Anthropophily was highest in An. funestus compared to An. arabiensis in the irrigated zone. These findings are consistent with previous studies that have reported An. funestus s.s. to exhibit anthropophagic behavior in Kenya and in other parts of Africa . However, in recent reports, they have been shown to also feed on bovine in the presence of LLINs. This plasticity of the feeding behavior of the vector may influence malaria transmission, leading to residual transmission after the densities of endophilic and endophagic vectors have been reduced by the interventions . The life histories of An. arabiensis population of southern Tanzania were simulated in a model by Killeen et al. and estimated that two-thirds of the vector feeds outdoor in an area where bednet usage is high . Studies have indicated that An. arabiensis exhibits behavior that mediates residual transmission such as feeding outdoors on humans or cattle and rapidly exiting houses without fatal exposure to insecticide-treated surfaces . Findings of the present study demonstrated that An. arabiensis fed on humans both indoors and outdoors with a higher HBI outdoors and predominantly fed on bovine. However, it remains capable of transmitting malaria whenever it can feed on humans. There was a significant difference in the risk of malaria transmission by An. arabiensis in the two zones, with higher transmission risk in the irrigated zone. These results show that irrigation has an effect on malaria transmission and An. arabiensis played a significant role in transmission. In addition, this species contributed almost equally to both indoor and outdoor transmission. In many studies, irrigated areas have been associated with increased malaria transmission than neighboring non-irrigated areas ; however, in some cases, introduction of irrigation schemes reduces or has no impact on malaria transmission . Hence,vertical farming equpment the impact of water development projects on malaria transmission is variable and the transmission dynamic likely depends on the local epidemiological setting.

Our data also suggest that the zoophagic behavior of An. arabiensis could be accounting for the low transmission in the irrigated zone whereas the low vector densities limited transmission in the non-irrigated zone. The zoophagic tendency of An. arabiensis indicates zooprophylaxis may be a potential strategy for malaria control. The limitation of our study is the lack of information on the movement of endophagic mosquitoes as they exit the house after feeding and/or resting. This information would have improved the understanding of the effect of insecticide based vector control interventions in the houses on the normal movement, density, and reticence feeding of endophilic species .Endotoxin is a cell wall component of the outer membrane of gram negative bacteria. Sources include animals and agricultural activities. In its purified form, it is known as lipopolysaccharide, which is both toxic and immunogenic. A small and variable mass fraction of fine particles < 2.5 μm in diameter may contain endotoxin. Experimental inhalation of endotoxin in humans leads to airway inflammation, characterized by activation and migration of neutrophils. Exposure to endotoxin has been associated with exacerbation of respiratory allergic diseases including asthma, and with increased asthma prevalence. Ryan et al.were the first to show that settled house dust endotoxin and estimated exposure to traffic related air pollution positively interacted in relation to risk of persistent wheeze at age 3 years in a birth cohort of 624 children. Many other studies have also assessed respiratory and allergic health effects of endotoxin using only house dust samples as a surrogate of subject exposures to airborne endotoxin, often with only one measurement. However, exposure studies have shown considerable within-home, and temporal variability of house dust endotoxin. Furthermore, the exposures of interest come from resuspended indoor dust and endotoxin infiltrated from outdoor air that both determine indoor airborne concentrations. Airborne endotoxin measurements are expected to reveal stronger associations between endotoxin and respiratory outcomes than settled dust measurements of endotoxin. Several studies have evaluated household and other determinants of house dust endotoxin, and of airborne endotoxin inside and outside of the residence of pediatric subjects.

There is a considerably larger literature regarding airborne endotoxin exposures in occupational settings with organic dusts. However, despite the potential importance of endotoxin in particle-related respiratory health effects, only one study has assessed the impact of personal airborne endotoxin exposure on acute asthma outcomes in children. It is also the only study to have evaluated whether personal endotoxin exposure relates to airborne micro-environmental endotoxin levels among children. Investigators followed a panel of 24 school children with asthma with personal exposure monitors operated at 2 L/min over 24 hours for 164 person-days. They found that personal PM2.5 endotoxin and PM10 endotoxin exposure was associated with decreased expiratory lung function and increased asthma symptoms. Geometric mean personal endotoxin was higher than indoor or outdoor school levels and was not correlated with these stationary site measurements. This finding suggested that personal endotoxin exposure likely included substantial contributions from other particle sources. Sources include many indoor and outdoor micro-environments and personal dust cloud exposures to particles generated from personal activities or from exposures to non-stationary sources near the subject . In the present study we tested the consistency of the personal exposure assessment findings of Rabinovitch et al.using a repeated daily measures in a cohort panel of 45 children with asthma followed over a period of up to 10 days, and using home rather than school endotoxin measurements in a subset of 14 subjects. We also evaluated potential household and other determinants of personal and indoor airborne endotoxin exposures. Data include 376 person-days of daily endotoxin data collected from PM2.5 quartz filters using personal exposure monitors operated at 4 L/min, daily ambient endotoxin measurements collected from central ambient sites, and daily indoor and outdoor home endotoxin measurements in a subset of 14 children at 12 residential sites in Riverside and Whittier, California.

