Vector Control Programs
Bowman, C., A.B. Gumel, P. van den Driessche, J. Wu, and H. Zhu (2005). A mathematical model for assessing control strategies against West Nile virus. Bulletin of Mathematical Biology 67(5): 1107-33.
Abstract: Since its incursion into North America in 1999, West Nile virus (WNV) has spread rapidly across the continent resulting in numerous human infections and deaths. Owing to the absence of an effective diagnostic test and therapeutic treatment against WNV, public health officials have focussed on the use of preventive measures in an attempt to halt the spread of WNV in humans. The aim of this paper is to use mathematical modelling and analysis to assess two main anti-WNV preventive strategies, namely: mosquito reduction strategies and personal protection. We propose a single-season ordinary differential equation model for the transmission dynamics of WNV in a mosquito-bird-human community, with birds as reservoir hosts and culicine mosquitoes as vectors. The model exhibits two equilibria; namely the disease-free equilibrium and a unique endemic equilibrium. Stability analysis of the model shows that the disease-free equilibrium is globally asymptotically stable if a certain threshold quantity (R0), which depends solely on parameters associated with the mosquito-bird cycle, is less than unity. The public health implication of this is that WNV can be eradicated from the mosquito-bird cycle (and, consequently, from the human population) if the adopted mosquito reduction strategy (or strategies) can make R0<1. On the other hand, it is shown, using a novel and robust technique that is based on the theory of monotone dynamical systems coupled with a regular perturbation argument and a Liapunov function, that if R0>1, then the unique endemic equilibrium is globally stable for small WNV-induced avian mortality. Thus, in this case, WNV persists in the mosquito-bird population.
Descriptors: theoretical models, West Nile fever, birds, communicable disease control methods, culicidae, insect control methods, insect repellents, protective clothing, West Nile virus.
Han, X.N., C.Y. Li, D. Feng, L.Q. Fang, and W.C. Cao (2006). Modeling the dynamics of West Nile virus and evaluation of control measure. Jishengchong Yu Yixue Kunchong Xuebao 13(2): 89-94. ISSN: 1005-0507.
Abstract: After the surprising detection of West Nile virus (WNV) in New York City in 1999 , the virus has spread dramatically in the Western Hemisphere, resulting in the largest epidemics since reported. In a total, just one year of 2005, 2799 human cases were reported in U. S till Dec. 20 . The epidemic through all the world warn us the introduction of WNV and increase the information about WNV transmission. In this work we formulate and analyze a mathematics model for the transmission of WNV infect between vector (mosquito) and host ( avian population and human population) , according to the ecology of WNV. The model concludes three populations (mosquito, avian and human) and provides the relationship between the populations. We build the formula of the Basic Reproductive Number (R0) in terms of WN epidemiology. R0 is the threshold condition that determines the dynamics of WNV infection. We can take the relevant control measure according to the changed parameters and provide a new platform for further research in preventing and controlling WNV disease.
Descriptors: aves, mathematical techniques, viral disease transmission model, dipteran vector, dipteran parasites, culicidae, West Nile virus vector, transmission model and control evaluation, viral diseases, West Nile virus.
Language of Text: Chinese; Summary in Chinese, English.
Kronenwetter Koepel, T.A., J.K. Meece, C.A. Miller, and K.D. Reed (2005). Surveillance of above- and below-ground mosquito breeding habitats in a rural midwestern community: baseline data for larvicidal control measures against West Nile Virus vectors. Clinical Medicine and Research 3(1): 3-12.
