Biomedical subjects

M L Wilson

Publications and source records attributed to M L Wilson.

At least 91 records · Page 5Linked to original sources

PubMed1994

Rift Valley fever in rural northern Senegal: human risk factors and potential vectors.

To investigate past infection in and transmission of Rift Valley fever (RVF) virus to humans within an endemic focus, we undertook a retrospective cohort study of the seminomadic Peul people living in sub-Saharan northcentral Senegal. Residents of the rural settlement of Yonofere five years of age or older were studied during February-May 1989. Anti-RVF virus IgG was found in blood samples of 22.3% of 273 persons who responded to a standard questionnaire; none had IgM antibodies. Seropositivity was similar for males (25.4%) and females (21.1%), increased markedly with age for both sexes, and varied considerably among compounds (groups of huts) (0-37.5%). Risk factors for past RVF virus infection were nursing sick people, assisting animals during abortions/births, and treating sick animals. In all age groups, odds ratios (ORs) for RVF viral antibody among females who reported treating sick animals were three to six times greater than for those who did not. The ORs for males who reported assisting with animal births/abortions and nursing sick people were approximately five times those for males who did not. Serologic prevalence of RVF viral antibody among sheep averaged 30.1% overall (0.8% IgM), but varied among compounds (0-66.7%) in a manner different from that of humans. The seasonal abundance and relative density of potential mosquito vectors were estimated by monthly samples captured in Centers for Disease Control and Prevention-type traps. Mosquito abundance varied seasonally with rainfall (> 90% captures during four months). Species diversity was large (28 spp.), dominated by Aedes and Culex. Rift Valley fever virus was not isolated from 142 pools of 2,956 unengorged mosquitoes tested, although three other arboviruses were found. Results indicate that RVF is endemic in this region, people are at considerable risk of infection, and that a heretofore unrecognized mode of human infection under nonepizootic conditions may be transmission via contact with infected animals or humans.

Adolescent↗

PubMed1994

[Crimean-Congo hemorrhagic fever in Senegal. Latest data on the ecology of the CCHF virus].

The authors finalize the knowledge on the ecology of the CCHF virus in Senegal, West Africa. They specify two new major data for the understanding of the viral ecology in West Africa. The recognition of a bird species, common and widely distributed in Senegal (Tockus erythrorhynchus, Coraciiformes, Bucerotidae), that replicates the virus and infects the immature stages of its current parasite Hyalomma marginatum rufipes in more than 90% of the cases, explains why the minimum infection rate of the adults of this species of tick is always very high. The implication of Rhipicephalus evertsi evertsi in the viral ecology and/or a high efficiency of the transovarial transmission of the virus in Hy. m. rufipes would help to explain the maintenance of the endemy in the sahelian area. In the sahelian zone, Hy. marginatum rufipes must play the leading part, together with Rh. e. evertsi if vector, for the maintenance of the endemy. Hy. truncatum, the adults of which can readily bite man, ensures the vectorial transmission to him. In the sudanian zone, Amblyomma variegatum must play the same part as the Hyalomma and Rh. e. evertsi (if vector), and is surely the main vector to man, giving perhaps rise to less virulent strains (non hemorrhagic ones).

Animals↗

PubMed1994

Blood cultures. Introduction.

Clinical microbiologists must be able to evaluate critically the blood culture literature for patient care purposes, for sound laboratory management, and for decision making in regards to purchase or lease of a new system. This skill has never been more important due to the many new commercially available blood culture products and technologies. Critical assessment of the literature requires familiarity with blood culture terminology and an understanding of those factors critical in designing scientifically valid clinical evaluations.

Bacteremia↗

PubMed1994

Recovery of select rare and fastidious microorganisms from blood cultures.

Most, if not all, rare or fastidious microbial pathogens can be recovered from standard blood culture bottles and media using routine laboratory methods. Because they are only rarely recovered from blood cultures, relatively few data exist concerning the ability of different blood culture systems to recover these microorganisms. Thus, clinical microbiologists should take a conservative approach when processing blood cultures that may contain one of the microorganisms reviewed in this article, including the use of additional media, media supplements, blind and terminal subcultures, or prolonged incubation and testing.

