Sentinel chicken seroconversions track tangential transmission of West Nile virus to humans in the greater Los Angeles area of California.

In Los Angeles, California, West Nile virus (WNV) has followed a pattern of emergence, amplification, subsidence, and resurgence. A time series cross-correlation analysis of human case counts and sentinel chicken seroconversions revealed temporal concordance indicating that chicken seroconversions tracked tangential transmission of WNV from the basic passeriform-Culex amplification cycle to humans rather than antecedent enzootic amplification. Sentinel seroconversions provided the location and time of transmission as opposed to human cases, which frequently were reported late and were assumed to be acquired 2-14 days before disease onset at their residence. Cox models revealed that warming degree-days were associated with the increased risk of seroconversion, whereas elevated herd immunity in peridomestic birds dampened seroconversion risk. Spatially, surveillance data collected within a 5 km radius of flock locations 15-28 days before the bleed date were most predictive of a seroconversion. In urban Los Angeles, sentinel chicken seroconversions could be used as an outcome measure in decision support for emergency intervention.

West Nile virus emergence and persistence in Los Angeles, California, 2003-2008.

West Nile virus (WNV) invaded Los Angeles in September 2003, and during the subsequent five-year period followed a pattern of amplification, subsidence, and resurgence. Enzootic transmission was tracked by abundance and infection incidence in Culex pipiens quinquefasciatus and Cx. tarsalis and by seroprevalence in peridomestic passerine birds, infection in dead birds, and seroconversions in sentinel chickens. Culex p. quinquefasciatus served as the primary vector of WNV, with gravid traps serving as the best sampling method and the most consistent indicator of viral activity. Spatial scan statistics applied to mosquito infection and positive dead bird data delimited three major clusters of WNV transmission, with introduction occurring in the Los Angeles Basin, and amplification and dispersal events carrying transmission to the San Fernando and Santa Clarita valleys. Los Angeles experienced major epidemics in 2004 and 2008, providing a unique opportunity to investigate specific patterns of enzootic amplification preceding epidemics.

Mosquitoes and their control

Mosquitoes and Their Control presents a wealth of information on the bionomics, systematics, ecology, research techniques and control of both nuisance and disease vector mosquitoes in an easily readable style, providing practical guidelines and important information for professionals and laymen alike. Ninety-two European species and more than 100 globally important vector and nuisance species are included in the book. Most of them, including all European species, are described in the fully illustrated identification keys, followed by a detailed description of the morphology, biology, distribution and medical importance of each species, including over 700 detailed drawings. Mosquitoes and Their Control includes: systematics and biology, medical significance, research techniques, illustrated identification keys for larval and adult mosquito general, morphology, ecology, and distribution of the species identified in the keys, biological, chemical, physical and genetic control of mosquitoes. Mosquitoes and Their Control is a valuable tool for vector ecologists, entomologists, and all those involved with mosquito control, biology, ecology, and systematics world-wide. It will especially benefit those professionals, scientists and students dealing with mosquitoes and their control on a day-to-day basis. Society as a whole stands to gain from improved, environmentally responsible mosquito management programs designed on the basis of a broader understanding of mosquitoes and their control, as provided in this enlightening book...

Mosquitoes and their control

Mosquitoes and Their Control presents a wealth of information on the bionomics, systematics, ecology, research techniques and control of both nuisance and disease vector mosquitoes in an easily readable style, providing practical guidelines and important information for professionals and laymen alike. Ninety-two European species and more than 100 globally important vector and nuisance species are included in the book. Most of them, including all European species, are described in the fully illustrated identification keys, followed by a detailed description of the morphology, biology, distribution and medical importance of each species, including over 700 detailed drawings. Mosquitoes and Their Control includes: systematics and biology, medical significance, research techniques, illustrated identification keys for larval and adult mosquito general, morphology, ecology, and distribution of the species identified in the keys, biological, chemical, physical and genetic control of mosquitoes. Mosquitoes and Their Control is a valuable tool for vector ecologists, entomologists, and all those involved with mosquito control, biology, ecology, and systematics world-wide. It will especially benefit those professionals, scientists and students dealing with mosquitoes and their control on a day-to-day basis. Society as a whole stands to gain from improved, environmentally responsible mosquito management programs designed on the basis of a broader understanding of mosquitoes and their control, as provided in this enlightening book

Role of corvids in epidemiology of west Nile virus in southern California.

