Mosquito Control Activities Research Articles

Multiple introductions of the dengue vector, Aedes aegypti, into California.

The yellow fever mosquito Aedes aegypti inhabits much of the tropical and subtropical world and is a primary vector of dengue, Zika, and chikungunya viruses. Breeding populations of A. aegypti were first reported in California (CA) in 2013. Initial genetic analyses using 12 microsatellites on collections from Northern CA in 2013 indicated the South Central US region as the likely source of the introduction. We expanded genetic analyses of CA A. aegypti by: (a) examining additional Northern CA samples and including samples from Southern CA, (b) including more southern US populations for comparison, and (c) genotyping a subset of samples at 15,698 SNPs. Major results are: (1) Northern and Southern CA populations are distinct. (2) Northern populations are more genetically diverse than Southern CA populations. (3) Northern and Southern CA groups were likely founded by two independent introductions which came from the South Central US and Southwest US/northern Mexico regions respectively. (4) Our genetic data suggest that the founding events giving rise to the Northern CA and Southern CA populations likely occurred before the populations were first recognized in 2013 and 2014, respectively. (5) A Northern CA population analyzed at multiple time-points (two years apart) is genetically stable, consistent with permanent in situ breeding. These results expand previous work on the origin of California A. aegypti with the novel finding that this species entered California on multiple occasions, likely some years before its initial detection. This work has implications for mosquito surveillance and vector control activities not only in California but also in other regions where the distribution of this invasive mosquito is expanding.

Imported Zika Virus in a European City: How to Prevent Local Transmission?

Background: On February 1st 2016 the WHO declared the Zika Virus (ZIKV) infection a worldwide public health emergency because of its rapid expansion and severe complications, such as Guillain-Barré Syndrome or microcephaly in newborn. The huge amount of people traveling to endemic areas and the presence of Aedes albopictus in Barcelona increase the risk of autochtonous transmission. The objective of this study was to describe the first ZIKV cases diagnosed in our city and to analyze the surveillance, prevention, and control measures implemented to avoid autochthonous transmission.Methods: An observational cross-sectional population-based study in Barcelona, Spain was performed.An analysis of the socio-demographic, epidemiological, clinical characteristics, and mosquito control activities of the ZIKV cases detected between January 1st and December 2016 was carried out using a specific ZIKV epidemiological survey of the Barcelona Public Health Agency.Results: A total of 118 notifications of possible ZIKV infections were received, and 44 corresponded to confirmed cases in Barcelona residents.Amongst these, the median age was 35 years and 57% were women. All cases were imported, 48% were Spanish-born and 52% foreign-born. Dominican Republic was the most visited country amongst foreign-born patients and Nicaragua amongst Spanish-born. The most frequent symptoms were exanthema, fever, and arthralgia. Among the 24 diagnosed women, 6 (25%) were pregnant. There was one case of microcephaly outside Barcelona city. Entomological inspections were done at the homes of 19 cases (43.2% of the total) and in 34 (77.3%) public spaces. Vector activity was found in one case of the 44 confirmed cases, and 134 surveillance and vector control were carried out associated to imported ZIKV cases. In all cases prevention measures were recommended to avoid mosquito bites on infected cases.Conclusion: Epidemiological and entomological surveillance are essential for the prevention of autochthonous transmission of arbovirosis that may have a great impact on Public Health.The good coordination between epidemiologists, entomologists, microbiologists, and clinicians is a priority in a touristic city with an intense relationship with endemic countries to minimize the risk of local transmission by competent vectors.

