Lethal effect of Rickettsia rickettsii on its tick vector (Dermacentor andersoni).

Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever, was lethal for the majority of experimentally and transovarially infected Rocky Mountain wood ticks (Dermacentor andersoni). Overall, 94.1% of nymphs infected as larvae by feeding on rickettsemic guinea pigs died during the molt into adults and 88. 3% of adult female ticks infected as nymphs died prior to feeding. In contrast, only 2.8% of uninfected larvae failed to develop into adults over two generations. Infected female ticks incubated at 4 degreesC had a lower mortality (80.9%) than did those held at 21 degreesC (96.8%). Rickettsiae were vertically transmitted to 39.0% of offspring, and significantly fewer larvae developed from infected ticks. The lethal effect of R. rickettsii may explain the low prevalence of infected ticks in nature and affect its enzootic maintenance.

Characterization of an endosymbiont infecting wood ticks, Dermacentor andersoni, as a member of the genus Francisella.

A microorganism (Dermacantor andersoni symbiont [DAS]) infecting Rocky Mountain wood ticks (D. andersoni) collected in the Bitterroot Mountains of western Montana was characterized as an endosymbiont belonging to the genus Francisella. Previously described as Wolbachia like, the organism's DNA was amplified from both naturally infected tick ovarial tissues and Vero cell cultures by PCR assay with primer sets derived from eubacterial 16S ribosomal DNA (rDNA) and Francisella membrane protein genes. The 16S rDNA gene sequence of the DAS was most similar (95.4%) to that of Francisella tularensis subsp. tularensis. Through a combination of Giménez staining, PCR assay, and restriction fragment length polymorphism analysis, 102 of 108 female ticks collected from 1992 to 1996 were infected. Transovarial transmission to female progeny was 95.6%, but we found no evidence of horizontal transmission.

Rickettsia peacockii sp. nov., a new species infecting wood ticks, Dermacentor andersoni, in western Montana.

Rickettsia peacockii, a new species of spotted fever group rickettsiae, was identified from Rocky Mountain wood ticks (Dermacentor andersoni) collected in the Sapphire Mountain Range on the eastern side of Bitterroot Valley, Montana. DNA from R. peacockii SkalkahoT (T = type strain) in naturally infected tick tissue was amplified by a PCR assay with primer sets derived from eubacterial 16S ribosomal DNA (rDNA), rickettsial citrate synthase, and 190-kDa surface antigen (rOmpA) genes. Partial 16S rDNA and rOmpA gene sequences exhibited levels of similarity of 99.7 and 93.2%, respectively, with the sequences of the spotted fever agent Rickettsia rickettsii R. By using Gimenez staining, fluorescent antibody tests, a PCR assay, and a restriction fragment length polymorphism analysis, 76 of 115 female ticks (minimal field infection rate, 66.1%) collected between 1992 and 1995 were found to be infected. The organism is passed transstadially and transovarially (minimal vertical transmission rate, 73.3%), and infections are localized in ovarial tissues. Attempts to cultivate R. peacockii were unsuccessful.

Dispersal and survival of Aedes albopictus at a scrap tire yard in Missouri.

Field-reared Aedes albopictus were marked with fluorescent pigment upon release and recaptured with a vacuum aspirator at a scrap tire yard and in surrounding vegetation in Potosi, MO, during 1989-90. In 8 dispersal trials, 8.1% (1,100/13,513) of the Ae. albopictus were recaptured with 84.4% (928/1,100) collected in the forest edge ecotone between 10 and 600 m from the release point. The maximum dispersal distance recorded was 525 m and 11.1% (122/1,100) dispersed further than 100 m. In 3 survival trials, 4.8% (2,660/55,284) of the mosquitoes were recaptured. Adult Ae. albopictus females survived an average of 8.2 days (probability of daily survival [PDS] = 0.89, range = 0-24) and males an average of 3.9 days (PDS = 0.77, range = 0-12). The dispersal and survival capacity of Ae. albopictus adults may contribute to the spread and potential health threat of this mosquito in the USA.

Blood hosts of Aedes albopictus in the United States.

Bloodfed Aedes albopictus were collected during 1989-91 by vacuum aspirator from rural and urban study sites in Missouri, Florida, Indiana, Illinois, and Louisiana. Blood hosts identified by ELISA and precipitin tests were rabbit (n = 91), Rattus sp. (n = 69), dog (n = 14), unidentified mammal (n = 14), cow (n = 13), human (n = 10), deer (n = 10), sciurid (n = 7), turtle (n = 5), murid other than Rattus sp. (n = 4), raccoon (n = 3), passeriform bird (n = 3), and cat (n = 2). As an opportunistic bloodfeeder, Ae. albopictus may be a potential vector of domestic arboviruses and a nuisance pest where infestations occur.