The invasion of different southern California landscapes by West Nile virus (WNV) and its subsequent amplification to epidemic levels during 2004 enabled us to study the impact of differing corvid populations in three biomes: the hot Colorado desert with few corvids (Coachella Valley), the southern San Joaquin Valley (Kern County) with large western scrub-jay but small American crow populations, and the cool maritime coast (Los Angeles) with a large clustered American crow population. Similar surveillance programs in all three areas monitored infection rates in mosquitoes, seroconversion rates in sentinel chickens, seroprevalence in wild birds, numbers of dead birds reported by the public, and the occurrence of human cases. Infection rates in Culex tarsalis Coquillett and sentinel chicken seroconversion rates were statistically similar among all three areas, indicating that highly competent mosquito hosts were capable of maintaining enzootic WNV transmission among less competent and widely distributed avian hosts, most likely house sparrows and house finches. In contrast, infection rates in Culex pipiens quinquefasciatus Say were statistically higher in Kern and Los Angeles counties with elevated corvid populations than in Coachella Valley with few corvids. Spatial analyses of dead corvids showed significant clusters near known American crow roosts in Los Angeles that were congruent with clusters of human cases. In this area, the incidence of human and Cx. p. quinquefasciatus infection was significantly greater within corvid clusters than without, indicating their importance in virus amplification and as a risk factor for human infection. In contrast the uniform dispersion by territorial western scrub-jays resulted in a high, but evenly distributed, incidence of human disease in Kern County.

Evaluation of the present dengue situation and control strategies against Aedes aegypti in Cebu City, Philippines.

The present dengue situation and methods to control Aedes aegypti larvae in Cebu City, Philippines, were evaluated for the development of an integrated community-based dengue control program. The study included the detection of dengue infection among Filipino patients, surveying mosquito breeding sites to determine larval population density of Aedes aegypti, an evaluation of public knowledge, attitude, and personal protection practices against dengue, and an evaluation of the efficacy of VectoBac DT/Culinex Tab tablets based on Bacillus thuringiensis israelensis against Ae. aegypti larvae. Of the 173 human sera samples that were assayed for dengue viruses, 94.9% were positive, 2.2% negative and 2.8% equivocal. Thirty households were randomly chosen per Barangay "Villages" (lowest level of formal local administration). Of the 489 breeding sites surveyed, 29.4% were infested with Ae. aegypti larvae, with discarded tires having the highest infestation rate (69.4%). A survey of people's knowledge, attitude, and practices for integrated community-based dengue control showed that 68.7% of the interviewees were aware that dengue is transmitted by mosquitoes, but only 4.3% knew that a virus was the cause of the disease. The efficacy of one and two tablets of VectoBac DT/Culinex Tab, based on Bacillus thuringiensis israelensis, was assessed against the larvae of Ae. aegypti exposed to sunshine and shaded water containers in semi-field and field tests. In semi-field tests, 100% mortality was achieved until the 18th and 30th day after the application of one and two tablets, respectively, in sun-exposed containers. In shaded containers, 100% mortality was observed until the 30th and 36th day after the application of one and two tablets, respectively. In field tests, the tablets were effective for approximately 3 weeks.

West Nile virus in California.

West Nile virus (WNV) was first isolated in California during July 2003 from a pool of Culex tarsalis collected near El Centro, Imperial County. WNV transmission then increased and spread in Imperial and Coachella Valleys, where it was tracked by isolation from pools of Cx. tarsalis, seroconversions in sentinel chickens, and seroprevalence in free-ranging birds. WNV then dispersed to the city of Riverside, Riverside County, and to the Whittier Dam area of Los Angeles County, where it was detected in dead birds and pools of Cx. pipiens quinquefasciatus. By October, WNV was detected in dead birds collected from riparian corridors in Los Angeles, west to Long Beach, and through inland valleys south from Riverside to San Diego County. WNV was reported concurrently from Arizona in mid-August and from Baja, Mexico, in mid-November. Possible mechanisms for virus introduction, amplification, and dispersal are discussed.

Field efficacy of deltamethrin for rodent flea control in San Bernardino County, California, USA.

A study was conducted to determine the initial and residual activity of deltamethrin (0.05% dust) applied to rodent burrows (at approximately 14 g/burrow) against fleas in the Silverwood Lake area of San Bernardino County. In initial toxicity (2-d post-treatment), deltamethrin provided 97% flea control and in residual toxicity it resulted in 68% control of the rodent fleas at 15-d post-treatment. The flea fauna consisted of Oropsylla montana (89.9%) and Hoplopsylls anomalus (10.1%). All rodents captured in this study were California ground squirrels, Spermophilus beecheyi. In mark-release-recapture trials, using the microchip identification implant method at the treatment site, the recapture rate of rodents was 29% from 2- to 58-d post-treatment, declining to 21% after 98 d. In the tail-clip method at the treatment site, the recapture rate of 40% at 15-d post-treatment rose to 87% and 73% at 56- and 58-d post-treatment, respectively. At the control site, the recapture rate of 100% at 15-d post-post-treatment dropped to 20% after 98 d. In another trial at Camp Cedar Crest in the Running Springs area, deltamethrin applied to rodent burrows resulted in 70% control of fleas infesting S. beecheyi. Based on the two trials, deltamethrin showed a good initial control of rodent fleas in enzootic or epizootic plague control.

