Field Evaluation of Indoor Thermal Fog and Ultra-Low Volume Applications For Control of Aedes aegypti in Thailand.

Efficacies of a handheld thermal fogger (Patriot™) and a backpack ultra-low volume (ULV) sprayer (Twister™) with combinations of 2 different adulticides (pyrethrin, deltamethrin) and an insect growth regulator (pyriproxyfen) were field-tested and compared for their impact on reducing indoor Aedes aegypti populations in Thailand. The effectiveness of the indoor space sprays was evaluated by sampling the natural Ae. aegypti population in houses and determining their physiological status, by monitoring mortality of sentinel caged mosquitoes (AFRIMS strain) and by assessing larval mortality in laboratory bioassays using water exposed to the spray. A total of 14,742 Ae. aegypti were collected from Biogents Sentinel traps in this study. The combination of ULD® BP-300 (3% pyrethrin) and NyGuard® (10% pyriproxyfen) sprayed either by the Patriot or Twister significantly reduced some Ae. aegypti populations up to 20 days postspray relative to the control clusters. The addition of pyriproxyfen to the adulticide extended how long household mosquito populations were suppressed. In 2 of the 4 products being compared, the Twister resulted in higher mortality of caged mosquitoes compared with the Patriot. However, neither machine was able to achieve high mortality among Ae. aegypti placed in hidden (protected) cages. The larval bioassay results demonstrated that the Twister ULV provided better adult emergence inhibition than the Patriot (thermal fogger), likely due to larger droplet size.

Congenital corneal anesthesia with retinal abnormalities, deafness, unusual facies, persistent ductus arteriosus, and mental retardation: a new syndrome?

Two sibs who had hypesthetic corneas, absence of the peripapillary choriocapillaris and retinal pigment epithelium, sensorineural hearing loss bilaterally, persistent ductus arteriosus, moderate mental retardation, and unusual facial appearance are described. Their mother had mild to moderate sensorineural hearing loss, retinal changes and similar facial features. The differential diagnosis is discussed. We believe this is a clinically distinct syndrome with autosomal dominant inheritance.

Community-based integrated control of Aedes aegypti: a brief overview of current programs.

Dengue viruses are maintained in endemic transmission cycles in tropical urban areas where epidemics periodically occur. Until about 30 years ago, there were long intervals (10-40 years) between epidemics but they are now occurring in many areas at 3-5-year intervals. These epidemics are most likely caused by virus strains with different epidemic potential. Accompanying this increased frequency in epidemic activity has been a change in the disease pattern with cases of the severe form of dengue (dengue hemorrhagic fever) becoming much more common. The occurrence of these factors and the expanding geographic distribution of dengue hemorrhagic fever in the past 15 years have made it necessary to re-evaluate currently recommended methods for prevention and control. The result has been increasing emphasis on the development of effective sustainable Aedes aegypti control programs based on source reduction using community participation. A brief overview of global programs using this approach is presented with emphasis on the Puerto Rican program, one of the earliest developed.

Short report: dispersal of Aedes aegypti in an urban area after blood feeding as demonstrated by rubidium-marked eggs.

Strategies for the control of Aedes aegypti during urban outbreaks of dengue or yellow fever assume that this species has a maximum flight range of 50-100 meters. Because Ae. aegypti distributes its eggs among several oviposition sites, we postulated that dispersal is driven by the search for oviposition sites, so an ovipositing female may have to fly much further than 50-100 meters to lay all of her eggs. We developed a method for marking Ae. aegypti eggs with a rare alkali metal (rubidium) and showed that in an urban area, oviposition activity in a single gonotrophic cycle lasts several days and covers an area at least 840 meters in diameter (55.4 hectares). We suggest that current practice for the control of dengue and yellow fever transmission by focal treatments with insecticides 50-100 meters around presumed or confirmed cases is unlikely to be effective. Moreover, source reduction (the elimination of breeding sites) may enhance dissemination of virus-infected mosquitoes by reducing the number of available oviposition sites.