Abstract: BACKGROUND: Mosquitoes in the genus Culex are thought to play a major role as vectors in the transmission cycle of West Nile virus (WNV) and other arboviruses in the United States. Effective control of mosquitoes through larviciding and adulticiding is expensive for communities and should be guided by reliable surveillance data on the distribution of mosquito breeding habitats. However, few small to medium sized cities in rural areas of the midwestern United States have this type of baseline information available. OBJECTIVE: During the summer of 2004, we investigated the characteristics of Culex and other mosquito-breeding habitats in a rural central Wisconsin community with a population of approximately 19,000. Such baseline information will aid in the development of rational strategies to control mosquito populations and prevent human exposure to WNV and other mosquito-transmitted viruses. METHODS: Mosquito larvae were collected and identified weekly from 14 below-ground storm water catch basins and 10 above-ground standing water sites distributed throughout the community. Collection began June 4, 2004 and continued through September 24, 2004. For each collection site the primary and adjacent land use patterns were determined. RESULTS: Over the study period, 1,244 larvae were collected from catch basins; 94% were Culex species. Breeding activity was first detected in early July. Peak breeding was observed during a period of several weeks when average daily temperatures were at the maximum observed and rainfall had declined. Organically enriched catch basins in low intensity urban sites adjacent to forests and wetlands were found to be more productive breeding habitats compared to catch basins having little organic debris located in isolated high intensity urban sites. Above-ground standing water sites produced 1,504 larvae; 66% of which were Culex species. Flood control ditches and permanent wetlands with stagnant water were most productive, while ditches with moving water were least productive habitats. Larvae were produced earlier in the season by above-ground sites than were produced by catch basins. However, larvae production was more variable in above-ground sites since half the sites became dry at some point during the study period. CONCLUSION: The observed differences in Culex larvae production based on the variables of habitat-type, temperature, and precipitation support the need for ongoing surveillance in communities to guide public health officials in planning for and prioritizing mosquito control efforts.
Descriptors: Culex, insect vectors, mosquito control, West Nile Virus, breeding environment, insect control methods, rain, rural population, seasons, temperature, time factors, water, weather, West Nile fever prevention and control, Wisconsin.
Macedo, P.A., R.K. Peterson, and R. Davis (2006). Human-health risk assessment for West Nile virus and insecticides used in mosquito management. Abstracts of Papers American Chemical Society 231: 8-AGRO. ISSN: 0065-7727.
Descriptors: West Nile virus, health risk assessment, insecticides, health risk, mosquito management, vector control, pesticides, nervous system disease, diagnostic techniques, public concern, meeting abstract.
Notes: Meeting Information: 231st National Meeting of the American-Chemical-Society, Atlanta, Georgia, USA; March 26 -30, 2006.
Palmisano, C., V. Taylor, K. Caillouet, B. Byrd, and D. Wesson (2005). Impact of West Nile virus outbreak upon St. Tammany Parish mosquito abatement district. Journal of the American Mosquito Control Association. 21(1): 33-38. ISSN: 8756-971X.
Descriptors: Culex pipiens, insect vectors, West Nile virus, disease outbreaks, disease surveillance, sentinel animals, dead animals, humans, disease incidence, vector control, mosquito control, adulticides, larvicides, Louisiana, Culex-pipiens-quinquefasciatus, arbovirus-surveillance, sentinel-chickens, dead-birds.
Park, H.W., D.K. Bideshi, M.C. Wirth, J.J. Johnson, W.E. Walton, and B.A. Federici (2005). Recombinant larvicidal bacteria with markedly improved efficacy against culex vectors of West Nile virus. American Journal of Tropical Medicine and Hygiene 72(6): 732-738. ISSN: antibodies.
Abstract: An urgent need exists for new agents to control mosquito vectors of disease. Mosquito larvicides based on the bacteria Bacillus thuringiensis subsp. israelensis (Bti) or B. sphaericus (Bs) are effective in many habitats, but use is limited by their high cost. Moreover, mosquito resistance evolves rapidly to Bs where it is used intensively. The efficacy of these bacteria is due to a binary protein (BsB) in Bs and four proteins (Cry4A, Cry4B, Cry11A, and Cyt1A) in Bti. Here we report the use of cyt1A promoters and a 5' mRNA stabilizing sequence to synthesize high levels of Bs2362 binary toxin in Bti strains. The recombinant BtiIPS-82/BsB showed high potency against fourth instars of Culex quinquefasciatus, a vector of West Nile virus, being 21-fold as potent as BtiIPS-82, and 32-fold as potent as Bs2362. Similar improved efficacy was obtained against larvae of Cx. tarsalis. Moreover, BtiIPS-82/BsB suppressed resistance to Bs2362 in Cx. quinquefasciatus.
Descriptors: bacillus pathogenicity, culex mosquitoes virology, insect vectors, biological pest control, West Nile fever, West Nile virus isolation and purification, polyacrylamide gel electrophoresis, genetic recombination genetic, species specificity.
Peterson, R.K., P.A. Macedo, and R.S. Davis (2006). A human-health risk assessment for West Nile virus and insecticides used in mosquito management. Environmental Health Perspectives 114(3): 366-372.
