untreated. Field-collected Anopheles albimanus contained in screen-top cages were strapped onto cattle at 2, 5, 7, and 14 days after treatment. Mosquito mortality was monitored once a day for 4 successive days. Surviving mosquitoes were dissected to assess blood meal digestion and ovarian development. Results: A total of 1078 female An. albimanus mosquitoes were fed and monitored for mortality. Both fpronil and ivermectin signifcantly reduced survivorship of An. albimanus for up to 7 days after treatment. By 14 days, efcacy had declined. The ivermectin treatment completely lost its efectiveness and even though the fpronil-treated heifers were still killing signifcantly more mosquitoes than the untreated heifers, the amount of mosquito killing had diminished greatly. Both treatments signifcantly reduced ovary development in mosquitoes fed on treated cattle for the duration of the 2-week trial. Conclusions: Treatment of cattle in northern Belize with topical fpronil and injectable ivermectin had signifcant lethal and sublethal efects on wild An. albimanus females. These results suggest that eforts towards eliminating residual transmission of malaria by zoophagic vectors in Central America may beneft by the judicious, targeted treatment of livestock with mosquitocidal compounds, such as fpronil or ivermectin

A New Classification System for the Actions of IRS Chemicals Traditionally Used For Malaria Control

Knowledge of how mosquitoes respond to insecticides is of paramount importance in understanding how an insecticide functions to prevent disease transmission. A suite of laboratory assays was used to quantitatively characterize mosquito responses to toxic, contact irritant, and non-contact spatial repellent actions of standard insecticides. Highly replicated tests of these compounds over a range of concentrations proved that all were toxic, some were contact irritants, and even fewer were non-contact repellents. Of many chemicals tested, three were selected for testing in experimental huts to confirm that chemical actions documented in laboratory tests are also expressed in the field. The laboratory tests showed the primary action of DDT is repellent, alphacypermethrin is irritant, and dieldrin is only toxic. These tests were followed with hut studies in Thailand against marked-released populations. DDT exhibited a highly protective level of repellency that kept mosquitoes outside of huts. Alphacypermethrin did not keep mosquitoes out, but its strong irritant action caused them to prematurely exit the treated house. Dieldrin was highly toxic but showed no irritant or repellent action. Based on the combination of laboratory and confirmatory field data, we propose a new paradigm for classifying chemicals used for vector control according to how the chemicals actually function to prevent disease transmission inside houses. The new classification scheme will characterize chemicals on the basis of spatial repellent, contact irritant and toxic actions