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ABSTRACT: Our objective was to determine the prevalence and risk factors for HIV infection among female sex workers in Johannesburg, South Africa. A cross-sectional survey of female sex workers was conducted using interviewer-administered questionnaires. Prevalent sexually transmitted infections including HIV were evaluated through standard laboratory testing. HIV infection was identified in 137 (46.4%) of 295 subjects tested. Increasing frequency of condom use was significantly negatively associated with HIV infection (odds ratio [OR] for moderate use = 0.21; 95% confidence interval [CI]: [0.09, 0.50]; OR for high use = 0.14; 95% CI: [0.06, 0.34]). Sex workers aged > or = 29 years reported significantly different patterns of behaviour than younger workers. Among women aged > or = 29, a negative association with HIV infection (OR = 0.16; 95% CI: [0.07, 0.38]) was found, but only among those not infected with Neisseria gonorrhoeae. Older women in the Johannesburg sex industry may have adaptive behavioural strategies besides condom usage which reduce their risk of acquiring HIV. However, older sex workers with gonorrhoea constitute a high-risk subgroup.
International Journal of STD & AIDS 03/2005; 16(3):256-61. · 1.09 Impact Factor
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ABSTRACT: To determine risk factors associated with dengue (DEN) virus infection among residents of Santa Clara, Peru, a rural Amazonian village near Iquitos, a cross-sectional serological, epidemiological and environmental survey was conducted. Demographic, social and behavioural information was obtained by standardized questionnaire from 1225 Santa Clara residents (61.3%) aged 5 years or older. Additional data were obtained on the environmental variables and immature mosquito species and abundance surrounding each household (n = 248). Sera that had been collected previously by the Peruvian Ministry of Health from residents were tested by an enzyme-linked immunosorbent assay (ELISA) for DEN virus IgG antibody. Antibody identity was verified as DEN by plaque reduction neutralization test. Data on individuals were analysed by univariate and multivariable methods, and independent sample t-tests. Spatial clustering was evaluated by comparing distances among DEN positive households. Overall, antibody prevalence was 29.4 % and more than doubled from the youngest to the oldest age groups, but did not differ by sex. Curiously, length of residence in Santa Clara was negatively associated with DEN virus antibodies. More frequent travel to Iquitos was positively associated with seroprevalence. Residents who obtained water from a river source rather than a local well also had significantly higher antibody prevalence. None of the environmental variables measured at each household corresponded to the patterns of antibody distribution. Of the larval mosquitoes found around residences, all were determined to be species other than Aedes. No evidence of spatial autocorrelation among antibody-positive households was detected. These results strongly suggested that recent DEN virus transmission did not occur in the village and that most infections of residents of this rural village were acquired while visiting the city of Iquitos.
Tropical Medicine & International Health 04/2001; 6(3):212-8. · 2.80 Impact Factor
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ABSTRACT: The emergence of rabies among terrestrial wildlife poses increasing but poorly defined risks to people. In particular, events leading to human exposure to rabies virus via mammalian reservoirs remain elusive. Thus, we determined those risk factors associated with human exposure to rabies-positive animals during a raccoon rabies epizootic in Connecticut. Existing passive surveillance data on animal rabies tests in Connecticut from 1991 through 1994 were evaluated for demographic, ecological, and behavioral characteristics of human exposure. Of 2,525 rabies-positive terrestrial animals identified, human contact was reported on 556 occasions (22%) and involved at least 939 individuals. The annual incidence of exposure rose from none during 1985-1990 to 66 in 1991 and then averaged 291 during 1992-1994. Exposure was most often indirect in nature, involved a rabies-positive raccoon, was mediated through a domestic animal, and occurred most frequently either near or inside the home. These results suggest that human exposure to rabid animals represents a significant, reemerging public health concern in the United States. Analysis of the epizootiology of rabies infection and of individual exposure risks could reduce inappropriate administration of rabies postexposure prophylaxis, as well as inform other proposed interventions.
