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Biomedical subjects

C J Mitchell

Publications and source records attributed to C J Mitchell.

At least 73 records · Page 4Linked to original sources
PubMed1992

Transmission of western equine encephalomyelitis virus by Argentine Aedes albifasciatus (Diptera: Culicidae).

Aedes albifasciatus (Macquart) has been considered a potential vector of western equine encephalitis (WEE) virus in Argentina because it has been found naturally infected, it is susceptible to infection per os, and its distribution and feeding habits are compatible with those of an epizootic and epidemic vector. Ae. albifasciatus females collected in the vicinity of Cordoba, Argentina, were highly susceptible to WEE virus perorally (ID50 less than 0.5 Vero cell plaque-forming units) when fed on viremic chicks. Virus transmission trials were done 9 to 16 d after infection by feeding potentially infected mosquitoes individually on chicks. Among 31 mosquitoes that survived the incubation period, six refed on susceptible chicks. Virus transmission by bite was demonstrated by five of six (83%) mosquitoes. Therefore, the final piece of evidence incriminating Ae. albifasciatus as a natural vector of WEE virus has been obtained. This is the first mosquito species to be incriminated as a vector of WEE virus in South America.

Aedes↗
PubMed1992

Comparison of Sentinel and Bactec blood culture systems.

AIMS: To evaluate the Sentinel automated blood culture system and to compare its performance with that of Bactec. METHODS: The Sentinel blood culture system was evaluated in three centres. The performance of the system was assessed in comparison with the routine blood culture method used in these centres, the Bactec system. RESULTS: Blood culture sets (n = 2180) consisting of Sentinel aerobic and anaerobic, and Bactec aerobic and anaerobic bottles yielded 218 (10%) clinically important isolates. One hundred and fifty five (71%) of the isolates were detected by both systems; 35 (16%) were detected by Sentinel only; and 28 (13%) by Bactec only. For the duration of the evaluation, the Sentinel system was deliberately configured so that it was impossible to detect positive results during the first 12 hours. The times to positivity after the first 12 hours were similar. Data gathered during and subsequent to the evaluation have been used by the manufacturer to refine the algorithm so that positive results can be detected at a minimum of 2.25 hours. CONCLUSIONS: After a period of familiarization the Sentinel system was considered easy to use. Sentinel is a useful addition to the methods available for the detection of bacteria in blood cultures.

Bacteriological Techniques↗
PubMed1992

Determination of whether tomato spotted wilt virus replicates in Toxorhynchites amboinensis mosquitoes and the relatedness of this virus to phleboviruses (family Bunyaviridae).

Tomato spotted wilt virus (TSWV) has been reported to be morphologically, molecularly and structurally similar to viruses in the family Bunyaviridae. By various types of enzyme-linked immunosorbent assays (ELISA) and Western blot hybridizations, we tested TSWV with antibodies to 12 viruses in the Phlebovirus genus of this family. Serological relatedness was not found between TSWV and phleboviruses. However, one preparation of antibody to Arumowot virus reacted with a 53-kD protein from healthy plant extracts. Six-day-old adult Toxorhynchites amboinensis mosquitoes were inoculated with purified TSWV. Infectious virus was not detected in any of the injected insects during the 5-week test period. However, TSWV antigens were detected in these mosquitoes by ELISA at the original injected level for at least a week after injection. TSWV antigen concentration began to decrease thereafter, but remained at detectable levels for as long as 5 weeks after injection. However, there was no evidence that TSWV replicated in mosquitoes.

Animals↗
PubMed1992

Detection of St. Louis encephalitis virus in mosquitoes by use of the polymerase chain reaction.

We recently developed an assay using the polymerase chain reaction (PCR) for the specific detection of St. Louis encephalitis (SLE) virus RNA. This assay was tested in a blind study on 7 samples of pooled mosquitoes (50 mosquitoes/pool) which were also characterized for SLE virus by plaque assay in Vero cell culture. One sample was positive for the SLE virus as determined by both the PCR assay and a combination of the plaque assay and the indirect fluorescent antibody assay. The remaining 6 samples were negative for the presence of SLE virus as determined by both methods. These data indicate that this PCR assay can be used to monitor for the presence of SLE virus in pools of homogenized mosquitoes. This approach could provide early data on which to base disease control decisions.

Animals↗
PubMed1991

A prospective and randomised study comparing the incidence of infusion phlebitis during continuous and cyclic peripheral parenteral nutrition.