Chikungunya virus outbreak in Sint Maarten, 2013–2014

ABSTRACTThis report describes the outbreak of chikungunya virus (CHIKV) in Sint Maarten, a constituent country of Kingdom of the Netherlands comprising the southern part of the Caribbean island of Saint Martin, from 22 December 2013 (first reported case) through 5 December 2014. The outbreak was first reported by the French overseas collectivity of Saint-Martin in the northern part of the island—the first site in the Americas to report autochthonous transmission of CHIKV. By 5 December 2014, Sint Maarten had reported a total of 658 cases—an overall attack rate of 1.76%. Actual prevalence may have been higher, as some cases may have been misdiagnosed as dengue. Fever and arthralgia affected 71% and 69% of reported cases respectively. Of the 390 laboratory-confirmed cases, 61% were female and the majority were 20–59 years old (mean: 42; range: 4–92). The spread of CHIKV to Sint Maarten was inevitable given the ease of movement of people, and the vector, island-wide. Continuing their history of collaboration, the French and Dutch parts of the island coordinated efforts for prevention and control of the disease. These included a formal agreement to exchange epidemiological information on a regular basis and provide alerts in a timely manner; collaboration among personnel through joint island-wide planning of mosquito control activities, especially along borders; notification of all island visitors, upon their arrival at airports and seaports, of preventative measures to avoid being bitten by mosquitoes; dissemination of educational materials to the public; and island-wide public awareness campaigns, particularly in densely populated areas, for both residents and visitors. The information provided in this report could help increase understanding of the epidemiological characteristics of CHIKV and guide other countries dealing with vector-borne epidemics.

From eggs to bites: do ovitrap data provide reliable estimates of Aedes albopictus biting females?

BackgroundAedes albopictus is an aggressive invasive mosquito species that represents a serious health concern not only in tropical areas, but also in temperate regions due to its role as vector of arboviruses. Estimates of mosquito biting rates are essential to account for vector-human contact in models aimed to predict the risk of arbovirus autochthonous transmission and outbreaks, as well as nuisance thresholds useful for correct planning of mosquito control interventions. Methods targeting daytime and outdoor biting Ae. albopictus females (e.g., Human Landing Collection, HLC) are expensive and difficult to implement in large scale schemes. Instead, egg-collections by ovitraps are the most widely used routine approach for large-scale monitoring of the species. The aim of this work was to assess whether ovitrap data can be exploited to estimate numbers of adult biting Ae. albopictus females and whether the resulting relationship could be used to build risk models helpful for decision-makers in charge of planning of mosquito-control activities in infested areas.MethodOvitrap collections and HLCs were carried out in hot-spots of Ae. albopictus abundance in Rome (Italy) along a whole reproductive season. The relationship between the two sets of data was assessed by generalized least square analysis, taking into account meteorological parameters.ResultThe mean number of mosquito females/person collected by HLC in 15′ (i.e., females/HLC) and the mean number of eggs/day were 18.9 ± 0.7 and 39.0 ± 2.0, respectively. The regression models found a significant positive relationship between the two sets of data and estimated an increase of one biting female/person every five additional eggs found in ovitraps. Both observed and fitted values indicated presence of adults in the absence of eggs in ovitraps. Notably, wide confidence intervals of estimates of biting females based on eggs were observed. The patterns of exotic arbovirus outbreak probability obtained by introducing these estimates in risk models were similar to those based on females/HLC (R0 > 1 in 86% and 40% of sampling dates for Chikungunya and Zika, respectively; R0 < 1 along the entire season for Dengue). Moreover, the model predicted that in this case-study scenario an R0 > 1 for Chikungunya is also to be expected when few/no eggs/day are collected by ovitraps.DiscussionThis work provides the first evidence of the possibility to predict mean number of adult biting Ae. albopictus females based on mean number of eggs and to compute the threshold of eggs/ovitrap associated to epidemiological risk of arbovirus transmission in the study area. Overall, however, the large confidence intervals in the model predictions represent a caveat regarding the reliability of monitoring schemes based exclusively on ovitrap collections to estimate numbers of biting females and plan control interventions.

Integrating Environmental Monitoring and Mosquito Surveillance to Predict Vector-borne Disease: Prospective Forecasts of a West Nile Virus Outbreak.