Vector Borne and Zoonotic Diseases 02/2001; 1(3):211-7. · 2.44 Impact Factor
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ABSTRACT: Early diagnosis of malaria followed by appropriate treatment can help reduce related morbidity and mortality as well as interrupt transmission. Previous studies of household responses to malaria have tended to focus on endemic areas where the burden of this disease is greatest. With the apparent increasing frequency of epidemics in African highlands, a better understanding of treatment behaviours in areas of unstable transmission may be important to future public health interventions. This study was undertaken following a serious epidemic of malaria in the highlands of south-western Uganda. Our objectives were to characterize actions taken by both adults and caretakers of children < or =5 years old during their most recent episode of self-diagnosed malaria, and to identify factors that were associated with prompt treatment at a health facility. A survey of 300 households selected in a 2-stage cluster sampling procedure produced 453 adult respondents and 133 caretakers of children < or =5 years old. We found that almost 65% of adults and 62% of children who had experienced an episode of malaria in the last year (most during the epidemic) had sought treatment from a health facility first as opposed to self-treatment. Most of these people had visited the health facility within 1 day of symptom onset. By the end of their malaria episode, over 87% of adults and 80% of children had visited a health facility at least once. Factors associated with prompt presentation at a health facility included severity of illness, household proximity to a health facility, and knowledge of malaria prevention methods. Our results indicate that there is an important role for the formal health care system in mitigating morbidity and mortality and reducing transmission during malaria epidemics in Uganda.
Tropical Medicine & International Health 12/2000; 5(12):865-75. · 2.80 Impact Factor
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ABSTRACT: Several highland regions of Africa recently have suffered malaria epidemics. Because malaria transmission is unstable and the population has little or no immunity, these highlands are prone to explosive outbreaks when densities of Anopheles exceed critical levels and conditions favor transmission. If an incipient epidemic can be detected early enough, control efforts may reduce morbidity, mortality, and transmission. Here we present three methods (direct, minimum sample size, and sequential sampling approaches) that could be used to determine whether the household indoor resting density of Anopheles gambiae s.I. has exceeded critical levels associated with epidemic transmission. Data on Anopheles density before, during, and after a malaria epidemic (December 1997-July 1998) in the highlands of southwestern Uganda were evaluated to demonstrate the application of these three approaches. During this epidemic, a density of 0.25 Anopheles mosquitoes per house was associated with epidemic transmission, whereas 0.05 mosquitoes per house was chosen as a normal level expected during nonepidemic months. The direct approach to calculating mean Anopheles density with an allowable error of 20-50% of the mean would require the sampling of 102-16 houses, respectively. In contrast, with only seven houses, the minimum sample size approach could be used to determine whether Anopheles density had exceeded the critical level. This method, however, would result in an overestimation of the risk of an epidemic at low Anopheles density. Finally, a sequential sampling plan could require as many as 50 houses to conclude that risk of an epidemic existed, but this disadvantage is offset by the ability to preset the probabilities of concluding that risk of an epidemic exists at both the critical and normal Anopheles densities. Our study illustrated that it is feasible, and probably expedient, to include monitoring of Anopheles density in highland malaria epidemic early warning systems.
Journal of Medical Entomology 10/2000; 37(5):664-74. · 1.76 Impact Factor
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ABSTRACT: As highland regions of Africa historically have been considered free of malaria, recent epidemics in these areas have raised concerns that high elevation malaria transmission may be increasing. Hypotheses about the reasons for this include changes in climate, land use and demographic patterns. We investigated the effect of land use change on malaria transmission in the south-western highlands of Uganda. From December 1997 to July 1998, we compared mosquito density, biting rates, sporozoite rates and entomological inoculation rates between 8 villages located along natural papyrus swamps and 8 villages located along swamps that have been drained and cultivated. Since vegetation changes affect evapotranspiration patterns and, thus, local climate, we also investigated differences in temperature, humidity and saturation deficit between natural and cultivated swamps. We found that on average all malaria indices were higher near cultivated swamps, although differences between cultivated and natural swamps were not statistically significant. However, maximum and minimum temperature were significantly higher in communities bordering cultivated swamps. In multivariate analysis using a generalized estimating equation approach to Poisson regression, the average minimum temperature of a village was significantly associated with the number of Anopheles gambiae s.l. per house after adjustment for potential confounding variables. It appears that replacement of natural swamp vegetation with agricultural crops has led to increased temperatures, which may be responsible for elevated malaria transmission risk in cultivated areas.
