Biomedical subjects
Publications and source records attributed to C J Mitchell.
A total of 4,169 adult mosquitoes were aspirated from 3 tire disposal sites in North Carolina for virus assays. Aedes albopictus was the dominant species, with a relative abundance of approximately 99%. Potosi virus was isolated from one pool of 68 female Ae. albopictus. Priorities for future Potosi virus research and the implications of the North Carolina isolate are discussed.
The recent rapid spread of Aedes albopictus to many areas previously free of such infestations, including Albania and Italy, has heightened concern among public health and vector control officials. Ae. albopictus is a proven or potential vector of several arboviruses, including some that are, or have been, actively transmitted in southern Europe. These virus/vector relationships are reviewed with a view toward assessing the risk posed by the current presence of Ae. albopictus in the region.
BACKGROUND/AIMS: Gut translocation of enteric organisms across the intact intestinal mucosa has been postulated as a potential source of sepsis in susceptible patients. However, little is known of its occurrence or significance in humans. The aim of this study was to determine the prevalence of gut translocation of bacteria in humans and attempt to identify any predisposing factors to its occurrence. METHODS: A consecutive series of 267 general surgical patients were examined for evidence of bacterial translocation by bacterial analysis of intestinal serosa and mesenteric lymph nodes taken at the time of surgery. RESULTS: Translocation occurred in 10.3% of patients overall. Both aerobic and anaerobic bacteria translocated. Excluding patients with distal intestinal obstruction and those with inflammatory bowel disease in whom translocation was more common, the prevalence was 5%. Neither jaundice, nutritional status, nor total parenteral nutrition predisposed to translocation. Similarly, mucosal atrophy did not predispose to this phenomenon. The development of postoperative septic complications was twice as common in patients with translocation as in those without, but mortality was unaffected. CONCLUSIONS: Translocation occurs as a spontaneous event in humans, but its clinical significance remains to be defined.
The virulence of a yellow fever (YF) virus (P-16065) isolated from a fatal case of vaccine-associated viral encephalitis was investigated. P-16065 appeared identical to its parent vaccine virus (17D-204 USA, lot 6145) when examined with monoclonal antibodies except that YF wild type-specific MAb S24 recognized P-16065 but not 17D-204 USA 6145. Thus, a mutation of at least one epitope on the envelope (E) protein had occurred. Unlike 17D-204 USA 6145 and other 17D vaccine viruses, P-16065 was neuroinvasive and virulent for mice after intranasal inoculation, and neurovirulent for monkeys after intracerebral inoculation. The E protein of P-16065 differed from 17D-204 USA by two amino acids at positions 155 and 303. Changes at amino acid position 155 are found in other YF vaccine viruses that are not neurovirulent, and it is therefore postulated that the change at position 303 is involved in the alteration of the phenotype of P-16065 and may be important for virulence of YF virus.
The relationship of larval nutrition and adult body size to the susceptibility of Aedes aegypti (L.) to Ross River virus infection was examined. Large adult mosquitoes produced by feeding larvae a high-level diet consumed significantly more virus particles than did smaller mosquitoes. However, when a correction for body size was made, smaller mosquitoes were found to consume significantly more virus per unit of body weight. A host viremia of 2.4 log10 PFU/ml failed to infect mosquitoes of any size. Large Ae. aegypti mosquitoes were significantly more susceptible than small mosquitoes when fed on hosts with viremias of 4.8, 5.7, 6.4, and 7.5 log10 PFU/ml, but differences in susceptibility were less apparent at higher viremias.
We previously described a reverse transcriptase-PCR using flavivirus genus-conserved and virus species-specific amplimers (D. W. Trent and G. J. Chang, p. 355-371, in Y. Becker and C. Darai; ed., Frontiers of Virology, vol. 1, 1992). Target amplification was improved by redesigning the amplimers, and a sensitive enzyme-linked immunosorbent assay (ELISA) technique has been developed to detect amplified digoxigenin (DIG)-modified DNA. A single biotin motif and multiple DIG motifs were incorporated into each amplicon, which permitted amplicon capture by a biotin-streptavidin interaction and detection with DIG-specific antiserum in a colorimetric ELISA. We evaluated the utility of this assay for detecting St. Louis encephalitis (SLE) viral RNA in infected mosquitoes and dengue viral RNA in human serum specimens. The reverse transcriptase-PCR-ELISA was as sensitive as isolation of SLE virus by cell culture in detecting SLE viral RNA in infected mosquitoes. The test was 89% specific and 95 to 100% sensitive for identification of dengue viral RNA in serum specimens compared with isolation of virus by Aedes albopictus C6/36 cell culture and identification by the indirect immunofluorescence assay.