Introduction:Predicting the timing and locations of future mosquito-borne disease outbreaks has the potential to improve the targeting of mosquito control and disease prevention efforts. Here, we present and evaluate prospective forecasts made prior to and during the 2016 West Nile virus (WNV) season in South Dakota, a hotspot for human WNV transmission in the United States.Methods:We used a county-level logistic regression model to predict the weekly probability of human WNV case occurrence as a function of temperature, precipitation, and an index of mosquito infection status. The model was specified and fitted using historical data from 2004-2015 and was applied in 2016 to make short-term forecasts of human WNV cases in the upcoming week as well as whole-year forecasts of WNV cases throughout the entire transmission season. These predictions were evaluated at the end of the 2016 WNV season by comparing them with spatial and temporal patterns of the human cases that occurred.Results:There was an outbreak of WNV in 2016, with a total of 167 human cases compared to only 40 in 2015. Model results were generally accurate, with an AUC of 0.856 for short-term predictions. Early-season temperature data were sufficient to predict an earlier-than-normal start to the WNV season and an above-average number of cases, but underestimated the overall case burden. Model predictions improved throughout the season as more mosquito infection data were obtained, and by the end of July the model provided a close estimate of the overall magnitude of the outbreak.Conclusions:An integrated model that included meteorological variables as well as a mosquito infection index as predictor variables accurately predicted the resurgence of WNV in South Dakota in 2016. Key areas for future research include refining the model to improve predictive skill and developing strategies to link forecasts with specific mosquito control and disease prevention activities.

KEPADATAN POPULASI DAN PREFERENSI HABITAT Anopheles ludlowae DI BERBAGAI EKOSISTEM DI SULAWESI TENGAH

Larvae monitoring cadres has an important role in Dengue vector control. Increasing community participation through larvae monitoring cadres needed to empower the community in the form of learning process. The purpose of study was to measure knowledge and skills of larvae monitoring cadres in managing activities of mosquito breeding place control activities before and after getting managerial learning. Samples were chosen purposively. Each community groups taken 2 larvae monitoring cadres in Sendang Mulyo Village. The number of respondents was 42. The study used quasy experiment with one group pre and posttest design. The results showed the largest age group of respondents was aged 41-58. Most respondents were housewives (81%). There were significant differences in respondents' knowledge scores before and after the study (p <0.05) in managerial knowledge. Training could improve cadre knowledge about managerial activities in mosquito breeding place control significantly. Cadres able to develop follow-up local specific activities in mosquito breeding place control in each community group region. Training of management was first received by the cadre PSN so that cadres should receive refreshing material.

Surveillance of Mosquitoes Larva at Selected Areas of Mymensingh District in Bangladesh

Mosquito borne diseases have a great impact on human and animal health throughout the world including Bangladesh. An entomological survey was conducted at the Bangladesh Agricultural University (BAU) campus and its surrounding areas from January to June, 2013 to identify the mosquito larvae and to investigate the different breeding site preferences of mosquitoes. Mosquito larvae were collected using dipper, ladle spoon, dropper and pipette from rice field, botanical garden, dairy farm, poultry farm, drains, lakes, ponds, staff quarters, residential halls and cattle sheds. A total of 1397 mosquito larvae were collected from the places. Ten species of mosquitoes under three genera were identified. The recorded genera were Anopheles (An.), Culex (Cx.) and Aedes (Ae.). The collected species were An. bengalensis, An. vagus, Cx. fuscocephala, Cx. quinquefasciatus, Cx. tritaeniorhynchus, Cx. gelidus, Cx. vishnui, Cx. whitmorei, Cx. sitiens and Ae. albopictus. Among the collected larvae, Culex was found most prevalent (64.3%), followed by Anopheles (26.7%) and Aedes were the least prevalent (9.0%). The results of this study provide evidence that drains were the most common aquatic habitat of Anopheles and Culex larvae in Boyra, Kewatkhali and Balashpur. In BAU campus, agronomy fields were found having the highest percentage (35.2%) of mosquito larvae than the other places of the campus. This study suggests that although drains and rice fields are the richest habitats, since Anopheles and Culex can breed in all available breeding habitats. This larval survey will help us to conduct future mosquito control activities and provide us useful information to schedule larvicide’s application to control the mosquito borne diseases in the study areas as well as throughout the country.DOI: http://dx.doi.org/10.3329/bjvm.v13i1.23962Bangl. J. Vet. Med. (2015). 13 (1): 79-88

Challenges encountered using standard vector control measures for dengue in Boa Vista, Brazil.