Bacteremia↗

PubMed1994

Automated blood culture systems.

For the first time, clinical microbiologists have the option of purchasing or leasing a variety of automated blood culture systems. Although the performance characteristics of the BACTEC radiometric and nonradiometric blood culture systems are well-documented, we are only beginning to learn the performance characteristics of CMBCS. Well-designed and executed controlled clinical trials are needed to establish performance characteristics and to address issues that are unique to CMBCS. In particular, controlled clinical comparisons of different CMBCS are needed. In terms of the impact on clinical microbiology laboratories, there are no published data to support claims that the use of these systems decreases laboratory workload, staffing, or costs. Although such an impact seems reasonable and even likely, unequivocal documentation of such savings would make it easier for many laboratorians to justify the cost of purchasing or leasing one of these systems. Similarly, there are no published data regarding the long-term reliability of these systems while in clinical use. A documented track record of mechanical and electrical reliability would be useful to clinical microbiologists contemplating the acquisition of a new blood culture system.

Autoanalysis↗

PubMed1994

Rapid detection and identification of microorganisms from blood cultures.

In an era characterized by increasing emphasis on minimizing laboratory costs, reliable and cost-effective methods for rapidly identifying bacteria and fungi directly from blood cultures have a great deal of appeal to clinical microbiologists. A variety of methods have been evaluated and found to be useful under certain conditions, although none of the methods has been standardized and questions remain as to whether their use improves patient care or reduces hospital costs. Even if these methods do not improve patient care or reduce hospital costs, their use and expense could be justified if they improve laboratory work flow or decrease laboratory costs or both. Several issues remain unresolved, one of which is whether the use of rapid identification methods with a continuous-monitoring blood culture system might allow for a clinically important decrease in the time required to identify blood culture isolates. Another issue is whether subsequent isolation by culture is necessary for microorganisms with predictable antimicrobial susceptibility patterns. These and other issues need to be studied further before the exact clinical usefulness of rapid methods will be known. At this time, no commercial product has been cleared or approved by the Food and Drug Administration (FDA) for the direct detection or identification of both of pathogenic microorganisms from blood culture bottles (Sharon Hansen, PhD, personal communication, 1993). Consequently, laboratory directors should exercise caution in the use of commercial or other products for direct blood culture testing, because manufacturers assume no liability for products that are used for purposes other than that for which they have been approved. In addition, such use of commercial products may be in violation of the rules set forth in the Clinical Laboratory Improvement Act of 1988. Furthermore, as discussed previously, the clinical performance characteristics of many products typically have not been determined, and, therefore, test reference ranges, sensitivity, specificity, and positive and negative predictive values have not been established. Other issues, such as the effect of different blood culture media and additives, also have not been studied adequately, nor are specific controls defined. Therefore, laboratory staff who would like to use commercial products to test blood cultures directly must themselves establish the performance characteristics of the product (keeping in mind the issue of liability) or, preferably, persuade manufacturers to sponsor large-scale controlled clinical trials both to establish performance characteristics and to obtain FDA clearance or approval for such usage of the product.(ABSTRACT TRUNCATED AT 400 WORDS)

Bacteremia↗

PubMed1994

General principles in the laboratory detection of bacteremia and fungemia.

Various factors are important in the laboratory detection of bacteremia and fungemia. These include clinical factors, the type of blood culture system, and laboratory processing of blood culture bottles. Most commercial blood culture products have been designed to take these factors into account and, thus, are relatively similar. There are differences, however, and it should not be assumed that these products have identical performance characteristics. To optimize microbial recovery, clinicians should order and collect the proper number of blood cultures at the earliest possible time and before the administration of antimicrobial agents. Clinical microbiologists should select a blood culture system that optimizes the recovery of common microbial pathogens and should use blood culture systems according to the manufacturers' recommendations.