Tropical Medicine & International Health 05/2000; 5(4):263-74. · 2.80 Impact Factor
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ABSTRACT: A cross-sectional serosurvey of a rural community near Iquitos, Peru was conducted to determine Oropouche (ORO) virus antibody prevalence and risk factors for human infection. Venous blood samples, and demographic, social, and risk factor data were obtained from people age five years of age and older who lived in the village of Santa Clara on the Nanay River, a tributary of the Amazon River. Sera were tested for ORO viral antibody by an ELISA. The specificity of viral antibody reactivity was determined by a standard plaque-reduction neutralization test. Interview data were analyzed by univariate and multiple logistic regression to determine which variables were statistically associated with previous ORO viral infection, as indicated by the presence of IgG antibody. Final models were evaluated based on log-likelihood and Wald chi-square. Clustering of seropositive residents within houses was analyzed by the method of Walter. Among 1,227 persons sampled, 33.7% (n=414) were positive for ORO viral IgG antibody. Overall, antibody prevalence was similar for males (33.9%) and females (33.6%), and increased significantly with age for both sexes to include more than half of persons more than 25 years of age. The length of residence in the village was positively associated with serologic status; persons who had moved to the village within the past 15 years were less likely to be seropositive than life-long residents of the same age. Antibody prevalence among immigrants who had lived in Santa Clara more than 15 years was similar to that in life-long residents. The activity most predictive of previous ORO viral infection was travel to forest communities and travel to Iquitos. No evidence of spatial heterogeneity in ORO virus antibody distribution was observed. Results suggested that endemic transmission of ORO virus in this region has been ongoing during many decades, and that people are at considerable risk of infection.
The American journal of tropical medicine and hygiene 12/1998; 59(5):710-6. · 2.59 Impact Factor
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ABSTRACT: The North American raccoon rabies epizootic continues to expand, now affecting most of New England. In 1990, raccoons became the vertebrate most often reported rabid in the United States. Emergence of this zoonosis poses increasing, but poorly defined risks to humans. This study analyzed various demographic, environmental, and behavioral factors associated with animal infection and human exposure before and during the epizootic in Connecticut. Rabies virus infections among terrestrial vertebrates were analyzed from 1985 through 1994. From March 1991, when the first case was diagnosed, through December 1994, 2,522 of 13,147 animals tested were found positive for rabies viral antigen. Forty-seven percent of the raccoons tested were infected, representing 88.0% of all animals found positive. Domestic animals constituted only 1.7% of positive test results, but 40.6% of the tests performed. The epizootic wave of transmission advanced approximately 30 km/year. Most rabies-positive wild animals were taken from private properties, usually near houses. Possible human exposures involved 939 people on 556 occasions through direct contact (20.7%) or indirectly through another animal (79.3%). Of 3,239 domestic animals exposed to rabies-positive wild animals, 18.4% lacked vaccination. Rabies has become enzootic in Connecticut and risk to humans and animals persists. The public health burden is considerable, yet knowledge is lacking to develop sustainable prevention strategies.
The American journal of tropical medicine and hygiene 11/1997; 57(4):457-63. · 2.59 Impact Factor
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ABSTRACT: The effects of habitat and microclimate on survival of unfed nymphal black-legged ticks, Ixodes scapularis Say (approximately I. damnini Spielman, Clifford, Piesman & Corwin), were studied under natural conditions in southcentral and northwestern Connecticut. At both coastal and inland locations, survival of 3 groups of 20 wild-caught questing nymphs placed in nylon mesh bags was monitored in each of 3 different habitats (field, forest canopy, and forest/field edge) during summer 1995. Simultaneously, soil temperature, ground-level air temperature, and relative humidity were measured continuously within each habitat at both sites. The number of ticks surviving in each habitat was monitored weekly. Average daily survival rates of nymphs were related inversely to soil temperature but were not related to air temperature or humidity. Overall, nymphal ticks at the inland site survived significantly longer than those at the coastal site; however, no significant differences in mortality rates were found among habitats. These results suggest that inland environmental conditions are suitable for lengthy survival of unfed nymphal I. scapularis in regions where this tick is not yet abundant.