The dengue and dengue hemorrhagic fever epidemic in Puerto Rico, 1994-1995.

From June 1, 1994 to May 31, 1995 a total of 24,700 cases of dengue (7.01/1,000 population) were reported to the laboratory-based surveillance system in Puerto Rico (1991-1994, annual average: 2.55/1,000). Dengue virus 2 predominated. The earliest indicator of epidemic activity was the virus isolation rate in May 1994 (14.0% versus 5.7% average). The male-to-female ratio among cases was 1:1.1; 65.4% were younger than 30 years (the 10 to 19 year age group had the highest incidence, 11.8/1,000). At least 5,687 cases (23.0%) showed a hemorrhagic manifestation; 4,662 (18.9%) were hospitalized, and 40 died (0.2%; 10 laboratory-positive). Two cases documented by laboratory were transmitted by unusual routes--intrapartum and through a bone marrow transplant. Among 2,004 hospitalized cases reported by infection control nurses, 139 (6.9%) fulfilled the criteria for dengue hemorrhagic fever (DHF) and another 13 cases (0.6%) had dengue shock syndrome. This epidemic produced the largest number of hospitalizations, DHF cases, and deaths from any dengue epidemic in Puerto Rico. Severity did not change throughout the year. Surveillance capabilities were maintained by temporary, simplified reporting methods, none of which could be recommended as the single method of choice for surveillance; each must be used (on site, or as a service available from a reference laboratory) at the right time in the epidemic cycle. The utility of comparisons of current and previous data underscores the value of long-term surveillance. Our analysis was unable to document whether significantly increased transmission occurred more often in cities where the water supply was rationed or where the local landfill was closed.

Persistence of La Crosse virus (California encephalitis serogroup) in north-central Illinois.

La Crosse (LAC) virus was first isolated in Illinois from a pool of 50 female Aedes triseriatus mosquitoes collected in July 1976, in Peoria Heights. From 1978 through 1981, 27 strains (11 from males and 16 from females) of LAC virus were recovered from 888 pools containing 22,021 adult A. triseriatus mosquitoes from the same study area. These mosquitoes had developed from larvae and pupae collected from 50 individually identified treeholes. Of the 14 trees that yielded LAC virus-positive mosquitoes, one was positive in 3 of 4 years and another was positive in all 4 years. The latter tree had minimum mosquito field infection rates (MFIR) ranging from 3.4 to 12.7/1,000. Eight (57%) of the trees with positive mosquitoes were red oak (Quercus rubra) while 10 (71%) were in the oak genus (Quercus). The four most productive treeholes accounted for 30% of mosquitoes tested and 52% of the LAC isolations. In 1979, 6,729 A. triseriatus mosquitoes were collected in man-baits and tested for virus. From 1,282 tested in 259 pools (mean = 5), 13 LAC isolates were made, resulting in a field infection rate (FIR) of 11.4/1,000. The remaining 5,447 were tested in 218 pools (mean = 25) and 48 strains of LAC were isolated for a FIR of 9.9/1,000. The relationship of these findings to the occurrence of human LAC encephalitis cases in Peoria County, Illinois is discussed. Repeated recovery of virus from this study area reflects a stable, yet dynamic, focus of LAC virus transmission.

Vector potential of selected North American mosquito species for Rift Valley fever virus.