Bacteremia↗

PubMed1993

Avermectins in arthropod vector management - prospects and pitfalls.

The proven impact of avermectins against a wide variety of arthropod vectors suggests that this new family of compounds holds promise in reducing the incidence of vector-borne disease. Experimentally, decreased survival and abundance of various vector species indicate that certain vector populations may be so manipulated. In addition, sublethal effects on individuals include lengthened development, decreased fecundity and diminished parasite uptake. Enthusiasm must be cautious, given possible impacts on non-target species and the eventual development of resistance. Here Mark Wilson emphasizes that the present challenge is to study how this new toxin may be integrated into vector-management schemes that already employ multiple, diverse interventions. Ultimately, the value of such action must be measured not simply in terms of reduced vector abundance, but also with the more complex equation of reduced parasite transmission in mind.

Journal Article↗

PubMed1993

Recovery of clinically important microorganisms from the BacT/Alert blood culture system does not require testing for seven days.

Recently, we published a comparison of the BacT/Alert blood culture system with the BACTEC 660/730 nonradiometric blood culture system using blood inocula of 5 ml per bottle. By reanalyzing data collected during that study, we found that, for true-positive isolates causing bacteremia or fungemia, 363 (97.6%) of 376 and 341 (97.7%) of 349 isolates were recovered by the end of day 5 of testing, and 364 (97.9%) of 376 and 343 (98.3%) of 349 isolates were recovered by the end of day 6 of testing for aerobic and anaerobic bottles, respectively. Most isolates recovered on days 6 (24 of 27) and 7 (20 of 25) of testing were either contaminants or indeterminate as a cause of sepsis. When used as recommended by the manufacturer, only six (1.3%) of 464 clinically important isolates recovered on test days 6-7 would have gone undetected had testing been limited to 5 days and four (0.9%) of 464 had testing been limited to 6 days. We conclude that BacT/Alert bottles can be tested for as few as 5 days and then discarded with minimal loss of true-positive isolates and maximal reduction of contaminants.

Bacteremia↗

PubMed1993

Reduced abundance of immature Ixodes dammini (Acari: Ixodidae) following incremental removal of deer.

The abundance of immature Ixodes dammini Spielman, Clifford, Piesman & Corwin was monitored for 9 yr (1983-1991) before and during the controlled, limited hunting of white-tailed deer, Odocoileus virginianus (Zimmerman), at a coastal Massachusetts site. Deer abundance was reduced from an estimated 350 during 1985 to approximately 60 during 1991. Although annual fluctuations were large, mean larval I. dammini abundance declined from 20.8 per white-footed mouse, Peromyscus leucopus (Rafinesque), during 1983-1986 before deer reduction to 10.3 per mouse following deer reduction (1987-1991). Similarly, mean nymphal I. dammini abundance declined from 2.7 per mouse before intervention to 1.6 per mouse after intervention. Immature I. dammini population fluctuations were not associated with those of P. leucopus. The total population of larvae infesting P. leucopus declined from 3,596 ticks before intervention to 1,535 ticks after intervention. Concurrently, the total nymphal population declined from 417 ticks before intervention to 187 ticks after intervention. The number of feeding adult female I. dammini on deer increased as deer density decreased.

Animals↗

PubMed1993

Dispersal of the sand fly Lutzomyia longipalpis (Diptera: Psychodidae) at an endemic focus of visceral leishmaniasis in Colombia.