Journal of Medical Entomology 04/1997; 34(2):167-72. · 1.76 Impact Factor
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ABSTRACT: Microclimate and other abiotic factors may be important in determining the survival of arthropod vectors, yet the impact of such variables rarely has received careful examination. The impacts of habitat, microclimate, and experimental confinement on survival rates of unfed adult blacklegged ticks, Ixodes scapularis Say, were studied in field enclosures in southcentral and northwestern Connecticut. At both locations, 2 enclosures were placed in each of 3 different habitats (field, forest canopy, and forest/field edge). Forty wild-caught adult ticks (20 males, 20 females) were placed in each enclosure. At one site, another 40 ticks were confined to nylon mesh bags placed inside each enclosure. Soil temperature, ground-level air temperature and relative humidity were measured within each habitat. The number of ticks surviving within each enclosure was monitored 1 or 2 times per week. Ticks that were confined in nylon bags had a lower survival rate than ticks that were able to move freely within the enclosures. Ticks survived longer in edge and forest habitats than in open fields, which were characterized by greater extremes in air temperature, soil temperature, relative humidity, and vapor pressure deficit than the other 2 habitats. The mean daily survival rates of free-ranging I. scapularis were negatively related to air temperature, vapor pressure deficit, and the coefficient of variation of relative humidity.
Journal of Medical Entomology 08/1996; 33(4):619-27. · 1.76 Impact Factor
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ABSTRACT: Ecological studies on the sand fly Lutzomyia longipalpis (Lutz & Neiva) were conducted during 1990-1992 in a small rural community in Colombia where American visceral leishmaniasis (AVL) is endemic. Subsamples of sand flies collected weekly from pigpens, the interior of houses, and natural outdoor resting sites were dissected to determine physiological age and Leishmania chagasi Cunha & Chagas infection rates. Eleven female L. longipalpis had flagellates in their gut, 2 of which were successfully cultured and identified as Leishmania chagasi. The reproductive status, stage of ovarian development, and trophic history of female sand flies varied among sites, habitats, and time of collection. The percentage of parous females ranged from about one-third to two-thirds overall and varied seasonally. Of most relevance to AVL transmission was the finding that 8% of L. longipalpis females were multiparous. In addition, our data suggest that L. longipalpis rest inside houses after blood-feeding outdoors, and that this species can blood-feed more than once during a single gonotrophic cycle.
Journal of Medical Entomology 09/1995; 32(5):618-29. · 1.76 Impact Factor
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ABSTRACT: Nocturnal activity of the sand fly Lutzomyia longipalpis (Lutz & Neiva) was studied from August 1991 to July 1992 in a small rural community in Colombia where American visceral leishmaniasis is endemic. During 2 or 3 nights each month, sand flies were collected with hand-held aspirators each hour between 1730 and 0630 hours, from a pigpen and a cattle corral located 30 m apart. Host-seeking activity of L. longipalpis adults was characterized by 2 general patterns: (1) adult sand fly activity increased shortly after sunset and continued until just after sunrise, and (2) peak sand fly activity was greatest early in the evening (1830-2330 hours) and then declined steadily toward morning. Female L. longipalpis activity generally increased after 2030 hours, whereas that of males remained constant or declined as the evening progressed. There were seasonal differences in sand fly abundance between the 2 sites: peak abundance in the cattle corral occurred during hot, dry periods, whereas maximum abundance in the pigpen occurred when relative humidity was higher. Influence of relative humidity on activity varied with season. Sand fly activity tended to decrease at temperatures below 24 degrees C and increase in the presence of moonlight.
Journal of Medical Entomology 09/1995; 32(5):605-17. · 1.76 Impact Factor
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ABSTRACT: Ecological studies on the sand fly Lutzomyia longipalpis (Lutz & Neiva) were conducted during 1990-1993 at a small rural community in Colombia where American visceral leishmaniasis is endemic. Weekly sand fly collections were made from pigpens, houses, and natural resting sites, using hand-held aspirators, sticky (oiled) paper traps, and opossum-baited Disney traps. In total, 263,094 sand flies were collected; L. longipalpis predominated (86.1%), followed by L. trinidadensis (11.0%), L. cayennensis (2.7%), and 8 other Lutzomyia species. The species composition and sex ratio of these sand flies varied among sites and by collection method. L. longipalpis were captured most efficiently by direct aspiration from animal bait. Conversely, sticky paper traps, especially inside houses and at rock resting sites, collected a greater diversity of species, but a lower relative abundance of L. longipalpis.