ProblemIn 2010, dengue virus (DENV) serotype–4 was detected during a dengue outbreak in the Amazonian city of Boa Vista. At that time Brazil was already endemic for DENV-1, DENV-2 and DENV-3. This was the first time DENV-4 was observed in the country after it was initially detected and eliminated in 1981.ApproachTo hinder the spread of DENV-4 throughout Brazil, standard vector control measures were intensified. Vector control professionals visited 56 837 households in 22 out of 31 districts of Boa Vista, to eliminate mosquito-breeding sites. Water storage containers were treated with the larvicide diflubenzuron, and deltamethrin was sprayed for adult Aedes aegypti mosquitoes. Fifteen days later, a second larvae survey and additional deltamethrin applications were performed.Local settingIn Brazil, dengue vector control is managed at all three government levels. Regular surveillance of Aedes aegypti is done four to six times a year to strengthen mosquito control activities in areas with high-vector density. Educational dengue control campaigns in communities are scarce, especially between outbreaks.Relevant changesIn spite of extensive implementation of all standard control actions recommended by the Brazilian dengue control programme, only a slight decrease in mosquito density was detected.Lessons learntThere is a need to redesign all levels of dengue control. Public consultation and engagement, behaviour change and actions that go beyond technical impositions are required. Vector control programme managers need to reflect on what constitutes good practices and whether intermittent information campaigns are effective measures for dengue prevention and control.

Mosquito Consumption by Insectivorous Bats: Does Size Matter?

Insectivorous bats have often been touted as biological control for mosquito populations. However, mosquitoes generally represent only a small proportion of bat diet. Given the small size of mosquitoes, restrictions imposed on prey detectability by low frequency echolocation, and variable field metabolic rates (FMR), mosquitoes may not be available to or profitable for all bats. This study investigated whether consumption of mosquitoes was influenced by bat size, which is negatively correlated with echolocation frequency but positively correlated with bat FMR. To assess this, we investigated diets of five eastern Australian bat species (Vespadelus vulturnus Thomas, V. pumilus Gray, Miniopterus australis Tomes, Nyctophilus gouldi Tomes and Chalinolobus gouldii Gray) ranging in size from 4-14 g in coastal forest, using molecular analysis of fecal DNA. Abundances of potential mosquito and non-mosquito prey were concurrently measured to provide data on relative prey abundance. Aedes vigilax was locally the most abundant mosquito species, while Lepidoptera the most abundant insect order. A diverse range of prey was detected in bat feces, although members of Lepidoptera dominated, reflecting relative abundance at trap sites. Consumption of mosquitoes was restricted to V. vulturnus and V. pumilus, two smaller sized bats (4 and 4.5 g). Although mosquitoes were not commonly detected in feces of V. pumilus, they were present in feces of 55 % of V. vulturnus individuals. To meet nightly FMR requirements, Vespadelus spp. would need to consume ~600-660 mosquitoes on a mosquito-only diet, or ~160-180 similar sized moths on a moth-only diet. Lower relative profitability of mosquitoes may provide an explanation for the low level of mosquito consumption among these bats and the absence of mosquitoes in feces of larger bats. Smaller sized bats, especially V. vulturnus, are likely to be those most sensitive to reductions in mosquito abundance and should be monitored during mosquito control activities.

Human Arthropod-Borne Viral Infections

Human Arthropod-Borne Viral Infections

A Leader’s Fight Against Malaria in Kolkata, India

Malaria is an age-old public health problem in Kolkata City, the cultural capital of India. In 2010, a popular political leader, Atin Ghosh, became the Member of the Mayor-in-Council (Health) of Kolkata Municipal Corporation at the behest of the Hon’ble Chief Minister of West Bengal, Ms Mamata Banerjee. Unlike his predecessors, Mr Ghosh took several unprecedented initiatives to fight against malaria and implemented them religiously. As a result of which, the situation improved remarkably. The number of malaria cases here downslided from a dispiriting 96,693 in 2010 to a comfortable 32659 in 2012 through 41,642 in 2011. No death due to malaria occurred in the city after 2010. The extent of decline in the number of Pf cases was from 14,226 in 2010 to a mere 3403 in 2012. The World Health Organization and the Directorate of National Vector Borne Disease Control Programme, Government of India, have officially appreciated the achievement of KMC in the field of malaria prevention. Truly, a new era of mosquito control activities so needed to prevent malaria and other mosquito-borne diseases began in KMC area soon after Atin Ghosh had taken over the charge of the health department of KMC as the MMIC. He proved himself to be a trendsetter. Political leaders around the country can learn a lesson from this leader of Kolkata.