Has Aedes albopictus established in California?

Significant numbers of the Asian tiger mosquito, Aedes albopictus, were detected on the west coast of the USA in mid-June 2001, in containerized oceanic shipments of "lucky bamboo" (Dracaena spp.) originating from South China. Wholesale nurseries in California importing large quantities of lucky bamboo became the focal points of infestation. Greater Los Angeles County Vector Control District immediately implemented an adulticiding protocol at the Los Angeles/Long Beach Harbors, followed by larviciding soon after the shipment was delivered to the wholesale nursery. Intensive surveys are currently being conducted above ground and in the underground storm drain systems using battery-operated CDC/CO2-baited light traps and ovitraps, both enhanced with an attractant (water rinse of tiger shrimps), to determine extent of infestation and perhaps establishment of Ae. albopictus locally.

Introduction and potential establishment of Aedes albopictus in California in 2001.

Aedes albopictus was discovered in Los Angeles, California, in June 2001 in a maritime cargo container from China containing a shipment of a commercial plant product known as "Lucky Bamboo" (Dracaena spp.). To keep the plants alive during the ocean transit, they were shipped in 5-8 cm of water, providing an excellent habitat for Ae. albopictus. Mosquito infestations were subsequently detected at 15 nursery distributors of Dracaena in 2 northern and 4 southern California counties. The distribution of the Ae. albopictus infestations was limited to the vicinity of those nursery distributors with documented infestations. Infestations persisted for more than 5 months near some of the nurseries, and eggs were found in ovitraps until mid-November 2001 up to 1,000 m from the original infestation sites. Overwintering Ae. albopictus populations were discovered in April, July, and August 2002 at original infestation sites in Chino, San Bernardino County, and Monterey Park and Rowland Heights, Los Angeles County, respectively. Specimens were found at some sites of overwintering populations until October 2002.

Flea, rodent, and plague ecology at Chuchupate Campground, Ventura County, California.

Chuchupate Campground in Ventura County, California, was closed to the public for 18 years (1982 to 2000) because of uncontrolled vector fleas and persistent plague antibody titers in rodents. The primary purpose of this study was to clarify the plague ecology of Chuchupate Campground by identifying involved rodents and their vector fleas and by determining many of their ecological parameters: abundance, flea and host preferences and diversities, and flea seasonality. Rodents and fleas were identified to species, some fleas were tested for Yersinia pestis, and rodent bloods were analyzed for the presence of antibodies to Y. pestis. During this study, 20 flea species were identified from 10 rodent and one lagomorph species collected. Five species of rodents were seropositive for plague during 13 of the 17 years in which plague testing was conducted. A likely reservoir species was not determined, but evidence of plague resistance was discovered in Merriam's chipmunks (Tamias merriami) and dusky-footed woodrats (Neotoma fuscipes). The "susceptible" rodent and flea complexes at Chuchupate are the California ground squirrel (Spermophilus beecheyi) and its fleas, Oropsylla montana and Hoplopsyllus anomalus, Merriam's chipmunk and its flea, Eumolpianusfornacis, and the dusky-footed woodrat and its flea, Orchopeas sexdentatus. Host preference, diversity, and seasonality of fleas are discussed, as well as the pivotal role of woodrat houses and nests as foci for hosts, fleas, and plague.

Introduction of Aedes albopictus (Skuse) in southern California and potential for its establishment.

Isolated incidences of Aedes albopictus in the continental U.S. were reported as early as 1946 and the first incidence in California was reported in 1972. These introductions were referred to as "isolated incidences" because very few immatures were observed in used tires shipped from Southeast Asia. The first major discovery of a large population and subsequent establishment of Ae. albopictus in the U.S. was reported in 1986 from Houston, TX, in a shipment of used tires from Japan. In early June 2001, infestations of this species associated with containerized oceanic shipments of "lucky bamboo" (Dracaena spp.) packaged in standing water were introduced into southern California from mainland south China. Focal points of infestation are currently at the wholesale nurseries in southern as well as northern California. A control protocol for adulticiding and larviciding has been implemented by the Greater Los Angeles County Vector Control District. Surveys are presently being conducted by local vector control agencies in southern and northern California to determine the extent of infestation. Potential forAe. albopictus establishment is discussed.