Journal of Medical Entomology 07/1995; 32(4):527-37. · 1.76 Impact Factor
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ABSTRACT: Ecological studies on the sand fly Lutzomyia longipalpis (Lutz & Neiva) were conducted during 1990-1993 in a small rural community in Colombia where American visceral leishmaniasis is endemic. Standardized weekly sand fly collections made from pigpens and natural resting sites displayed a bimodal annual abundance cycle, with a small peak occurring in October-November and a larger one in April-May. Time series analysis was employed to quantify the associations between sand fly abundance and weather factors (temperature, relative humidity, and rainfall). In addition to a prominent 6-mo cycle. Fourier analysis of the collection data demonstrated that the L. longipalpis population also exhibited a 5- to 8-wk cycle that may represent the length of larval development. Autoregressive moving average models were fit to weekly collection data and their residuals were regressed against rainfall, temperature, and relative humidity. A significant positive association between female L. longipalpis abundance and the relative humidity and rainfall recorded 3 wk earlier was found, indicating that these factors may be of value in predicting sand fly abundance. Additionally, these data indicated that L. longipalpis larvae may become quiescent during adverse conditions.
Journal of Medical Entomology 07/1995; 32(4):538-48. · 1.76 Impact Factor
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ABSTRACT: 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)
The American journal of tropical medicine and hygiene 09/1993; 49(2):227-35. · 2.59 Impact Factor
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ABSTRACT: 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.
Journal of Medical Entomology 04/1993; 30(2):427-35. · 1.76 Impact Factor
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ABSTRACT: The aphid alarm pheromone, trans-beta-farnesene (TBF), was found to stimulate feeding in both male and female Lutzomyia longipalpis Lutz & Neiva. Four other structurally related compounds (farnesol; 808 farnesene; trans, trans-farnesyl acetate; farnesyl methyl ether) were slightly less stimulating to these insects. The effect of TBF varied with sand fly age and the concentration of the chemical used. In contrast, TBF did not stimulate feeding in either sex of four other sand fly species (L. shannoni Dyar, Phlebotomus papatasi (Scopoli), P. argentipes Annandale & Brunetti, P. perniciosus Newstead). TBF might be useful in enhancing L. longipalpis field collections or in developing a poison bait for the control of this species.
Journal of Medical Entomology 03/1992; 29(2):226-31. · 1.76 Impact Factor
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ABSTRACT: Malaria epidemics in African highlands cause serious morbidity and mortality and are being reported more frequently. Weather is likely to play an important role in initiating epidemics but limited analysis of the association between weather conditions and epidemic transmission parameters has been undertaken. We measured entomological variables before and during an epidemic of malaria (which began in February 1998) in a highland region of south-western Uganda and analysed temporal variation in weather data against malaria incidence (estimated from clinic records), mosquito density and entomological inoculation rates (EIR). Indoor resting density of Anopheles gambiae s.l. was positively correlated with malaria incidence (r = 0.68, P < 0.05) despite extremely low vector densities. EIR totalled only 0.41 infectious bites per person during the entire 8-month study period. Rainfall during and following the El Niño event in 1997 was much higher than normal, and rainfall anomaly (difference from the mean) was positively correlated with vector density 1 month later (r = 0.55, P < 0.05). Heavier than normal rainfall associated with El Niño may have initiated the epidemic; the relationship between temperature and transmission parameters remains to be defined. The results from this study indicate that, in this highland population, epidemic malaria may occur at extremely low inoculation rates.
Transactions of the Royal Society of Tropical Medicine and Hygiene 93(5):480-7. · 2.16 Impact Factor
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Transactions of the Royal Society of Tropical Medicine and Hygiene 95(5):502-3. · 2.16 Impact Factor