Lessons learned from Chikungunya

Chikungunya virus (CHIKV) is an Arbovirus belonging to Alphavirus genus, which is transmitted by Aedes spp mosquitoes. Since late 2004, CHIKV caused several outbreaks in coastal Kenya, in Indian Ocean (especially on island of La Reunion), and on Indian subcontinent, where it caused more than 1.5 million cases. Although Aedes aegypti is most commonly involved vector, other Aedes spp mosquitoes, such as Aedes albopictus, appear to have a good vectorial capacity for CHIKV. The vectorial capacity of Aedes albopictus is of special concern, since this mosquito is widespread in several countries in Southern Europe and in other areas of world, outside tropical areas. In summer of 2007, an unexpected outbreak of CHIKV fever, caused more than 200 human cases in Emilia-Romagna Region of Italy; most of cases were recorded in two villages in Province of Ravenna, but smaller clusters were also detected in other towns in same Region (i.e., towns of Cervia, Cesena, Ravenna, Rimini, and Bologna). The tropical virus was introduced in Italy by a man from Kerala (an Indian district affected by a large outbreak) and sustained by local mosquitoes (Aedes albopictus, the tiger mosquito), which transmitted infection to other persons. The epidemic can be said to have been result of globalisation of vectors and humans, which occurred through a two-step process: i) introduction and adaptation of Aedes albopictus to a new environment (i.e., an area with a temperate climate); and ii) introduction of Chikungunya virus (CHIKV) in a previously infection-free country, as a result of population movement. The CHIKV strains introduced in Italy contained a mutation in E1 glycoprotein which was responsible for a single amino-acid substitution (A226V) able to increase infectivity of virus for Aedes albopictus. CHIKV outbreaks did not reoccur in areas that had been affected by 2007 outbreak. This was probably consequence of three combined factors: i) lack of human cases during winter season, due to extremely reduced Ae. albopictus activity; ii) mosquito control activities performed during and after outbreak; and iii) extremely low rate of transovarial transmission of infection (i.e., transmission from adult mosquito to larvae). By contrast, on island of La Reunion, although number of human cases decreased during dry season, they did not completely disappear, and a second epidemic wave ravaged local population determining significant increase in mortality. Investigations conducted during recent outbreaks provided a unique opportunity to improve our knowledge on epidemiological, clinical and virological aspects of CHIKV infection (i.e., estimate of CHIKV infection R0, definition of clinical spectrum of disease, duration of viremia, antibody dynamics), and on evolutionary changes leading to virus adaptation to different vectors. In conclusion, re-emergence of CHIKV is paradigmatic of infectious threat in era of globalisation and emphasises need for preparedness and response to vector-borne infections and other emerging infectious threats.

Importance of Eaves to House Entry by Anopheline, But Not Culicine, Mosquitoes

Screening homes is an effective way of reducing house entry by mosquitoes. Here, we assess how important blocking the eaves is for reducing house entry by anopheline and culicine mosquitoes for houses that have screened doors and no windows. Twelve houses, with two screened doors and no windows, in which a single adult male slept, were included in a simple crossover design. In the first period, six houses were randomly selected and had the eaves blocked using a mixture of rubble and mortar; the other six were left with open eaves. Mosquitoes were sampled using CDC light traps from each house twice a week for 4 wk. Mosquito control activities and the number and type of domestic animals within the compound was recorded on each sampling occasion. Before beginning the second sampling period, homes with blocked eaves had them opened, and those with open eaves had them closed. Mosquitoes were then sampled from each house for a further 4 wk. When houses had their eaves closed, a three-fold reduction in Anopheles gambiae s.l. Giles caught indoors was observed. However, there was no reduction in total culicine numbers observed. This study demonstrates that the eaves are the major route by which An. gambiae enters houses. By contrast, culicine mosquitoes enter largely through doors and windows. Sealing the eave gap is an important method for reducing malaria transmission in homes where doors and windows are screened.