Phlebitis is a major obstacle to successful and prolonged peripheral parenteral nutrition (PPN). This study evaluated the effects of elective changes of the intravenous cannula and cyclic infusion of PPN on the incidence and the severity of phlebitis. 51 consecutive patients requiring PPN were randomised into three groups. Group 1 received PPN continuously through a line which was changed only on evidence of phlebitis. In Group 2 intravenous lines were changed every 24h. Group 3 patients received PPN as a 12-h infusion after which the intravenous cannula was withdrawn. All patients received 1800 non-protein calories and 9.4g nitrogen daily. Infusion sites were assessed daily for phlebitis and this was scored using a modified Maddox scale. The mean (range) duration of PPN was 7.5 (1-13), 10.0 (2-42) and 8.2 (3-14) days in the three groups respectively. Severe phlebitis occurred more frequently (p < 0.05) in Group 1 compared to Group 2 or Group 3. The overall incidence of phlebitis assessed from the mean value of the Maddox scores for each group was highest in Group 1 and was significantly greater than that observed in either Group 2 (p < 0.05) or Group 3 (p < 0.001). Group 3 patients who received cyclic PPN had the lowest incidence of phlebitis. The results of this study suggest that the incidence of infusion phlebitis is minimised during PPN by the cyclic infusion of nutrient solutions.

Journal Article↗
PubMed1991

Genetic selection of a flavivirus-refractory strain of the yellow fever mosquito Aedes aegypti.

Two inbred (isofemale) Aedes aegypti mosquito lines were derived that manifested a resistant or susceptible phenotype following ingestion of yellow fever virus; lack of virus movement from the midgut defined the resistant phenotype. Other flaviviruses, including dengue 1-4, Uganda S, and Zika, viruses behaved in a similar fashion in the two mosquito lines. Crosses between the two lines produced progeny that were of intermediate susceptibility, indicating codominance; F2 backcrosses to the parents yielded results consistent with a major controlling genetic locus and provide evidence of a second locus capable of modulating the phenotype of the major gene. The rapid selection necessary to fix the susceptible and refractory phenotypes support the hypothesis of a single major controlling locus. Viral movement across the midgut is likely to be governed by a single major gene and modifying minor genes or a group of closely linked genes. These inbred mosquito lines will be useful in discovering the molecular basis for flavivirus resistance in Ae. aegypti.

Aedes↗
PubMed1991

Vector competence of North and South American strains of Aedes albopictus for certain arboviruses: a review.

Since the introduction of Aedes albopictus into North and South America, 18 viruses in 3 families have been used in vector competence studies involving 10 North American and 4 South American geographic strains of Ae. albopictus. This review summarizes the results of these studies and discusses the potential of Ae. albopictus to become a vector of arboviruses of public health importance in areas of the Western Hemisphere where it has recently become established.

Aedes↗
PubMed1991

Localized eastern equine encephalitis in Santiago del Estero Province, Argentina, without human infection.

In 1981, a localized epizootic of Eastern Equine Encephalitis (EEE) occurred in irrigated areas of four counties in the province of Santiago del Estero, Argentina. The diagnosis was confirmed by serology, and there was no evidence of involvement of Western or Venezuelan equine encephalitis viruses. The overall incidence of equine encephalitis was estimated 17%, the case-fatality rate at 61% and the inapparent: apparent infection ratio less than or equal to 2.9:1. This is the first localized epizootic defined in Argentina and the first in which EEE has been found as the sole etiologic arbovirus. This posed the possibility to look for human infection in the area. In spite of a careful surveillance, no evidence of human disease or infection was found, differing from the situation in USA where EEE virus is a public health problem. Nevertheless vector/s and vertebrate hosts involved in the transmission cycle in Argentina remain unknown, precluding at present speculations on the potential human risk.

Animals↗
PubMed1991

Detection of Staphylococcus aureus in blood cultures: evaluation of a two-hour method.

Aurease--one of three tests on the RAPIDEC staph system for two-hour identification of the main clinically important staphylococci--was used for the direct detection of Staphylococcus aureus from 102 blood culture broths in which Gram-positive cocci were seen. A pellet of centrifuged blood culture broth was used as the inoculum. The method was compared with the thermonuclease test and subsequent isolates subjected to probabilistic identification based on biochemical reactions. A positive aurease test and the presence of thermonuclease were detected in 27 samples, subsequent identification showing all to be Staph. aureus. A further Staph. aureus strain was aurease negative but thermonuclease positive. None of the remaining 74 specimens was positive by the aurease test, which is rapid, sensitive and specific for detection of Staph. aureus in blood culture broths.

Bacteriological Techniques↗
PubMed1990

Diagnosis of abdominal masses with percutaneous biopsy guided by ultrasound.