Abstract: West Nile virus (WNV) has been a major public health concern in North America since 1999, when the first outbreak in the Western Hemisphere occurred in New York City. As a result of this ongoing disease outbreak, management of mosquitoes that vector WNV throughout the United States and Canada has necessitated using insecticides in areas where they traditionally have not been used or have been used less frequently. This has resulted in concerns by the public about the risks from insecticide use. The objective of this study was to use reasonable worst-case risk assessment methodologies to evaluate human-health risks for WNV and the insecticides most commonly used to control adult mosquitoes. We evaluated documented health effects from WNV infection and determined potential population risks based on reported frequencies. We determined potential acute (1-day) and subchronic (90-day) multiroute residential exposures from each insecticide for several human subgroups during a WNV disease outbreak scenario. We then compared potential insecticide exposures to toxicologic and regulatory effect levels. Risk quotients (RQs, the ratio of exposure to toxicologic effect) were < 1.0 for all subgroups. Acute RQs ranged from 0.0004 to 0.4726, and subchronic RQs ranged from 0.00014 to 0.2074. Results from our risk assessment and the current weight of scientific evidence indicate that human-health risks from residential exposure to mosquito insecticides are low and are not likely to exceed levels of concern. Further, our results indicate that, based on human-health criteria, the risks from WNV exceed the risks from exposure to mosquito insecticides.
Descriptors: environmental exposure to West Nile virus (WNV), environmental pollutants, insecticides, piperonyl butoxide, theoretical modelling, mosquito control.
Reddy, M.R., A. Spielman, T.J. Lepore, D. Henley, A.E. Kiszewski, and P. Reiter (2006). Efficacy of resmethrin aerosols applied from the road for suppressing Culex vectors of West Nile virus. Vector Borne and Zoonotic Diseases 6(2): 117-127. ISSN: 1530-3667.
Abstract: We determined whether aerosol applications of resmethrin, delivered from the road, suppress the reproductive activity of Culex pipiens pipiens and Cx. restuans mosquitoes in suburban sites located near Boston. Oviposition implies a prior blood-feeding event and hence a potential West Nile virus (WNV) transmission-related event. Droplet size, rate of delivery and meteorological conditions were monitored. The target populations proved to be fully susceptible to the insecticide that was used. The roads in the test sites generally gave adequate opportunity for insecticidal coverage. We found that the aerosol plume may have failed to contact the target mosquitoes and conclude that such insecticidal aerosols, delivered from the road, may not effectively reduce the force of transmission of WNV in our test sites.
Descriptors: culex mosquitos, insect vectors, insecticides, mosquito control methods, pyrethrins, dosage, Boston, Massachusetts, oviposition, weather, West Nile fever.
Zou, L., S.N. Miller, and E.T. Schmidtmann (2006). Mosquito larval habitat mapping using remote sensing and GIS: implications of coalbed methane development and West Nile virus. Journal of Medical Entomology 43(5): 1034-1041. ISSN: 0022-2585.
Abstract: Potential larval habitats of the mosquito Culex tarsalis (Coquillett), implicated as a primary vector of West Nile virus in Wyoming, were identified using integrated remote sensing and geographic information system (GIS) analyses. The study area is in the Powder River Basin of north central Wyoming, an area that has been undergoing a significant increase in coalbed methane gas extractions since the late 1990s. Large volumes of water are discharged, impounded, and released during the extraction of methane gas, creating aquatic habitats that have the potential to support immature mosquito development. Landsat TM and ETM+ data were initially classified into spectrally distinct water and vegetation classes, which were in turn used to identify suitable larval habitat sites. This initial habitat classification was refined using knowledge-based GIS techniques requiring spatial data layers for topography, streams, and soils to reduce the potential for overestimation of habitat. Accuracy assessment was carried out using field data and high-resolution aerial photography commensurate with one of the Landsat images. The classifier can identify likely habitat for ponds larger than 0.8 ha (2 acres) with generally satisfactory results (72.1%) with a lower detection limit of approximately 0.4 ha (1 acre). Results show a 75% increase in potential larval habitats from 1999 to 2004 in the study area, primarily because of the large increase in small coalbed methane water discharge ponds. These results may facilitate mosquito abatement programs in the Powder River Basin with the potential for application throughout the state and region.
Descriptors: potential larval habitats, coalbed methane gas, aquatic habitats, immature mosquitoe development, water discharge ponds.