Mark-release-recapture studies were carried out during 1990-1991 in El Callejón, Colombia, an endemic focus of American visceral leishmaniasis, to study the longevity, dispersal, and flight range of the principal vector, Lutzomyia longipalpis Lutz & Neiva. Several groups of wild-caught (n = 1,539) and laboratory-reared F1 (n = 2,208) sand flies were marked with fluorescent dusts and released. Recaptures at daytime resting sites, on animal bait, and in CDC light traps were made for 20 d following each release. From 2 to 9% of L. longipalpis were recaptured, a rate which differed between the sexes (7.7% male, 1.5% female). Overall, 49% of the L. longipalpis were recaptured between 0 and 50 m, 48% within 100 and 300 m, and nearly 3% at > or = 0.5 km from the release site. Sex differences in recapture site, distance flown, and direction were observed. Our results indicate that the dispersal behavior of peridomestic populations of L. longipalpis compares more closely with that of Old World sand fly species from similar habitats than to the sylvan Neotropical phlebotomines.

Animals↗

PubMed1993

Temperature- and humidity-dependent longevity of unfed adult Hyalomma truncatum (Acari: Ixodidae).

The survival of unfed adult Hyalomma truncatum Koch held under different regimes of constant temperature (5, 17, 24, and 30 degrees C) and relative humidity (10, 50, and 80%) was monitored during > 1 yr. Longevity of this medically important African tick was shortest at the highest temperature and lowest relative humidity (100% dead at week 25). Conversely, H. truncatum lived longest at lower temperatures and higher relative humidity (< 100% dead at week 64). The combined effects of temperature and humidity, measured as vapor pressure deficit, were strongly related to survival of these ticks. The survival of males and females was similar and was independent of the weight of ticks. These findings have implications for the maintenance and study of laboratory colonies of H. truncatum and for the development of tick control strategies to reduce vectorial capacity.

Animals↗

PubMed1993

Experimental vector incompetence of a soft tick, Ornithodoros sonrai (Acari: Argasidae), for Crimean-Congo hemorrhagic fever virus.

Adults and nymphs of a soft tick, Ornithodoros sonrai Sautet & Witkowski, were allowed to feed on suckling mice that had been experimentally infected with Crimean-Congo hemorrhagic fever (CCHF) virus (IbAr 10200 strain). The mean viral titer of mouse blood at the time of tick feeding was 10(3.2) plaque-forming units (PFU) per ml. Samples of ticks were assayed on 12 occasions between days 0 and 31 after the viremic blood meal. Mean CCHF viral titers were 10(2.1) PFU per tick immediately after the viremic meal but declined to 10(1.2) PFU per tick after 2 d, and no virus was detected beyond 8 d. The percentage of ticks with detectable virus was 92% (22/24) immediately after the viremic meal, but then declined to 20% (2/10) after 4 d and to 0% (0/44) after 11 or more days. Ticks were allowed to feed on sets of three naive suckling mice on days 0, 2, 5, 8, 11, 14, 21, and 28 after the viremic blood meal, but CCHF viral transmission did not occur. Similarly, no transovarial transmission of virus from CCHF virus-exposed O. sonrai to their progeny was observed. These results strongly indicate that O. sonrai is not a vector of CCHF virus.

Animals↗

PubMed1993

Association of ticks (Acari: Ixodoidea) with rodent burrows in northern Senegal.

Four species of ticks were retrieved from burrows of 64 multimammate rats, Mastomys erythroleucus (Temminck), 55-gerbils, Taterillus gracilis (Thomas) or T. pygargus (Cuvier), 13 Nile rats, Arvicanthis niloticus (DeMarest), and five Geoffroy's ground squirrels, Xerus erythropus (Geoffroy) from May 1987 through August 1988 at two study sites in northern Senegal. Ornithodoros sonrai Sautet & Witkowski were recovered from 95% (74/78) of burrows near Bandia and 6% (4/66) of burrows near Yonofere. Eight Hyalomma truncatum Koch, four Rhipicephalus guilhoni Morel & Vassiliades, and one R. sulcatus Neumann were recovered from 144 rodent burrows (nine tick-positive burrows) from both locations. No seasonal trend of tick abundance or activity was noted, nor was any pattern of burrow preference by ticks detected. Rodent burrows in either location appeared to be little used by ixodid ticks.

Animals↗

PubMed1993

Intestinal parasites and HIV infection in Tanzanian children with chronic diarrhea.