We also assessed the relationship between personal endotoxin exposures and concurrent personal exposure to air pollutants, including PM2.5 mass, PM2.5 EC, PM2.5 organic carbon , and NO2. We then assessed the relationship of personal endotoxin exposures to central site measurements of the same air pollutants, and to indoor and outdoor home PM2.5 mass, PM2.5 EC, and PM2.5 OC.We conducted a longitudinal study with 10 daily repeated measurements of health outcomes and exposures in a panel cohort of school children with diagnosed persistent asthma who were ages 9-18 years , nonsmoking, and unexposed to environmental tobacco smoke in the home. Results relating to asthma outcomes and air pollutants have been previously published. Two regional panels were conducted during warmer seasons of southern California. The first panel was conducted in Riverside, California, from August through early October 2003. This is a down-wind smog receptor site,4×4 grow tray which is a consequence of being just inland from Los Angeles County. The second panel was conducted in Whittier, California from July through November 2004. This is a region of eastern Los Angeles County that is immediately down-wind of vehicular emission sources. Riverside experiences higher temperatures and lower relative humidity than Whittier as a result of being further from the Pacific Ocean and closer to the inland desert. The Institutional Review Board of the University of California, Irvine approved the study protocol. Informed written consent was obtained from all subjects and one of their legal guardians. Subjects were recruited through notification of parents by local public schools. We recruited only subjects with mild to moderate persistent asthma. The present study focused on assessing endotoxin exposures in 45 subjects with complete outcome data including four 10-d periods in Riverside involving 13 subjects and eight 10-day periods in Whittier involving 32 subjects. The expected predominance of asthma among males vs. females was evident in this population . This was a diverse population with a majority of subjects identifying themselves as Hispanic along with 5 African American subjects and 14 white non-Hispanic subjects.Harvard Impactors were used to collect ambient PM2.5 and operated at a flow rate of 10 L/min. They were sited at a central site within 10 km of homes in Riverside and 5 km of homes in Whittier. We also collected indoor and outdoor home PM2.5 with Harvard Impactors in one subject’s home during each of the 12 tenday sampling periods. Indoor samplers were located in or near the main activity area of the home, usually the living room or family room. There were a pair of sibling subjects in two of the homes . PM2.5 , and PM2.5 EC and OC were collected at the stationary sites simultaneous with personal samples. PM mass on Teflon filters was estimated using standard gravimetric methods. For both personal and stationary site quartz filter samples, particulate carbon was speciated into organic and elemental carbon using the thermal manganese dioxide oxidation technique [20]. Criteria pollutant gases were measured by the South Coast Air Quality Management District at central sites and they included hourly O3 and NO2.Endotoxin was measured from extracts of archived PM2.5 quartz filters collected as described above . We do not have quartz PM10 samples. Although endotoxin is found in the coarse PM fraction , the respirable PM2.5 fraction is more relevant to lower airway dose and thus airway inflammation. All quartz filters were baked to remove organic carbon before sampling.

Only around 10% of the filters’ surface area was punched out using heat sterilized instruments for the EC-OC measurements, leaving sufficient filter media for endotoxin assays. The remaining surface area for personal endotoxin measurement was calculated for each filter to estimate particle mass using mass data from the 24-hr average PEM PM2.5 or gravimetric measurements from the Harvard Impactor PM2.5 Teflon filters for the stationary site measurements. For the endotoxin assay, we developed a rapid and thorough method of extracting endotoxin from quartz PM2.5 filters. Briefly, the extraction procedure combines the efficient disruption of quartz filter membranes by using a high speed, reciprocating instrument with conventional sonication. First, the quartz filters were transferred into pyrogen-free extraction tubes with 4 mL pyrogen-free water. The tubes were loaded into the FastPrep and processed at 6.5 m/second for 60 seconds to efficiently homogenize the filter membrane. The extraction tubes were then rotated for 30 min followed by 15 minute sonication and clearing of the aqueous extracts of quartz fibers and particles by centrifugation . The undiluted supernatants were then directly used for endotoxin assay using the Limulus Amoebocyte Lysate kinetic chromogenic assay according to the manufacturer’s protocol .The detection limit for the overall method was estimated at 0.004 endotoxin units /m3 air .Descriptive analyses of exposures were used to determine the shape of the distribution, central tendency, and spatial trends . We examined the Spearman rank correlation of personal endotoxin to ambient endotoxin measured at a central site in the 45 subjects, and to outdoor and indoor home endotoxin in the subset of 14 subjects. This was intended to establish the extent to which fixed site home and regional measurements are related to personal endotoxin exposure. Similar to other studies we found notable regional differences in concentrations and in correlations between Riverside and Whittier. Therefore, we present these correlation results separately for the two regions. House dust samples for endotoxin were not collected because the study objective of the parent project was to assess daily acute changes in asthma outcomes and airborne exposures. Because the endotoxin data for all measurement types were log-normally distributed, we used natural log transformation of the endotoxin variables prior to all regression analyses. We first examined the relation of indoor to outdoor endotoxin in linear regression models. Multiple regression analyses of the relation of continuous log-transformed personal endotoxin to stationary endotoxin measurements were conducted using the general linear mixed model. The mixed model estimates both fixed and random effects and incorporates the basic longitudinal design of the study in which multiple measurements are taken on each subject. Subject random intercepts were modeled to reflect the principle that measurements taken for the same individual are likely to be correlated . The following a priori adjustments were made in the mixed models for prediction of personal endotoxin by stationary site endotoxin: personal temperature and relative humidity , and study region. We fit an autoregressive-1 correlation structure given the observed error covariance.