Selected North American mosquito species were evaluated as potential vectors of Rift Valley fever virus. Field populations of Aedes canadensis, Ae. cantator, Ae. excrucians, Ae. sollicitans, Ae. taeniorhynchus, Ae. triseriatus, Anopheles bradleyi-crucians, Culex salinarius, Cx. tarsalis, and Cx. territans perorally exposed to 10(6.2)-10(7.2) plaque forming units of Rift Valley fever virus readily became infected. Infection rates ranged from 51% (65/127) for Cx. salinarius to 96% (64/67) for Ae. canadensis. Disseminated infection rates were generally greater at 14 days than at 7 days after the infectious bloodmeal, and, with the exception of An. bradleyi-crucians, they were not significantly different than the pooled rate of 59% for each species tested. Only 5/55 (9%) of the An. bradleyi-crucians developed a disseminated infection. For most of the species, about half of the mosquitoes with a disseminated infection transmitted an infectious dose of virus to hamsters. While all species, with the exception of An. bradleyi-crucians, transmitted virus, Ae. canadensis, Ae. taeniorhynchus, and Cx. tarsalis had the highest vector potential of the species tested. Following inoculation of approximately 10(1.6) plaque forming units of virus, 100% of the mosquitoes of each species became infected. For most species, transmission rates were similar for inoculated individuals and those that developed a disseminated infection following peroral infection. Viral titers of transmitting and nontransmitting-disseminated individuals were similar for all species tested. These data suggest that, if Rift Valley fever virus was introduced into North America, several mosquito species would be capable of transmitting it.

Using disability-adjusted life years to assess the economic impact of dengue in Puerto Rico: 1984-1994.

This study presents the disability-adjusted life years (DALYs), a non-monetary economic measure of impact, lost to dengue in Puerto Rico for the period 1984-1994. Data on the number of reported cases, cases with hemorrhagic manifestations, hospitalizations, and deaths were obtained from a surveillance system maintained at the Dengue Branch, Division of Vector-Borne Infectious Diseases, Centers for Disease Control and Prevention (San Juan, PR). The reported cases were divided into two age groups (0-15 years old and >15 years old), and then multiplied by predetermined factors (10 for 0-15 years; 27 for >15 years) to allow for age-related under-reporting of cases. Severity of dengue was modeled by classifying cases into three groups: dengue fever, dengue with severe manifestations, and hospitalized cases. Each group was assigned a different number of days lost because of dengue-related disability. Dengue caused an average of 658 DALYs per year per million population (SE = 114, range = 145-1,519). A multivariate sensitivity analysis, which simultaneously altered the values of six input variables, produced a mean of 580 DALYs/year/million population, with a maximum average of 1,021 DALYs/year/million population, and a maximum, single-year estimate for 1994 of 2,153 DALYs/million population. The most important input was the number of days lost to classic dengue. The DALYs/year/million population lost to dengue in Puerto Rico are much greater than previous estimates concerning the impact of dengue hemorrhagic fever alone. The loss to dengue is similar to the losses per million population in the Latin American and Caribbean region attributed to any of the following diseases or disease clusters; the childhood cluster (polio, measles, pertussis, diphtheria, tetanus), meningitis, hepatitis, or malaria. The loss is also of the same order of magnitude as any one of the following: tuberculosis, sexually transmitted diseases (excluding human immunodeficiency virus), tropical cluster (e.g., Chagas' disease, leishmaniasis), or intestinal helminths. The results objectively suggest that when governments and international funding agencies allocate resources for research and control, dengue should be given a priority equal to many other infectious diseases that are generally considered more important.

Dengue activity in Puerto Rico during an interepidemic period (1995-1997).

From 1995 to 1997 dengue was reported in Puerto Rico at an average annual rate of 1.75/1,000 population, compared to 6.73 in 1994, an epidemic year. Dengue virus serotypes 1 (DEN-1), -2, and -4 were isolated each year, with DEN-2 predominating in 1995 and 1996, and DEN-4 in 1997. From 1995 through 1997 incidence was highest (0.61-0.77/1,000) in persons under 30 years of age; males and females were equally affected. Among positive cases, 28.3% to 37.9% were hospitalized; 28.9% to 35.2% had hemorrhagic manifestations; at least 1.1% to 1.6% fulfilled the criteria for dengue hemorrhagic fever/dengue shock syndrome; and 0.2% to 0.3% died. Neither hurricane preparations (1995) nor widespread floods (1996) seem to have affected dengue incidence. Most municipalities with the highest laboratory-diagnosed dengue rates in 1995 were in the eastern foothills of the central mountains, an area relatively spared by the 1994 epidemic. In the next two years, at least half of the municipalities with the highest laboratory-diagnosed dengue rates were in the west. The most intense municipal outbreak of this period (DEN-2, Villalba, 1995, rate of 11.67/1,000) is described to highlight the importance of local conditions and epidemiologic history in determining the risk of dengue.

