Search PubMed⌕ Search

Biomedical subjects

Robert Novak

Publications and source records attributed to Robert Novak.

14 recordsLinked to original sources
PubMed2006

Survival of immature Anopheles arabiensis (Diptera: Culicidae) in aquatic habitats in Mwea rice irrigation scheme, central Kenya.

BACKGROUND: The survivorship and distribution of Anopheles arabiensis larvae and pupae was examined in a rice agro-ecosystem in Mwea Irrigation Scheme, central Kenya, from August 2005 to April 2006, prior to implementation of larval control programme. METHODS: Horizontal life tables were constructed for immatures in semi-field condition. The time spent in the various immature stages was determined and survival established. Vertical life tables were obtained from five paddies sampled by standard dipping technique. RESULTS: Pre-adult developmental time for An. arabiensis in the trays in the experimental set up in the screen house was 11.85 days from eclosion to emergence. The mean duration of each instar stage was estimated to be 1.40 days for first instars, 2.90 days for second instars, 1.85 days for third instars, 3.80 days for fourth instars and 1.90 days for pupae. A total of 590 individuals emerged into adults, giving an overall survivorship from L1 to adult emergence of 69.4%. A total of 4,956 An. arabiensis immatures were collected in 1,400 dips throughout the sampling period. Of these, 55.9% were collected during the tillering stage, 42.5% during the transplanting period and 1.6% during the land preparation stage. There was a significant difference in the An. arabiensis larval densities among the five stages. Also there was significant variation in immature stage composition for each day's collection in each paddy. These results indicate that the survival of the immatures was higher in some paddies than others. The mortality rate during the transplanting was 99.9% and at tillering was 96.6%, while the overall mortality was 98.3%. CONCLUSION: The survival of An. arabiensis immatures was better during the tillering stage of rice growth. Further the survival of immatures in rice fields is influenced by the rice agronomic activities including addition of nitrogenous fertilizers and pesticides. For effective integrated vector management, the application of larvicides should target An. arabiensis larvae at the tillering stage (early vegetative stage of rice) when their survival in the aquatic habitats is high to significantly reduce them and the larvicides should be long-lasting to have a significant impact on the malaria vector productivity on the habitats.

Animals↗
PubMed2006

Spatio-temporal analyses of West Nile virus transmission in Culex mosquitoes in northern Illinois, USA, 2004.

After a severe outbreak of West Nile virus (WNV) in Cook County, Illinois, in 2002, detections of WNV in mosquitoes were frequent across the state in the following years despite small numbers of human cases. We conducted a spatio-temporal analysis of Culex (subgenus Culex) mosquitoes collected in 2004 in three mosquito abatement districts (MAD) in Cook County by calculating monthly estimates of mosquito density, prevalence of infected mosquitoes, and exposure intensity, which in turn is a product of mosquito density and infection rates. Mosquito infections were detected early at three sites in late May and were widely detected throughout the three MADs in the summer with infection rates as high as 13 per 1000 in August. Exposure intensities were higher at sites adjacent to the Des Plaines River, especially in August and September. The aggregated pattern of WNV transmission along the river might be related to the existence of substantial forest preserves and wetlands that might produce ecological conditions favorable for mosquito proliferation and interactions between mosquitoes and birds.

Animals↗
PubMed2006

Culex population dynamics and West Nile virus transmission in east-central Illinois.

Temporal changes in the abundance Culex restuans and Culex pipiens were monitored in east-central Illinois for over a decade using infusion-baited oviposition traps. The 2 species typically exhibited a seasonal shift in relative abundance with a mean crossover date (when the proportion of egg rafts from both species is equal) of August 10 or 11, depending on leap year, with a 95% confidence interval of +/- 10.7 days. The date of crossover was linearly related to the date of last spring frost and occurred on average about 123 days after the last spring frost. Despite the predictability of crossover, the weekly pattern in the proportion of Cx. pipiens before and after crossover varied considerably, even between years with similar crossover dates. After West Nile virus became established in our area, we found that transmission based on Culex from gravid traps did not increase until Cx. pipiens abundance increased in oviposition traps. Infection rates peaked within the half-month period after crossover. The peak in Cx. pipiens abundance in oviposition traps during this 3-year period was between the 2nd half of August and the end of September. A higher magnitude of transmission in 2002 coincided with warmer temperatures during July and August and an extended period in which the 2 Culex species were in relatively equal abundance.