OBJECTIVE: To determine whether specific intestinal parasites are associated with HIV infection in Tanzanian children with chronic diarrhea. DESIGN: A prospective, cross-sectional study. SETTING: Muhimbili University College of Health Sciences, Dar es Salaam, Tanzania. SUBJECTS: All children aged 15 months to 5 years admitted with chronic diarrhea, and age-matched controls. METHODS: Standardized history, physical examination, HIV serology, and stool parasitology were evaluated for all subjects. We compared three groups: HIV-infected and non-HIV-infected children with chronic diarrhea and controls without diarrhea. MAIN OUTCOME MEASURES: Fecal parasites and nutritional status. RESULTS: Chronic diarrhea accounted for one-quarter of all cases of diarrheal disease in the defined age range, and children with chronic diarrhea were severely malnourished. Forty per cent of subjects with chronic diarrhea were HIV-seropositive. Although intestinal parasites were detected in approximately 50% of all three groups, diarrheagenic parasites were detected in up to 40% of children with chronic diarrhea. Blastocystis hominis was detected only in HIV-infected patients. CONCLUSIONS: HIV infection was common in children with chronic diarrhea, and parasitic agents of diarrhea may be important in children with chronic diarrhea both with and without HIV infection in this setting. B. hominis was more frequent in HIV-infected children. The immunocompromising effects of severe malnutrition may have diminished the difference between HIV-infected and non-HIV-infected children.

Child, Preschool↗

PubMed1993

Controlled comparison of the BACTEC high-blood-volume fungal medium, BACTEC Plus 26 aerobic blood culture bottle, and 10-milliliter isolator blood culture system for detection of fungemia and bacteremia.

The BACTEC high-blood-volume fungal medium (HBV-FM) (Becton Dickinson Diagnostic Instrument Systems, Sparks, Md.) was compared with the Isolator (IS) tube and the BACTEC Plus 26 (BP26) blood culture bottle for the ability to recover fungi from the blood of adult patients suspected of having fungemia. A total of 6,836 blood culture sets that fulfilled criteria for inclusion in the study were received. Three separate comparisons were performed: 4,907 HBV-FM versus IS, 4,886 BP26 versus HBV-FM, and 4,949 BP26 versus IS. For the HBV-FM versus IS comparison, 218 isolates were recovered: 125 (57.3%) were bacteria and 93 (42.7%) were fungi. HBV-FM was comparable to IS for recovery of yeasts, but IS was superior for recovery of Histoplasma capsulatum (25 versus 0 isolates recovered [P < 0.001]). Growth of Torulopsis glabrata was detected earlier (P < 0.05) in HBV-FM bottles. For the BP26 versus HBV-FM comparison, 229 isolates were recovered: 161 (70.3%) were bacteria, and 68 (29.7%) were fungi. HBV-FM was superior for recovery of T. glabrata (P < 0.025) and all fungi combined (P < 0.025). There were no statistically significant differences in the speed of detection of microbial growth. For the BP26 versus IS comparison, 251 isolates were recovered: 165 (65.7%) were bacteria, and 86 (34.2%) were fungi. IS was superior for recovery of H. capsulatum (P < 0.001), T. glabrata (P < 0.05), and fungi other than H. capsulatum (P < 0.025). BP26 was superior for recovery of all bacteria combined (P < 0.001) and viridans group streptococci (P < 0.01). Growth of T. glabrata (P < 0.05) was detected earlier in IS tubes. Growth of Staphylococcus aureus (P < 0.01), viridans group streptococci (P < 0.01), Pseudomonas aeruginosa (P < 0.05), and all microorganisms combined (P < 0.05) was detected earlier in BP26 bottles. For yeast, 57 of 59 (96.6%), 79 of 80 (98.7%), and 64 of 67(95.5%) were recovered from BP26 bottles, HBV-FM bottles, and IS tubes, respectively, by day 14; for H. capsulatum, 14 of 36 (38%) isolates were recovered from IS tubes by day 14. Mean times of recovery were similar for BACTEC bottles and IS. We conclude that (i) for recovery of fungi from blood cultures, HBV-FM is equivalent to IS (with the exception of H. capsulatum); (ii) for recovery of bacteria, BP26 is superior to IS; (iii) BP26 bottles are inferior to both HBV-FM bottles and IS tubes for recovery of T. glabrata; and (iv) HBV-FM bottles must be paired with another blood culture bottle or system to optimize detection of bacteremia.