Occurrence of La Crosse (California serogroup) encephalitis viral infections in Illinois.

La Crosse (LAC) virus (California encephalitis serogroup) was identified as the etiologic agent of disease in 61 cases of California encephalitis (CE) that occurred in Illinois between 1976 and 1980. This group represented 54% of all 114 laboratory-diagnosed cases of CE between 1966 and 1980. Key epidemiologic observations included: 88% of the 61 cases had onset in July, August, or September; the 5- to 9-year-old age group represented 48% of the cases; the male:female sex ratio was 2:1; 97% of the cases occurred in the northern half of the state; and 61% of the cases occurred in Peoria County. Four instances of probable common source of exposure were reported. Average length of hospitalization was 8.3 days (range 3-31 days). Hospitalization costs were estimated at $3,967-$5,750 per case. An "average" year in Illinois yields 12 cases of LAC encephalitis with direct hospitalization costs of $47,604-$69,000.

Dengue surveillance in Texas, 1995.

Dengue epidemics have been occurring in the Caribbean and Central and South America, including Mexico. In 1995, the proximity of these epidemics increased the possibility of cases occurring in Texas. In response, medical and community educational materials were distributed and active surveillance for dengue cases was initiated. By the end of the year, sera from more than 360 patients were tested for anti-dengue antibody. Twenty-nine cases were detected statewide; seven cases in southern Texas were locally acquired.

Malpais spring virus: a new vesiculovirus from mosquitoes collected in New Mexico and evidence of infected indigenous and exotic ungulates.

Two virus isolates, 1 each from Aedes campestris and Psorophora signipennis mosquitoes collected in south central New Mexico in August 1985, were shown by neutralization tests to be identical to each other, but not to any of more than 250 arthropod-borne and other viruses. Electron microscopy of 1 isolate (85-488NM, chosen as the prototype) indicated that this strain shares morphologic characteristics with viruses of the family Rhabdoviridae. Indirect fluorescent antibody tests indicated that this virus is a member of the genus Vesiculovirus, but is not closely related to any of the North American or other rhabdoviruses with which it was tested, including vesicular stomatitis (Indiana) and vesicular stomatitis (New Jersey) viruses. The name Malpais Spring virus is proposed for this newly recognized vesiculovirus. A serologic survey indicated that Malpais Spring virus infects indigenous (mule deer and pronghorn) and exotic (gemsbok) ungulates at and near the sites where the mosquitoes from which the virus strains were isolated were collected. Antibody prevalence in wild animals indicates that the pronghorn and gemsbok may play roles as hosts for Malpais Spring, epizootic hemorrhagic disease (New Jersey), and bluetongue viruses in this area.

Effect of a community-based Aedes aegypti control programme on mosquito larval production sites in El Progreso, Honduras.

This paper describes the results of a trial to assess the efficacy in reducing the density of larval production sites of utilizing community involvement in the planning and implementation of an Aedes aegypti control programme, in a dengue-endemic city in Honduras. In addition to a substantial increase in knowledge about dengue transmission and prevention, a relative reduction in Ae. aegypti larval infestation indices was found in those city neighbourhoods where community involvement was utilized compared with their untreated counterparts. Several methods of improving the impact of this type of programme are discussed.

Community involvement in the control of Aedes aegypti.

In the past 15 years, there has been a dramatic resurgence of dengue and dengue hemorrhagic fever worldwide, with increased frequency of epidemics and geographic expansion of both the mosquito vectors and the viruses. The reasons for this resurgence are not well understood, but include uncontrolled and unplanned urbanization, increased movement of people and viruses by airplane and lack of effective control of Aedes aegypti, the principal mosquito vector of dengue viruses. The recommended method for Ae. aegypti control during the past 20 years has been ultra-low volume (ULV) application of insecticides, a method which targets the adult mosquito. Lack of efficacy of the ULV approach led to a reevaluation of recommended strategies for prevention and control of epidemic dengue and ultimately, resulted in development and widespread use of community-based, integrated approaches to Ae. aegypti control. This chapter reviews the use of community participation for controlling Ae. aegypti via larval source reduction and critically discusses programs in four countries from the standpoint of effectiveness and sustainability. It is concluded that a combination of vertically structured centralized and community-based approaches should provide short-term success as well as long-term sustainability.