Host-feeding patterns of Aedes albopictus (Diptera: Culicidae) at a temperate North American site.

Precipitin tests and ELISA were used to investigate host-feeding patterns of 172 blood-fed Aedes albopictus (Skuse) collected at Potosi, MO, during the summers of 1989 and 1990. One hundred ten (64.0%) mosquitoes had fed on mammals, 29 (16.9%) on birds, and none on turtles or snakes. Thirty-three (19.2%) mosquitoes failed to react in all tests. Eighty-six (78.2%) of the 110 mammalian feeds were positive for lower taxa as follows: rabbit, 24.5%; deer, 14.5%; dog, 13.6%; human, 8.2%; squirrel, 7.3%; opossum, 4.5%; myomorph rodents other than Rattus, 3.6%; raccoon, 0.9%; and bovine, 0.9%. Positive feeds were not detected for the following mammals: cat (n = 99); horse (n = 95); Rattus (n = 84); and swine (n = 84). Fourteen (48.3%) of the 29 avian feeds were positive for lower taxa as follows: Passeriformes, 24.1%; Columbiformes, 17.2%; Ciconiiformes, 3.4%; and quail, 3.4%. These data, the first on host-feeding patterns for Ae. albopictus populations in the New World, indicate that Ae. albopictus is an opportunistic feeder that utilizes a wide variety of hosts and, therefore, has the potential to become involved in the transmission cycles of indigenous arboviruses.

Isolation of eastern equine encephalitis virus from Aedes albopictus in Florida.

Fourteen strains of eastern equine encephalitis (EEE) virus were isolated from Aedes albopictus mosquitoes collected in Polk County, Florida. These are the first isolations of an arbovirus of proven public health and veterinary importance from naturally infected Ae. albopictus in the United States since established populations of this introduced mosquito were first discovered in 1985. The widespread distribution of Ae. albopictus in Florida and in other areas of the United States where EEE is endemic raises concern that this species may become an epizootic and epidemic vector of EEE virus.

Blood-feeding of Culex mosquitoes in an urban environment.

The modified capillary tube precipitin test was used to identify blood meal sources of Culex quinquefasciatus emerging from sewage ditches in East Baton Rouge Parish, Louisiana. Canines were the primary hosts, but Passeriformes and humans were also suitable blood meal sources. The percentage of Cx. quinquefasciatus feeding on these 3 hosts fluctuated with the habitat and the season.

Transmission of a newly recognized virus (Bunyaviridae, Bunyavirus) isolated from Aedes albopictus (Diptera: Culicidae) in Potosi, Missouri.

Aedes albopictus (Skuse) mosquitoes collected in Potosi, Mo., were tested for their ability to transmit a newly recognized Bunyamwera sero group virus isolated from the same mosquito population. Mosquitoes were fed artificial blood meals containing 4.5-6.2 log10 TCID50 of virus per ml. After 7-29 d at 25 degrees C, 79-99% of the mosquitoes had disseminated infections and 0-26% transmitted virus to fluid-filled capillary tubes. Transmission was first observed after 7 d of extrinsic incubation. Tests failed to detect transovarial transmission in 5,145 progeny from ovarian cycles 2-4. Following parenteral inoculation with 5.3-6.0 log10 TCID50 of virus, four of nine adult hamsters developed viremia. Ten of 16 suckling mice died following intracerebral inoculation of 5.0 log10 TCID50 of virus (fifth Vero cell passage); the average survival time was 8.8 d (SD, 3.5). No mortality occurred in 10 suckling mice inoculated with 3.6 log10 TCID50 of virus (second Vero cell passage).

A new arbovirus from Aedes albopictus, an Asian mosquito established in the United States.

Ten strains of a new arbovirus belonging to the Bunyamwera group (Bunyaviridae) were recovered from field-collected Aedes albopictus mosquitoes in Potosi, Missouri. This evidence indicates that this species may serve as an arbovirus vector in the United States. The urban-suburban distribution, aggressive biting behavior, and broad viral susceptibility of Ae. albopictus may lead to the transmission of viruses of known public health importance and perhaps of viruses hitherto not transmitted to humans because of the feeding pattern of their usual vectors.

A self-marking device for emergent adult mosquitoes.

A portable, tent-like device with powdered fluorescent pigment for marking emergent adult mosquitoes was evaluated in the field using Culex quinquefasciatus adults. The top of the device was equipped with cheesecloth partitions impregnated with the pigment. Eighty-six percent of the emergent adults passed through the partitions, and all were marked.