Aerobiosis↗

PubMed1993

Rationale for selective use of anaerobic blood cultures.

Because of the declining frequency of anaerobic bacteremia, routinely using half the collected blood volume for anaerobic culture has been challenged. There is no data indicating whether more clinically relevant isolates would be recovered if all or most of the given blood sample were cultured aerobically. In this two-part study, we reviewed cases of anaerobic bacteremia to determine what proportion occurred in situations when anaerobes would be expected and then estimated the yield of different culture approaches by reanalyzing the data from a large prospective clinical blood culture study. The records of 61 patients who had an anaerobic isolate (excluding Propionibacterium species) recovered only from an anaerobic bottle were examined to define clinical settings in which such isolates occur. Fifty-six (92%) patients had clinically important isolates, and the source of infection was obvious at the time of culture in 47 of the 56 (84%). Of 56 patients, 36 (64%) had abdominal signs and symptoms, including 12 with recent abdominal surgery. Of nine patients without an obvious source of infection, six were on high-dose steroids. Relative yields were compared for (i) one aerobic bottle and one anaerobic bottle (5 ml to each) for all blood cultures, (ii) two aerobic bottles (5 ml to each), or (iii) two aerobic bottles plus an extra anaerobic bottle (only for clinically suspected anaerobic sepsis) (5 ml to each). The third approach had the highest yield (475 isolates), because the routine use of two aerobic bottles recovered more Candida spp., members of the family Enterobacteriaceae, and nonfermenters than did the first approach (448 isolates) (P < 0.02), and clinically directed culturing for anaerobes would recover anaerobes missed with the second approach (458 isolates). Our data suggest that the use of two aerobic bottles with selective culturing for anaerobes could increase the number of clinically relevant isolates by at least 6% compared with the current practice of inoculating an aerobic bottle and an anaerobic bottle with equal volumes of blood.

Adult↗

PubMed1993

Field studies on the epidemiology of Venezuelan hemorrhagic fever: implication of the cotton rat Sigmodon alstoni as the probable rodent reservoir.

During February 1992, field studies on the epidemiology of Venezuelan hemorrhagic fever (VHF) were carried out in a rural area of Portuguesa State in central Venezuela. The objective of this work was to determine the prevalence of infection with Guanarito virus, the etiologic agent of VHF, among wild rodents and humans living within an endemic focus of the disease. A total of 234 rodents, representing nine different species, were collected and their spleens were cultured for virus. Thirty-one Guanarito virus isolates were made from two rodent species: 19 from 40 Sigmodon alstoni and 12 from 106 Zygodontomys brevicauda. Guanarito virus antibody rates among these two species were 5.1% and 15.0%, respectively. Nine of the 12 Z. brevicauda that yielded virus from their spleens also had Guanarito virus antibodies in their sera. In contrast, none of the 19 Guanarito virus-positive S. alstoni had antibodies to the virus. These data suggest that S. alstoni usually develops a persistent nonimmunizing infection with Guanarito virus, while Z. brevicauda develops an immunizing infection. Based on knowledge of the behavior of other human pathogenic arenaviruses, these results imply that S. alstoni is the principal rodent reservoir of Guanarito virus in nature. To determine the prevalence of Guanarito virus infection among humans in the same region, 195 people living near one of the rodent collecting sites were bled and their sera were tested for antibodies to the virus. Five individuals (2.6%) had Guanarito virus antibodies; all were adults, and two had been diagnosed previously as having VHF.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