Egg of Aedes (Gymnometopa) mediovittatus (Diptera: Culicidae).

The egg of Aedes mediovittatus (Coquillett) is described from scanning electron micrographs. The egg is black, slightly tapered toward the posterior pole, and is approximately 771 microns long and up to 175 microns wide. On the entire egg surface there are about 970 polygonal outer chorionic cells, each bounded by a raised outer chorionic reticulum which forms a wall around each cell. Incorporated into the inner surface of this wall are 13-18 relatively small, poorly defined and variably shaped tubercles. In the center of each cell there is a large, buttonlike, more or less round tubercle with a pitted upper surface. Over most of the egg surface, the walls of this tubercle are connected by spokelike bridges of variable diameter to the cell floor or reticulum wall. The structure of the outer chorionic cells is somewhat modified in areas approaching the anterior and posterior poles.

Life table study of Aedes aegypti (Diptera: Culicidae) in Puerto Rico fed only human blood versus blood plus sugar.

Life table studies were performed in 1996 with Aedes aegypti (L.) during the low (cool/dry) and high (hot/rainy) dengue virus transmission seasons in Puerto Rico. Mated adult females from field-collected pupae were placed individually in cages and divided into 2 treatment groups: one was fed only human blood and the other human blood plus a 10% sucrose solution. Survival and number of eggs laid were recorded daily for each female. During both seasons, age specific survivorship was higher for the blood plus sugar group, groups fed only human blood had higher reproductive outputs (mx), and net replacement rates (Ro) for blood only groups were higher than for those fed blood plus sugar. Intrinsic rates of growth (r) were the same for both treatments during the low (cool/dry) transmission season, but higher for the blood-only treatment during the high (hot/rainy) transmission season. Our results indicate that feeding on only human blood provides an evolutionary advantage to Ae. aegypti females in Puerto Rico. These results are similar to those from an earlier study carried out with Ae. aegypti in Thailand; the advantage of feeding on human blood does not seem to be restricted to a particular geographic region. We also found that the benefits associated with human feeding persist through epidemiologically different times of the year. We conclude that feeding on human blood is reproductively beneficial for Ae. aegypti, which may increase their contact with human hosts, and therefore may influence their vectorial capacity for dengue viruses through frequent feeding on blood.

Survival of starved Aedes aegypti (Diptera: Culicidae) in Puerto Rico and Thailand.

Survival of adult Aedes aegypti (L.) was studied in Thailand (1995) and Puerto Rico (1996) during periods of high and low dengue virus transmission. Resting males and females were collected inside houses by aspiration. Females were separated into different cages by their degree of engorgement and ovarian development. Teneral adults were obtained from pupae collected from natural breeding sites. All mosquitoes were given access to water, held at ambient temperature in the shade, and their survival monitored daily. We calculated median survival for each stage to estimate when mosquitoes had to feed again or die. No differences in survival between seasons were observed in Thailand. In Puerto Rico, except for wild males, survival was longer in the cool/dry season than in the hot/rainy season, indicating that mosquitoes may need to feed more frequently during the high than low dengue transmission season. During both study periods and at both sites, blood-engorged females survived as long or longer than mosquitoes in other gonotrophic or developmental stages. Except in Puerto Rico during the cool season, when females had a relatively high probability of surviving 3-4 d without feeding, females needed to feed approximately every other day to avoid death caused by starvation. Our results indicate that in some regions, there are seasonal differences in the length of time female Ae. aegypti can survive without feeding, females with a blood meal can survive for a longer time than those without blood, and teneral males can live longer without food than teneral females.