Animals↗
PubMed2006

Mosquito species diversity and abundance in relation to land use in a riceland agroecosystem in Mwea, Kenya.

We conducted an entomological survey to determine the mosquito species diversity and abundance in relation to land use in the Mwea rice scheme, Kenya. Adult mosquitoes were collected by indoor spraying of houses and outdoors by CDC light traps in three villages representing planned (Mbuinjeru) and unplanned (Kiamachiri) rice agroecosystems and a non-irrigated agroecosystem (Murinduko). During the 12-month sampling period, a total of 98,708 mosquitoes belonging to five genera and 25 species were collected. The five most common species collected during this study were Anopheles arabiensis Patton (52.5%), Culex quinquefasciatus Say (36.7%), Anopheles pharoensis Theobald (5.2%), Anopheles coustani Laveran (1.4%), and Anopheles funestus Giles (1.3%). Anopheles arabiensis, Cx quinquefasciatus, and An. pharoensis were more abundant in rice agroecosystems than in the non-irrigated agroecosystem, and in planned than in the unplanned rice agroecosystems. In contrast, An. funestus was more abundant in the non-irrigated agroecosystem. The mosquito species diversity (H) and evenness (E(H)) in the non-irrigated agroecosystem (Shannon diversity Index, H = 1.507, EH = 0.503) was significantly higher than in the rice agroecosystems (H) = 0.968, E(H) = 0.313, unplanned; and H= 1.040, E(H) = 0.367 planned). Results of lag cross correlation analysis revealed a strong relationship between rainfall and the abundance of An. arabiensis, and C. quinquefasciatus in the non-irrigated agroecosystem but not in the rice agroecosystems. It is inferred from the data that different levels of habitat perturbations with regard to rice cultivation have different effects on mosquito diversity and abundance. This provides an understanding of how mosquito diversity is impacted by different habitat management and rice cropping strategies.

Agriculture↗
PubMed2005

Evaluation of environmental data for identification of Anopheles (Diptera: Culicidae) aquatic larval habitats in Kisumu and Malindi, Kenya.

This research evaluates the extent to which use of environmental data acquired from field and satellite surveys enhances predictions of urban mosquito counts. Mosquito larval habitats were sampled, and multispectral thermal imager (MTI) satellite data in the visible spectrum at 5-m resolution were acquired for Kisumu and Malindi, Kenya, during February and March 2001. All entomological parameters were collected from January to May 2001, June to August 2002, and June to August 2003. In a Poisson model specification, for Anopheles funestus Giles, shade was the best predictor, whereas substrate was the best predictor for Anopheles gambiae, and vegetation for Anopheles arabensis Patton. The top predictors found with a logistic regression model specification were habitat size for An. gambiae Giles, pollution for An. arabensis, and shade for An. funestus. All other coefficients for canopy, debris, habitat nature, permanency, emergent plants, algae, pollution, turbidity, organic materials, all MTI waveband frequencies, distance to the nearest house, distance to the nearest domestic animal, and all land use land cover changes were nonsignificant. MTI data at 5-m spatial resolution do not have an additional predictive value for mosquito counts when adjusted for field-based ecological data.

Animals↗
PubMed2005

The emergence of west nile virus during a large outbreak in Illinois in 2002.

In 2002, the world's largest outbreak of neuroinvasive West Nile virus (WNV) disease occurred. Illinois reported 21% of the total cases in the United States, the most among all states. The epidemiology of WNV in Illinois in 2002 was examined to determine factors associated with severe disease and death. A total of 884 cases were identified and there were 66 deaths. The overall attack rate of WNV infection was 7.1 per 100,000 population and this increased with age. The median ages of patients and patients who died were 56 and 78 years, respectively. Among patients who died, 91% were diagnosed with encephalitis and the case-fatality rate for patients with encephalitis was 18.6%. Patients more than 50 years old had a significantly higher risk of being reported with encephalitis (relative risk [RR] = 3.3, 95% confidence interval [CI] = 2.6-4.3%) and death (RR = 22.3, 95% CI = 5.5-90.4%). Clinicians evaluating elderly patients with WNV infection should assess patients closely for progression of disease.

Adolescent↗
PubMed2004

Optimal diagnostic testing for urinary tract infection in young children.