Estimates of worst case baseline West Nile virus disease effects in a suburban New York county

Serosurveys conducted where West Nile Virus (WNV) caused health impacts were used to construct a model of potential worst case health impacts in a suburban setting. This model addressed two common public perceptions regarding mosquito control activities and WNV disease: it is not a disease of major consequence, and exposed populations quickly become immune. Comparisons to blood bank infection and serious disease incidence data were similar to some of the serosurvey model results. Accounting for theoretical increasing immunity, even over a 20-year period, did not substantially reduce the potential impacts. The model results were approximately an order of magnitude greater than those actually experienced in Suffolk County, NY; differences in mosquito populations and/or the degree of mosquito control between Suffolk County and serosurvey sites seem to be the reason for the differences.

Risk factors for house-entry by culicine mosquitoes in a rural town and satellite villages in The Gambia

BackgroundScreening doors, windows and eaves of houses should reduce house entry by eusynanthropic insects, including the common African house mosquito Culex pipiens quinquefasciatus and other culicines. In the pre-intervention year of a randomized controlled trial investigating the protective effects of house screening against mosquito house entry, a multi-factorial risk factor analysis study was used to identify factors influencing house entry by culicines of nuisance biting and medical importance. These factors were house location, architecture, human occupancy and their mosquito control activities, and the number and type of domestic animals within the compound.Results40,407 culicines were caught; the dominant species were Culex thalassius, Cx. pipiens s.l., Mansonia africanus, M. uniformis and Aedes aegypti. There were four times more Cx. pipiens s.l. in Farafenni town (geometric mean/trap/night = 8.1, 95% confidence intervals, CIs = 7.2–9.1) than in surrounding villages (2.1, 1.9–2.3), but over five times more other culicines in the villages (25.1, 22.1–28.7) than in town (4.6, 4.2–5.2). The presence of Cx. pipiens s.l. was reduced in both settings if the house had closed eaves (odds ratios, OR town = 0.62, 95% CIs = 0.49–0.77; OR village = 0.49, 0.33–0.73), but increased per additional person in the trapping room (OR town = 1.16, 1.09–1.24; OR village = 1.10, 1.02–1.18). In the town only, Cx. pipiens s.l. numbers were reduced if houses had a thatched roof (OR = 0.70, 0.51–0.96), for each additional cow tethered near the house (OR = 0.73, 0.65–0.82) and with increasing distance from a pit latrine (OR = 0.97, 0.95–0.99). In the villages a reduction in Cx. pipiens s.l. numbers correlated with increased horses in the compound (OR = 0.90, 0.82–0.99). The presence of all other culicines was reduced in houses with closed eaves (both locations), with horses tethered outside (village only) and with increasing room height (town only), but increased with additional people in the trapping room and where cows were tethered outside (both locations).ConclusionThe findings of this study advocate eave closure and pit latrine treatment in all locations, and zooprophylaxis using horses in rural areas, as simple control measures that could reduce the number of culicines found indoors.

Risk factors for house-entry by malaria vectors in a rural town and satellite villages in The Gambia