Detection of multiple blood feeding in Aedes aegypti (Diptera: Culicidae) during a single gonotrophic cycle using a histologic technique.

We evaluated a histologic technique for its usefulness in detecting multiple blood feeding by Aedes aegypti (L.) in a single gonotrophic cycle. To standardize the procedure, we carried out a laboratory study in which 166 mosquitoes imbibed two blood meals at known intervals. Eighty percent (78/98) of the multiple meals were detected when the interval between meals was from 1 to < to = 24 h and the time from the second meal to fixation ranged from 0 to 12 hr. At intervals outside this range, only 34% (23/68) of the multiple meals were detected. Overall, 61% (101/166) of the double meals were detected. Examination of 96 engorged Ae. aegypti collected by aspiration from inside houses in San Juan, Puerto Rico, indicated that 50% had imbibed multiple meals. Most wild-caught mosquitoes took their last meal the day before capture, and most multiple feeders fed twice on consecutive days. A dark line of digested blood, or heme, around the first meal and a physical separation between meals were the most useful histologic parameters for detecting multiple feeding in wild Ae. aegypti. An association of multiple feeding with advanced stages of oocyte development suggests that, at the time of collection, most Ae. aegypti from the study site had fed twice in each gonotrophic cycle. We conclude that, although it is labor intensive, histologic examination is an appropriate technique for a longitudinal, community-wide survey of multiple feeding by Ae. aegypti.

Analysis of survival of young and old Aedes aegypti (Diptera: Culicidac) from Puerto Rico and Thailand.

It generally is assumed that the daily probability of survival of wild adult mosquitoes is independent of age. To test this assumption we conducted mark-release-recapture studies in Puerto Rico and Thailand to determine if estimated daily survival rates between two different age cohorts of the dengue vector Aedes aegypti (L.) were the same. Survivorship was estimated with nonlinear regression analysis using bootstrapping to obtain estimates of errors. Initial recapture success of the younger cohort was greater than the older cohort at both locations. Our analysis revealed a significantly greater survival rate for the younger cohort of females in Puerto Rico, and no significant differences between age cohorts in Thailand. For comparison, a traditional approach for analyzing these type of data, linear regression of log-transformed captures over time (exponential model), was used to calculate the probability of daily survival based on slopes of linear regression lines for recaptured mosquitoes. With this method, the estimated daily survival rate of older females (13-23 d old) was significantly greater than survival of younger ones (3-13 d old) in Puerto Rico and Thailand. In addition, short-range movement of mosquitoes was observed in Puerto Rico; maximum dispersal distance detected was 79 m. Survival rates of adult Ae. aegypti may be age-dependent and nonlinear regression analysis is a sensitive approach for comparing patterns of mosquito survival based on mark, single release, multiple recapture data.

Aedes aegypti (Diptera: Culicidae) movement influenced by availability of oviposition sites.

Marked Aedes aegypti (L.) (5-6 d old) were released inside 2 groups of 5 houses (100 females per house) in a residential community in Florida, PR, to compare behavior of gravid females at sites where oviposition containers were absent to sites where containers were abundant (i.e., 2 tires and 10 ovipots were added to each yard). Two sequential releases were made so that both groups of houses were evaluated with oviposition containers removed and added. Mosquitoes resting inside the 10 release houses plus 20 additional neighboring houses were collected with backpack aspirators for 4 consecutive days, beginning 2 d after release. Because 172 of the 185 recaptured females (93%) were collected in the same houses in which they had been released, dispersal patterns were not directly comparable. However, the recapture rate in houses with containers added (13%) was significantly higher (P < 0.0001) than in houses with containers removed (6%). No difference was observed in the mean number of potential oviposition containers among the nonrelease houses at the 2 sites (3.9 versus 3.8 aquatic containers per house in the prerelease survey). Our results are consistent with the hypothesis that availability of oviposition sites is inversely correlated with the potential for female Ae. aegypti to disperse. These results have important implications because campaigns to reduce Ae. aegypti larval sites during dengue epidemics could have the undesirable effect of inducing the dispersal of infected adult female mosquitoes.