Urinary tract infection (UTI) is a major concern in young febrile children. Current recommendations favor use of urine obtained by bladder catheterization or aspiration, but opinion varies as to the best ancillary tests to predict a positive culture and guide initial management. The utility of dipstick leukocyte esterase, blood, and nitrite; unspun urine leukocyte count; gram stain of cytocentrifuged urine; and standard spun sediment examination was evaluated in 142 febrile, < 5-year-old children seen in the Emergency Department, 25 of whom had culture-proven UTI. Using sensitivity and negative predictive values as criteria for performance, unspun urine leukocyte count and gram stain of cytocentrifuged urine used in parallel was the best approach but still failed to detect some UTI. Analysis of the nature of the specimens evaluated provided explanation of differences from previous observations. Adoption of this modified approach to prediction of urinary tract infection appears to improve prediction but has operational implications and creates potential problems for the laboratory.

Bacteriological Techniques↗
PubMed2004

West Nile virus and high death rate in American crows.

We document effects of West Nile virus (WNV) on American Crows. More than two thirds of our crows died of WNV infection, peaking when the proportion of infected mosquitoes at roosts was greatest. WNV antibody prevalence in crows was low. Local ecologic effects can be dramatic as WNV inhabits new areas.

Animals↗
PubMed2003

Larval habitat diversity and ecology of anopheline larvae in Eritrea.

Studies on the spatial distribution of anopheline mosquito larvae were conducted in 302 villages over two transmission seasons in Eritrea. Additional longitudinal studies were also conducted at eight villages over a 24-mo period to determine the seasonal variation in anopheline larval densities. Eight anopheline species were identified with Anopheles arabiensis predominating in most of the habitats. Other species collected included: An. cinereus, An. pretoriensis, An. d'thali, An. funestus, An. squamosus, An. adenensis, and An. demeilloni. An. arabiensis was found in five of the six aquatic habitats found positive for anopheline larvae during the survey. Anopheles larvae were sampled predominantly from stream edges and streambed pools, with samples from this habitat type representing 91.2% (n = 9481) of the total anopheline larval collection in the spatial distribution survey. Other important anopheline habitats included rain pools, ponds, dams, swamps, and drainage channels at communal water supply points. Anopheline larvae were abundant in habitats that were shallow, slow flowing and had clear water. The presence of vegetation, intensity of shade, and permanence of aquatic habitats were not significant determinants of larval distribution and abundance. Larval density was positively correlated with water temperature. Larval abundance increased during the wet season and decreased in the dry season but the timing of peak densities was variable among habitat types and zones. Anopheline larvae were collected all year round with the dry season larval production restricted mainly to artificial aquatic habitats such as drainage channels at communal water supply points. This study provides important information on seasonal patterns of anopheline larval production and larval habitat diversity on a countrywide scale that will be useful in guiding larval control operations in Eritrea.

Animals↗
PubMed2003

Distribution of anopheline mosquitoes in Eritrea.

The spatial distribution of anopheline mosquito species was studied throughout Eritrea during the 1999-2001 malaria transmission seasons from October to December for the highlands and western lowlands and February to April for the coastal region. Of the 302 villages sampled, 59 were visited in both the first and second year. Overall, 13 anopheline species were identified, with the Anopheles gambiae complex predominating during the first year (75.6%, n = 861) and the second year (91.9%, n = 1,262). Intrazonal variation accounted for 90% of the total variation in mosquito distribution. Polymerase chain reaction results indicated that 99% (n = 1,309) of the An. gambiae s.l. specimens were An. arabiensis, indicating that this was the only member of the gambiae complex present. There was a high degree of aggregation of anophelines within zones and villages, with more than 80% of the total anophelines being collected from less than 20% of the villages and from only 10% of the houses sampled. At least 80% of the anopheline mosquitoes were collected from grass-thatched Agudo-type housing. Vector abundance showed an inverse relationship with elevation, with highest densities in the low-lying western lowlands. Multiple regression analysis of log-transformed mean density of An. arabiensis with rainfall and the normalized difference vegetation index (NDVI) (average NDVI, minimum NDVI, and maximum NDVI) showed that these independent variables were not significantly associated with mosquito densities (R2 = 0.058). Our study contributes to the basic understanding of the ecology and distribution of malaria vectors with respect to species composition and spatial heterogeneities both that could be used to guide vector control operations in Eritrea.