BackgroundIn the pre-intervention year of a randomized controlled trial investigating the protective effects of house screening against malaria-transmitting vectors, a multi-factorial risk factor analysis study was used to identify factors that influence mosquito house entry.MethodsMosquitoes were sampled using CDC light traps in 976 houses, each on one night, in Farafenni town and surrounding villages during the malaria-transmission season in The Gambia. Catches from individual houses were both (a) left unadjusted and (b) adjusted relative to the number of mosquitoes caught in four sentinel houses that were operated nightly throughout the period, to allow for night-to-night variation. Houses were characterized by location, architecture, human occupancy and their mosquito control activities, and the number and type of domestic animals within the compound.Results106,536 mosquitoes were caught, of which 55% were Anopheles gambiae sensu lato, the major malaria vectors in the region. There were seven fold higher numbers of An. gambiae s.l. in the villages (geometric mean per trap night = 43.7, 95% confidence intervals, CIs = 39.5–48.4) than in Farafenni town (6.3, 5.7–7.2) and significant variation between residential blocks (p < 0.001). A negative binomial multivariate model performed equally well using unadjusted or adjusted trap data. Using the unadjusted data the presence of nuisance mosquitoes was reduced if the house was located in the town (odds ratio, OR = 0.11, 95% CIs = 0.09–0.13), the eaves were closed (OR = 0.71, 0.60–0.85), a horse was tethered near the house (OR = 0.77, 0.73–0.82), and churai, a local incense, was burned in the room at night (OR = 0.56, 0.47–0.66). Mosquito numbers increased per additional person in the house (OR = 1.04, 1.02–1.06) or trapping room (OR = 1.19, 1.13–1.25) and when the walls were made of mud blocks compared with concrete (OR = 1.44, 1.10–1.87).ConclusionThis study demonstrates that the risk of malaria transmission is greatest in rural areas, where large numbers of people sleep in houses made of mud blocks, where the eaves are open, horses are not tethered nearby and where churai is not burnt at night. These factors need to be considered in the design and analysis of intervention studies designed to reduce malaria transmission in The Gambia and other parts of sub-Saharan Africa.

STATUS OF PLASMODIUM VIVAX MALARIA IN THE REPUBLIC OF KOREA DURING 2001–2003

The Republic of Korea experienced a re-emergence of Plasmodium vivax malaria in 1993. The incidence of this disease increased rapidly through 2000 with its geographic distribution expanding from the vicinity near the Demilitarized Zone to the adjacent outlying areas. However, the number of cases of P. vivax malaria since that time period has decreased. A total of 2,538 cases occurred in 2001, and this decreased to 1,761 cases and 1,164 cases in the two subsequent years. A total of 5,463 cases of P. vivax malaria were reported from 2001 through 2003; 25.26% (1,380) were reported among Republic of Korea military personnel, 27.48% (1,501) were among veterans who had been discharged from the military within two years, and 47.26% (2,582) were among the civilian population. Mosquito control activities by the North Korean and South Korean governments, chemoprophylaxis of Republic of Korea Army personnel, and the low level of Anopheles mosquitoes in 2001 may have been factors responsible for the decreasing number of malaria cases. However, local transmission might have taken place in urban regions of the malaria-risk areas that are within 30 km south of the Demilitarized Zone. Extensive intervention and continued surveillance are warranted to prevent the epidemic from re-expanding and to eliminate this disease in the Republic of Korea.

Human Exposure to Mosquito-Control Pesticides—Mississippi, North Carolina, and Virginia, 2002 and 2003

Public health officials weigh the risk for mosquito-borne diseases against the risk for human exposure to pesticides sprayed to control mosquitoes. Response to outbreaks of mosquito-borne diseases has focused on vector control through habitat reduction and application of pesticides that kill mosquito larvae. However, in certain situations, public health officials control adult mosquito populations by spraying ultra-low volume (ULV) (<3 fluid ounces per acre [oz/acre]) mosquito-control (MC) pesticides, such as naled, permethrin, and d-phenothrin. These ULV applications generate aerosols of fine droplets of pesticides that stay aloft and kill mosquitoes on contact while minimizing the risk for exposure to persons, wildlife, and the environment. This report summarizes the results of studies in Mississippi, North Carolina, and Virginia that assessed human exposure to ULV naled, permethrin, and d-phenothrin used in emergency, large-scale MC activities. The findings indicated ULV application in MC activities did not result in substantial pesticide exposure to humans; however, public health interventions should focus on the reduction of home and workplace exposure to pesticides.

West Nile virus southeast conference.

West Nile virus southeast conference.

Provisional Surveillance Summary of the West Nile Virus Epidemic—United States, January–November 2002

This report presents provisional summary surveillance data about West Nile virus (WNV) activity that were reported to CDC during January 1-November 30, 2002, through the ArboNET surveillance network. In 2002, the reported numbers of human and animal infections increased, and the geographic range of WNV activity expanded substantially. These data underscore the need for intensive surveillance to detect and quantify WNV activity in areas where humans are at risk, public education to teach persons how to prevent mosquito bites, and sustained and integrated mosquito-control activities.