OBJECTIVE: To assess the accuracy and safety of percutaneous biopsy of abdominal masses guided by ultrasound. DESIGN: Prospective study. SETTING: Combined gastroenterology service, Scarborough Hospital. PATIENTS: 108 Consecutive patients identified as having a discrete mass on diagnostic ultrasound examination of the abdomen. INTERVENTION: A sample of tissue was obtained with an aseptic technique under local anaesthesia: an 18 steel wire gauge needle (Tru-Cut) was mounted in a spring loaded firing device (Biopty gun) that was advanced under simultaneous ultrasound scanning, permitting precise localisation of the target organ. MAIN OUTCOME MEASURE: Results of histological examination of tissue specimens. RESULTS: Biopsy failed in four patients. Adequate histological specimens were obtained in 104 patients with masses in the liver (31), pancreas (37), kidney (10), and adrenal glands (six) and in 20 undiagnosed abdominal and retroperitoneal masses. Follow up was until death or confirmation of the diagnosis. Three complications but no deaths occurred. Malignancy was suspected in 84 patients before biopsy. This was confirmed in 70 patients, in 26 of whom confirmation of dissemination obviated the need for further investigation. In 10 patients biopsy indicated a previously unsuspected primary tumour, and in 12 it showed only a benign lesion. Among 24 patients considered to have benign disease biopsy showed an unsuspected neoplasm in seven. Use of biopsy thus had a major effect on clinical management in 55 patients. Four false negative but no false positive diagnoses resulted from the procedure. CONCLUSION: Percutaneous biopsy of abdominal and retroperitoneal masses under ultrasound guidance is a safe and accurate method of obtaining a histological diagnosis. The results obtained have a considerable effect on clinical management.

Abdominal Neoplasms↗
PubMed1990

Peroral susceptibility of Aedes albifasciatus and Culex pipiens complex mosquitoes (Diptera: Culicidae) from Argentina to western equine encephalitis virus.

The transmission cycle of western equine encephalitis (WEE) virus in South America is unknown. A WEE virus strain was isolated from Aedes albifasciatus in Argentina during the WEE epizootic of 1982-83. Also, Culex pipiens from Argentina was reported to be able to transmit WEE virus experimentally, but other results indicate that Cx. pipiens from the USA is refractory to this virus. We determined the susceptibility of Argentina strains of Ae. albifasciatus and Culex pipiens complex mosquitos to infection by WEE virus by the oral route. Adult females were fed on chicks infected with a WEE virus strain isolated in Cordoba Province, Argentina, or were fed on a blood/virus suspension. Each mosquito ingested between 10(1.6) to 10(6.4) vero cell plaque-forming units of virus. Each of 28 Ae. albifasciatus was positive for virus from the fourth day postfeeding, and there was evidence for virus replication. In contrast, 0/44 Cx. p. quinquefasciatus and only 1/15 Cx. p. pipiens was positive. Aedes albifasciatus is susceptible to infection by WEE virus and should be considered a potential vector of this virus in Argentina. Both subspecies of Cx. pipiens are refractory to peroral infection by WEE virus and probably do not play a role in the WEE virus cycle in Argentina.

Aedes↗
PubMed1990

Vector competence of Aedes albopictus for a newly recognized Bunyavirus from mosquitoes collected in Potosi, Missouri.

The vector competence of a Kentucky strain of Aedes albopictus was assessed for a newly recognized Bunyavirus isolated from Ae. albopictus collected in Potosi, Missouri. Females are susceptible to peroral infection and 44.7% became infected after ingesting about 15 Vero cell plaque-forming units (PFU) of virus. Virus replicated and reached average titers of 10(5.4)-10(6.0) PFU/mosquito by day 7 postfeeding. Fourteen (40%) of 35 females tested in an in vitro virus transmission experiment were infected, and 3 (21.4%) of the infected females transmitted virus. There was no evidence of vertical transmission among 1,196 progeny of a group of mothers exposed to infection perorally or among 6,635 progeny of mothers infected by parenteral inoculation. The absence or infrequency of vertical transmission suggests that the virus was not introduced into Missouri via infected Ae. albopictus eggs. Nonetheless, Ae. albopictus is a competent vector of this virus and we provide the first experimental evidence for incriminating Ae. albopictus as a vector in a natural arbovirus transmission cycle in the United States.

Aedes↗
PubMed1990

Vertical transmission of dengue viruses by strains of Aedes albopictus recently introduced into Brazil.

Three strains of Aedes albopictus from Brazil were examined for their ability to vertically transmit dengue 1 (DEN-1) and dengue 4 (DEN-4) viruses. Parental females were uniformly infected by parenteral inoculation of virus, and 8,121 F1 progeny from DEN-1 and DEN-4 infected mothers were pooled in lots of approximately 50 and tested for virus. Seven of 60 pools were positive for DEN-1 virus, and 1 of 121 pools was positive for DEN-4 virus. In DEN-1 assays, the minimum infection rate (MIR) for larvae (2 pools tested) was 1:84. Among positive cohorts of adults, pooled by sex and by geographic strain of mosquito, the MIR ranged from 1:193 to 1:626 for males and from 1:187 to 1:311 for females. Only a single pool of adult females was positive for DEN-4 virus (MIR 1:1022 for an adult female cohort from Santa Teresa). These results indicate that Brazilian Ae. albopictus have the potential to play a role in the maintenance of dengue viruses in nature.

Aedes↗