Animals↗
PubMed2003

High seasonal variation in entomologic inoculation rates in Eritrea, a semi-arid region of unstable malaria in Africa.

Entomologic studies were conducted in eight villages to investigate the patterns of malaria transmission in different ecologic zones in Eritrea. Mosquito collections were conducted for 24 months between September 1999 and January 2002. The biting rates of Anopheles arabiensis were highly seasonal, with activity concentrated in the wet season between June and October in the highlands and western lowlands, and between December and March in the coastal region. The biting rates in the western lowlands were twice as high as in the western escarpment and 20 times higher than in the coastal region. Sporozoite rates were not significantly different among villages. The risk of infection ranged from zero on the coast to 70.6 infective bites per year in the western lowlands. The number of days it would take for an individual to receive an infective bite from an infected An. arabiensis was variable among villages (range = 2.8-203.1 days). The data revealed the presence of only one main malaria transmission period between July and October for the highlands and western lowlands. Peak inoculation rates were recorded in August and September (range = 0.29-43.6 infective bits/person/month) at all sites over the two-year period. The annual entomologic inoculation rates (EIRs) varied greatly depending on year. The EIR profiles indicated that the risk of exposure to infected mosquitoes is highly heterogeneous and seasonal, with high inoculation rates during the rainy season, and with little or no transmission during the dry season. This study demonstrates the need to generate spatial and temporal data on transmission intensity on smaller scales to guide targeted control of malaria operations in semi-arid regions. Furthermore, EIR estimates derived in the present study provide a means of quantifying levels of exposure to infected mosquitoes in different regions of the country and could be important for evaluating the efficacy of vector control measures, since Eritrea has made significant steps in reducing the burden of malaria based on the Roll Back Malaria initiative of the World Health Organization.

Animals↗
PubMed2002

Testing for group a streptococci.

CONTEXT: Laboratory diagnosis of group A streptococcal pharyngitis in physician office and small-hospital laboratories. OBJECTIVE: To characterize laboratory practices for the diagnosis of group A streptococcal pharyngitis and to identify opportunities for improvement. DESIGN: Voluntary self-assessment questionnaire, used to assess the laboratory practices of 790 laboratories subscribing to the College of American Pathologists Excel Microbiology Proficiency Testing Program. RESULTS: We observed discrepancies between self-reported and recommended specimen collection and laboratory testing practices for some laboratories. The most notable discrepancies were failing to provide a written specimen-collection procedure (17.8%), sampling the tongue and oral mucosa (2%), failing to always perform back-up cultures when rapid antigen test results were negative (57.5%), and finalizing culture reports within 24 hours or less (34.0%). Additionally, among those respondents who used the bacitracin disk, 57.9% (277 respondents) applied the disk directly onto a primary plate. CONCLUSIONS: Opportunities exist to improve testing practices for the diagnosis of group A streptococcal pharyngitis for some physician office and small-hospital laboratories.

Humans↗
PubMedDate not supplied

Gait analysis in low lumbar myelomeningocele patients with unilateral hip dislocation or subluxation.

The surgical indications for the treatment of unilateral hip dislocations or subluxations in patients with low lumbar myelomeningocele remain highly debatable. This study examines the influence of unilateral hip dislocation or subluxation on the gait of these patients using three-dimensional gait analysis. Twenty patients with a diagnosis of low lumbar myelomeningocele underwent three-dimensional gait analysis. All patients were community ambulators with solid ankle-foot orthoses and crutches who presented with unilateral hip dislocation or subluxation and no scoliosis. The patients were divided in two groups. Group 1 comprised 10 patients who demonstrated either no evidence of hip flexion or adduction contractures or symmetric hip contractures. Group 2 comprised 10 patients with unilateral hip flexion and/or adduction contractures. Pelvic and hip kinematics were assessed to determine the symmetry of motion between the involved and the noninvolved side during walking. Seven patients from group 1 walked with a symmetric gait pattern; only two patients from group 2 walked with a symmetric pattern. Gait symmetry corresponded to the absence of hip contractures or bilateral symmetrical hip contractures and had no relation to the presence of hip dislocation. The authors concluded that reduction of the hip is unnecessary.

Adolescent↗