The vector competence of Aedes albopictus from Pine Bluff, AR, was assessed for a St. Louis encephalitis (SLE) virus strain isolated during the 1991 epidemic. Aedes albopictus were fed on hamsters with viremia levels of 10(4.6)-10(4.9) Vero cell plaque-forming units (PFU)/ml. At 7 and 15 days postbloodfeeding, transmission trials were conducted using individual suckling mice. Three of 313 Ae. albopictus were determined to be infected with SLE virus with titers of 10(6.3)-10(7.0) PFU/mosquito. At 15 days postbloodfeeding, one of 209 Ae. albopictus that refed transmitted virus resulting in a 15-day population transmission rate of 0.5%. The infection threshold (i.e., the amount of virus required to infect from 1 to 5% of mosquitoes) was determined to be approximately 10(2.3) PFU/mosquito. Virus inoculated intracoelomically into Ae. albopictus replicated and reached mean titers above 10(6.0) PFU/mosquito on day 6. The combination of low susceptibility to infection and a mammalophilic bloodfeeding pattern suggests that Ae. albopictus is unlikely to play a significant role in SLE transmission.
An improved method for the extraction of viral RNAs was developed to facilitate the reverse transcription (RT)-PCR detection of mosquitoes infected with Western equine encephalitis virus or La Crosse virus. The solubilization method, which uses only EDTA and sodium dodecyl sulfate (SDS) followed by dilution of sample, allows accurate viral detection through the use of random hexamers for the RT followed by specific primers for the PCR. Identities of the reaction products were confirmed either by sequencing or restriction endonuclease digestion. Previous methods for the extraction of RNA for the coupled RT-PCR depended on combinations of guanidinium isothiocyanate, acid phenol, detergents and multiple centrifugations. Ideally, routine detection of viral RNAs for diagnostic purposes should bypass many of the above steps, while still providing a sensitive assay. Our level of detection is 1 infected mosquito in a group of 100.
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51 consecutive gastroenterological patients who required total parenteral nutrition (TPN) were entered into this study. Two patients were withdrawn because of specific nutritional requirements, leaving 49 patients for randomisation. 23 patients were allocated to receive peripheral parenteral nutrition (PPN) and 26 to receive feeding through a central venous line (CPN). There was no significant difference between the groups with respect to the median duration of feeding (9.4 +/- 3.6 days; 12.0 +/- 7.8 days) but significant morbidity occurred more frequently in the CPN group (11%) compared to the PPN group (0%). TPN by the designated route was not possible in 4 patients in the PPN group and in 3 of the CPN group. Of the 19 patients commenced on PPN, 13 continued without complication until resumption of oral feeding (median 10.7 +/- 3.2 days); 6 of these patients had to be converted to central venous feeding for completion of their nutritional requirements. Of the 23 patients commenced on CPN, 21 completed their nutritional course (median 11.8 +/- 5.3 days), 2 patients in the CPN group required conversion to PPN to complete their nutritional course. This study shows that PPN is a feasible, safe alternative to CPN in many patients. It is not necessary to subject all patients who require TPN to the risks and expense of central venous cannulation.
Aedes albopictus (Skuse) mosquitoes were fed on snowy egrets, Egretta thula (Thayer and Bangs), that had been infected by subcutaneous inoculation of eastern equine encephalitis (EEE) virus. Freshly fed mosquitoes were frozen and tested to determine how much virus they had ingested. Other fed mosquitoes from the same lots were incubated for 7 d at 27 degrees C before testing. Seven lots of Ae. albopictus fed on viremic birds. Based on average amounts of virus ingested and day 7 virus infection rates in mosquitoes from the same lots, the amount of virus required to infect 50% of the mosquitoes was calculated to be 10(2.8) Vero cell plaque-forming units (PFU). The infection threshold (i.e., the amount of virus required to infect from 1 to 5% of mosquitoes) was determined to be < or = 10 PFU per blood meal. These parameters indicate that Ae. albopictus is sufficiently susceptible to infection with EEE virus to enable it to acquire infectious doses from a wide variety of viremic birds and possibly from equines.
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.
The Signal blood culture system was compared with the Bactec NR-660. A total of 1617 blood culture sets yielded 143 (8.8%) significant isolates; 113 (79.0%) were from positive bottles in both the Bactec and Signal systems. Twelve organisms (8.4%) were detected and isolated from the Signal system only and another 18 (12.6%) from the Bactec system only. Of these 18, five were Signal-positive but the organism was not recovered and four organisms were isolated from negative Signal bottles on terminal subculture. The time taken to detection for each system was similar; the Signal system detected 68% and the Bactec 63% of significant positives within 24 h. At 48 h Bactec detected 91% and the Signal 85%. A significantly-reduced number of bottles which gave a positive signal but were negative by microscopical and cultural methods was found, compared with previous reports. The 1 h incubation period prior to the insertion of the Signal growth indicator device was considered to be the cause of this reduction in the proportion of false positives. Fifty-five percent (42/77) of the Bactec false positives were due to delta growth value. This is when there is an increase in the growth index of > or = 15 without the positive threshold level of 30 being attained. This occurred in the anaerobic bottle on day 2 with 42 bottles. Another 40% (31/77) of the false positives had a growth value between the positive threshold of 30 and a value of 35. Eighty (4.9%) of Bactec and 65 (4.0%) of Signal sets yielded clinically non-significant isolates.(ABSTRACT TRUNCATED AT 250 WORDS)
AIMS: To evaluate the Questor automated bacteriuria and pyuria screening system; to compare its performance with that of a reference method; and to assess its usefulness in a routine clinical laboratory. METHODS: The Questor urine screening system was compared with a comprehensive regimen to detect urinary tract infection, using pour-plate viable counts to determine the numbers of bacteria present in urine samples, a wide range of other cultural methods, microscopic findings and clinical information. RESULTS: The optimal performance in detecting significant growths was a sensitivity of 93%, a specificity of 74%, a positive predictive value of 43% and a negative predictive value of 98%. The list price per test is 0.17 pounds and the capital cost of the system is 39,950 pounds. Questor can test 50 samples an hour and can be operated by one member of the laboratory staff, who is not required to make interpretative judgments--for example, a medical laboratory assistant. CONCLUSIONS: The sensitivity and specificity of the Questor was better than that obtained from other screening systems using the same protocol. The system was easy to use and is a useful addition to the methods available for screening for bacteriuria.
An outbreak of Japanese encephalitis (JE) occurred on Saipan, Commonwealth of Northern Mariana Islands, in October 1990. Adult and larval mosquitoes were collected during September-October 1991 to retrospectively determine the probable mosquito vector(s). Virus was not isolated from 119 mosquito pools composed of 7,250 adult specimens as follows: Aedes vexans nocturnis (14%), Culex tritaeniorhynchus (39%), Cx. sitiens group (11%), Culex (Culex) species (35%), and < 1% each of Ae. albopictus, Ae. oakleyi, Aedes saipanensis, Cx. annulirostris marianae, and Cx. fuscanus. Three additional species were collected only as larvae: Anopheles indefinitus, Ae. neopandani, and Cx. quinquefasciatus. Among the vectors of JE incriminated in other areas, Cx. tritaeniorhynchus was the predominant species in our collections and the principal species feeding on swine. This is the first published record of the occurrence of this species on Saipan. Culex tritaeniorhynchus is abundant and widely distributed on the southern half of Saipan where human JE cases occurred in 1990, and where swine seroconversions were detected. Although the identity of the mosquito vector(s) responsible for the 1990 outbreak cannot be established with certainty, our results suggest that Cx. tritaeniorhychus was probably involved.
An epidemic of St. Louis encephalitis (SLE) occurred in Jefferson County, Arkansas during July-August 1991. At least 26 human cases were involved, with 25 cases in the town of Pine Bluff. Twelve isolates of SLE virus were obtained from mosquitoes collected in Pine Bluff between August 13 and 24: 11 from pools of Culex pipiens quinquefasciatus, resulting in a minimum infection rate of 1.6 per 1,000 (n = 6,768) for this subspecies, and one isolate from a pool of 22 mosquitoes identified as Cx. (Culex) spp. Three of the SLE-positive pools, two from Cx. p. quinquefasciatus and one from Cx. (Cux.) spp., also yielded isolates of Flanders virus. Larval surveys resulted in the collection of seven species in four genera from 28 larva-positive habitats and the identification of one significant site of Cx. p. quinquefasciatus production. Ecologic assessments conducted at 12 randomly selected residences resulted in the identification of 17 larva-positive habitats, for an average mosquito-positive habitat rate of 1.4 per residence, and a Cx. p. quinquefasciatus larva-positive habitat rate of 0.6 per residence. Aedes albopictus and Cx. p. quinquefasciatus were the species most frequently encountered in larval surveys in residential neighborhoods.
During 1990 and 1991, adult mosquitoes were collected along the Ob River and its tributaries in western Siberia from approximately 51 degrees 18'N to 66 degrees 4'N. Fifteen virus strains were isolated from 74,196 mosquitoes tested in 1,874 pools. These included Tahyna virus from Aedes cataphylla-punctor subgroup (one) and Ae. excrucians (one), and Inkoo (INK) virus from Ae. communis (one), Ae. communis subgroup (one), Ae. hexodontus (two), Ae. punctor subgroup (two), Ae. punctor complex (one), and unidentified Aedes species (three). In addition, a single Ae. euedes yielded a strain of snowshoe hare (SSH) virus and a strain of Getah, an alphavirus. A Bunyamwera serogroup virus was isolated from Ae. excrucians. With the exception of the two isolates from a single mosquito, minimum infection rates among mosquito taxa ranged from 0.4 to 16.7 per 1,000. The INK virus isolates were widely distributed geographically; however, seven of the 10 isolates were from two sites north of the Arctic Circle. During 1991, sera from two mouse species, five vole species, and four shrew species were collected along the upper Ob River for serologic tests. The prevalence of neutralizing antibody to SSH virus in these sera was 80%. Prevalence rates in the four most abundant species were Apodemus agrarius, 73%; Clethrionomys rutilus, 71%; Microtus arvalis, 80%; and Sorex araneus, 91%. This is the first attempt to clarify the vector and vertebrate host relationships of California serogroup viruses in western Siberia.
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.